Fossil records indicate that the earliest primates probably appeared as prosimians only during the Paleocene (up to 65 MYA) and Eocene (up to 55 MYA) epochs. Animals more nearly like monkeys appeared in the Oligocene epoch (23-38 MYA). Fossil records reveal remains of monkey-like creatures for 10 million years, from 18-8 MYA. It has been postulated that the common ancestor of chimpanzees and humans lived about 6 to 7 MYA. The oldest fossil hominid yet discovered, Sahelanthropus tchadensis, found at the Toros-Manalla site near Lake Chad, was dated to between 6 and 7 MYA. The small skull was almost compete and was found to have small teeth, and a short face, but the upper face has strong brow ridges; and the teeth have thick enamel. This combination of traits has not been seen in any fossil ape. Sometime thereafter, the two species–chimpanzees and humans–went their separate ways.

Tim White, Ph.D., from the University of California, Berkeley, and his Ethiopian colleagues in the Middle Awash Project, Berthane Asfaw and Giday WoldeGabriel, working in the Afar Desert of Ethiopia, made a crucial discovery in 1994. They unearthed a nearly complete skeleton–125 bones in all–of a 4.4 million year old female Ardipithecus ramidus, which comes very close to what would be expected in the common ancestor of chimpanzees and humans, one of evolution’s holy grails. Ardipithecus’s foot was of special interest in that it had the ape feature of a separate grasping big toe, but was in all other respects similar to that of modern humans, built for bipedalism. Indeed, the skeletal remains were a fascinating mosaic of traits, some very primitive, some quite advanced, and some definitely hominid. The creature was both quadruped and bipedal, which makes it a very important intermediate ancestor between apes and humans.

Fossils were found in the Great Rift Valley of Africa dated to around 3.5 million years ago (MYA), by the work of the Leakeys, that showed the emergence of human form, Australopithecus africanus, which had obvious characteristics indicative of having come out of nonhuman antecedents. The complete skeleton of an adult female, informally called Lucy, which was found in Hadar in the badlands of Ethiopia, provided a superb specimen for study. Brain size was not much different than that of antecedent apes (about 1/3 the size of modern man’s), but the spinal cord entered the skull from below and not toward the back which meant that this creature walked upright; and this was confirmed by the structure of the pelvis. There are multiple evidence in Lucy’s skeleton that suggest that she was an intermediate species between  Ardipithecus and the genus Homo. The genus, Homo, began to appear about 2.3 MYA, the earliest representative being Homo habilis, the handy or skillful man. Habilis had a larger brain (including a brain case that showed indentations from Broca’s and Wernicke’s areas), smaller teeth (especially reduced rear molars), an erect posture, relatively gracile (slender and delicate) features, and a thumb which was more flexible than that of modern chimps. Homo habilis is the first unequivocal complex tool user, having been found with a variety of flaked stone tools. He co-existed, at least in time, if not in actual proximity, with at least three other hominins—Paranthropus (or Australopithecus) boisei, robustus, and aethiopithecus. All of these had massive skulls, heavy chewing teeth, sturdy bones, and small brains; and all were extinct by 1.1 MYA. Habilis also lived during the same time period as three other members of genus Homo—ergaster, rudolfensis, and erectus. Homo habilis, dated from about 2.3-1.85 MYA, is a questionable human ancestor because its body was too small. It did have a similar skull with about a 750 milliliter capacity and with no vertex cresting. Many experts consider habilus to be more closely related to the australopithecines.

The genus, Homo, began to appear about 2.3 MYA, the earliest representative being Homo habilis, the handy or skillful man. Habilis had a larger brain (including a brain case that showed indentations from Broca’s and Wernicke’s areas), smaller teeth (especially reduced rear molars), an erect posture, relatively gracile (slender and delicate) features, and a thumb which was more flexible than that of modern chimps. Homo habilis is the first unequivocal complex tool user, having been found with a variety of flaked stone tools. He co-existed, at least in time, if not in actual proximity, with at least three other hominins—Paranthropus (or Australopithecus) boisei, robustus, and aethiopithecus. All of these had massive skulls, heavy chewing teeth, sturdy bones, and small brains; and all were extinct by 1.1 MYA. Habilis also lived during the same time period as three other members of genus Homo—ergaster, rudolfensis, and erectus. Homo habilis, dated from about 2.3-1.85 MYA, is a questionable human ancestor because its body was too small. It did have a similar skull with about a 750 milliliter capacity and with no vertex cresting. Many experts consider habilus to be more closely related to the australopithecines.

scientiffic reconstruction of a Homo habilis עברית: שחזור מדעי של הומו הביליס (Photo credit: Wikipedia)

The genus, Homo, began to appear about 2.3 MYA, the earliest representative being Homo habilis, the handy or skillful man. Habilis had a larger brain (including a brain case that showed indentations from Broca’s and Wernicke’s areas), smaller teeth (especially reduced rear molars), an erect posture, relatively gracile (slender and delicate) features, and a thumb which was more flexible than that of modern chimps. Homo habilis is the first unequivocal complex tool user, having been found with a variety of flaked stone tools. He co-existed, at least in time, if not in actual proximity, with at least three other hominins—Paranthropus (or Australopithecus) boisei, robustus, and aethiopithecus. All of these had massive skulls, heavy chewing teeth, sturdy bones, and small brains; and all were extinct by 1.1 MYA. Habilis also lived during the same time period as three other members of genus Homo—ergaster, rudolfensis, and erectus. Homo habilis, dated from about 2.3-1.85 MYA, is a questionable human ancestor because its body was too small. It did have a similar skull with about a 750 milliliter capacity and with no vertex cresting. Many experts consider habilus to be more closely related to the australopithecines.

A skeleton of an adult female with a transition form from 200,000 years ago (KYA) was found to have mtDNA (mitochondrial DNA) almost exactly like that of modern humans; so, she was informally dubbed “Eve”. Mitochondrial DNA is better preserved, more abundant, easier to work with, than chromosomal or especially Y chromosomal DNA and is passed only through maternal lines, hence the reference to the first mother. H. erectus was abundant after the middle Pleistocene Era 7-10 KYA, and there is evidence that erectus, habilis, and the australopithicines occupied the same territories during their more ancient existence. Some experts believe that erectus and habilus hunted the australopithicines to extinction. The lateness of existence of erectus puts H. erectus and H. sapiens sapiens (wise, or knowing man) on the earth at the same time indicative of the evolutionary change that took place. Homo erectus holds the distinction of being the first human to leave Africa. Erectus disappeared from the fossil record between 300 KYA and 60,000 KYA, the differences being for different populations spread around the world, after an earthly presence of 1.5 million years. Homo heidelbergensis–which appeared around 600-500 KYA–was more human in appearance and characteristics, and most experts consider heidelbergensis to be a highly likely direct ancestor of our species. Heidelbergensis had very heavy brows and large strong tibias. The species was tall. Heidelbergensis appears to be an intermediary species possessing a strong reinforcing ridge rising up above the acetabulum similar to erectus, and absent from sapiens. They were excellent tool makers and adept hunters like the Neanderthals. Anecdotal histories suggest that H. floresceinsis were sighted by historically modern men on the island of Flores, one of the Indonesian Sunda Islands.

Other specimens have been found that contribute to the concept that the human phylogenetic tree was more aptly a bush. Human-like species branched and re-branched into multiple dead-end species, and the evolutionary interrelationships of the animal fossils discovered are a source of continuing debate. At several points in ancient history, several different humanoids occupied the earth at the same time–including Neanderthals–a species that scientists estimate never exceeded 15,000 individuals even at the height of their occupation of Western Europe. They became extinct around 28 KYA.

Neanderthals–though very similar in genomes and possibly even able to interbreed with Homo sapiens sapiens–were not intermediate forms between apes and men according to most researchers. Neanderthals had large brains, some even larger than those of modern humans. They made cave paintings of life-like creatures and also some designs that were suggestively symbolic. Some Neanderthal burial sites contained funerary offerings and ochre pigments, which, along with the cave paintings, are suggestive of the first indication of human-like religion. They vanished from the fossil record about 28 KYA. Aside from the few remaining Neanderthals, after 60 KYA, only modern human skeletal remains have been identified. Intermediacy has been roundly challenged and denied by creationists and hotly debated by evolutionists. As noted above, human-like species branched and re-branched into multiple dead-end species. Neanderthals co-existed with modern humans for thousands of years and apparently copied some of the artistic accomplishments of Homo sapiens. The general physical features of Neanderthals early on were highly suggestive that sapiens and neanderthalis were directly linked in the chain of evolution. It is known, for example, from research by Lalueza-Fox, and Holger Rompler of the University of Leipzig, et al, who isolated a pigmentation gene from a Neanderthal fossil from El Sidron, that some Neanderthals had red hair, pale skin, and freckles. They appear to share the gene MCIR, and superficially, this would appear to be evidence of a direct linkage.

The discovery that this direct linkage is untrue is one of the remarkable achievements of evolutionary science and a strong evidence of the ability to make corrections in suppositions by utilizing the scientific method. The MCIR of Neanderthals and red-haired humans of today have been found to be quite unlike, so much so that it is evident that Neanderthals and humans developed the trait independently (convergent evolution). The recent (1987, verified by scientists working independently in laboratories in Munich and Pennsylvania) spectacular finding of measurable DNA in a Neanderthal arm bone from a specimen found in Neander Valley, Germany in 1856 revealed dramatic differences from all living humans in a study of 1000 people from around the world, differences more extensive than the differences between chimpanzees and humans. Further evidence from CT scans of the ear ossicles of Neanderthals and modern humans revealed distinct differences in shape. The DNA studies indicate that Neanderthals and humans separated genetically more than 500 KYA. Recent evidence indicates at least eight–found by a third generation of Leakeys–humanoid lines appeared and eventually disappeared, lacking the survivorship of H. sapiens sapiens.

The cultural record reveals very simple chipped stone tools found in conjunction with the hominin/humanoid fossils of around 2 million year old age for the earliest time. They were found near the broken bones of other, smaller animals suggesting that they may have been used for butchering and/or cleaning hides. Homo habilus fossils, found in Kenya’s Olduvai Gorge overlooking the Serengeti plain and dated to 1.8 MYA were found with stone tools and bones with evidence of butchering. An Israeli site yielded hand axes, evidence of elephant butchery, and slabs of worked wood dated to 800 KYA. During the next 500,000 years the tools became more sophisticated and were associated with the remains of larger animals. Aurignacian tool-making (finer stone point and even wood spear shaft construction) appears to have come from Asia to Europe.

The origin of man is the most contentious aspect of evolution in the minds of many religious people because it flies in the face of biblical writings and traditions, and the concepts of evolution are incompatible with their faith. The majority of Americans believe that it is probably not true that human beings developed from earlier species. Others can grudgingly accept that flies, worms, and bacteria might have evolved but draw an emphatic line when it comes to human beings. Charles Darwin was so discomfited by the inevitable conclusions of his seminal work, The Origin of the Species, published in 1859, that he delayed inclusion of the bulk of his data about humans until 1871 when he published The Descent of Man. Inclusion of man in the evolutionary tree came as a personal struggle for Darwin. The basic argument against evolution–based on the Bible–is rooted in a condemnation of evolution science related to a dogmatic religious belief that cannot accept observable design as having any other origin than God. The logical fallacy the Creationists convey is called the fallacy of personal incredulity—“I cannot believe it; therefore it cannot be true”.

The accumulated evidence of scientific research, without invoking the supernatural–as it stands at present–offers firmly verified conclusions about the origins of man, of Homo sapiens sapiens. Human beings, anthropoid apes, monkeys, tarsiers, lemurs, and lorises are grouped into the Linnaean order Primates, a classification originally based solely on the recognition of shared anatomical similarities. More than a century after Linnaeus, scientists realized that his classification was evidence of a community of descent. The spectrum runs from the simplest members to that most modified and aberrant species which is also the most accomplished and successful, and, in fact, the only survivor of the genus Homo–Homo sapiens sapiens.

The evolutionary study of man is complicated by the daunting facts that early members of the genus, and especially of the species, were of limited number—perhaps as few as 10,000 breeding pairs, living in small groups—and their fossils are few and widespread. Also, there are a number of unrelated hominid lines making the evolutionary tree for man decidedly bushy at its beginning. The directness of lines is not only blurred by branches but by the finding of fossils that do not seem to connect to a single coherent ascent. Predictions for human evolution are also complicated by the fact that there are irregular rates of evolution because environmental changes are irregular. A good discussion of the complexities of determining which animals might be considered human ancestors and clear artistic renderings of those possible ancient humans in detail beyond the scope of the present rather brief synopsis is found in Sawyer, G.J., and Deak, V. et.al., The Last Human-A Guide to Twenty-two Species of Extinct Humans, a Peter N. Nèvraumont Book, Yale University Press, 2007. Developmental molecular biological and therefore evolutionary studies in man are necessarily limited since it is not possible (not ethical on an absolute scale) to experiment with human embryos. Visualization of gene expression patterns which have taught us a great deal about other animals will be scarce in human embryos.

Aside from the obvious appearance of humans, there are four fundamental criteria which need to be applied to any candidate from the past to qualify the subject as human: 1.Tool making ability, 2. Bipedalism, 3. Enlarged head and brain, 4. Highly dexterous tongue, effective jaw, and multiple types of teeth. Only humans have the ability to make, reproduce, and to convey information about such manufacture to other population members and to succeeding generations, about complex tools. Of all animals, only humans walk upright. The most unique attribute of humans is the skull with its markedly larger brain      case holding not only an enlarged brain but a highly myelinated brain with a thick cerebral cortex. The cerebral cortex is rudimentary in primates, scarcely measurable in other mammals, and nonexistent in most other animals.  The muscles and articulations of the mouth and jaw including the larynx and vocal cord apparatus afford the intricacies necessary for modulated and complicated meaningful greater range of sounds for human speech-which no other animal has, not even our nearest relative, the chimpanzee. As stated above, the eyes look forward affording both near and far vision and stereoscopic vision, all necessary for bipedalism. Modern human teeth are smaller than apes and are adapted for a frugivore [fruit eating] diet primarily with thin enamel but with sharp enough incisors and large enough canines to afford successful meat eating but not adequate for catching and holding prey, a combination not otherwise found.

Less often recognized–but nonetheless important–features of anatomy and physiology separate humans from other animals. These features lend survival and success qualities that contribute to the dominance of our species. There are eight especially important differences: 1. The brain, 2. The specialized skin which lends itself to efficient energy production and conservation and to breast feeding on the move from strong, durable nipples. Humans have more abundant and more nutritious milk for their own kind than other animals. Humans have abundant melanin in their skin to protect against ultraviolet light from the sun. 3. Jaws, 4. Efficient sex, 5. Energy producing and conserving  gut and its biotome. The human microbiome—the collective genomes of a microbial community—has had to respond to its constantly changing environment with dramatic changes in genomic structure. Humans are exposed to incredibly varied environments; human guts come into contact with a diet more complex, variable, and changing than any other animal. Our microbiome has a truly incredible capacity to evolve—to make and to pass on heritable DNA changes that are incorporated into the collective genome and to do so quickly and safely. This capacity of our gut microbiome is a dynamic contribution to human adaptation, survival, and persistence and is a significant evolutionary advantage for humans. 6. The ability to communicate, especially in abstractions and creativity and to create beneficial and protective social interconnections, and 7. Shorter gestation period than in other animals of comparable size which allows a smaller fetal head and therefore a smaller female pelvis, and 8. Unfused cranial bones that are collapsible upon each other to permit further reduction in head size and allows easier birth and a lower infant mortality.

The ability of humans to run and thereby to catch prey and to avoid predators is based on 27 special human features including such evolution endowments not shared with other animals as:

1. powerful gluteal muscles
2. stiff feet
3. short toes
4. long Achilles tendon
5. longer legs
6. generally elongate morphology
7. head stabilization including a powerful nuchal ligament
8. short snout
9. the right kind of skin for heat dissipation and adaptation to differing temperatures
10. humans have been major beneficiaries of those evolutionary changes which have made a significant contribution to our ability to have large, complex, facile, high energy requiring, and extremely useful brains.

Predators, such as cheetahs, can run faster than humans and other predators and prey species in a sprint, but they can only sustain the chase for about one hundred yards or so before having to stop—a deucedly inconvenient situation when you are being chased by a lion or when you have used up your last ounce of energy going after prey and now must face the specter of starvation. Animals other than humans have predominantly apocrine glands in their skin which produce secretions that are high in fat content, and a good lubricant, but does not bathe the body in evaporating water. All of them must eventually stop or go into thermal shutdown. Those animals must depend on panting, an inefficient method in comparison to effective sweating. Human morphology and biochemistry enables marathon running, an advantage over sprinting.

The ability to communicate—linked to thought–is of indisputable value to humans. The ability did not come in one miraculous event, nor was it present until fairly recently in human evolution. Development of the brain favored primates in general and particularly in the evolution of crucial improvements in communication culminating in the tremendous advantage afforded by the brain and speech apparatus structure in humans. There appears to have been a fairly rapid burst of increased brain size about 1.8 MYA and another between 600 and 150 KYA during periods of severely changing climate. Brain size doubled over some 50,000 hominin generations during those climatic conditions. Tracing gene mutations back to the time that chimps and humans separated, it was noted that humans underwent rapid changes about 200 KYA which spread throughout our species. Intracranial size expanded significantly 50 KYA at about the same time the FOXP2 gene mutated and facilitated speech.

Further specialization in humans led to the formation of the planum temporale which is crucial to spoken language, gestural communication, and music. These specialized areas and hemispheral dominance for various functions are present in apes, but have come to fruition in humans. In evolutionary terms, it must be presumed that apes and humans have a common ancestor with such defined neuroanatomy that led from the common and basic pre-ape, pre-hominid condition to the specializations found in the two major divisions of the hominins and hominids. Evolutionary “tinkering” in the microanatomy of human brains over hundreds of thousands of years altered the number, arrangements, and connectivity of neurons.

Finally, my opinion on how the ongoing and increasingly acrimonious issue of same-sex versus traditional man and woman only marriage versus polygamy in any of its several forms should be dealt with. My opinions are based on a grasp of what has happened, what is happening, and what should happen from a practical point of view, absent the scintillating emotions that the several sides have.

First: Polygamy—but not bigamy—has been declared legal. That means that a man or a woman may cohabit in a family relationship wherein more than one “spouse” exists. However, this relationship may only have a single marriage license recognized by state or federal governments. That is a fiat accompli. I disagree with it because it has been my observation that women and children are mistreated and deprived of important rights in such relationships. However, my opinion is irrelevant.

Second: Same-sex marriage is on a trajectory to become part of the law for the entire United States. Eighteen states have already approved the practice, citing the law over legislative vote; and the nineteenth—Idaho—started the same process May 13, 2014, literally as I was writing this blog post. It appears to me that the time is not far off when the Supreme Court will conclude finally that same-sex marriage is legal and bans against the practice are unconstitutional in all of the states. Furthermore—in my opinion–like the legalization of marriage between persons of different races, the same-sex marriage issue will fade away over time, and people in traditional marriages will no longer feel such an intense threat.

Third: It appears to me that the time has come for a different definition of legal marriage. This is my modest proposal (certainly not the first time it has been articulated). All marriages-whether between a man and a woman or between persons of the same gender—should be conducted and legalized in a civil ceremony in a county courthouse devoid of religious context, and that marriage should be the binding legal contract of marriage. Then, the couple and their family and friends can celebrate any kind of acknowledgement of the union they prefer, religious or secular. The Catholics can have the grand union in the cathedral; the Mormons can be joined for time and all eternity in their temples; the Jews can have the joyous ceremony which includes stamping on the goblet; Protestants can enjoy their church ceremonies; others can have individualized ring ceremonies; and nonChristians can celebrate and commemorate the union of a couple in their own way. No one needs to attack the marriage rituals, traditions, or customs of any other group. The vociferous protests against one kind of marriage or another can be relegated to the realm of intolerance where they belong. Perhaps, it will be possible to see peace in our time.

This way of dealing with marriage acknowledges that it is a crucial personal and societal event with lasting consequences. There is no violation of the Constitution. No one is deprived of the right to marry, nor is anyone obligated to marry. However, married persons have obligations and rights that persons who elect to cohabit without marriage do not have under this legal structure—which does not represent any change from the way marriage is now accepted under the law. continued…

The adult human brain of today averages about 1,300 grams in weight, compared to an elephant’s 5,000 grams, and a whale’s 10,000 grams, both of which are much smaller than the human in terms of brain to body mass. The human brain has about 100,000 neurons per cubic centimeter and between 100 and 300 billion per brain. This is about the same number as there are stars in our galaxy. In comparison, rats have about 10,000 neurons per cubic centimeter, and monkeys just triple that. The human neocortex—cerebrum—has a surface area of 5.0 meters or 16 feet squared. In short, there was another great evolutionary leap from primates to humans. Part of the reason for the success of humans is that evolutionary mutations gave us much more myelin in ratio to nerve cells which is protective to the nerve tissue itself and acts to prevent leak of electrochemical pulses with attendant errors of transmission, an important factor in intelligence. Gene modifications made that possible in humans, and the same genetic changes are not found in other primates which are more similar to the common ancestor than are humans. Myelin aids in the speed of nerve conduction, an attribute that differentiates high from low intelligence. It is safe to conclude that no other creature was ever capable of managing such a level of complexity or could provide the energy to produce and maintain it, or is ever likely to do so.

Myelin is relatively chemically inactive and uses less glucose than functional neuronal tissue. Thus, the lower energy use in more intelligent brains may be related to the higher percentage of myelin which somehow imparts greater efficiency to neuronal work—fewer energy-demanding neurons are required for any specific task than in the more primitive animals.

65 million years ago, the mammalian family was represented by the simple Didelphodon, a small, four-legged creature similar to the opossum of today. Over that time period, every mammal seen today evolved through the process of mutation accompanied with the pressure of natural selection. Evolution was an efficient system, utilizing genes and proteins contained in the molecular structure of preceding animals.  In the last two million years, humans have added 50 billion neurons to the Homo erectus brain, and the human female pelvis was enlarged and redesigned by evolutionary forces to permit the passage of that enlarged cranium at delivery. In order to accomplish the phenomenal changes found in human brain size, complexity, and performance, it would have required an evolutionary velocity unknown previously. Assuming that Homo erectus was able to reproduce every 10 years (probably a considerably higher rate than actually occurred); in two million years, there would have been 200,000 generations possible to add 50 billion cells to the heritable brain structure. That means that every generation would have had to add 200,000 new neurons; every 200,000 years, 2.5 billion new cells would have been added.

Researchers have identified tiny changes in one amino acid on a single gene that have had a profound effect on speech processing in humans. It is clear that tiny changes in single genes can have very large effects on a species, and it is necessary to conclude that changes on the order required had to have happened in order to produce the modern human brain in an evolutionary very brief period of time. Those changes have yet to be fully identified or clarified. The book, Molecular Biology of the Cell, puts it this way:

“Humans–as a genus distinct from the great apes–have existed for only a few million years. Each human gene has therefore had the chance to accumulate relatively few nucleotide changes since our inception, and most of these have been eliminated by natural selection. A comparison of humans and monkeys, for example, shows that their cytochrome-c molecules differ in about 1 percent and their hemoglobins in about 4 percent of their amino acid positions. Clearly, a great deal of our genetic heritage must have been formed long before Homo sapiens appeared, during the evolution of mammals–which started about 300 million years ago)–and even earlier. Because the proteins of mammals as different as whales and humans are very similar, the evolutionary changes that have produced such striking morphological differences must involve relatively few changes in molecules from which we are made. Instead, it is thought that the morphological differences arise from differences in the temporal and spatial patterns of gene expression during embryonic development, which then determine the size, shape, and other characteristics of the adult.”

This, then, is how the human genome with around 25-26,000 genes, at most, is able to specify the creation, control, and maintenance of the human body containing trillions of cells, billions of carefully wired neurons, and hundreds of different cell types and to react of profound changes, both negative and positive, occasioned by small mutational events. Small collections of DNA mutations can and do have a very large effect on the final result. The remarkable phenotypic evolution of the human nervous system has a salient molecular correlate, i.e., accelerated evolution of the underlying genes, particularly those linked to nervous system development. The overall brain connectivity–like development of neurons and neural specificity–is remarkably similar in arthropod and vertebrate representatives and among mammals—humans and cows differ in only 11 of 437 amino acids that produce neurotransmitter receptors. Based on acetylcholine receptors, humans are very closely related to cows. It appears that the human system makes more efficient use of the genetic material at its proposal. continued…

A major evolutionary leap took place with the evolution of the brain in mammals. Mammals–which appeared in the fossil record after the first fishes, amphibians, and reptiles–are the only vertebrates to possess the evolutionarily recent, outermost portion of the cerebral cortex—the neocortex. The neocortex of the more primitive monotremes–duck-billed platypus and several species of spiny anteaters–as well as that of marsupials–kangaroos, koalas, opossums, wombats, and Tasmanian devils–lack the convolutions—sulci and gyri—found in the neocortex of most placental animals–eutherians, including humans), the more recent and more advanced animals. Within placental mammals, the size and complexity of the neocortex increased over evolutionary time. The area of the neocortex of mice is only 1/100^th that of monkeys, and that of monkeys is only about 1/10^th that of humans, the latest evolving primate. In addition, rats lack convolutions in their neocortex, in part related to their smaller size, whereas the neocortex of cats, the later evolving animal, has a moderate degree of convolutions. The human neocortex exhibits very extensive convolutions.

Most invertebrates have reached evolutionary dead ends. The great leap forward–another of those greatest milestones–that propelled vertebrates into domination and produced ever improving interaction with the environment and other creatures, was the development of a true central nervous system. Having a CNS is a decidedly anomalous capability compared to what invertebrates have—to the great invertebrate failure. The development of specialized sensory organs, especially with their connection to an effective CNS, added to the intellectual dominance of vertebrates over invertebrates. Nevertheless, there is a remarkable similarity between fly bristles and the vertebrate octavolateral system (inner ear + lateral line), so much so that there is little doubt that both are derived from a common ancestor—another insight into the parsimony of genes in evolution.

The usual example exemplifying increase in complexity is the eye, which originated as a very simple photosynthetic organ in invertebrates whose initial function was to use light as a source of energy, but which benefited from mutations and through selection pressure over eons to evolve into photoreceptors using light to provide a source of information. Sight, even primitive light vs dark detection, played an extremely important role in the advancement of vertebrates over time. Fossil records record a ripening over time of an increasingly enlarged visual portion of the brain. Mutations contributed advantages to certain fish enabling them to use improved eyesight to move faster and with more agility, to survive and to reproduce better in water than other fish and other species. The sense of smell became a rival somewhat later and added a refinement to the evolution of earth life; the tubes that were devoted to the sense of smell were present in fish about 300 MYA.

Competition between senses of sight and smell continued for millions of years. It is likely that the tetrapods which left the seas and invaded land lacked sufficient brain to cope with two dimensional vision, hence they continued with one dimensional sight. Smell–a one dimensional sense–was within the power of their small brains, and it was more practical for them. The fossil record shows how the occipital lobe shrank, and the cerebral hemispheres enlarged over ensuing generations. Gradually–in the evolutionary record–as mammals became larger, the sense of vision regained heightened usefulness. There is some question as to which was the earlier or greater influence on the acquisition of increased vision—was it improving eyes that ramped up brain growth in size, sophistication, and speed, or did the mutations that enhanced mammalian brains allow, even push, the development of eyes? Whichever is the case, the larger brains of mammals could accommodate and process the increased demands created by improving sight. In mammals, the neocortex–including the occipital lobe /visual cortex–becomes disproportionately large as absolute brain size increases, whereas most other regions become disproportionately smaller; larger brain size comes largely at the expense of olfactory lobes. As in all evolution driven by natural selection, the creatures with larger brains and better sight were better suited to survive and to reproduce in a changing terrestrial environment even though their sense of smell diminished. Once again, however, obvious similarities have been noted between sense organs of arthropods and of vertebrates, highly suggestive of a common origin and of conservation of genes which perform different functions up the evolutionary ladder.

Enlargement of the mammalian brain came at a cost. As with previous steps, the need for energy and energy efficiency was core and increased in mammals until it became a self-limiting evolutionary factor. “The nervous system has a unique position as the interface between morphology, physiology, and behavior, but at the same time is subject to costs related to the amount of energy it consumes. Characterizing this trade-off between costs and benefits is essential to understanding the evolution of nervous systems, including that of humans.” [Jeremy E. Niven and Simon B. Laughlin from the Department of Zoology, University of Cambridge, and Smithsonian Tropical Research Institute, República de Panamá, Energy Limitation as a Selective Pressure on the Evolution of Sensory Systems, Journal of Experimental Biology, 211: 1792-1804, 2008]. They went on to conclude from their extensive studies, “The high energetic costs associated with neural tissue favor energy efficient coding and wiring schemes, which have been found in numerous sensory systems.” This drove the acquisition of genetic systems to make larger and more effective brains and also a better gut, circulatory and respiratory system to better oxygenate and to deliver nutrition to accommodate the remarkable advancements in the mammalian→primate→human brains. There are about a dozen neurochemicals involved in the brain’s electrochemical processes. The human brain is one of the most complex aspects of all evolution, and it should come as no surprise that it consumes more energy than any other organ—burning up 20% of all of the energy taken in by humans.

The concept that humans evolved is one of the most contentious of all issues in the world of modern education. It flies in the face of the common-place and common-sense understanding of religious thinking people around the world. Beginning in this blogpost, the science of human evolution will be presented, and the profound philosophical and religious arguments about the subject will be left to the antagonists. There are a considerable number of interrelated changes found in modern-day humans that favor survival and even dominance in the biological world. Probably foremost of those beneficial traits is that of having a larger, more complex, more subtle, and more efficient brain.

Like other aspects of evolution, the brains of human beings did not spring whole and complete in a short time. What follows in this blogpost is a much abbreviated presentation of the highlights of evolution of nervous systems—note the use of the plural. If the reader wishes a much more detailed and complete exposition, consider doing the work to get through Jon K. Hass, Editor-in-Chief, Evolution of Nervous Systems, A Comprehensive Reference, four volumes, 2000 pages, Elsevier/Academic Press, 2007.

All animal life can be traced back to a common ancestor, and the great variety in nervous systems that exists is the result of imperfect copying of the genetic code from generation to generation as shaped by selection. With little or no lateral gene transfer across lines of descent, complex animal life represents a true hierarchy with a single beginning and multiple branching points. This phylogenetic structure means that nervous systems more or less resemble one another, with accumulated differences that reflect times of branching and rates of change. This relationship greatly simplifies the task of understanding the diversity that exists. As a result of more than a century of work from around the world, we have more accurate phylogenic trees and well-developed methodologies for reconstructing what evolved from what. With the advent of evo-devo, we also know how to link evolutionary changes in genes, anatomy, and physiology to evolutionary changes in behavior by means of both correlative and experimental analyses. As a result, we can construct scenarios of how evolution ‘tinkered’ with nervous systems to help adapt species to their environments for greater fitness, success, and a better rate of reproduction. We know a great deal about how nervous systems scale and how conserved sets of genes and processes are used in a frugal fashion to produce nervous systems that, to previous generations of evolutionary neuroscientists, seemed completely dissimilar.

The nervous system of any animal collects, coordinates, integrates, and disseminates diverse types of information regarding both the external and internal environments. Processing of this information leads to appropriate physiological and/or behavioral responses. The genes and the proteins they produce play crucial roles in embryological development and in evolution, and much is known about them, including the important facts that nature has conserved the DNA templates over eons of time and in a most parsimonious fashion.

Broadly integrative studies by a great many scholars have revealed that invertebrate nervous systems vary dramatically in size, complexity, and functionality, but still are built from highly conserved sets of genes. In that respect, they are quite similar to vertebrate nervous systems, though the diversity is more extreme in vertebrata. It is well to note–at a fundamental level–that all animals engage in some degree of interaction with their environment where they identify and respond to external stimuli. Living creatures have–during their evolution–acquired an implicit knowledge of their environment. They have–by selective pressures in the flow of many generations–been shaped to respond sensibly to their usual environment. This biological process has led to phylogenetic (ancestral) cognition. Cognition is expressed in the body forms and functions that exactly fit their environment. For example: the wings of birds carry information about the density of air. Ever since their reptilian ancestors acquired wings, birds have been the experts in air transport. The flight muscles of insects are equipped for the rapid oscillations of their wings that are so much smaller than birds’ wings. The fins of fish have, during their formation, acquired knowledge of the density of water, and so are equipped for motion in their particular environment. The sensory functions of animals and their feeding behaviors reveal that during phylogeny, they have acquired the necessary knowledge about their usual sources of food.

An accurate way to understand the evolution of the nervous system and the brain is to see it as the addition of higher and higher levels of control. For a sexually reproducing organism to survive and to leave viable progeny, it must be able to control many different types of perceptions, i.e., sensed aspects of its environment. At a minimum, the animal must be able to find food, avoid predators, and to select an appropriate mate. As the environment changed and become more complex and less forgiving and with increasing numbers of enemies, life forms evolved apace with robustness and complexity. The possession of an evolving, and improving nervous system gives a considerable advantage to be able to perceive and to control the increasingly complex and dangerous aspects of the environment.

Here is a very simple synopsis of the graduated steps in the early development of nervous systems:

1. crude nervous reactive system (single-cell amoeba haphazard movement)

2. primitive intercom system with crude memory (single-cell paramecium coordinated movement)

3. clustered cells had no more intelligence than single cells

4. multi-cellular animals lacking a nervous system but possessing the genes for one and neurosynapse proteins (sponges)

5. development of neurons and synapses—simplest true nervous system [decentralized nerve net and simple receptors] (cnidarians, e.g. hydra)

6. increased development of the anterior end of the nervous system and concentration of sensory cells into a primitive central nervous system

7. development of neurons and their specialization internalized into a CNS—one billion years ago (earthworms and planarians—which have CNS genes shared with humans)

8. development of a great diversity of nervous systems (e.g. mollusks)

9. Arthropods (insects and crustaceans) developed a nervous system made up of a series of ganglia, including a brain—or supraesophageal ganglion–connected by a ventral nerve cord made up of two parallel connectives running along the length of the belly and well developed, complex sense organs.

Worms are the simplest creatures to have a central nervous system and to gain the power to have more complex behavior. Mollusks show a great diversity of nervous systems including some such as bivalves that have no cephalization. Arthropods [insects and crustaceans] have a nervous system made up of a series of ganglia, connected by a ventral nerve cord made up of two parallel connectives running along the length of the belly. Although miniscule by human standards, the range of abilities made possible by the brains of insects is impressive; these creatures show a remarkable range and variety of behaviors for locomotion, obtaining food, mating, and aiding in the survival of their offspring. Insects can crawl, hop, swim, fly, burrow, and even walk on water. The brain of the Leafcutter ant is programmed such that it harvests leaves and brings them into its nest where the leaves are used to cultivate indoor gardens of edible fungus. Honeybees have nervous systems that enable them to live in social communities where there is a strict division of labor.

There is extensive evidence that all vertebrate brains are amazingly similar at very early stages of development and are often strikingly similar to phylogenetic changes observed in invertebrates. Evo-devo scientists have found that several conserved genes–notably Pax6–are critical to eye development in both invertebrates and vertebrates. Vertebrates have complex sense organs and exhibit complex behaviors that require a complex, high energy consuming nervous system. Cephalization in vertebrates and the distinction between CNS and PNS [Peripheral Nervous System] is dramatically increased and is much more highly complex than that found in the urbilaterians, worms, and mollusks.

The basic pattern of the CNS is highly conserved throughout the different species of vertebrates and during evolution. During the long evolution leading to the bird and especially the human brain, nervous systems changed in five principle ways: 1. They became increasingly complex, 2. They became progressively centralized, 3. They tended toward cephalization, 4. The size, number, and variety of the elements of the brain increased; and 5. There developed an increase in plasticity, i.e., the brain’s ability to modify itself as a result of experience to make memory and the learning of new perceptual and motor abilities possible and progressive. The major trend that can be most readily observed in vertebrates is towards a progressive telencephalization: In the reptilian brain that region is only an appendix to the large olfactory bulb, but it represents most of the volume of the mammalian CNS. In the human brain, the telencephalon (that region farthest forward, consisting of the cerebral hemispheres) covers most of the diencephalon and mesencephalon (brain stem); and those oldest parts of the vertebrate brain still deal with reflex coordination and life preserving vegetative functions. The newer neocortex region interneurons receive, store, and retrieve information all the while weighing possible responses, a dramatic step beyond reflex function. The allometric–measuring relative growth rate–study of brain size among different species shows a striking continuity from rats to whales. However, with humans, the relative size of the brain does not fit the trend curve”. The human brain is disproportionately larger even than the brains of other non-human primates, including our closest relatives, the bonobos and chimpanzees. Researchers found that the genes of the human brain had gone through an intense amount of evolution in a relatively short amount of evolutionary time, a process that outstripped the evolution of the genes of the other animals. continued…

In my earlier blog; and in Blog 1. of this group of Friday blog posts, I avoided opinion as much as possible on this volatile issue and tried to stay with a dry presentation of the legal arguments and their convoluted progress through the state and federal court systems. Some of the readers of my blog posts consider that my description of the legal issues bespeaks advocacy for same-sex marriage and that; instead, I should limit myself to supporting the married-father-mother-sister-brother family concept. So far as I can determine, evidence for that belief has not been compelling in the courts thus far. Feelings and beliefs are paramount driving forces for the maintenance of the status quo of traditional man-woman marriage. An editorial in the Deseret News, inouropinion editorial section—the newspaper wholly owned and operated by the Church of Jesus Christ of Latter-day Saints in Salt Lake City—dated April 12–presented the strongly felt arguments of the Mormon church which would likely be accepted by the Catholics and other traditionalist religious groups. I will liberally quote from that printed opinion so as not to be misunderstood about what pro-traditional marriage people feel.

The editorial begins, “When a man and a woman marry and have children, that union has a strong impact on those children, and consequently, on the society of which those children become a part. For decades, social science researchers have investigated how family structure affects children by measuring their social and academic progress.” On that much both sides of the question and the courts are in agreement. The editorial quotes a research summary for ChildTrends by K.A. Moore, S. Jekielek, and C. Emig: ‘It is not simply the presence of two parents, as some have assumed, but the presence of two biological parents that seems to support children’s development.’ The opinion writers conclude, “…should this wealth of existing evidence about family structure be ignored? No. In fact, family structure research is more relevant than ever before.” The editorial characterizes the issue before the 10^th circuit court thus: “Indeed, emotion is at the heart of the effort to redefine marriage from a conjugal relationship of responsibility for the rearing of children to a romantic attachment for adults.” The editorial applauds the governor and the attorney general of Utah for their defense of traditional marriage because “…Utah citizens and lawmakers have many sound and rational policy reasons to retain the traditional definition of marriage.”

The Utah argument brief is lauded and quoted, “’the two sexes bring different talents to the parenting enterprise…the weight of scientific evidence seems clearly to support the view that fathers matter.’ The brief went on to state that the absence of a father places a daughter at special risk for early sexual activity and that children reared in same-sex households experience lower high school graduation rates, have higher rates of depression, delinquency, and substance abuse (among children conceived through sperm donation).

The Deseret News opinion took note of the fact that 59 social studies have been conducted which found no disadvantage for the children of same-sex marriages but went on to say, “…Louisiana State University professor Loren Marks examined these 59 studies in excruciating detail and found that each of them relied upon small, self-selected samples of lesbian or gay parents.” Professor Marks’s conclusion was that “The aggregation of these convenience-based samples is less statistically significant than results for robust comprehensive data sets now in use by researchers in the U.S. and Canada.”

Douglas Allen, an economics professor at Simon Fraser University, reported his findings based on the 2000 U.S. and Canadian Census Reports. “…Allen found that girls in a home with homosexual fathers had a 15 percent chance of graduating, compared with girls in a home with a mother and a father. Girls in a home with lesbian mothers had a 45 percent chance of graduating, relative to the mother and father.” Similar decreases in graduation were found in single parent households and cohabiting unmarried couples.

The Deseret News article concluded: “Large-sample social science examining family structure finds that children raised by their biological parents, on average, fare better. That’s one reason state policies promoting traditional marriage are both rational and beneficial.” continued…

In the complicated processes of genetics described in blogpost 20, it is evident that there are multiple areas where even minor alterations in the function of genes, the production of proteins, and the influence of external factors can result in hereditary changes that are profound over time. Evolutionary changes take place over a wide range of time scales, from days to millennia. Macroevolution refers to large scale evolutionary changes that take place over long time periods, such as the splitting of one species into two. Although some processes of macroevolution are observable in human time frames, such as the hereditary increase in size of humans, biologists usually must make inferences about macroevolution based on fossil records or patterns in existing organisms. Microevolution refers to small survivable changes in the characteristics of a population–a group of individuals of the same species that live in the same geographic area and are therefore capable of interbreeding. Microevolution, which includes changes in a single gene, small alterations in the process of protein production and degradation, physical traits, or behavior, can occur over very short periods, especially in organisms with short gestation periods or brief life spans, and often can be observed by biological scientists. A regular example is seen in the rapid development of antibiotic resistance in bacteria.

Population geneticists examine a population’s gene pool (the total of all the different variations of genes that exist in a given population) and observe changes in the frequency of different alleles over time which can be documented using the Hardy-Weinberg Theorem as described in evolution blogpost 5. Any deviation from the Hardy-Weinberg Theorem suggests that the population is adapting and that the process of microevolution is taking place.

There are five basic causes of microevolution: 1. Mutation, 2. Genetic drift, 3. Gene flow, 4. Non-random mating, and 5. Selection. Any of the five processes may alter the genetic structure of a population, including allele frequencies, genotype frequencies, and genetic variation–the number of different alleles per gene; and, in sum, may lead to the eventual profound change of speciation.

The following is a very brief note on each of the five processes:

1. Mutation is the random change in the DNA sequence of a gene–the only process that produces new alleles. As the number of alleles present in a gene pool increases, the likelihood of mutation and genetic variation in the population also increases. A number of events in DNA replication can bring about a mutation: changes in sequencing, positioning, loss or duplications, or insertion of a foreign substance into the gene. In general, because the rates of mutation are so low, they have a relatively minor effect compared with the other evolutionary processes. Genetic and molecular biologists estimate that one mutation occurs in every 100,000 genes per generation. Humans have 25-26,000 genes which means that approximately one in every four babies has a new mutant. The chances are slim that the mutation will have an effect on survival and will be selected as a trait contributing to fitness to produce a change that is reflected in the population. Nevertheless, mutation is the key to evolution, and without it, evolution would not take place. Because of the rarity of beneficial mutations, the process of evolution as dependent on mutation is understandably extremely slow.
2. Genetic drift is an unpredictable, chance change in allele frequency that causes one allele to become more common in a population than another allele. Genetic drift can occur slowly over time, or it can occur as the result of a sudden decrease in population size due to bottlenecks and what is known as founder effects. In most instances, the larger a population is, the more stable its allele frequencies are, and the less likely it is to experience genetic drift.

Bottlenecks occur when a population undergoes a sudden and drastic reduction in size. Natural disasters can cause bottlenecks, and the rapid reduction in a population size may lead to the loss of alleles if they are not present in the surviving population. There are then fewer alleles available to be passed on to the next generation.

Founder effects occur when a few individuals are isolated from their original group and form a new population. When two individuals colonize an island, for example, they may not have all the alleles that were once present in the original population. The result is a change in allele frequency and a decrease in genetic variation, much like that seen in the more global effect of bottlenecks. Both bottlenecks and founder effects lead to changes in allele frequencies if the few surviving or colonizing individuals are not representative of the original population. Often rare alleles are lost during these events as individuals who possess them die off or leave, thereby lowering the genetic frequency of the entire population.

For example, northern elephant seals were hunted to the brink of extinction during the late nineteenth century. As a result, many alleles were lost. Although the population has recovered since that time owing to the intervention of international laws about seal hunting, the effects of the human-caused bottleneck are still present. Northern elephant seals today share many of the same alleles and possess extremely low genetic variation across the entire species. Similar effects are seen in families and cultures that favor consanguineous marriage (e.g. the retention of the hemophilia trait in the French hereditary monarchy).

3. Gene flow occurs when organisms migrate from one population to another. A population might lose some alleles when individuals leave the population and might gain new alleles when other individuals join the population.

4.         Nonrandom mating occurs when mating takes place unequally between members of a population. Mates may match up due to individual choice, or selection, as members of a population favor certain characteristics possessed by some members over those possessed by others. Nonrandom mating is likely to alter both alleles and genotype frequencies in a population, since the alleles for the preferred characteristics will increase in frequency in the population. Other types of nonrandom mating, such as inbreeding, may alter genotype frequencies as well.

A dramatic example of this phenomenon is found in a question that has puzzled zoologists for more than a century: How did the Peacock get his tail? Charles Darwin first noted that the very choosy peahen plays a crucial role in the evolution of this extravagant sexual display. It is safe to conclude, as he did “that…those males which are best able by their various charms to please or excite the female, are under ordinary circumstances, accepted. If this be admitted, there is not much difficulty in understanding how male birds have gradually acquired their ornamental characters.” However, the magnificent tail comes at a large energy cost: it must be regrown every year; and the resplendent colors of the large tail attract predators. Hamilton and Zuk (1982) first suggested that more showy males were signaling to females that they were, if not parasite free, then at least had a reduced load of parasites. Until recently, there has been little evidence to support this hypothesis. Anders Pape Moller and Marion Petrie, Condition Dependence, Multiple Sexual Signals, and Immunocompetence in Peacocks, Behavioral Ecology 13, No. 2: 248-253, 2002, from Laboratoire d’Ecologie Evolutive Parasitaire, Université Pierre et Marie Curie, and Evolution and Behavioral Research Group, Department of Psychology, University of Newcastle, UK, now suggest that the plumage of the male may specifically convey the strength of the male’s immune system and therefore his desirability as a mate. They took blood samples from male Blue Peafowl (Pavo cristatus) and recorded the numbers of B and T cells, and also measured the peacocks’ tails and counted the number of eye spots. The researchers discovered that the condition and length of the peacock’s tail was related to the production of B cells, and the size of the eye spots was related to the male’s T cell production. That is, females look at aspects of the males’ immune competence as reflected in the degree of elegance of the males’ tails. In effect, the males strut about advertising their health and fitness. Other research in chickens and quails had demonstrated that the immune system is under genetic control; so, offspring will inherit their parents’ ability to fight parasites. The enhanced immunity from parasites for offspring trumps the problems of the energy costs and attractiveness for predators because of enhanced reproductivity. Therefore, the ostentatious adaptation persists.

5. Selection, both natural and sexual, occurs when some individuals leave more progeny than others, resulting in dramatic changes in allele frequencies in a population. Selection is often classified according to those individuals favored, or more fit, to issue more offspring. There are three basic kinds of selection: stabilizing, directional, and disruptive.

Stabilizing selection occurs when individuals with average phenotypes are favored, and those with phenotypic extremes are selected against.

Directional selection occurs when individuals of one phenotypic extreme are favored, and those at the other extreme are selected against.

Disruptive selection occurs when individuals of both phenotypic extremes are favored, and those with intermediate phenotypes are selected against.

An example of disruptive selection can be observed in populations of sticklebacks, a species of fish found in freshwater lakes of Canada. These fish often have two distinct phenotypes: a variation which specializes in feeding at the bottom of the lake, and one that specializes in feeding at the top of the lake. These morphs represent two phenotypic extremes demonstrated in the number of spiny plates they possess. More plates yields more protection against predators. Alterations in the availability to obtain food in the water depth to which evolution has placed them may alter survival.  Individuals with intermediate phenotypes are selected against because they cannot feed efficiently at either the top or the bottom of the lake.

The evolution of stickleback fish is more complicated that just being directed by disruptive selection, however. The geologic/fossil record indicates that the oceanic threespine stickleback fish that invaded the lakes and streams created by melting glaciers at the end of the ice age became isolated as the glaciers disappeared. The original ocean form of stickle-backs has a continuous row of more than thirty armor plates running from head to tail. In many fresh water populations, this number has been reduced to a range of from 3 to 9 plates. The selective advantage of plate reduction in freshwater lakes and streams may be due to greater body flexibility and maneuvering while swimming. The evolutionary effect was seen dramatically in Loberg Lake, Alaska when oceanic sticklebacks colonized the lake after a chemical eradication program exterminated the resident populations in 1982. Over a span of just twelve years, from 1990-2001, regular sampling revealed that the frequency of the oceanic form dropped steadily, from 100% to11%, while a form with low plate number rose to 75%, an example of directional selection and a striking example of very rapid microevolution which has occurred during the lifetime of most of the adults of the world.

The evolution of populations proceeds by rules that have been found by researchers over the many years that population genetics have been studied. The rules for constructing phylogenetic trees are:

1. Maximum parsimony—A phylogenetic tree is designed to demonstrate the fewest possible evolutionary events–changes in characters–and the fewest instances of homoplasy–shared character states not inherited by a common ancestor; parallel evolution or convergence–between branches. Trees constructed using the rule of maximum parsimony seek to simplify relationships by requiring the fewest assumptions about relatedness as possible.
2. Maximum likelihood—Evolutionary events are weighted according to the likelihood of occurrence. As genomic research advances, biologists are finding that DNA characters evolve at different rates, which suggests that homoplasy may happen more often than the rule of maximum parsimony would allow. continued…

Although researchers made brilliant discoveries that contributed to the understanding of heredity and of evolution before mid-twentieth century, the discovery of DNA–a biological molecule in the shape of a double helix–changed the rate of acquisition of knowledge and understanding of the two pillars of biology to an explosive degree. After a race to see who would be first to publish on DNA, Watson and Crick succeeded: Watson, J.D., and Crick, F.H.C., A Structure for Deoxyribose Nucleic Acid, Nature 171:737-738, 1953. DNA is composed of two chains, strands of nucleotides wrapped around each other in a helical—sort of a spiral staircase—configuration. Each individual nucleotide is composed of three parts: a phosphate group, a deoxyribose sugar, and a nitrogenous base. A covalent bond forms between the phosphate group of one nucleotide and the sugar group of an adjacent nucleotide, resulting in a strong sugar-phosphate frame. Hydrogen bonds form between the nitrogenous bases of two nucleotide chains to form the unique double helix of the DNA molecule. Because hydrogen bonds are much weaker than covalent bonds, the two strands of DNA can unzip from each other relatively easily.

A single DNA chain contains an arrangement of nitrogenous bases: Adenine (A), cytosine (C), guanine (G), and Thymine (T). The bases on one chain form complementary base pairings with the bases on the opposite chain in a single DNA molecule with specific rules governing those pairings. With the discovery of DNA and its function it soon became established that genes are the basic unit of heredity, and they are housed in the DNA structure of every organism. DNA houses an organism’s genome, which is that organism’s complete genetic material. When a cell divides, its DNA must be duplicated in a process called DNA replication so that both resulting cells receive a complete copy of the genome. During replication, the two strands of DNA unwind; each strand then serves as a template for the formation of the new opposite strand, built with near perfect accuracy according to rules of complementary base pairing. If a template strand has an A in one spot, then a T is placed in the opposite strand. Because each DNA molecule consists of one old strand and one new strand, DNA replication is said to be semiconservative.

Assembled human PCNA (PDB ID 1AXC), a sliding DNA clamp protein that is part of the DNA replication complex and serves as a processivity factor for DNA polymerase. The three individual polypeptide chains that make up the trimer are shown. (Photo credit: Wikipedia)

The process of DNA replication occurs in six basic steps: 1. The enzyme helicase unwinds DNA at specific sites along the chain. 2. RNA primers are laid down along the template strand by the enzyme primase. The RNA acts as the starting point for DNA to build on. 3. Elongation begins with the enzyme DNA polymerase adding nucleotides to the end of the growing strand. Elongation proceeds in a different manner in each strand. Nucleotides are added continuously to the leading strand with replication occurring in pieces. 4. The RNA primers are removed and replaced with DNA by the DNA polymerase. 5. The enzyme DNA ligase binds together the fragments of the lagging strand. 6. Chemical proofreading processes take place to remove nucleotide mistakes by DNA polymerases reversing direction. In this post synthesis process, enzymes conduct mismatch repair by scanning the newly formed DNA strand and repairing any errors that are found. It is of significance to note that mutations in mismatch repair genes, which encode the enzymes that proofread and correct errors in DNA, are known to be responsible for certain hereditary forms of cancer. Other mutations may prove to be lethal in and of themselves. Rarely, a mutation is actually beneficial and adds an incremental change which favors survival. Francis Crick went on to establish the process by which DNA produces protein: DNA→RNA→Protein.

Gene expression is the synthesis, or production, of proteins according to the information encoded in DNA. Gene expression is the accumulated phenotypic characteristics, or physical and functional display of a specific genotype. Since proteins determine the structure and function of the cell, gene expression, in effect, controls the cell. Genes are not expressed randomly, or even at equal frequency, within the cell. Instead, the timing and frequency of gene expression is controlled by the individual cell. Many biologists are of the opinion that the differences between humans and chimpanzees arise mainly from differences in gene expression, rather than differences in the genes themselves. The genes of humans and chimpanzees are 98.8% exactly the same and 99% similar, yet the patterns of where and when each gene is expressed in the body are vastly different between the two species. Regulation of gene expression in animals with which we are most familiar occurs at every stage of protein synthesis and is an extremely complex process with multiple sites where mutations can result in profound alterations in function and outcome, most of which are lethal. continued…

Dominant and recessive phenotypes. (1) Parental generation. (2) F1 generation. (3) F2 generation. Dominant (red) and recessive (white) phenotype look alike in the F1 (first) generation and show a 3:1 ratio in the F2 (second) generation Originally from en:Nupedia, by Benutzer:Magnus Manske (Photo credit: Wikipedia)

The findings described in Evolution Blogspot 18 make it no longer tenable to presume that the myriad different forms of organisms currently extant or those that preceded modern organisms came by specific and different mutation-produced adaptations, separate and distinct from each other. It is highly improbable that such directed diversity could have happened over any amount of time. A more simple, rapid, and efficient basis for evolution has been delineated. This evolutionary efficiency is based on Hox “tool-kit” transcription factors that turn tool-kit genes on and off, signaling cell groups that communicate with other crucial clusters of amino acids, and “switch” genes, and the changes they undergo. Perhaps the most dramatic aspect of these findings is the common ancestry of such diverse creatures as worms, fish, flies, and humans. The finding of the genetic basis of heredity and evolution has now been convincingly linked to the abundant fossil record; the present is a key to the past.

Developmental regulatory genes–also called master control genes–constitute a small fraction of the genome, and encode transcription factors or signaling proteins, that directly–through direct DNA binding–or indirectly–through signal transduction cascades–regulate the expression of other genes and control key aspects of development and formation of specific body parts. (Sean B. Carroll, et.al, From DNA to Diversity. Molecular Genetics and the Evolution of Animal Design. Blackwell Science, 2001).

This very brief elucidation of Evolutionary Development leads to an understanding of the mechanisms of evolution which will be equally briefly described in this blogpost. Beginning with the ancient Greeks and on through the Jews, early Christians, and Muslims until the twentieth century, most people, even educated ones saw human reproduction, and indeed, all animal reproduction as the implanting of a seed passed from the male into the female as passive receptacle. The concept of heredity was on the level of a “mixing of bloods”.

The scientific understanding of heredity and thence to the

Other rules related to the fact that not all alleles are strictly dominant or recessive, although the characteristics Mendel studied were. The more complex hereditary principles related to differing degrees of dominance came from later researchers and included such elements as: incomplete dominance, co-dominance, polygenic inheritance, epistasis, and pleiotropy, which are less basic to the understanding of evolution and will not be further described here. In the next blogspot, a discussion of genes, gene expression, and DNA will be presented along with the tie of that area of molecular biology/genetics to the process of evolution. continued…understanding of evolution began in the nineteenth century. Austrian monk Gregor Mendel (1822-1884) in experiments with pea plants discovered the underlying principles of inheritance. Using the pea plant, Pisum salivum, which had a short generation time, many offspring, was small and easy to grow, had many varieties, and had eggs that could be manually fertilized with sperm thereby guaranteeing known parentage, he derived laws of inheritance that hold today. Mendel postulated rules of inheritance based on his hypothesis, his scientific experimentation, and finally on his validated theory. His rules produced and understanding of what was happening in heredity: 1. The units that determine characteristics, or traits, come in more than one form or allele. 2. Each gamete–a sperm or egg cell–contains one copy of a particular gene. When gametes fuse during fertilization, the resulting offspring contain two copies of each gene–the principle of segregation–which states that pairs of genes separate during meiosis and form new pairings as gametes fuse during fertilization. 3. Each organism possesses two alleles for each gene, one from each parent. An organism is said to be homozygous for a specific trait if it inherits two identical alleles for the corresponding gene. An organism is heterozygous if the two genes are different. 4. In a heterozygous organism, one trait may be fully expressed, or dominant, while the opposing trait is not expressed at all, or recessive. Recessive alleles are only expressed if the organism is homozygous for that gene. 5. The alleles of different genes are assorted randomly and are independent of each other–this rule of independent assortment.