There is a grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one: and that whilst this planet has gone cycling according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being evolved.
-Charles Darwin, The Origin of the Species
The previous blogspot is an oversimplification of the elements of evolution. In the first place, many definitions are left out in order to keep this very complicated subject as simple as possible and yet to leave enough to convey an understanding of what evolution is and how it takes place. This blogspot selects certain of the most important concepts and amplifies them to further bring to understanding the core concepts of evolutionary processes.
1. Adaptation:It is incorrect to say that selection acts on a trait thereby leading to evolution. Selection is a passive and indifferent process with significant results, but is not a mechanism that is imposed on an organism or a species from the outside. Rather, it is a process of genes in organisms in an environment that produce better adaptations for that environment becoming more prevalent, more frequent, and resulting in better reproduction of organisms to survive in that environment. Adaptive traits—modifications–are best said to be undergoing the process. Mutations occur at random and by chance, but it is the filtering of that variation by natural selection, which is not random, that produces adaptations and imposes the order and design seen in species. Richard Dawkins described the process as “the non-random survival of random variants”. Natural selection is the cause of all adaptive evolution except for that produced by genetic drift.There are a multitude of examples that could be chosen to illustrate the process, but let three suffice:
i. ~The Asian giant hornet–four inches long, two inches around, with a three inch wing span, armed with huge clasping and slicing jaws, and a quarter inch long poisonous stinger that can kill humans–is a malevolent marvel of evolution. It is ferocious and a voracious eater. It eats introduced European honeybees and relatively docile wasps. A single giant hornet scout finds a nest and marks the nest with a pheromone. The scout’s nest mates then descend on the honeybee nest and twenty to thirty of them slaughter 30,000 bees at the rate of 40 per minute until every bee is dead. Then the giant hornets eat every drop of honey in the hive and take the bee grubs back to their own nest and feed them to their ravenous offspring. The honeybees, having never encountered such powerful predators are defenseless.
However, Japanese honeybees have been subjected to the Asian giant hornet predation for a considerable period of time and have adapted admirably to the threat. Evolution provided a highly successful answer to the alternative of being devoured. The Japanese bees react to the scout wasp as soon as it arrives at their hive. The bees lure the scout inside their hive then swarm all over and around the wasp. Other hundreds of bees block the entrance. The wasp becomes covered in a tight ball of living bees which vibrate their abdomens, quickly elevating the temperature inside the ball and around the wasp to 117º F. The bees tolerate that temperature without difficulty, but the wasp cannot and is cooked to death before it can spread the information about the bees back to its nestmates. Unlike the European honeybees which evolved in an environment lacking giant hornets and are defenseless, Japanese honeybees lived for a long time with the predatory giant hornets and adapted to have an ingenious defense. The Japanese honeybees adapted and live; the European honeybees must adapt or die. That is the way of evolution—“Nature red with tooth and claw”, as Tennyson described.
ii. ~Birds and larger insects eat katydids but do not eat rotten vegetation. Some katydids, however, have adapted a phenotype that mimics leaf patterns complete with rotten holes appearing on them. Over time, the mimicry became so exact and precise, that the katydids are difficult to pick out from a patch of real vegetation. The katydids’ natural predators are fooled, at least sufficiently to allow a goodly proportion of the katydids to escape predation and to live and procreate. Over vast periods of time and in tiny increments, the genes of the katydid survivors came to produce the faux leaf phenotype. This is the essence of evolution by the process of selection.
iii. ~Common oldfield mice (Peromyscuspolionotus) burrow in dark brown soils. They have brown coats. A few such mice have varying degrees of lighter color in their coats. Hawks, herons, and owls hunt for the mice and, in the dark soil habitats selectively capture the lighter coated mice, and significantly more of the dark mice survive. However, in the white sand beaches ofFlorida, there are oldfield mice that are white. The same hunters fail to succeed sufficiently in their attacks on the mice that the colony survives in a healthy balance with its predators. Scientists performed an experiment with mice with multiple different color shades and patterns. The scientists isolated mice of different colors in an equal mix on habitats of dark and on habitats of light soil. They then released very hungry owls into the separate areas of habitat. The findings were as expected. The dark mice in the light colored soil habitat were decimated. The light colored mice on the light colored soil habitat survived and vice versa. The more the mouse color blended with the environment, the greater was the survival of that color of mice. The adaptive process was quite rapidly translated into selection and evolution with the color of the mice in the given habitat adapting over a few generations to the protective coloration in the majority. This evolutionary process was evident and persistent within a few hundred generations of mice, which are short enough, that the scientists could visualize the process during the period of their experiment (and not in a huge geologic time frame). In nature, the adaptive evolutionary process occurred about 6,000 years ago.
This heritability requires changes in genes—mutations. Other scientists working with the same strain of mice isolated two genes that have been involved in the dark/light adaptive transitions: Agouti, which is responsible for the dark color of some domestic cats and McIr, which is responsible for the productions of skin freckles and red hair, which mutation and trait is seen in abundance in the Irish. Obviously, the mutation–when it occurs–must allow the adaptive trait–in this case hair color–to be heritable, i.e., the mutation must not be lethal or cause the possessor of the mutation to be sterile. In the case of these mice, the mutation was benign.
Many adaptations observed by either scientists or lay people are relatively direct, simple, and observable during the lifetime of the observers like those described above; but the same processes of random mutation, natural selection, genetic plasticity and heritability, and adaptation have worked over eons of time to produce the fascinatingly complex flagellum of e-coli, the delicate wing feathers of birds, and the host of intricate eyes seen in nature. No magic, no sudden creation of something from nothing, just a natural process—one that is well studied and understood by science.
2. Biogeography: There are three islands in the Juan Fernández group, which lies 400 miles west of Chili. They are among the most isolated of all locations on earth and; as such, they are considered an international treasure as a laboratory for the study of evolutionary change. One of the islands, Más a Tierra, is now called AlejandroSelkirkIsland, after the famous mariner who was marooned on the island at his own request and after four and a half years of isolation, became the real life model for the book, Robinson Crusoe. Besides Selkirk himself, the only mammals were goats, rats, and cats introduced by other sailors. Otherwise, the vast majority of the plants and animals are endemic to the island—i.e., they are present nowhere else on the planet. Those unique animals and plants include five species of birds—such as a giant rust-brown hummingbird, and the endangered Juan Fernándezfirecrown—126 species of plants including bizarre members of the sunflower family, a unique fur seal, and a handful of insects. There are more endemic species on the island than anywhere comparable. The truly remarkable finding is that there are no amphibian, reptile, or mammal species at all.
In fact, the same classes of animals and fresh water fish are missing on all oceanic islands–land masses that came up out of the sea de novo–because of the great difficulty for those land-based animals to get there. Air and sea borne animals can get there as established by myriads of studies and experiments. Amphibians, reptiles, mammals, and fresh water fish are found in abundance on continentalislands–land masses that broke off from continents–because they were there from the beginning. Especially on oceanic islands, transport of animals is a relatively rare occurrence accounting for the very few mammals such as flying bats which do get there. Although some nonflying insects raft to oceanic islands or are carried there by birds or wind, most oceanic island insects are fliers, and most plants and animals and their fossils are most similar to those found on the nearest land masses despite the common finding of marked differences in environments in the two locations. The few species that do make it out to oceanic islands adapt and thrive in the new environment, and undergo speciation in remarkable numbers, e.g., Darwin’s finches; the Juan Fernández woody, treelike sun flower; and the few primates that made it to Madagascar 60 MYA and developed 75 different endemic species there over time. This thesis of the “Robinson Crusoe effect” is borne out powerfully by following the evidence of fossils and gene changes that comes from the study of evolution:
Fossil seashells are found on mountain tops around the world. All native mammals inAustraliaare marsupials while almost all mammals elsewhere are placentals. These biogeographical oddities depend on three things: dispersal followed by evolution and then a changing earth. In addition, there had to be convergent evolution—different routes of evolution to achieve the same, or what is apparently the same, visible result, e.g., different flightless birds on multiple continents and animals such as marsupial moles inAustraliaand moles inAmericawith different genetic constructs which could not possibly have happened from dispersal alone. On the other hand, there are some plants and animals that are endemic to widely separated earthly locations and are the same or extremely similar: skunk cabbage, magnolias, and tulip trees, wild pigs and monkeys, European red deer and North American elk, which can only be explained by having lived in the same areas before continents separated and began their evolution after the separation.
A prime example, and one which was predicted by evolutionary theory, is the study of fossil marsupials. The earliest marsupial fossils are found inNorth Americaand as time passed, they moved southward. Marsupial fossils dated to 35-40 MYA are found on the tip ofSouth America. The theory of continental separations predicts that fossil marsupials should be found on Antarctica with the same geologic time frame; the two continents separated about 35-40 million years ago. That could only have happened hadAustraliaandAntarcticaseparated carrying the same marsupials away toAntarctica. Indeed such fossils were found there as predicted. In brief, the only explanations which make any sense for the examples given above lie in the principles of evolution. Creationism is stumped by these biogeographicaloddities, and the subject is all but absent from creationism literature.
One would expect fossil remains of specific animal strains to be found on the same continents upon which they live today, and that is the regular finding. The co-occurrence of fossils and modern animals lies at the biogeographical base for the evidence of an African origin for Homo sapiens and that species’ dispersal throughout the world. Extinct ape fossils and modern living apes inhabitAfrica, and the earliest human progenitor fossil forms are found there. Very few scientists doubt the very early origins of human-like creatures (~6-7 MYA) or that they began in southernAfrica.
3. Chromosome: In most sexually reproducing organisms, chromosomes occur in pairs, with one member of the pair inherited from each parent, and the two chromosomes are strongly bonded between the pairs of bases on opposite stands. The sequence of nucleotides in DNA can change from one generation to the next because of mutations—to beneficial, or to harmful, or to neutral traits. Beneficial traits often result in new DNA being spread within a population over multiple generations. Both neutral and beneficial mutations leave a record in DNA which can be seen in chromosomes. By comparing the DNA sequences of two organisms, biologists can see the genetic changes that have occurred since those organisms shared a common ancestor. For example, one of the most studied is the cystic fibrosis gene found in humans and is almost identical to a gene found in chimpanzees. Another is the gene that forms leptin which is involved in the metabolism of fats. There are only 5 differences between the two species in the 250 nucleotides that make up that gene in each species.
4. Co-Evolution:There are two fundamental kinds of processes or series of environmental stressors coupled with genetic changes involving more than one organism or gene that result in actions, changes, or change of function that bring about an evolutionary result:
i. Co-adapted genotypes. A gene has a particular effect that it causes only if there exists a structure upon which to work. Obviously a gene that causes wiring up of the brain in the developing embryo cannot work if there is no brain. These co-adaptations are built into the existing embryological process; and they may be determined, changed, deleted, or activated by genes. The gene’s environment is all the other genes in the body, and the genes persist in the cells of each successive individual body.
An interesting example of the adaptation process was found by Professor Charles Clarke and his colleagues at the Royal Roads University in Canada. They reported the discovery of a large, carnivorous pitcher plant in the Philippine Highlands which had evolved an alternative strategy from that of the same plant located inBorneo. TheBorneoplant eats insects and spiders, and the Philippine counterpart prefers that diet but where those are in short supply, the pitchers have grown to a size that accommodates an alternative source of crucial nitrogen. Over time, these pitchers have added a feature that allows them to produce copious amounts of nectar which attracts the tiny mouse-like tree shrew to harvest the nectar. The shrews, trapped inside the plant, leave nitrogen rich droppings directly on the precise spot where the pitcher plant can consume them and thereby survive until its preferred source of nutrition–insects and spiders–increase in sufficient supply to fulfill the needs of the plant.
ii. Arms-race. The complex interplay over time between predator and prey species–mortal enemies–results in changes linked to survival or extinction, both elements of evolution. Every morning on theSerengeti Plain, a Gazelle wakes up early and begins to run. In order to survive, the Gazelle must run faster than the fastest lion, or it will be caught and eaten.
Every morning in the same area, a lion awakens and begins to run. He or she must be able to outmaneuver and outrun the slowest Gazelle, or the lion will use up too much energy on failures. If there are too many failures, the lion will starve. Each of the paired prey and predator species evolves incremental features that enhance survival.In this case, a significant part of the environment is the other animal and its innate capabilities. Mutations occur and a fraction of the Gazelles develop longer legs and can run faster. The lions which cannot catch the new generation of Gazelles die out, but among the population of lions are a few who are bigger, stronger, fleeter, have longer endurance, and have a greater proportional hunting success. They alone do not starve and live to pass on their beneficial genes. The Gazelles who are to survive the predation of these stronger, faster lions must themselves become still quicker, have faster reactivity, be more agile, have more endurance, and have keener senses of smell, hearing, and sight. And the lions facing the better adapted Gazelles live only if they come from a genetic population with greater ability to cooperate with other members of the pride in the hunting process, and on, and on, in an inexorable escalating stalemate.
Cheetahs catch prey 70% of their predatory attempts, lions 50%. 3-5 million years of evolution provided cheetahs with a streamlined body that can achieve strides that carry them 23 feet on average. However, that streamlining came at a price: they lack bulky powerful muscles, jaws, or teeth; they are not able to fight well. 90% of their cubs succumb to predation and 50% of their food is stolen by more aggressive predators like lions and hyenas. They are quick but lack endurance and often cannot run long enough to catch their intended Gazelle or to evade the lion chasing them. 500 MYA the common ancestor of cheetahs, sail fish, and peregrine falcons evolved for speed, and its subsequent branches became the fastest animals in their differing environments.
The genus Lepidoptera—butterflies and moths—provides an especially clear example of the arms race in action. Lepidoptera metamorphose from larva→pupa→adult. The first phase of life is spent as a caterpillar whose sole reason for being, for practical purposes, is to accumulate enough food and energy to complete pupation, making it little more than an eating machine. Caterpillars generally feed on only one or two plant species. In the rain forest, they must specialize because most rain forest plants produce toxic, sticky, or indigestible substances which deter herbivorous insects. In order to avoid starvation, the caterpillar has had to evolve counter measures by producing a veritable army of toxin neutralizing enzymes. The problem for the caterpillar is that the production of such large amounts of proteins is a highly expensive activity from the aspect of energy production. Hence, the caterpillar must conserve on the amount of enzymes it can make. The trade-off is that the caterpillar can only produce enough enzymes to neutralize the defenses of a few different plants. As one plant type evolves greater defenses, the caterpillar must produce more and more enzymes to deal with the defenses of just that one plant leaving little left over energy to deal with different plants. Inevitably, the caterpillar must evolve to become increasingly more specialized to be able to feed on just one or two plants. Such runaway co-evolution is known to be an important speciation producing mechanism.
But the arms race for Lepidoptera is more complicated. As the caterpillar eats plants out in the open, it leaves evidence of its energy consuming activities. These evidences come to the attention of birds or other predators. Then begins a second co-evolutionary arms race. The predator must find ways to overcome the defenses of the caterpillar, and the caterpillar must evolve to avoid becoming a meal and for the species to avoid extinction. Lepidoptera has evolved two basic defense strategies.
Deception or mimicry is one method. The caterpillar and other mimicking species evolve in a way that makes them appear to be a copy of some natural object, such as a twig, or eyes or other parts of larger and more dangerous creatures. One species of moth caterpillar resembles the whole head of a snake complete with a wiggling tongue appendage. Another looks like a bird dropping.
In order not to starve, the predators in this co-evolutionary duel must evolve the ability to identify better and better the caterpillars’ deceptions. The caterpillar must become more and more like the object it mimics—better and better at camouflage. It is an eternal battle between species in a deadly interplay with life and death consequences and ultimately, species extinction as the result of failure in the arms race.
Another strategy employed by caterpillars is to use poison and bright identifying colors. Often they acquire their toxins from their host plants. Rather than starve, the predators evolve ways to deal with poisons; so, in turn, the caterpillars become even more poisonous. This adds a complicated and sophisticated chemical warfare aspect to the co-evolutionary arms race. When the energy requirements to make toxins become overburdensome, some caterpillars evolve mimicry of still more toxic caterpillars to avoid predation (discovered by Henry Walter Bates during his investigations of moths and butterflies in the rain forests ofBrazil—BatesianMimicry).
The examples of co-evolution among prey and predators seem nearly infinite. An extra pair of eyes, even phony ones, can be a boon to insects hunted by predators that target by sight. A saw-noses plant hopper’s first defense is camouflage. But if a bird, lizard, or other hunter takes aim, the insect can startle its foe by unveiling red spots that could be mistaken for the eyes of a larger animal. A butterfly pupa–a species discovered in Costa Rica by Daniel Janzen of the University of Pennsylvania–also shows a false face. “Peering” from a rolled-leaf shelter, its eyespots may deter small birds exploring the foliage for insect prey. Though a prevalent ploy in nature, the fake-eye look is not fool-proof. Animals that get caught may have secondary defenses, like a foul taste or toxic secretion. The plant hopper takes a more spirited approach, buzzing like a stinging wasp to provoke a quick release.
The Hyalymenus nymph hides in plain sight. It has evolved to look and act like sap-eating ants, much fiercer creatures that can sting or wield toxins, spines, and communal grit. Predators that learn to avoid the ants are likely to bypass this imposter. At times the ants discover the copycat among them and attack Hyalymenus. Both ants and Hyalymenus are in a constant state of evolutionary flux in order for their species to survive.
Moths and bats have a similar arms race. Bats emit sonic clicks to detect the movement of aerial insects at night. Some poisonous moths emit warning clicks to announce their lack of palatability. Nonpoisonous moths have tiny hairs that detect the slight air vibrations generated by the bat’s click, and the moth instantly drops beyond the bat’s flight path. As a consequence, over time, bats’ ears have become larger and more sensitive; and they have become more capable of rapid direction changes in flight. The moths have become more and more alert to the presence of bats and more and more capable of lightening quick and erratic movements. There appears to be no predictable end to this complicated dance macabre of nature.
Other examples abound in the natural world: Cows are the enemies of grass; short trees must increase in height to compete with taller trees or lose out, and this drives the average height up and up in the canopy. The coevolution of diet and other factors plays a role in the evolutionary arms race. An interesting example is found in Barlow, A., et. al., Co-evolution of Diet and Prey-Specific Venom Activity Supports the Role of Selection in Snake Venom Evolution. Proceedings of the Royal Society (Biological Sciences) 276: 2443-2449, July 7, 2009.
Biologist Leigh Van Valen called this the ‘Red Queen Effect’ alluding to Lewis Carroll’sbook, Through the Looking Glass, where the Red Queen seizedAlice by the hand and dragged her faster and faster on a frenzied run through the countryside. No matter how fast they ran, the Red Queen and Alice always stayed in the same place. ToAlice’s complaint that in her country when you run fast you get someplace, the Red Queen replied, “Now, here, you see, it takes all the running you can do to keep in the same place. If you want to get somewhere else, you must run twice as fast as that.” The arms race produces bigger, better, faster, more cunning, more enduring, better adapted predators and prey species—the essence of evolution.