Stephen Hawkings and Leonard Mlodinow, writing in their book, The Grand Design, published August 25, 2010, defined a model [or theory, for the present purposes] this way: “A model is a good model if it:
- Is elegant (i.e., is the most clear, concise, and complete statement that explains observable phenomena).
- Contains few arbitrary or adjustable elements.
- Agrees with and explains all existing observations.
- Makes detailed predictions about future observations that can disprove or falsify the model if they are not borne out.”
In every particular, the Darwinian Theory of Evolution, is in agreement with the definitions of those two famed theoretical physicists and their colleagues in the biological sciences. That leads us to Darwin’s theory.
20. The Darwinian Theory of Evolution: The theory has been modified since Charles Darwin and Alfred Russel Wallace first articulated it in 1858, and Darwin presented his thesis in 1859—The Origin of Species. The theory of evolution or natural selection holds that measurable change in animals and plants over time comes from the changes in heritable traits as measured by allele frequency of a population through successive generations—Mendelian transmission genetics. Natural selection is, therefore, the process by which species–not individuals–adapt to their environment in small incremental steps over time, usually, a long period of time. In addition, branching phylogenes result in branching speciation expressed in hierarchal patterns. The process leads to relentless and directed evolutionary change wherein individuals with certain characteristics have a greater survival or reproductive rate than other individuals in a population and pass on those heritable genetic characteristics to their offspring. An evolutionist put it this way, “variation proposes, and selection disposes”.
While mutations occur at random and by chance, the process of natural selection is far from directionless. The direction is not pre-designed, but once a mutation has occurred and survives, selection is driven by environmental pressures and developmental constraints to produce an organism and a population that can adapt and survive. DNA can accurately be said to exert power over its own future which expands, diversifies, becomes more complex, and uses the changes wrought to advance still further and sometimes faster. The structures, organs, and bodies that develop become instruments of DNA’s power to continue to produce salutary advancements. The embryological developmental constraints–and therefore an element of direction to evolution–come from the channeling of genetic mutations, or by filtering them, through mechanisms of development that favor the emergence of some phenotypes. Some structures may be impossible for embryos to develop; others are likely to emerge and to persist in the DNA; so, they can be passed on to successive generations. Natural selection, therefore, chooses not from an entirely random selection, but from a structured set that is determined–or at least biased–by the mechanisms of development. Evolution is constrained by diverse physical principles, by rules of construction and good design, and by some scaling rules. The result of these constraining influences of development and principles of construction is to drive the direction of evolution and to hasten the evolution of a certain structure or characteristic at a pace that exceeds what would be predicted by mathematical statistical expectations alone.
Evo-devo [evolutionary development] scientists tend to accept the concept that natural selection is the most prominent determinant of who thrives and who dies or fails to reproduce, no matter how constrained development might be. They also stress that development itself is subject to descent with modifications, i.e. evolution. Successfully adapted populations achieve an additive and persistent rather than subtractive and destructive overall evolutionary progress. Opportune moments in evolutionary history such as the Cambrian Explosion (543-490 MYA) occurred. The environmental conditions during the Cambrian era led to the production of a plethora of new marine forms when the glaciers receded, and a long period of global warming followed. Evolutionary history is punctuated by conditions in the environment along with an organism living on the edge of mutation which occasionally result in definitive leaps forward.
A specific example of selective forces is one that gave a mighty push to our own class, mammalia. The end of the Cretaceous era, about 65 ±0.3 MYA saw a rapid and severe extinction of many—over 90%–of life forms including large dinosaurs. It was a dark and difficult time to be on earth, and there was a progressive decline in bio-diversity during the late periods suggesting an ecological crisis. On the tail of the Cretaceous Era, there came the Cenozoic age of opportunistic new life. Mammals diverged from a few small, simple, furtive, generalized forms hiding in holes and in the branches of trees into a diverse collection of terrestrial, marine, and flying animals; birds evolved substantially in the Cenozoic as well. Mammals grew and flourished from then until the present to become the dominant animals on earth.
There are trillions of molecules in complex organisms, and the possibility of their being present as a result of pure chance is all but impossible. A sense of such improbability can be gained by considering the odds that–by chance alone–each of four players could receive a complete suite of cards in a single deal during a game of bridge. The odds against that happening are an unfathomable 2,235,197,406,895,366,368,301,599 to 1 (2+ septilion or more than 2 billion billion to 1). And that is dealing with the permutations and combinations involving only 52 entities. The difference produced by natural selection is that over the eons of geologic time, changes occur and accumulate which favor survival of animals and plants with more adaptable characteristics, and those characteristics are passed on to future generations. The process is then directional, and continues to be driven by the requirements of the environment, and not just chance. Complex structures and organ systems such as eyes, hands, and brains did not occur by random gene drift, but by a process driven by mutation, natural selection, and time.
“Survival of the fittest”, as natural selection is often termed, is an inadequate and misleading slogan, an oversimplification of a much more complex process. The phrase suggests some sort of match between gladiators, but natural selection is a far more subtle power of selection which depends on very small differences in overall survival and fecundity. Some changes result in a better adaptation to different parts of the environment and location and reproductive success may depend on that adaptation. Other genetic changes may produce a truly fitter, more aggressive, or more enduring sub-species that in time dominates. For example, primitive creatures such as flatworms have photosensitive cells that could have been present in primordial life forms and which evolved into the complex eyes of animals of today–at all stages, of definite survival value. Natural selection is primarily a matter of reproductive success that includes the ability to survive to the age of reproduction (improvement in differential mortality), increased fertility (differential fertility), or may involve a sub-group that has an enhanced physical or chemical ability for successful union of gametes, or may be a matter of size or color or scent that enhances the attraction of the opposite sexes to each other (sexual selection). Colors and scents of flowers attract bees to ensure pollination and propagation of the species of flowers. An interesting example is that of the Malaysian Rafflesia kerri flower. Spikes at the center of the flower help disperse its characteristic odor of rotting meat throughout its jungle habitat. This attracts carrion flies that pollinate the plate sized bloom. Ecological selection occurs when organisms that survive and reproduce increase the frequency of their genes in the gene pool over those that do not survive in a given location. continued…