No other scientific subject generates as much suspicion and mistrust among lay people as evolutionary biology. A good deal of the confusion about evolutionary biology stems from its being labeled ‘Darwinism’ or ‘neo-Darwinism’. The term has been injected into public debate by people who object to evolution by natural selection, so as to make the latter look like an ideological position rather than a well-established fact.
Evolutionary biology is the only scientific field subjected to this kind distortion. Modern chemistry is nowhere imputed to be neo-Lavoisierism; one never sees quantum mechanics described as neo-Einsteinism; and I have yet to hear anyone say that modern psychology is so much neo-Jamesianism or mere Wundtism.
Evolutionary biology is not an ideology; it is one of many specialized branches in the general field of biology. Like their colleagues in other sciences, evolutionary biologists adhere to the most rigorous processes in collecting and examining data, and in testing and explaining their findings.
When casting doubt on the blind, undirected, non-designed force of natural selection, anti-evolutionists (who are ideologues) present questions and arguments and descriptions that seem informed by the most recent literature on the subject. But if you turn to peer-reviewed scholarship or read a plain language text by a scientist who has dedicated her professional life to a particular line of research, you will find that the propositions advanced by the critics are inaccurate and the questions they raise irrelevant or already explained.
Although the literature on the subject is too great to summarize here, it is right that people ask a couple of basic questions about evolution in order to determine its explanatory force.
What are the features of evolution?
Evolutionary biology is based on the idea of evolution. Central to the idea of evolution is that species undergo genetic change over a period of time. This happens over many generations, and during that time a species can evolve into something different. The changes are based on mutations in DNA, which is conditioned by environmental and other physical factors. When scientists say that mutation is random, they do not mean arbitrary. They mean random in the literal sense of a set of probable outcomes based on a particular set of conditions. The operative force here is natural selection, which Darwin describes in a perfectly succinct way in The Origin of Species:
“Man selects only for his own good: Nature only for that of the being which she tends.”
Natural selection requires that individuals within a species vary genetically so as to survive and reproduce in their environment. They must adapt in a way that makes them fit for the struggle of existence within their environment, and they must be able to pass on their genes if their form of life is to continue down the line.
Another tenant of evolution is gradualism. It takes a great deal of time for substantial evolutionary changes to appear—hundreds of thousands or even millions of years in most cases. When someone makes the claim that no one has ever seen evolution, they are right. It would be impossible for anyone to do so. Though there have been cases of minor changes occurring within a human lifetime, the really big evolutionary changes take place over a long period of time.
A final tenant of evolution is speciation. This is the phenomenon of a species splitting. Whenever two populations evolve genetic differences to the point that they can no longer interbreed, speciation occurs. Jerry A. Coyne, a leading expert in this particular field, says it best:
“Speciation doesn’t happen very often. But each time one species splits into two, it doubles the number of opportunities for future speciation, so the number of species can rise exponentially.”
What is the evidence for evolution?
Genetic science gives ample evidence of the interrelation of all living species. This alone would suggest the common ancestry of animal life. However, the fossil record offers the kind of documentary evidence that most people need in order to form a mental picture of how evolution has worked throughout history.
In Darwin’s day, the fossil record was thin. Since then, it has become much more robust. The sequence of rock strata that have been unearthed proves that early life was simple, and that more complex species appeared over time. The many fossils that have been dug up over the past century show one species of animal or plant changing into something different. Each fossil is found exactly where one would expect to find it in the rock strata.
The human body itself bolsters the case for evolution. We are filled with remnants of our primate ancestry. Our bodies show little sign of intelligent design, but rather the clunky adaptations of a physically weak primate struggling to survive in the African savannah. Our sense of smell is very poor compared to our cousins in the wild. We intake food and drink through the same orifice through which we breathe—an arrangement bound to lead to constant choking. And in one of the more curious developments in our bodies, we expunge our waste through the same organ through which we pro-create: which is akin, as one observer put it, to running a sewer system through an amusement park.
Another interesting vestige of our evolutionary past is the phenomenon known as the furry fetus. At six months, the human fetus becomes completely covered with a coat of hair. This lanugo, as it’s called, is shed about a month before birth and replaced by the short, sparse, evenly distributed hair that we keep throughout our life. Monkeys also develop a coat of hair at about the same stage of embryonic development. The human womb is warm enough to keep its fetus safe, so that is not a sound explanation for this sudden growth of hair. The best explanation is that the lanugo is a remnant of our primate ancestry.