In 1859 Charles Darwin, a British naturalist, published a book, “On the Origin of The Species by Means of Natural Selection”, which after its publication, caused a great deal of controversy that still continues today. It is the only scientific theory that has engendered so much vilification and the only one non-scientists feel they can comment on even though the overwhelming majority do not know anything about evolution.
No one questions Einstein’s theory of relativity or quantum theory, but many still question the theory of evolution even though 99 per cent of US scientists accept the theory as fact.
What is the theory of evolution and how does it work? A simple but long way of putting it is that life on earth began with one primitive species and gradually over a period of 3,500 million (3.5 billion) years, through small (or occasionally large) changes which could be passed on to the next generation (known as heritable changes) produced many new and diverse species. The mechanism for most, but not all, of evolutionary change is natural selection. Lesser mechanisms include genetic drift, sexual selection and symbiogenesis.
The process by which small changes occur is called mutation and is an entirely random event. However, natural selection is far from random. Natural selection is the process where those small changes endow the organism with favourable or deleterious traits making it more or less likely to live to reproduce. The organism with favourable traits will survive and reproduce, those with unfavourable traits will not. Eventually all of the subsequent generations will possess this trait.
Natural selection is unconscious; it cannot anticipate what changes are going to be needed to survive. The evolutionary watchmaker is blind. Evolution is also not about how life began, but how it has evolved.
One should also realise that the evolutionary time scale is measured in hundreds of thousands to millions of years. One only has to look at the common dog which arose from the Asian grey wolf approximately 15,000 years ago and see the enormous variations that have been produced by unnatural selection. Could not the same thing happen over millions of years by natural selection? Evolution therefore is gradual, it produces different species over time, there is a common ancestor and there is natural selection.
The theory does not predict that species will be constantly evolving or how rapidly they will evolve. Some groups like whales and humans have evolved “rapidly”, while others have hardly changed over hundreds of millions of years. When the selection pressure is strong it can occur quickly, but once a species becomes well-adapted evolution will slow down.
Evolutionary biology is a historical science that depends not on a single piece of evidence, but on the convergence of numerous lines of inquiry. It draws on the knowledge of such fields as geology, palaeontology, biogeography, comparative anatomy and physiology, embryology, molecular biology and genetics to name a few. Detectives using various branches of science can reconstruct a murder scene 30 years later using the same technique of convergence of evidence.
One of the strongest pieces of evidence for evolution is the fossil record. Fossils are traces of once living organisms. The process of fossilisation is an uncommon occurrence and usually requires death where sediments (of rivers, lakes, etc) or volcanic ash can be deposited. Over time the hard parts of the organisms become impregnated with or replaced by minerals leaving a cast of that organism, although less common, soft-bodied organisms have also fossilised. Some insects have been preserved in resin from trees. The ages of fossils can be deduced from the geological strata in which they are found and with radiomimetic dating. From the field of geology we know that there were different geological periods stretching over billions of years, with the oldest layers at the bottom and the youngest on top.
According to evolutionary theory, certain testable predictions can therefore be made. They include the following:
The fossil records confirm these predictions. Starting with the Cambrian age rocks, the layers have shown that about 600 million years ago simple organisms like the jelly-fish, worms and sponges arose; fish came about 400 million years ago and amphibians come about 50 million years later. Fifty million years after, reptiles appeared and birds about another 50 million years later. The first mammals showed up about 250 million years ago. Humans are very recent as our lineage branched off from other primates about 7 million years ago. In order to disprove evolution, one only needs to find the fossils of birds in the amphibian geological stratum, but to date none has been found.
If, as evolutionary theory contends, reptiles appeared in the fossil record before birds it can be predicted that the common ancestor of birds and reptiles was an ancient reptile and would look like one. In this case the common ancestor was a dinosaur. Contrary to popular misconceptions, dinosaurs could be huge or small. In 1890 a crow-sized fossil, Archaeopteryx lithographia, was found in Germany having just the traits one would expect to find in a transitional form. Its age was estimated to be about 145 million years, which would place it at exactly where evolution predicted it would be found. Other transitional fossils have been since found in China as well.
As these fossils get younger they showed that the basic skeletal plan of birds, and essentially feathers, evolved before birds could fly. What this tells us is that structures developed for one purpose can be adapted for other uses. A similar transitional form was found in Ellesmere Island in Canada’s north in 2004 and named Tiktaalik. It had features that make it a direct link between earlier lobe-finned fish and amphibians, one of which was that it had a neck, something fish do not have but amphibians do. It was also found in rocks 380 million years old, exactly where it was predicted such a fossil would be found. In the case of humans, in November 1974 a fossil nicknamed Lucy was found in Ethiopia which was transitional between the great apes and man. Its pelvis and femurs (thigh bones) were decidedly human showing that it walked upright, its middle was a mixture, but its head was apelike. The fossil was about 3.2 million years old, the age at which one would expect to find a human transitional form. Since then many other transitional human fossils have been found.
Genetics can also show that apparently different species had a common ancestor. The chimpanzee is 98.5 % homologous in its genome (that is the entire DNA sequence) to that of humans. We share many so-called dead genes, which are genes that are no longer used to produce a gene product, but are kept in the genome. We also have many particles of viral DNA incorporated in our genome which have been rendered harmless by mutations. We find that some of these remnants sit in exactly the same positions in chimpanzees as in humans.
Primates, bats and guinea pigs do not, as other mammals do, make vitamin C as we are able to extract enough from our diets. It turns out that we still possess those 4 genes needed to make vitamin C, but one has been inactivated by a mutation. In humans and other primates the same mutation is found in the same gene. Guinea pigs and bats have different mutations. The evidence clearly shows that we have a common ancestor and this separation has been estimated to have taken place 7 million years ago. Lucy and other transitional forms could, therefore, not be more than 7 million years old and none have been shown to be.
Some, including those calling themselves Intelligent Design (ID) scientists, contend that while micro-evolution occurs it is never enough to produce a new species. When asked how new species are produced they say an Intelligent Designer does it. Michael Shermer in his book, “Why Darwin Matters”, says, according to IDers, micro-evolution occurs and “then a miracle happens” to form species. What is a species? A species can be defined as a reproductive community—a gene pool. New species arise as evolutionary accidents when a group in a species is isolated from its relatives. Over long periods of time, the genomes of the two groups change to the point where they no longer mate with each other. One can use language to illustrate this point. Latin was once the language of the Iberian Peninsula and Italy. Today there is Italian, French, Spanish and Portuguese. The common root of all these languages can be found in Latin, but today they do not understand each other. We also see that Spanish and Portuguese are fairly close to each other suggesting a more recent split e.g. humans and chimpanzees.
Sexual selection can also play a part whereby females prefer to mate with males having certain characteristics. Over time those characteristics will become dominant and females will only mate with males exhibiting those characteristics.
Embryology (the study of the developing foetus) and comparative anatomy have shown that all vertebrates develop in the same way. They all begin development looking like a fish and as it proceeds different species begin to diverge. Fish embryos develop what are called branchial arches which eventual go on to form the gills with its nerves and blood vessels. The foetuses of other vertebrates, including man, also develop branchial arches, but they eventually become different structures. In man the 6th branchial arch with its blood vessel and nerve move down into the chest to form the heart and great vessels. Sometimes these arches do not close and the child is born with a branchial cyst.
In looking at the sequence of development of foetuses a fish embryo’s circulatory system develops straight into that of a fish. An amphibian embryo’s circulatory system at first looks like a fish embryo and then changes to develop into an amphibian circulation. A reptile goes from looking like a fish to an amphibian and eventually into a reptile. The human circulatory system goes from first looking like that of a fish, then to an amphibian, to a reptile and finally to human. These stages happen to follow the evolutionary sequences of its ancestors. Embryonic whales and dolphins form hind limb buds which then disappear, indicating that they evolved from land animals. To prove the point, rarely, whales are born with hind limbs; and, again rarely, humans are born with tails demonstrating our descent from animals with tails.
If there is an intelligent designer, why are there so many instances of unintelligent design? Of what use is a male breast with nipples? Why does the recurrent laryngeal nerve in order to go from the brain to the larynx (voice box) travel down the neck, into the chest and back all the way up again to the larynx? The evolutionary reason can be seen by referring back to the fish where the 6th branchial arch’s blood vessel moves with its nerve into the chest to form the heart, and the nerve, the recurrent laryngeal nerve, can only follow. The larynx is situated in front of the oesophagus (the gullet) so that food has to pass over the larynx to get to the oesophagus. We can all remember choking on food as a result and many persons have died because of this unintelligent design. The reason again can be found in how the organs evolved.
This has been a brief and, of necessity, a simple look as to why evolution happens to be true. The assault against it by the evangelical Christian community has been strong because it brings into question the story of Genesis and the flood. Evolution has been accused of belittling man’s place in creation making him into just another animal. It has also been said that if evolution is true we are no more than animals with no morals and conscience. One should realise that before 1859, we had incest, genocide, wars, the crusades, the Inquisition, slavery and other forms of depravity, so these acts of immorality could not have been due to evolutionary theory.
Evolution has taught Man altruism, to be cooperative and to abhor certain types of behaviour in order to survive as a group and individually, and even in primitive societies these traits exist. Accepting the theory of evolution will not turn one into a vicious beast ready to commit immoral acts. The Vatican and many other religious organisations and faiths accept the theory, one of the greatest scientific theories of our time, as it allows us to look back from whence we came and our place in the universe. As Michael Shermer said, “Darwin matters because evolution matters. Evolution matters because science matters. Science matters because it is the pre-eminent story of our age, an epic saga about who we are, where we came from and where we are going.”
W. S. Lofters, is a Jamaican physician (retired) in Kingston, Ontario