Life on earth

Why Evolution Is True

By Jerry A Coyne

Oxford University Press, 2010, £8.99

Reviewed by Niall Mulholland

IN A 2006 BBC poll in Britain, people were asked about how life formed and developed, with 48% accepting the evolutionary view, 39% agreeing with creationism or intelligent design and 13% saying they did not know. Over 40% felt either creationism or intelligent design should be taught in school science classes. These sorts of findings, writes Jerry A Coyne in Why Evolution Is True, show that there is a battle over evolution, "part of a wider war, a war between rationality and superstition". The stakes, he writes, are "nothing less than science itself and all the benefits it offers to society".

Natural selection was "the part of evolutionary theory considered most revolutionary in Darwin’s time, and is still unsettling to many". This is because it "explains apparent design in nature by a purely materialistic process that doesn’t require creation or guidance by supernatural forces". Another giant thinker of the mid-19th century, Karl Marx, immediately recognised the significance of The Origin of Species, writing that, "Darwin’s work is most important" because it could "demonstrate historical evolution in nature".

Coyne, a professor in the Department of Ecology and Evolution at the University of Chicago, gives a concise, lucid explanation of what evolution is, as well as its robust defence against the falsifications of its opponents, including religious creationists. "Evolution is a fact", Coyne asserts, "the evidence gathered by scientists over the past century and a half supports it completely, showing evolution happened, and that it happened largely as Darwin proposed, through the workings of natural selection".

Coyne summarises the modern theory of evolution as: "Life on Earth evolved gradually beginning with one primitive species – perhaps a self-replicating molecule – that lived more than 3.5 billion years ago; it then branched out over time, throwing off many new and diverse species; and the mechanism for most (but not all) of evolutionary change is natural selection".

He describes the process as consisting of six components: evolution, gradualism, speciation, common ancestry, natural selection and non-selective mechanisms of evolutionary change. The idea of evolution is that a species undergoes genetic change over time and can evolve into something quite different. Those differences are based on changes in DNA, which originate as mutations.

Gradualism refers to the many generations needed to produce a substantial evolutionary change, such as the evolution of birds from reptiles. Speciation, or the splitting of one species into two, does not happen often and is slow. When it occurs, however, it doubles the number of opportunities for future speciation, so the number of species rises exponentially.

The great evolutionary biologist, Ernst Mayr, proposed the ‘gold standard’ definition of species for evolutionary biology: "a group of interbreeding natural populations that are reproductively isolated from other such groups". Although this ‘biological species concept’ is not foolproof – what about organisms that do not reproduce sexually, such as bacteria? – it remains the concept biologists prefer when studying speciation.

Like speciation, the idea of common ancestry has been hugely vindicated by fossil research since Darwin’s time and by modern knowledge of genetics. Natural selection occurs "if individuals within a species differ genetically from one another and some of these differences affect an individual’s ability to survive and reproduce in its environment, then in the next generation the ‘good’ genes that lead to higher survival and reproduction will have relatively more copies than the ‘not so good’ genes". Over time, the population will gradually become more suited to its environment "as helpful mutations arise and spread throughout the population, while deleterious ones are weeded out. Ultimately, this process produces organisms that are well adapted to their habitats and way of life". Natural selection "does not yield perfection – only improvements over what came before". It therefore produces "the fitter, not the fittest".

Processes other than natural selection can also cause evolutionary change, such as "simple random changes in the proportion of genes caused by the fact that different families have different numbers of offspring" leading to "evolutionary change that, being random, has nothing to do with adaption". Coyne believes the influence of this process on important evolutionary change is "probably minor" because it does not have the "moulding power" of natural selection.

Coyne shows that Darwin’s ideas are supported by "testable predictions" – on what we should find in living or ancient species when we study them – and by what Coyne calls "retrodictions" – facts and data that "aren’t necessarily predicted by the theory of evolution, but make sense only in the light of the theory of evolution".

In the 150 years since the publication of The Origin of the Species, fossil evidence, as well as modern fields of science, including molecular biology and systematics (the study of how organisms are related), "leads ineluctably to the conclusion that evolution is true". The creationist argument that there is a gulf in the fossil record proving evolution false is simply not true. Whales have very good fossil records revealing the evolution from terrestrial to aquatic form. There are very many ‘intermediary’ fossil examples. The startling 2004 discovery of the fossil species Tiktaalik roseae – a transitional form between fish and amphibians – informs us about how vertebrates came to live on the land. Fossil finds, molecular data from DNA and protein sequences tells us that humans are most closely related to chimpanzees and we diverged from our common ancestor about seven million years ago.

Vestigial traits are also evidence for evolution because they no longer perform functions for which they evolved. Humans have many vestigial traits, such as the appendix – the remnant of an organ of our leaf-eating ancestors. If organisms were built by an intelligent designer, as creationists argue, why would they have such bad designs that mean every species is imperfect in many ways? So called ‘bad design’ only makes sense if it evolved from features of earlier ancestors.

Biogeography – the study of the distribution of species – provides so much powerful evidence for evolution that "creationists simply pretend that the evidence doesn’t exist". Since the 1960s, scientists have accumulated information that adds tremendously to Darwin’s estimations of this process. Continental drift (the shift, joining and separation into parts of super-continents in past geography) and molecular taxonomy (information from DNA sequences that tell us about evolutionary relationships between species and the approximate times they diverged from common ancestors) explains the geographical distribution of animals and plants on continents and islands.

Coyne gives an incredible, if gruesome, example of adaptive behaviour. The ferocious Asian giant hornet is especially common in Japan. Hornet scouts mark the nests of introduced European honey-bees, bringing 20-30 giant hornets against a colony of up to 30,000 honey-bees. But with their slashing jaws, the hornets decapitate each bee until all are dead. The hornets go on to ravage the hive’s honey and to bring the bee grubs back to feed their own voracious young.

But the honey bee native to Japan can resist the giant hornets, with its own amazing adaptive behaviour. When a hornet scout enters their nest, the honey-bees quickly lure it further in and hundreds of worker bees surround the guest in a ball. Vibrating their abdomens, the bees cause the temperature inside the ball to rise to over 45 degrees C, roasting the hornet scout to death. The native bees can withstand these temperatures, thereby saving the nest from the deadly hornets’ army.

Evolution is a scientific fact but "that doesn’t mean that Darwinism is scientifically exhausted, with nothing left to understand… evolutionary biology is teeming with questions and controversies". On what he terms the "sticky question" of race, Coyne rejects previous racial classification based on prejudice. Human races do exist, just like other evolved species, Coyne says, with recent genetic research showing about 10-15% of all genetic variation in humans is represented by differences between races that are recognised by difference in physical appearance. The remainder 85%-90% occurs "among individuals within races". At a genetic level, modern humans are "a remarkably similar lot", DNA data showing genetic differences between humans are minor. This is "just what you would expect if modern humans left Africa a mere 60,000 or 100,000 years ago", giving little time for genetic divergence.

As to whether humans are ‘genetically programmed’ to behave in certain ways – displaying selfishness or altruism, for example – Coyne states that there may be elements of behaviour that come from our evolutionary heritage, but behaviour is "largely acts of choice, not of genes". Today’s universally abhorred practice of human sacrifice, for example, is nothing to do with evolution because the changes in social attitudes are taking place too fast to be caused by genes.

Coyne ends this engrossing, accessible book by stating that evolution operates in a "purposeless, materialistic way". But "far from constricting our minds, the study of evolution can liberate our minds".