Happy Birthday, Dear Darwin
This year marks significant anniversaries of two of the most important events in the history of science. February 12 is the two hundredth anniversary of the birth of the English naturalist Charles Robert Darwin; November 24 is the one hundred and fiftieth anniversary of the publication of his most famous work, On the Origin of Species, in which he outlines his theory of evolution through natural selection. On the Origin of Species is among the most important works in the history of science, ranking with such works as De Revolutionibus, by Copernicus; the Principia Mathematica, by Isaac Newton; and The Discourse on Method, by René Descartes. Each of these works caused a fundamental and irreversible shift in the way people thought about the world, and the consequences of each are still very much with us.
Darwin's theory of evolution by natural selection is, in a very simplified form, that organisms have a common ancestry; that they change (evolve) over time; and that favorable inherited traits become more common in successive generations of a population of reproducing organisms, while unfavorable inherited traits become less common. Natural selection is the process which describes the way that favorable traits are passed on to successive generations, essentially because favorable traits tend to make organism who possess them survive long enough to breed more often than competing organisms with less favorable traits do. It is, to paraphrase Herbert Spencer, survival of those fit enough to survive.
The theory of evolution through natural selection is one of the most basic elements of modern biology, which cannot be taught without reference to evolution through natural selection any more than physics can be taught without mention of gravity. Despite this, it is not accepted by as true by a surprisingly large percentage of Americans. A 2006 study by Michigan State professor John D. Miller showed that about one in every three Americans do not believe in evolution. The study surveyed twenty countries, mostly Western European, but also including Japan, Turkey, and the United States. The percentage of Americans who accept evolutionary theory was lower than all of the surveyed countries except Turkey. The study also showed that, since 1985, the percentage of Americans who accept evolution has declined by 5% (45% to 40%), the percentage who reject it has declined by 9% (48% to 39%), and the percentage who identify themselves as unsure had risen by 14% (7% to 21%).
The relative disrepute of evolutionary theory in the United States is partly caused by the perception by certain religious denominations that it is in conflict with their faith. It is also partly caused by the failure of the scientists in the field that Darwin founded, evolutionary biology, to properly educate the public. This purpose of this article is not primarily to summarize the evidence in favor of evolutionary theory, though the evidence is overwhelming, but rather to clear up some of the misconceptions that have arisen in part because of the lack of public education, and in part because of disinformation spread by its opponents.
First, we will start with one of the hoariest and least informed objections to evolutionary theory, “Why aren't the apes turning into people now?” This is because neither Darwin nor any other evolutionary biologist has ever proposed that human beings descended from modern apes such as chimpanzees, gibbons, or gorillas. What is universally accepted by evolutionary biologists is that humans and modern apes share a common ancestor, and that at some point the two groups diverged into separate lines of descent and went their own ways. While it is true that some proto humans looked more like modern chimpanzees than modern humans, these proto humans were not the same as modern chimpanzees.
Next, “Evolution is only a theory.” This is, in a sense, true, but it is also usually meant in a misleading way. Every dictionary gives several meanings for the word “theory.” One meaning is the way it is used in the ordinary conversational sense: a theory is a conjecture or a guess. In science, however, a theory is a set of principles devised to explain a group of facts or phenomena, especially one that has been repeatedly tested or is widely accepted and can be used to make predictions about natural phenomena. Examples of scientific theories include the heliocentric theory of Copernicus (that the earth orbits the sun, and not vice-versa), and the germ theory of disease (that infectious diseases are caused by the activity of microorganisms within the body). No scientist, and hardly any minimally educated person, doubts either either the heliocentric theory or the germ theory, or believes that they will soon be overthrown by competing theories. Evolution by natural selection, as a scientific theory, has a level of plausibilitycomparable to that of the heliocentric theory or the germ theory. In fact, although there are disputes among evolutionary biologists as to the mechanism by which changes in organisms occur, there is no scientific theory which competes with the theory of evolution through natural selection. The so-called “intelligent design theory,” which received a great deal of press a few years ago, has repeatedly been demonstrated to have none of the characteristics of a scientific theory. A good summation of this can be found in the opinion of the court in the case of Kitzmiller v. Dover, which can be found here: http://www.pamd.uscourts.gov/kitzmiller/kitzmiller_342.pdf.
Opponents of evolutionary theory will often point out that “Darwin was wrong.” This is partly true, but largely irrelevant. This also stems from a lack of understanding as to the nature and magnitude of Darwin's accomplishment. Darwin did not, for example, originate the idea that organisms evolve; his own grandfather Erasmus Darwin had speculated about it, and nine years before Darwin's birth Jean-Baptiste Lamarck had published an extensive, although ultimately incorrect, account of his own views about the mechanism by which evolution worked. Darwin's idea of what caused changes in organisms, natural variation and inheritance of acquried characteristics, is now accepted by almost no one. But his failure to work out that evolution is caused by mutation in the genetic material of organisms is easily explainable by the fact that the science of genetics had yet to be invented in his lifetime. What Darwin got spectacularly right was the idea that the evolution of organisms occurs by means of natural selection. The philosopher Daniel Dennett calls this, “The best idea anyone has ever had.” Even in this insight Darwin was not alone. Darwin's Origin of Species was presented to the British Royal Society simultaneously with a short essay by Alfred Russell Wallace in which Wallace arrives at a very similar theory. But Darwin's fame outshines that of the admirable Wallace because the mountain of evidence Darwin had accumulated in the twenty years that he worked on the Origin of Species was persuasive in a way that Wallace's intuitions could never have been.
It is worth noting that other originators of still-accepted scientific theories got parts of them wrong. Copernicus, for example, was right about the planets orbiting the sun, but also believed that the planets had circular orbits. As this didn't fit the observable data, Copernicus posited that the planets moved in circular epicycles, the centers of which moved in circular orbits around the sun. He was wrong. Eventually this was sorted out by Johannes Kepler, who showed that the planets had elliptical orbits. But this does not diminish the accomplishment of Copernicus. Any scientific theory is subject to revision by later scientists in light of the accumulation of new data.
“Evolution is atheistic.” Evolution is an explanation of a natural process. It does not employ God as a component of its explanatory process, but neither does, for example, an explanation of how an internal combustion engine works. Although the evolutionary biologist Richard Dawkins claims that Darwin made it possible to be an intellectually fulfilled atheist, this was clearly not one of Darwin's goals. Darwin was a baptized Anglican and trained for a while to become a minister. He delayed publication of The Origin of Species for years out of concern for the sensibilities of his devout wife. He denied that he was an atheist. Later in life he was clearly a religious skeptic, although his writings suggest that this might have been more as a result of the deaths of two of his children in childhood rather than his scientific work.
The theory of evolution does pose problems for those who believe in the literal truth of scripturally-based creation accounts, be they Christians, Jews, or Muslims. A Gallup poll in May of 2007 reported that 31% of Americans believe in the literal truth of the Bible. However, a great many religious denominations have no problem accepting evolution, although they usually interpret it as a process guided by God. The Roman Catholic church has accepted evolutionary theory at least as far back as the Papal encyclical Humani Generis, published by Pius XII in 1950, and endorsed in 1996 by John Paul II in an address to the Pontifical Academy of Sciences. The Orthodox Rabbinical Counsel of America has stated that evolution is not incompatible with the belief in a divine creator. Many Protestant denominations hold that evolutionary theory is compatible with their theology. It is also worth noting that the theory of evolution by natural selection propounded by Darwin had nothing to say about the origins of life, merely its development. Thus, acceptance of evolutionary theory in no way requires a particular belief about the existence of a diety.
One of the biggest barriers to understanding what evolution by natural selection really means is to envision it as a guided process. It is not by its own terms, although it does not preclude someone from believing that it is guided by something divine. It is simply an explanation of something that happens naturally. Think of erosion. Erosion can wear away rocks or take down mountains, but no one describes erosion as having a purpose. It is simply what happens. Natural selection is the same way. Species are not perfected by it; either they survive long enough to propagate and maintain a breeding population, or they become extinct. Changes in the environment, such as climate changes, alter what traits are favorable in an organism and what traits are not. And it's happening right now, before our eyes. A New York Times weblog, Wild Side, by Olivia Judson, has recently given two examples. One is that an insect called an apple maggot appears to be splitting into two species because there are two groups that find two different types of fruit to be congenial habitats. Another is the marsupial mammal called the Tasmanian Devil. It has become subject to an infectious and fatal form of facial cancer. As a result, female Tasmanian Devils are now reaching sexual maturity almost twice as fast as they used to, because females who do so propagate more often than females who don't.
For anyone wishing to know more about Darwin and his theories, I recommend “Darwin's Legacy,” a ten-part lecture series posted by Stanford University which can be downloaded from iTunes U. Also, The Origin of Species itself remains perfectly readable for the general reader. PBS has an excellent series entitled “Evolution,” which is available on DVD. The BBC recently aired two specials, “The Genius of Charles Darwin,” hosted by Richard Dawkins, and “Darwin and the Tree of Life,” hosted by Sir David Attenborough, that will likely be aired on US television in the near future. In the meantime, on February 12, feel free to hoist a glass of your favorite beverage in honor of Charles Robert Darwin for his revolutionary theories, and to your own ancestors in honor of their passing the rigorous test of natural selection.