Don’t say “Darwin” when you mean “evolution”. Don’t say “theory of evolution” when you mean the established historical facts of change over time and common descent. And above all, don’t say “Darwin’s theory of evolution” except in the historical context of the evolution of ideas. If you do, you are guilty of scientific, logical, historical, and pedagogical errors, and playing into the hands of our Creationist opponents.
Dalton is to the modern atomic theory, and the modern atomic theory is to chemistry, as Darwin(not to forget Wallace) is to evolution, and as evolution is to biology. But we don’t call our present perspective on atoms “Dalton’s theory”, and indeed, unless we are speaking historically, it sounds odd to even talk about “atomic theory” when we discuss atoms. So why should we refer to “Darwin’s theory”, and indeed why should we talk about the “theory of evolution” when we really mean the fact that evolution has taken place? I argue here that we shouldn’t, and that, given the ongoing opposition to the central facts of biology, it is actively damaging to do so.
John Dalton produced his “atomic theory” in the early 19th century. He arrived at it by way of a theory of gas pressure that we now know to be totally erroneous. Wielding Occam’s Razor rather too energetically, he assumed that the simplest compound between two elements contained just one atom of each, so that water would have the formula HO. He rejected what now seems to us perhaps the most striking validation of his theory, Gay-Lussac’s observation that gases combine according to simple ratios, because it pointed towards what later became known as Avogadro’s Hypothesis, which in turn required some gaseous molecules to be divisible, and when it came to gaseous elements Dalton had not grasped the distinction between atoms (the fundamental particles of chemical composition) and molecules (the fundamental particles of gas pressure). It was half a century before his theory was generally accepted, and even then some remained sceptical, on the grounds that no one had ever observed the effects of individual atoms or molecules, until in 1905 Einstein pointed out that that was exactly what people were doing when they looked at Brownian motion. These days, however, individual atoms are routinely observed by the methods of high resolution transmission electron microscopy, and scanning tunnelling microscopy, both of which depend on concepts far beyond any available to Dalton.
Charles Darwin produced his theory of the mutability of species as the result of natural selection (he did not himself use the term “evolution”) in the mid-19th century. Central to the theory is the existence of sufficient heritable variation to explain the diversity of life, and a major stumbling block is the prospect that favourable variations will disappear through dilution. He appealed to the experience of animal breeders, but as a solution to the problem of dilution this is grossly unfair, since breeders can and do deliberately select rare variants to breed between. He lamented the absence of fossil evidence, in terms still quoted by creationists despite the tons (literally) of such evidence that have been unearthed in the intervening 150 years. He was unaware of the digital nature of inheritance, as established by his contemporary, Gregor Mendel, but not widely known until that work was rediscovered (or more accurately, perhaps, reinterpreted) at the beginning of the 20th century. He fully realised that evolution required many millions of years, and had no good answer when Lord Kelvin, his “ogre”, used thermodynamic arguments to show (correctly) that the then known sources of energy could only have kept the sun shining for a mere 20 million years or so. He had no inkling of the nature of the genetic material, and could not have conceived of the methods of molecular biology that now allow us, using much the same kind of evidence that the courts use to establish paternity, to compare related species and to chart their divergence in exquisite detail. Least of all did he have any notion of the source of the variations of which evolution depends, or of how the supply of variants is constantly replenished by mutation, a process that we can now observe at the level of an individual’s DNA.
The first half of the 20th century saw the formation of what became known as “the neo-Darwinian synthesis”, bringing together by the 1940s the concept of selection and the methods of population genetics. (The expression “neo-Darwinian” should now properly be restricted to the evolutionary thought of that time, although Creationists persist in applying it to current biology, for reasons discussed in part II). The second half saw an explosion in our understanding of inheritance, based on laboratory studies, while the final decades saw breakthroughs in our understanding of human evolution, with the discovery of the fossilised remains of over a dozen species of our early relatives in eastern and southern Africa. By the end of the 20th century, evolution denial could fairly be compared with Holocaust denial. Given what we have learnt from molecular biology in the present century, it could now more fairly be compared with denying that Hitler ever invadedPoland in the first place.
So why does the name of Darwin still provoke controversy, why do people still speak of “the theory of evolution”, when as often as not they are referring, not to theory, but to the established historical facts, why does it matter, and how should we respond? These topics will be the subject of my next posting, “Naming and Framing”.
(You will find more on Dalton and his times, and on Kelvin and the age of the earth, in my book, From Stars to Stalagmites, and the arguments in these two posts are developed at greater length in an article that I wrote with Britt Holbrook; Putting Darwin in his Place; the Need to Watch our Language)
 Two volumes of hydrogen combine with one volume of oxygen to make two volumes of steam. If, as required by Avogadro’s Hypothesis, equal volumes of gas contain equal numbers of molecules, then each molecule of oxygen must contain (at least) two atoms, as shown in the way we now write this equation: 2H2 + O2 = 2H2O
 Imagine a favourable red variant in a population of white flowers. Under the blending theory of inheritance then current, its first generation offspring will be deep pink, the second generation somewhat paler, and so on until the descendants are indistinguishable from the general population.
 See Genesis; the Evolution of Biology, Jan Sapp, OUP, 2003, pp 117-122