Tuesday, April 09, 2013

The early evolutionists

kw: book reviews, nonfiction, evolution, evolutionary theory, short biographies, history of science

The fundamental divide between the facts of evolution and the theory of evolution has been at the root of both the scientific and theological debates about "transformation of species" for centuries. In Charles Darwin's correspondence he once referred to "us transformationists", using the word derived from ancient speculations about species change. As Rebecca Stott brings out in Darwin's Ghosts: The Secret History of Evolution, some early attacks upon On the Origin of Species were accusations of plagiarism!

Poor Darwin was assailed from all sides. The religious censured him for impiety (as many still do), and most scientists either decried his theory of natural selection or denied his priority. Claimants to priority put forward by various "correspondents" included Aristotle, nearly 2,200 years earlier, and Jahiz of Basra "only" 1,000 years before Darwin's publication. As Professor Stott shows, these first two at least are bogus claims. Anything that either man may have written about mutability of species served only as a foil to clear statements on their eternal fixity. Aristotle in particular may have been curious about the apparent ambiguity of sponges, but seems to have concluded that they were rather peculiar plants. It was not until the 1820s that the motile larvae of sponges were observed, giving the first clue to their animal nature.

However, numbers of earlier students of natural history did speculate about species change. Such speculations were based on observations that the boundaries of "kinds" were not as fixed as one might like. Certain hybrids were known, for example, some sterile and others not. In the 16th to the early 19th Centuries, however, just to speculate in print could get you in serious trouble with the theocratic governments of Europe. There were notions that all species might have somehow been derived from a "primordial filament". Those who published such views were at great risk.

Prior to Jean-Baptiste Lamarck in 1800, though, nobody put forward a theoretical explanation for a mechanism of species change. His theory is called "Inheritance of Acquired Characteristics", and the best-known example is the giraffe, which is imagined to have arisen as ancestral forms stretched their necks to reach the leaves of trees; those which could stretch the best passed on longer necks to their descendants. Charles Lyell effectively demolished this view before Darwin had developed his own theory.

As the mini-biographies in Darwin's Ghosts show, those who published "transformationist" views prior to 1840—including Erasmus Darwin—and thus risked censure, persecution and death, laid the groundwork for Darwin to publish Origin and survive with his skin intact. The only person who clearly enunciated a theory of Natural Selection, independently of Darwin, was Alfred Wallace. The gentlemanly way both Darwin and Wallace and the scientists Darwin consulted handled the priority question is a highlight of scientific history.

The priority question arose only because the theocratic risk had induced Darwin to spend some twenty years gathering added examples and refining his arguments, so there would be no refuting his theory (so greatly did he underestimate the persistence of Pharisaical creationists!). Had he published his theory soon after he had confirmed it, Wallace would likely have known about it, and possibly had the book in hand during his expeditions in the Malay Archipelago. Think what a different route his collecting activities might have taken were he searching for further confirmation of the theory! However, his independent derivation of Natural Selection, based on Malthusian theory for both him and Darwin, strengthened Darwin's supporters when the debates heated up in the decades after 1860.

The debates continue, sad to say. While proponents of Judaism don't seem to care much, both Christian and Muslim apologists decry all aspects of evolutionary theory, from the great spans of time it needs to the notion that human dignity is denigrated (We're apes, folks. Get used to it). Now that millions of fossils and their stratigraphic relations have shown that extinction and evolution are factual, many are forced by the evidence to admit that "life has changed through time", which is how evolution is defined. But the Theory of evolution! Now, that's where the Shinola "hits the fan". The Theory is Natural Selection. Its outline is simple:
  • Most individuals of all species die young and thus do not reproduce.
  • There is variation among the members of any species.
  • Certain variations tend to help an individual survive and reproduce, while others tend to hinder or prevent survival and reproduction.
  • There is a mechanism that leads to increased variation within a species, nowadays called mutation.
  • Over long periods of time, variations that promote survival and reproduction increase, even as others decrease.
All this together is also called Descent with Modification, a term Darwin first used. By contrast, in the prior theory, Lamarckian evolution,  modification precedes descent.

The matter of mutation was unknown to Darwin and his contemporaries. So was the digital nature of inheritance. When I was young, "mutation" in popular culture was thought to be some sudden, monumental change, such as the radioactive spider biting Peter Parker to turn him into Spider Man. Actual mutations are tiny, tiny variations in DNA. Every one of us contains between 50 and 100 such mutations that make each person genetically different from being exact replicas of the parental mix that produced the egg and sperm that fused to form the embryo that became him or her. Even "identical" twins are different in this way. Most mutations have no effect. Of the very few that do, some cause the embryo to die very early, some lead to birth defects or other debilities, while a few may be beneficial. These last are most likely to help us or our descendants survive better.

In a later edition of Origin, Darwin was persuaded to add a Historical Sketch, to outline the ideas of his predecessors. This Sketch is included as the last chapter of Darwin's Ghosts. So what is the secret of this Secret History? That Darwin and Wallace really did produce an entirely original theory. Natural Selection has been called the most successful scientific theory (proponents of quantum electrodynamics or the general theory of relativity notwithstanding). It has been said that without Natural Selection, none of biology makes any sense, but with it, everything does.

For me, the book placed a solid stamp on the originality of the theory of Natural Selection. Those who accused Darwin of plagiarism were mistaken. No theory of descent with modification preceded Darwin and Wallace. No substantial variant theory has stood the test of time. Subscripts such as "punctuated equilibrium" add details that explain the effect of sudden shifts of environment, for example, without changing the essential nature of Darwinism.

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