Bayesian Selection. Trouble Brews.
All natural functional biological complexity arose through the mechanism of non-teleological heritable variation and natural selection.
That's the Neo-Darwinian synthesis, in a nut-shell, and it's the cornerstone of biology.
The Neo-Darwinian synthesis may be divided into two professions, so to speak, the union of which constitutes the orthodoxy. Jacques Monod called them "chance" and "necessity," and it's a useful shorthand.
Monod's "chance" means absence of design. Chance means random in the sense of lacking teleology. There is no purpose in the raw material of Darwinian evolution. Of course, that doesn't mean that the "random heritable variation" generator doesn't obey natural laws. It does, like everything else, but it has no foresight. It's random like flipping a coin is random. The coin obeys all the laws of physics, yet the outcome of the flip is random, in the sense that there's no design to the result. If there is design, then the flip is dishonest, and not random at all.
Of course, most biological events that happened are invisible in the mists of deep time. Randomness is difficult to ascertain in modern casinos, and randomness is damned difficult to ascertain in the Precambrian. This not to say that we can't draw reasonable inferences from the available evidence, but drawing self-evident inferences from helical blueprints and purposeful arrangements of parts "isn't science," so the Neo-Darwinian inference to chance is confessional, not empirical.
Monod's "necessity" means survival; more rigorously, it means relative reproductive advantage. Natural selection. Whatever got here won the "relative reproductive advantage" death match. That's what "survived" means. It got here.
So here's the Neo-Darwinian Synthesis, colloquially:
Biological events happened, randomly, and things that survived got here.
Evolution is "a highly sophisticated scientific principle not deeply understood by most people", but on this synopsis -- "random things that survived got here" -- the architects of the Neo-Darwinian synthesis concur. Yet the consilience pulls up short. What is the unit of selection? What kind of "survivors" survived? There is a war in the pews about which things are the salient survivors, and which things are the superfluous survivors. Selfish Gene Adaptationists (Dawkins, Williams, Hamilton) insist that genes are the salient survivors, and that higher level survivors like individuals or groups are superfluous. San Marco Spandrelists (Gould, Mayr, Lewontin) insist that higher level survivors are often the salient survivors, and that genes are sometimes superfluous. Some evolutionary biologists -- like E.O.Wilson -- switch sides.
So is it all against all in evolutionary biology? Perhaps evolutionary biologists can find a way to embrace the ambiguity at the heart of their science -- a Neo-Neo Darwinian Synthesis. Perhaps natural selection acts subtly, sculpting life without revealing her handwork. Perhaps there is consilience in the more subtle grandeur of forms most wonderfully evolved -- survivors that are neither salient nor superfluous, but shy: surreptitious survivors.
But I'm pessimistic. The kerfuffle between those who believe that selection occurs only at the gene level and those who believe that selection occurs at higher levels of organization is unlikely to be resolved, at least until deeper misunderstandings are resolved. In evolutionary biology there are very deep misunderstandings. One would have thought that on the eve (no pun intended) of the Darwin Sesquicentennial the site of action of the most proven "fact" of science (natural selection) would be more or less worked out. After all, we've figured out that gravity acts on matter and that electromagnetism acts on charged particles and magnetic dipoles. Yet, in evolutionary biology, the salience of survivors remains a matter of ferocious dispute. Here's my take on natural selection, for what it's worth:
Survivors survive. Natural selection is a tautology, and speculation about the "unit of selection" is less testable inference than meaningless post-hoc guessing. Call it Bayesian Selection (B.S.). The only meaningful thing that Neo-Darwinists assert is that all life arose without purpose, an assertion not even remotely congruent with the evidence.
The salient debate -- the elephant in the room -- is whether there's evidence for teleology in biology, and that's the debate that Darwinists are scrambling to suppress. So why the ferocious debate about the "unit of natural selection," and the cone of silence about the evidence for design? There's an adage in academics: "The intensity of an academic debate is proportional to its irrelevance."
The "unit of natural selection" is the most intensely debated issue in evolution. When a scientific theory is vacuous, trouble brews.