#25: Evolution (Yet Again!)

Most of the European 18^th century was fascinated with “natural history” and with the question of speciation. Yes, this was an important issue long before Darwin came upon the scene. It became important almost immediately once the Aristotelian and Christian world view of fixed species came into question. One interesting thesis was that species are a kind of illusion, that in fact there exist creatures who imperceptibly fill the apparent gaps between the different kinds with which we are familiar. We can see the beginnings of evolutionary thinking in the writings of David Hume. An explicit effort to grapple with the problem came from Jean-Baptiste Lamarck (1 August 1744 – 18 December 1829) who hypothesized that acquired characteristics were heritable. This was the not-so-good evolutionary theory. Thus, Federer’s skills as a tennis player would automatically be transferred to his progeny. None of this theorizing hit the jackpot until Darwin’s On The Origin of Species came out in 1859. The huge advantage of this theory came from it’s providing a purely mechanical and intuitively satisfying explanation of the appearance of new species, namely the doctrine of “natural selection.”

In the interest of fairness, and not to detract from Darwin’s achievement, I should mention that the doctrine of natural selection already appeared in Lucretius’s (ca. 99 BC- ca. 55 BC) De Rerum Natura (the passage is too long to cite, but the interested reader should look at the section entitled “Origins of Vegetable and Animal Life” in any edition of the poem).

Now as I said, the notion of natural selection is indeed intuitively satisfying, but this might in fact be a burden for the theory. The reason I say this is that the attractiveness of the doctrine may well be responsible for a kind of carelessness with respect to detail. In particular, I have a problem with the theory that I am hoping one of our readers will successfully address. I suspect that I’m missing something obvious, but try as I might, I still don’t have an answer to my puzzle. Here is my problem.

Here is the theory of speciation by natural selection as I understand it. We assume a limited amount of food and space to be available to a population of creatures. We further assume that the creatures of this population compete for the food and space. We thirdly assume that those creatures less well equipped in the fight for survival die in greater numbers and sooner than their better equipped competitors. We finally assume that the creatures are subject to random mutations, some of which improve their chances in the battle for survival and others do not.

We can easily see the intuitive attractiveness of this idea if we consider a fictitious population of raptors alike in all respects, except that some of them have eyes and the rest do not. It seems immediately plausible to expect the eyed ones to prevail and the blind ones to die out. The eyes ones would find the food before the blind ones, the eyed ones would find the strong, good-looking raptor women before the blind ones, and in conflict, the eyed ones would presumably beat the blind ones. After not too long a time, the only remaining raptors of this group would be eyed. So goes the theory of natural selection.

The problem with this story, for me, is that it works really well if we assume a fully functioning eye as the adaptation, but not so much if we assume a non-functional transitional eye still in the process of “evolving.”

That is: if the theory of natural selection forces us to hypothesize instantaneous mutations introducing fully functional eyes (or whichever organ you prefer), then its initial intuitive attractiveness disappears.

Having a fully functional eye involves an enormous amount of structural change on the organism’s part. The eye itself is very complicated, but, in addition, in order for the eye to be functional, the brain must also be altered and there has to exist appropriate neurological connection between eye and brain. It stretches probability to the breaking point to assume that one of the raptors is born complete with such an enormous and functional mutation. It doubles the stretch of this probability to yet further assume this raptor finds another one like itself with whom to breed a race of eyed raptors.

What is far more likely is evolution is a kind of creeping adaptive change. What I mean is that one or a few of the raptors are born with one or a few new cells where eyes will eventually be. If we can figure out 1) why these raptors will breed with enough other raptors like themselves to eventually created a “new cell” population, and 2) why these raptors are better at surviving than their fellows, we might be in position to see how eventually an eyed population could evolve. But the stages that precede being eyed do not bring any survival advantage with them – it is sight, and only sight, that is an aid in the contest for survival. Until the collection of new cells actually confers sight on the raptor that owns them, it is in exactly the same position as all the others, no better at surviving and no worse.

The theory works on the assumption that the population ratio of more adaptive to less adaptive changes in favor of the adaptive group, which is why there is more adaptive-adaptive reproducing and why eventually there are only the adaptive ones left. But there is no reason to assume this ratio will change during the period before the eye actually functions and gives the creature an adaptive advantage. Which entails that no uniformly improved population will be produced on which yet further mutations will occur to eventually produce a functional eye.

In a nutshell, then, I cannot understand how the evolutionary process, i.e. natural selection, works during the interim period between no eye at all, on the one hand, and a functional eye, on the other.

The only way I can see the theory working is with some ad hoc assuming.

If we assume that pre-functional eye cells confer some other adaptive advantage over the creatures that have it, then the rest of the process can be taken to work. If, for example, pre-functional-eye cells have the ability to “sense” danger in some manner that doesn’t involve great neurological or structural complexity, then they could give a competitive advantage to their owners. Perhaps there are yet other possibilities of this kind. The problem would lie in finding some kind of empirical evidence that supports such an auxiliary hypothesis.