Sunday, February 24, 2008

Evolving Sex

The International Herald Tribune has an interesting article on parthenogenesis in Komodo dragons and other species. Parthenogenesis occurs when an ovum produces offspring without benefit of male fertilization, making the offspring a genetic clone of the mother. In other words, it's a form of virgin birth.

Here's one passage of several from the article which caught my attention:

The big question these virgin births raise is this: If some females can get along without males, why does any species have males? The reason is simple. With virgin birth, hatchlings are simply genetic duplicates of the mother. In a world of clones, there would not be enough variation for populations to adapt. Virgin birth, then, is a great stopgap measure to ensure the survival of a species, but works against it in the long haul.

Ah, so easy. Sexual reproduction is necessary to produce genetic diversity, diversity helps a species survive, therefore sexual reproduction evolved through the blind, purposeless processes of natural selection and genetic mutation. This is what some scientists and philosophers refer to as a wave of the wand explanation. It tells us why sexual reproduction evolved while glossing over the much more intractable question of how such a process evolved.

Think of all the changes that have to occur, most of them simultaneously, in order to produce two different sexes of the same species. The evolution of meiosis and the production of gametes in both males and females (before males and females ever evolved), the means of getting the gametes from the male to the female, the entire complex of reactions which occurs when a male gamete encounters the female ovum allowing the male's DNA to penetrate to the nucleus of the ovum, the synchronization of the two sets of chromosomes, the coordination of embryonic development and the entire panoply of anatomical structures and behaviors which need to evolve in order to facilitate the process, along with the physiological and biochemical adaptations which must also be in place. It's no wonder that evolutionary treatments of sex almost always focus on the advantage that sexual reproduction affords, they almost never address the problem of how sex evolved. The problems are staggeringly difficult.

Consider, too, how rare it is that mutations occur that are beneficial to an organism, much less simultaneous beneficial mutations occurring in the same populations of the proto-sexes. Each of these mutations had to confer a survival advantage even before sexual reproduction was possible. Moreover, since both plants and animals reproduce sexually we can assume that this ability evolved pretty early on in the evolutionary process, so it must have unfolded with comparative rapidity.

Well, maybe it all did happen, but the more one learns about the extremely complex series of events and the sheer number of adaptations that must have occured in order to produce fertilization in all sexual species the more skeptical one becomes that chance and nature could, with no conscious intention, produce such a breathtaking process.

The Darwinian, perhaps, can trace out a long, elaborate hypothetical scheme which results in the emergence of sexual reproduction among protists and conclude that, since it is logically possible that it could have happened that way, that therefore it's plausible that it did happen, and since it's plausible then it's probable that it indeed happened because, after all, here we are, and we're sexual creatures.

But logical possibility is hardly a sufficient condition for plausibility, much less probability. Whether evolution produced sexual reproduction, I don't know, but I am quite certain that if it did, it was not the blind, unguided evolution of the Darwinian materialists. Their story of the evolution of sex is a fairy tale of magic wands and pixie dust.