Why sex evolved is in fact one of evolution’s greatest mysteries.
We should be deeply suspicious of speculations that come unaccompanied by hard evidence.
Both of these come from Jerry Coyne’s Why Evolution Is True. The first is in the chapter “How Sex Drives Evolution,” (155) and the second is from the final chapter, “Evolution Redux” (230). When Coyne says “why” in the first quote, he also means “how” because he only offers a theoretical possibility, not hard evidence for what actually happened. To the significance of this and expand the actual argument, we need a quick rabbit trail.
Extending a point I made yesterday (that evolution is not a cut and dry issue), I want to highlight a little more of where I’m coming from. If you were to ask me point blank if I believe in evolution, I would have to say “yes,” but then almost immediately qualify the answer. The reality is that evolution is true, but depending on what you mean by “evolution,” it may not be 100% so. Jerry Coyne gives us this definition:
Life on earth evolved gradually beginning with one primitive species – perhaps a self-replicating molecule – that lived more than 3.5 billion years ago; it then branched out over time, throwing off many new and diverse species; and the mechanism for most (but not all) of evolutionary change is natural selection (3).
This, according to Coyne, yields six components of evolutionary change:
- Common Ancestry
- Natural Selection
- Nonselective Mechanism
I think at this point it would be hard to look at the evidence and coherently argue that species do not undergo genetic change and that this happens over a period of time. You’d also have to at least grant that speciation happens, but maybe not to the extent that an ardent evolutionist would. Case in point, I think we can all agree that wolves and domestic dogs share a common ancestor, but no creationist would say the same for birds and snakes.
85% of a True Story
All of this means that evolution is undeniably 50% true. Given that, when Richard Dawkins says over and over again in opening chapter of The Greatest Show on Earth, “evolution is a fact,” he is no less than exactly half right. We could even go a bit farther and grant that from a purely scientific vantage point, natural selection does occur. Whether or not it is purely natural is not for the scientist to decide however. I find it more plausible myself when thought of as natural explanation of divine providence in creation, but that is a result of my philosophical presuppositions that are not shared by most atheistic scientists.
But, since the first three components are almost self-evident, and the last two are at least observable and documented, evolution as defined by Coyne is roughly 85% true. That remaining 15% though, the common ancestry part, is where things get interesting. And by “interesting,” I mean uncomfortable.
The Survival Value of Half A Genital
In order for common ancestry to be true, we must all share a single common ancestor. In order for that to be true, at some point genetic reproduction would have to have evolved from being purely asexual to also including coitus (to use Sheldon Cooper’s preferred term). Keep in mind that this had to happen gradually. And not just gradually, but in two separate streams (so to speak). One set of genes in a population of organisms would need to focus on gradually perfecting the vagina, while another focuses on the penis. Somehow, this genetic adaptation needs to provide survival value to continue developing.
Supposing it does, once we have organisms with fully formed genitals, they need to find each other. And then, well, they need to get it on (or at least fumble around enough to exchange fluids). Now, there is no evidence for exactly how this took place, much less evidence that it did in fact take place. Given Coyne’s two statements in the beginning of this post, I am inclined to deny common ancestry on the basis of a comically incomplete amount of evidence. Reproduction evolving from asexual to sexual doesn’t even make sense in an evolutionary paradigm as Coyne himself points out:
Biologists still question whether any known advantage outweighs the twofold cost of sex (156).
If you see how the reasoning works you’ll understand this isn’t particularly a problem for someone already committed to evolution in its totality. Because we all share a common ancestor, at some point reproduction had to evolve into the sexual realm, and because that has clearly happened, it must offer some kind of genetic advantage even if we don’t know what it is. I don’t know about you, but that sounds like faith in the absence of evidence to me.
I can see though that if one is an evolutionist and a naturalist, there really isn’t another option. You have to believe in common ancestry because it’s part of the overall theory. Likewise, you have to believe that sexual reproduction evolved gradually even if there is no evidence that this happened because it is the only way to link lower and higher forms of life to a single spontaneous evolution of non-life to life.
The Sex Life of Fossils
What applies to the issue of common ancestry in general also applies to human-primate relations in particular. While we can find fossils of primates that no longer exist, unless we can establish reproductive connections it would be hard to both distinguish different species and put them in a proper progression.
In other words, if a species is a “reproductively isolated” population or community of organisms, how can we know who these hominid fossils were shagging? While we can determine the sex of a fossil, from I’ve read it seems like it would hard to determine the sex life of a fossil, but that’s precisely what you would need to know in order to prove it is a separate species from another similar fossil find. If they weren’t “reproductively isolated” then they might not be separate species. You may be able to establish “reproductive compatibility” (like the fact we can mate tigers and lions) but that doesn’t validate that pre-historic coitus was actually taking place.
In short, I think we would need to know quite a bit more about who these hominid fossils where shacking up with before we can really establish firm boundaries between species. We also need this kind of information to better understand the sequence of species. Until there is more clear evidence on both of these fronts, I’m inclined to deny common ancestry both in the larger sense (all of life goes back to a single organism) and in the particular sense of man’s relation to the apes. This latter sense is what unnecessarily leads scientifically naive people to rethink the creation of man in Genesis (e.g. Peter Enns’ The Evolution of Adam). If you’re able to look at the available scientific evidence with a philosopher’s eye however, this kind of revisionism is unnecessary. But who knows, one day we may have all the intimate sexual details we need to fill in the blanks.
Or, to quote the great Sheldon Cooper after he’s made a joke, “Bazinga.”