Science Reader Question: Which Came First, the Sinner or the Sin?

In the previous installment of my ongoing series on evolutionary biology questions, I shared my conversation with Mike Stell about original sin within the context of an evolutionary natural history. That topic leads naturally to a related question about who the original sinners were. Actually, both the blog commenter whose questions inspired this series and Mike Stell independently asked me very similar questions. What exactly does evolutionary biology say about the first humans?

Indeed, the story of the Fall is made even more implausible by scientific claims that the first human male and the first human female arose separately from large populations. I’ve never quite understood the claim that we should not conceive of a first male or female human because they arose in a large population. The odds of several female somethings giving birth to homo sapiens essentially simultaneously seems rather unlike IMHO. There had to be a first human male and a first human female, regardless of how many creatures were present when that took place.

To be honest, even as a biologist it took me a while to puzzle through these issues when I encountered them, partly because the answers are very counter-intuitive. It doesn’t help that popular imagination about evolution reinforces our intuition at the expense of what evolutionary biology actually says. The recent film X-Men: Apocalypse is just the latest example of a science fiction property that dips its toes in the waters of evolution but only serves to muddy them in the process. I wrote a more detailed x-amination of the film for BioLogos; one of the key difficulties is the way the film’s titular antagonist seems to blend evolution with a sort of Platonic idealism or essentialism.

It is common to hear that human beings evolved from apes. This is a convenient shorthand that is imprecise in ways that can create confusion. For starters, modern humans did not evolve from modern apes, rather both evolved from a common ancestor. Still, that common ancestor would probably seem to us very ape-like, so on that score the shorthand isn’t entirely misguided. But there’s a more subtle problem with both of these descriptions: species don’t evolve.

Dividing all organisms into distinct species is not straightforward. At any given moment, it may be possible to define boundaries. Looking back at the fossil record, which only offers snapshots of different points in history, drawing lines of demarcation seems natural. Ultimately, the idea that all species have sharp boundaries breaks down when trying to account for the taxonomy of every individual. One can no sooner set a minimum number of grains of sand that make a heap than draw species barriers between every living thing that has ever existed.

We might imagine an ideal or reference human and decide whether every organism is a human or not by how far they deviate from that ideal. If we make our assessment based on anatomy or on capabilities, we might find that infants or developing babies in the womb don’t come close enough. We can wait until adulthood to make our assessment, but then again we don’t wish to deny human dignity to amputees or those whose development was inhibited in some fashion. We can appeal to the genome, but then we are really splitting hairs if we say that one can be a human with 1,000 mutations but not 1,001. And that’s before we ask “mutations relative to what?” or account for the fact that 10,000 mutations of one sort could have no discernible effect, while 100 mutations of a different sort could have dramatic consequences.

Now just because species get fuzzy at their edges doesn’t mean they are a useless concept. There is no doubt that I am not a cuttlefish or a chimpanzee. A cow is never going to lay an egg from which a chicken then emerges. Turkey bacon will never be a perfect substitute for pork bacon. It’s just that species are categories we define after the fact, not entities unto themselves that can transform from one to another.

At the same time, the notion that there was a first Homo sapiens ultimately doesn’t work. If we followed humanity backwards in time, there would be no obvious place to draw a line between H. sapiens and earlier hominins. If we went all the way back to the common ancestor of humans and chimpanzees and then followed those individuals forward, what we would see would be two populations that stopped interbreeding and so eventually diverged enough that we would call one group chimps and the other humans. The population that eventually became human would never drop below about 10,000 individuals. We infer this from present day genetic diversity among humans; if the population size was substantially smaller than 10,000 we would see less diversity now. There wasn’t a single first human male or single first human female somewhere amongst this population; everyone in this population were ancestors to present day humans.

As to the bit in the original question about the first male and the first female arising separately, I believe this refers to the unhelpfully named “Y chromosomal Adam” and “Mitochondrial Eve.” These individuals aren’t the first human male and first human female. Rather, they are the most recent common ancestors of all men via patrilineal descent and of all women via matrilineal descent, respectively.

Men only get Y chromosomes from their fathers. Trace the son-to-father lineages back far enough and every living male line goes back to the same man; that’s Y chromosomal Adam. He wasn’t the only human male alive at the time, nor was he the only male ancestor of living humans who was alive at that time. Rather, any lineages from living people back to those other males have a female somewhere along the way.

Similarly, men and women only get their mitochondrial DNA from their mothers. Go back far enough up the son-and-daughter-to-mother lineages and you get to a single woman. She wasn’t the only human female, nor the only female ancestor. Any lineages from living people back to those other females have a male somewhere along the way.

This doesn’t necessarily mean that the Biblical couple Adam and Eve weren’t actual humans who lived at some point in history. They just couldn’t have been the only two humans, which is why I proposed an alternative way we could have inherited original sin from them.

As to the nature of that sin:

My point is that there isn’t any reason to think that the population from which humans arose was not violent as well. Indeed, there are violent species through all the phyla I know of, depending upon how one defines violence, so which one committed the first act of violence that could be called “sin”?

It’s not clear to me that the first sin was an act of violence. The event described in Genesis is not what we usually consider violence. Furthermore, when predators now act violently, we don’t consider that to be sin. Sin seems to be a combination of particular acts, including but not limited to certain forms of violence, and the knowledge that performing them is a rebellion against God. So the first sin was not the first time someone was violent, but the first time someone rebelled against God after God explicitly communicated which acts would be rebellious.

Next time we’ll look at whether an evolutionary perspective has anything positive to offer to make these challenges worthwhile.