Imagine a small crowd of people – a hundred or so – in a public place. A few minutes earlier they were all in transit to various other destinations, but a momentary spectacle has drawn them together. They do not, for the most part, know each other and in most cases they’ll never see each other again once they go their separate ways. They include representatives of every age group from infancy to dotage; there are people of various ethnic backgrounds, political and religious persuasions, socioeconomic status and states of mental and physical health. There is little consensus among them with respect to tastes or aspiration. Some are happier than others.
The people in this crowd have come to be together purely by accident, and it is the kind of accident that will never again draw this same crowd: the crowd has no identity, no “meaning.” Many people would be tempted to say of the people who make up that meaningless crowd, “They have nothing in common.”
But that sweeping statement, “They have nothing in common,” is not entirely true is it? They are all human, so they have that in common. Since they are all human, they are all the offspring of two biological parents, even if one of them merely traded his semen for cash at a sperm bank, or if in vitro fertilization was involved. And this makes it possible to list a great many other commonalities: they all have 23 pairs of chromosomes; they’re all bipeds; they’re all mammals; they’re all vertebrates; they’re all mortal; they’re all subject to the laws of physics and chemistry that make life possible, sets its limits, and so forth.
Moreover, since they’re all human, they’re all cousins (unless some of them happen to be related as siblings or enjoy a relationship of direct descent). In most cases, that cousinhood is so distant that it would be very difficult if not impossible to trace – but that doesn’t make it untrue in principle. (Even creationists will acknowledge that. Of course, they’ll trace their cousinhood through the fictitious biblical character Noah.)
If you start to trace the pedigrees of those who make up the crowd, you’ll find that most of them peter out in the fog of history after just a few generations – four or five, in most cases. A few will perhaps have worked it out to as many as ten. That’s not nearly enough to establish cousinhood between those whose forebears have lived on the North American continent for over 20,000 years, and those who came from Europe more recently. If you let twenty years stand for a human generation – a reasonably good back-of-the-envelope approximation – that makes a span of five generations equal to about a century. By that reckoning, the United States is about twelve generations old, and Jesus lived approximately a hundred generations ago. Since there are populations that have been separated from each other for as much as 50,000 years, we can say that their cousinhood is traceable through some 2,500 diverging generations.
Because everyone in our imaginary crowd is human, you can therefore generalize meaningfully about them: the fact that you don’t have access to the family tree of any one of them does not mean that the individual in question has no family tree. (In other words, it simply is not true that a single one of them was a uniquely created individual who popped into existence by divine fiat, with no pedigree.) Even if the details of that family tree have disappeared so completely that they are unrecoverable in practice, that doesn’t mean that they didn’t exist. Very few humans can trace their lineage back any farther than the late Middle Ages, but that doesn’t mean they aren’t human, or that they aren’t related to all other humans.
The biosphere – the totality of living things both currently and over the lifespan of this living planet – is exactly like that. And because evolution works so slowly, its effects mostly noticeable only over spans of thousands of generations, we can best see evolution in action in cases of organisms whose generations are reckoned in hours not decades – whose evolution is therefore observable. That’s what we have in bacteria. It is certainly possible to see evolution in action at those sped-up scales.
Using my proffered 20-year generation for humans, let’s do some more back-of-the-envelope calculations. The agricultural revolution happened about 500 generations ago. Homo sapiens is currently thought to be about 200,000 years old, or about 10,000 generations. So, is it possible in principle to trace our ancestry all the way back to the time when our species attained its anatomical modernity, made a clear break from its precursor H. erectus? Yes, it is. Is it possible in practice to do that? Of course not. Does this mean that there are “gaps” in those generations? Only in the minds of those who need to see fossil evidence of every generation of humans since the dawn of H. sapiens in order to believe that such continuity exists. What kind of person would demand that kind of evidence? Is there anything reasonable about such a demand? Is it even meaningful? Would meeting its impossible evidentiary standard tell us anything that we don’t already know? What would you say about someone who demanded it; what would be true of a person like that?
The questions I just asked are equally applicable to those who deny the evolutionary history of the human species, along with the evolutionary history of every other species on the planet. The cousinhood of all species is demonstrable: it’s common ancestry all the way back.
A creationist is someone who refuses to generalize from that which is known to that which is evident albeit in absentia. In other words, the creationist has no capacity for deductive reasoning. No matter how much evidence you offer, he cannot, will not, look at it and draw the conclusions that are obvious to anyone with a mind uncluttered with religious nonsense. He will instead dig in his heels. As John Kenneth Galbraith observed, “Faced with the choice between changing one’s mind and proving that there is no need to do so, almost everyone gets busy on the proof.”
Coming to intellectual maturity demands that we stop feeding our prejudices, that we determine to look at the world honestly and discover it for ourselves. Once we do that, the evidence for evolution hits us square in the face: it’s all around us, and can only be avoided by the most sustained and thoroughgoing practice of Bad Faith, of self-deception.
For the past century and a half, many lines of evidence have converged on a conclusion that is absolutely inescapable: life has evolved on this planet, starting with very simple organisms. All living things are descendents of those first simple organisms. Every living thing on this planet thus enjoys cousinhood with every other living thing. This is not only a profoundly beautiful notion: it is unavoidable, to anyone who’s looked honestly at the evidence.
In light of this fact, what are we to make of adults who believe in a dirt-man, a rib-woman, a talking snake, a thunder-god who gets pissed off and destroys his creation in a hissy fit, an Earth that was created several thousand years after the Sumerians invented glue, and countless biblical miracles – and who subscribe to a cult of human sacrifice, finding it not the least bit abhorrent or credulity-straining?
I can’t for a moment imagine that Christianity is the pinnacle of human intellectual achievement, the best we can do.