When The Facts Change, I Change My Mind – What Do You Do, Sir?

The left gets a good chuckle out of the "Intelligent Design" movement: fundamentalist Christians and fellow travelers who let their religious ideology cloud their scientific judgement. And rightly so. We should indeed have a good laugh at the expense of those who value ideology over science. As Keynes famously said, "When the facts change, I change my mind – what do you do, sir?"

But it is not only creationists who refuse to let the scientific facts of evolution change their ideologically-determined minds. The left does this too when it comes to certain aspects of evolution and genetics, especially when race is involved.

Daniel Dennett begins Darwin's Dangerous Idea with the following mission statement: (p.11)

Darwin's theory of evolution by natural selection has always fascinated me, but over the years I have found a surprising variety of thinkers who cannot conceal their discomfort with his idea, ranging from nagging skepticism to outright hostility. I have found not just lay people and religious thinkers, but secular philosophers, psychologists, physicists, and even biologists who would prefer, it seems, that Darwin were wrong.

Why this disconnect? Dennett explains, (p.22-23)

[W]hat happens when the same [evolutionary] thinking is extended to the species we care about most: Homo sapiens[?] Darwin himslef fully recognized that this was going to be the sticking point for many people, and he did what he could to break the news gently. More than a century later, there are still those who want to dig a moat seperating us from most if not all of the dreadful implications they think they see in Darwinism.

A few weeks ago, my co-blogger Patri opened up a can of worms on his personal blog, asking, "Is there a Jewish race?" Despite the fact that Ashkenazi Jews are much more likely to be carriers of the Tay Sachs gene than the general population, many of his readers strongly resisted the inference that this and other genetic similarities among Jews (breast cancer, IQ) is enough to conclude that Jews can be grouped together as a "race."

Part of the problem is that the concept of "race," like the concept of "species" or "mammal," is quite fuzzy. Let's go back to Dennett for a moment, this time from Freedom Evolves: (p.126)

You may think you're a mammal, and that dogs and cows and whales are mammals, but really there aren't any mammals at all - there couldn't be! Here's a philosophical argument to prove it (drawn, with alterations, from Sanford 1975).

  1. Every mammal has a mammal for a mother.
  2. If there have been any mammals at all, there have been only a finite number of mammals.
  3. But of there has been even one mammal, then by (1), there have been an infinity of mammalsm which contradicts (2), so there can't have been any mammals. It's a contradiction in terms.

Since we know perfectly well that there are mammals, we take this argument seriously only as a challenge to discover what fallacy is lurking within it. Something has to give. And we know, in a general way, what has to give: If you go back far enough in the family tree of any mammal, you will eventually get to the therapsids, those strange, extinct bridge species between the reptiles and the mammals. A gradual transition occurred from clear reptiles to clear mammals, with a lot of hard to classify intermediaries filling in the gaps. What should we do about drawing lines across this spectrum of gradual change? Can we identify a mammal, the Prime Mammal, that didn't have a mammal for a mother, thus negating premise (1)? On what grounds? Whatever the grounds are, they will be indistinguishable from the grounds we could also use to support the verdict that that animal was not a mammal - after all, its mother was a therapsid. What should we do? We should quell our desire to draw lines. We don't need to draw lines. We can live with the quite unshocking and unmysterious fact that, you see, there were all these gradual changes that accumulated over many millions of years and eventually produced undeniable mammals.

Philosophers tend to like the idea of stopping a threatened infinite regress by identifying something that is - must be - the regress-stopper: the Prime Mammal, in this case. It often lands them in doctrines that wallow in mystery, or at least puzzlement, and, of course, it commits them to essentialism in most instances. (The Prime Mammal must be whichever mammal in the set of mammals first had all the essential mammalian features. If there is no definable essence of mammal, we're in trouble. And evolutionary biology shows us that there are no such essences.)

As with mammals, the concept of species cannot be understood if we look for the essense of species; rather, we must "live with the quite unshocking and unmysterious fact that, you see, there were all these gradual changes that accumulated over many millions of years and eventually produced undeniable species."

The theoretical concept of species that predates Darwin's theory had two fundamental ideas: that species members have different essences, and that "therefore" they don't/can't interbreed. What we have subsequently figured out is that in principle there could be two subpopulations that were different only in that their pairings were sterile due to a tiny genetic incompatibility. Would these be different species? They could look alike, feed alike, live together in the same niche, and be genetically very, very similar, yet reproductively isolated. They would not be different enough to count as salient varieties, but they would satisfy the primary condition for being two different species. In fact, there are cases of "cryptic sibling species" that approximate this extreme. As we already noted, at the other extreme we have the dogs, readily distinguished into morphological types by the naked eye, adapted to vastly different environments, but not reproductively isolated. Where should we draw the line? Darwin shows that we don't need to draw the line in an essentialist way in order to get on with our science. We have the best of reasons to realize that these extremes are improbable: in general, where there is genetic speciation there is marked morphological difference, or marked difference in geographical distribution, or (most likely) both. If this generalization weren't largely true, the concept od species would not be important, but we need not ask exactly how much difference (in addition to reproductive isolation) is essential for a case of real species-difference.

Darwin shows us that questions like "What is the difference between a variety and a species?" are like the question "What is the difference between a peninsula and an island?" Supposed you see an island half a mile offshore at high tide. If you can walk to it at low tide without getting your feet wet, is it still an island? If you build a bridge to it, does it cease to be an island? What if you build a solid causeway? If you cut a canal across a peninsula (like Cape Cod Canal), do you turn it into an island? What if a hurricane does the excavation work? This sort of inquiry is familiar to philosophers. It is the Socratic activity of definition-mongering or essence-hunting: looking for the "necessary and sufficient conditions" for being-an-X. Sometimes almost everyone can see the pointlessness of the quest - islands obviously don't have real essences, but only nominal essences at best. But at other times there can still seen to be a serious scientific question that needs answering.

More than a century after Darwin, there are still serious debates among biologists (and even more so among philosophers of biology) about how to define species. Shouldn't scientists define their terms? Yes, of course, but only up to a point. It turns out that there are different species concepts with different uses in biology - what works for paleontologists is not much use to ecologists, for instance - and no clean way of uniting them or putting them in an order of importance that would crown one of them (the most important one) as the concept of species.

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