28 April 2011

Evolution as Path Dependence

In a message board to which I go now and then to vent, I initiated a discussion of evolution. My own view, FWIW, is that humans almost certainly evolved from non-human primates, who in turn almost certainly evolved from non-primate mammals, and so forth. On the question of mechanism, I am skeptical about the explanatory value of natural selection. Still, I wanted the sense of my fellow posters'/venters' opinions, and not surprisingly got an earful.

I was also challenged, appropriately enough, to present a fuller statement of the reasons for my own view. I'll reproduce part of what I said in response, here:

Of course, macroevolution involving Australopithecus, Homo Habilis, and the rest of that cast of characters cannot be “observed” in 2011, any more than Julius Caesar can be. We have no choice but to rely on inferences in either case. But I’m not willing to give up on knowledge of the past of either thousands or millions of years ago.

If that is all I had to say, though, I’d be evading your sensible call for reasons. So here, with that as qualification and introduction, is a fuller statement of some of the lines of evidence that lead me to infer that the origin of our species is likely not that of a separate creation, but a matter of evolution from other less brainy primates.

To begin, there are our own bodies. In some respects, these do not seem to have been the product of any one-time intelligent design. Consider our appendix. This has been the subject of much contention. ID and creationist literature has made the point that the appendix can do various valuable things here.

Yet there is still the fact that a lot of us manage to live long lives long after the appendix has been removed – and that it had to be removed because it posed a threat to our lives. This seems, on the face of it, a counter-example both to intelligent design and to natural selection. But I'm just making a case here for path dependence, for the notion that our very distant ancestors were very different creatures from ourselves, and that this fact helps make us who we are. It does seem that the appendix continues to qualify as a dangerous vestige of earlier periods. Confusion comes about because of the misuse of the word “vestige” in this context, but let us avoid purely semantic quarrels. I'll link to a detailed discussion here.

Second, still looking inward, even aside from vulnerabilities such as the appendix, there are oddities such as the way Ostriches use their wings for balance when running. (Okay, this is a non-human example, but it relates to the broad issue of macroevolution). Surely an engineer, an intelligent designer, could have designed a more efficient way for a creature to balance itself. Lots of creatures run very quickly without falling over, and without the help of wings.

It seems to me (yes, making inferences, indulging in speculation) reasonable to suppose that the ostrich is descended from other species of bird that flew. Over time, creatures evolved from them that did not fly. Why? Because flight itself is a great expenditure of energy for those creature that rely upon it, and that energy could well be redirected into, say, finding a mate and caring for the young. Survival pressures might have started working against flight as soon as predators disappeared from a particular environment for whatever reason, so the energy use of flight became a waste. The wings, as pre-existing material, were then available for use as a balance, and that functionality was built into further evolutions, until we got to the ostrich. I suppose, if you wish to consider all birds simply as birds, that particular hypothesis could even be accepted and labeled as “micro-evolution.” But if that is micro, then the evolution of humans from other primates is micro, too. If the development of humans qualifies as macro, then I submit so does the development of the ostrich.

Thirdly, let’s talk about fossils. What are we to say of the Tiktaalik roseae?.

According to the University of Chicago, this is the fossil of a creature with a mix of fish and amphibian traits. It seems to have moved about on land without having been ready for that quite yet. The adaptations that would make sense for a more determined land dweller weren’t there, and some that make sense only for a sea creature were still there. Further, the specimens are dated to 375 million years ago, which fits nicely into the story that evolutionary biology had been putting together about life on earth before these fossils came into the ken of human observation … in 2005.

Fourth, let’s move up to something a little more recent. A mere 47 million years ago. Only one-eighth as old as Tiktaalik. What are we to say of the Darwinius Masillae? You can figure out what its discoverers thought of it (the name they gave it is a hint.).

The photograph there is a thing of beauty. The actual cladistic significance will be a subject of debate for a long time, since that is how science works. Plenty of room for inferences yet undrawn, not to mention wilder speculations here. But underneath it all, Darwinius seems “designed” to point in two different directions, toward lemurs on the one hand, and toward monkeys on the other.

Further, note the dating in each case. Yes, evolution would have suffered something of a blow if the Tiktaalik had been dated to only 47 million years ago and the Darwinius to 375. But that did not happen. Each fossil is where it ‘should’ be in the timeline.

Finally, let’s come to the paleontology of primates. The cluster of Ardipithecus, Australopithecus and Homo species and debate about them continues of course. Competing museums, universities, and paleontological egos are at stake, so we can be sure there is a big future for such debates.

Recent excitement, though, (including some of my own) centers on Michel Brunet and his discovery in Chad, the Sahelanthropus Tchadensis.

Teeth and skull seem “human,” and these fossils date to between 6 and 7 million years ago. My own best inference from such fossils is that they will in time coalesce to tell a coherent story of development through various sorts of primate of the features of modern homo sapiens. You can always prefer to believe that God simply decided to create the Sahelanthropus, and the Orririn Tugenesis, and the Ardipithecus kadabba, and so forth – the whole range of species in the Africa of millions of years ago as indicated by such fossils – that each was specially created and involved no transitions to one another. Yet that seems uneconomical, and seems more a matter of giving up at explanation than of having found one.

My own conviction is that our bodies like our minds are the consequence of the will of a Prime Mover, and many of their particulars are path dependent, the product of the various secondary causes through which that Prime Mover has deigned to work. These big cerebral hemispheres with which we ended up can be put to few better uses than to work out the connections, which will surely over time shed light on our present condition.

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