So, I get an email informing me of a link post at John Wilkins' Evolving Thoughts. I go there where I click through to James Winters's A Replicated Typo, which has a post, Answering Wallace's challenge: Relaxed Selection and Language Evolution. I start reading and find out that it's mostly about a recent article by Terrence Deacon in the Proceedings of the National Academy of Sciences. So I click through to the paper, A role for relaxed selection in the evolution of language capacity. And, naturally, I start reading that, not too much, just a little to get the flavor.
Then I start poking around in the immediate neighborhood, as Winters had indicated that Pinker, too, had a recent paper on language evolution. As indeed he does: The cognitive niche: Coevolution of intelligence, sociality, and language. So I read a little of that and did some more poking.
And what do I find? PNAS has a whole pile of articles on human evolution in that issue, and you can read them all online. For free, though, if you wish, you can pony up $25 and spend a week downloading PDFs to your heart's content. I might just do that. Douglas Wallace has a paper, Bioenergetics, the origins of complexity, and the ascent of man, which looks particularly interesting. It's the energetics and complexty stuff that has my attention. Here's the abstract:
Complex structures are generated and maintained through energy flux. Structures embody information, and biological information is stored in nucleic acids. The progressive increase in biological complexity over geologic time is thus the consequence of the information-generating power of energy flow plus the information-accumulating capacity of DNA, winnowed by natural selection. Consequently, the most important component of the biological environment is energy flow: the availability of calories and their use for growth, survival, and reproduction. Animals can exploit and adapt to available energy resources at three levels. They can evolve different anatomical forms through nuclear DNA (nDNA) mutations permitting exploitation of alternative energy reservoirs, resulting in new species. They can evolve modified bioenergetic physiologies within a species, primarily through the high mutation rate of mitochondrial DNA (mtDNA)–encoded bioenergetic genes, permitting adjustment to regional energetic environments. They can alter the epigenomic regulation of the thousands of dispersed bioenergetic genes via mitochondrially generated high-energy intermediates permitting individual accommodation to short-term environmental energetic fluctuations. Because medicine pertains to a single species, Homo sapiens, functional human variation often involves sequence changes in bioenergetic genes, most commonly mtDNA mutations, plus changes in the expression of bioenergetic genes mediated by the epigenome. Consequently, common nDNA polymorphisms in anatomical genes may represent only a fraction of the genetic variation associated with the common “complex” diseases, and the ascent of man has been the product of 3.5 billion years of information generation by energy flow, accumulated and preserved in DNA and edited by natural selection.
That third sentence is the one that got me: "The progressive increase in biological complexity over geologic time is thus the consequence of the information-generating power of energy flow plus the information-accumulating capacity of DNA, winnowed by natural selection." Sweet. What's especially sweet is the casual assertion of "biological complexity over geologic time." That's certainly how I see it, but I was under the impression that biologists bridle at the notion of increasing complexity over time. Has that notion become more acceptible while I was looking the other way? I surely hope so. In any event, David Hays and I wrote a little article on the subject, A Note on Why Natural Selection Leads to Complexity, which you may download here.
But let's get back Winters' post at A Replicated Typo. Here's a passage that get me thinking a bit:
The first aspect we need to appreciate is how Darwinian-like processes operate at the developmental-level. Deacon cites many instances, such as the fine-tuning of axonal connection patterns in the developing nervous system, where developmental processes are achieved through selection-like operations. Importantly, though, the logic differs from natural selection in one respect: “selection of this sort is confined to differential preservation only, not differential reproduction. In this respect, it is like one generation of the operation of natural selection”.The point he’s trying to get across is that these intraselection processes are taking place right across nature.
That fine-tuning of axonal connections, that, of course, has been known for some time, and Gerald Edelman has built his own theories of the brain around such phenomena, talking of neural Darwinism. What happens is this: At some relatively early stage in ontogenetic development a population of neurons sprouts dendrites like mad, forming random connections all over the place. These connections are then "pruned back" through use. Those connections that are used become stronger; those that are not, weaken and the dendrites die away. In this way the pattern of neural connectivity is "sculpted" to "match" the affordances (to use J.J. Gibson's term) offered by the environment.
It's the problem of design all over again. The brain's got billions of neurons, each of which has thousands of connections. All of these must be wired up just right. How's the brain to do this? That is to say, how do you cram all the necessary wiring information into the genome? You don't, because you don't have to. You just set up a process of random variation and selective retention, one that operates inside the organism.
One must keep in mind, of course, that those neurons that constitute the brain are each living entities and, as such, are trying to survive and thrive in their environment, which is filled with other neurons (not to mention the glial cells which surround them). The neurons don't "know" that they're "strapped" together in an organism such that they ALL survive or die according to the fate of that organism. And, there was a time when all life on earth consisted of single-celled organisms, each trying to survive, and variously cooperating and competing with their fellows.
And I've recently been making the same argument with respect to culture, especially in my recent post on design. What I haven't talked about, and what may prove a tricky little business, is where we get random variation among memes. Recall that I've defined memes as physical properties of cultural artifacts and processes, namely those properties that allow individuals to cooperate through those artifacts and processes. Certainly there will be variations in the way those memetic properties are expressed in individual performances. Indeed, there may be downright errors.
That's certainly the case in improvisation. You intend the line to go that way, but it doesn't. Maybe a finger slipped, causing a wrong note to come out, or one of the other musicians did something that changed the "valence" of your intended line. Whatever. Things got off track. So you've got to scramble to get them back on track. If you're successful, and your invention is particularly felicitous, you'll repeat it, and others will copy it, and before you know it, another meme is born.
But enough of this. I'm rambling. More later.
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