The answers keep coming in for my query about "what is evolution?" RPM took me to task for basically answering "what is selection" with my initial response. This is a good criticism...honestly, I wanted to focus on selection because I think random genetic drift confuses many people, and it quickly turns into a black box incantation that explains everything and nothing. But here's another point of interest: selection is stochastic as well! That is, selection favors fitness, and fitness tends to exhibit particular characteristics in particular environments (e.g., extremely fast vertebrate aquatic creatures seem to converge upon similar forms because of the constraints of physics), but at least in the short term there are often many solutions to the same problem. You want an example? High altitude peoples, different genetic and physiological responses. Now, I did say "short term," because I am to understand that the Tibetans, for example, seem to have "better" strategies in regards to optimizing fitness than the peoples of the Andes. Why might this be? Well, Tibet and (or its environs) have been inhabited by modern humans for at least 50,000 years. In contrast, the Andes probably hasn't seem human habitation for more than 12,000 years. Selection takes time. And, selection has to work with the variation it has on hand, and Tibet is demographically much more "hooked in" than the Andes, which had to replenish selection after the Beringian bottlneck. Of course, the Andeans have hit up a local fitness optimum, but given enough time it seems possible that would they keep ascending toward the Tibetan strategies (which are less stressful on the body). Or would they? Perhaps they would hit upon modifier genes and wander down an alternative developmental path from the Tibetans altogether...cycles within cycles, and so it never ends. My overall point is that sometimes selection simply reduces the sample space from nearly infinite opportunies to explore genetic variants (e.g., neutrality) to only having recourse to dozens of strategies. How does selection select from those strategies? God knows....
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Stochastic hill-climbing for the layman: You can't always get what you want, but if you try sometimes, you might find, you get what you need.
expectations within expectations.... :)
This is one of the most intellectually challenging(to me at least) entries I've seen here.
Do all populations, given enough time in a single region, experience customized fitness peaks, at which point nothing more could be better suited, in perfect harmony w/ their environments? Though I do realize that culture could be taken into account as well. What a culture wants, & what is best for a culture's people could be at odds? What if altiplano "indians" had decided 10ky ago that big chests were ugly? Or if ancient NE asians selected against flatter faces? Would evironmental adaptation still proceed? Well, my surmising might be idiotic if traits are advantageous in the extreme(i.e, big chested people simply died less frequently at high altitudes, and flatter faces survived better in NE Asia. Culture will be irrelevant I guess.
My overall point is that sometimes selection reduces the sample space from nearly infinite . .. .. ....How does selection select from those strategies? God knows....
The overall point & last sentence, which seem quite fascinating, went completely over the top of my head. I regret not being able to conclude the entry with the same comprehension I was capable of for the rest.
I have a feeling that you're getting deep into issues of probability, stochasticity, etc., but I'm not sure. Hopefully you can elaborate on the same topic in future entries. I'll be re-reading that last passage, trying to figure it out, forever.
Thanks, razib, for something to think about over the weekend:)