Selection or elimination?

23 01 2007

After finishing George Page’s Inside the Animal Mind I started on Ernst Mayr’s What Evolution Is (an assertive title if there ever was one). So far it’s just so-so, Mayr glossing over or ignoring lots of illustrations or important points, as well as assuming the reader is going to know what a coelomate or polyplacophoran is off the top of their heads. Surprisingly, he also included Haeckel’s embryos during the discussion of development despite the edition of the book I have being published in 2001 (I have not seen the 2002 edition so I don’t know if this is changed). I would also dispute his assertion that Archaeopteryx is derived from thecodonts rather than dinosaurs, but such discussions will most likely come later when I finish the book this week.

All these issues could be jumping-off points for discussion, but one point Mayr attempts to make sticks out in my mind. I’ll have to go back and get the exact page/reference when I’m back at my desk (I don’t have the book handy at the moment), but Mayr suggests that Herbert Spencer’s phrase “survival of the fittest” accurately explains natural selection. Darwin liked the phrase as well, later including it in later editions of On the Origin of Species…, but I find it quite detestable (and not just for its connection to eugenics and “social Darwinism”). Natural selection is often described as a force than selects the “most fit” individuals (or individuals that are best adapted to their environment) and these individuals reproduce more frequently in a population and therefore their characteristics get carried on. In essence, natural selection is shown to almost have will, picking and choosing the best and brightest among all life, those that pass the test get the reward of living and reproducing, and it would follow that what is “most fit” is what survives better than other members of that population or species. This sounds fine, but it doesn’t work with what we know about the world and chance; the “fittest” don’t always survive.

Take the dinosaurs as an example. They were greatly abundant for a long period of time, coming in a plethora of shapes, sizes, and (inductively) habits, of course subject to natural selection. It could be argued that they were fit to survive, proliferating in the wake of the massive Triassic extinction to fill various niches, but by 65 million years ago (right at the Cretaceous/Paleogene boundary) all the dinosaurs are extinct (I’m not counting birds as dinosaurs here, although they are derived from dinosaurs). It’s rare that extinctions occur with such severity to wipe out an entire Superorder of animals, but that is what occurred, a chance catastrophe paying no heed to what was “more fit” or “less fit.” How can an animal possibly be adapted to successful survival of an extraterrestrial impact unless such catastrophes are a near-constant occurrence? In the wake of the Cretaceous extinctions, mammals won out (although taking losses of their own) and proliferated, carrying on the legacy of the cynodonts before them.

Indeed, oftentimes freak events that do no occur often enough to have species be adapted to such catastrophies, the only way of surviving being the chance of having adaptations or characteristics that prove to be of some advantage in such an event. On the individual level, many predators are “fit” to survive but may make a mistake or slip and fall, breaking a leg; something that could happen to any of them. How can less-breakable legs be selected for in any case? Further, a healthy and fit population in one area may suffer from a drought and die out, while those rains start to fall on an area inhabited by a “less fit” or less-well adapted population, allowing them to survive and even flourish. Even among “normal” populations there is variation in size, behavior, and characteristics in a species, for instance some males may put all their energy into becoming big so they can fight others for harems while there are more “gracile” males in the population that breed more efficiently by sequestering females when the big male isn’t looking (bighorn sheep show this behavior). Which is “more fit”, the alpha male or the sneaky male? They both enjoy reproductive success and the types exist in the population together, so which is “better”?

All these examples lead to this conclusion; natural selection is primarily an eliminative force. Whether by freak accident, injury, or maladaptive mutation/behavior certain members of a population are eliminated and those that remain carry on to greater or lesser reproductive success. What survives is not necessarily always the “most fit”, and as we know a creature can be supremely adapted to a niche but when something changes they may not be able to cope (thus why 99.9% of all species to ever exist are extinct). It is comforting to think of natural selection as a process that is constantly weeding out the undesirables so that the population will continue on, but the qualification of what is desirable and what isn’t seems to be ascribed by scientists and not nature itself, thus undermining the entire idea. Thus, natural selection is best understood as the elimination of certain individuals because of certain circumstances, those individuals (regardless of how well-adapted they may be) reproducing and contributing their genetic material to the population to allow for further variation and change. In this way, elimination can only be a create force if the survivors mate (otherwise the individual is a dead-end) and natural selection acts upon the fruits of their union (or not, in the case of parthenogenesis or asexual reproduction, but that’s another story), the “creative” aspect of the process only occurring through the mutations, recombinations, or other changes that occur which the offspring inherits and natural selection then acts upon.

Post script; This reminds me of another idea I had, in that natural selection is ever-present. It does not start when the animal is born, but rather the developing embryo must overcome various hurdles in development and outside factors even to be born. Sandtiger sharks are notorious for eating each other in the womb, and various mammals have reproductive hierarchies where a dominant female will induce a submissive female to abort her baby if the submissive female becomes pregnant. Many of the examples of natural selection seem to revolve around adult animals, but we’d be mistaken to forget the various trials and pressures exerted on any form of life from the time of fertilization onward.




One response

6 02 2007

[…] February 06th 2007, 11:25 am Filed under: Ecology, Evolution, Behavior After writing my previous posts, I started thinking more and more about the idea of “fitness” in organisms, and why we […]

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