Hi, Straggler.
Straggler writes:
How closely related do species have to be in order to successfully breed a hybrid? What do we actually mean by "closely related"? What does this mean in terms of DNA, genetics, chromosomes etc. etc.?
Given all the subjectivity involved in biological definitions, I’m not sure we can actually say that hybridization really means all that much. Hybrid is, itself, a rather vague term, defined as the fusion of two other things that were previously classified as distinct from one another based on equally vague and subjective terms.
I’m quickly learning that this is one of the central themes of biology: we like things to live by rules, so we can define them and categorize them and organize our information about them... but, life simply isn’t bound by any of the rules we think apply to it.
We can design theories that effectively explain patterns of behavior across populations of organisms, but we can’t use these theories to predict, with any useful degree of accuracy, the behavior of any particular individual organism.
The Theory of Evolution has provided us with at least two frameworks for evaluating the likelihood of the occurrence of certain behaviors: one called optimization theory and one based on game theory. Optimization obviously refers to the tendency of natural selection to amplify the segment of a population whose behaviors are most successful in their environment. Thus, under this criterion, we expect that nature will be largely full of species that are optimized, or well-adapted, to their environment. Game theory refers to the interplay between different organisms all competing for the same resource or payoff.
But, evolution works on a scale to which individual organisms are largely insensitive. So, evolution does not
drive the behavioral patterns of organisms, because it can only function
ex post facto, and its only means of feedback is through differentialy success of phenotypes. Thus, the reason an organism performs some certain behavior (e.g. sex) has nothing to do with its evolutionary benefits: nobody has sex for an evolutionary advantage: they do it because it tickles their pleasure centers. A pleasure center is nothing but a way to attach a short-term reward to a successful long-term strategy.
So, that some organisms end up being attracted to the wrong kind of potential mate, evolutionarily speaking, doesn’t really mean much, except that there is lots of wild, random variation within populations. From an evolutionary standpoint, hybridization, homosexuality, and other things that have long been thought of as sexual perversities are dead-ends. But, because the behaviors of individual organisms do not respond to evolutionary pressures, we shouldn’t expect all behaviors to be adaptationist.
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As far as genetics go... biological molecules are also insensitive to evolution. If a hybrid is viable, all it means from the standpoint of molecules is that a massive network of chemical reactions is proceeding in a stable, cyclical fashion. The more divergence you have between the interacting parts of the chemical network, the more chances you have to throw the reaction off balance.
But, context defines everything... I think it’s going to be very difficult to discuss the genetics behind hybridization without some serious equivocation on the rules that define the process.
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Bed time for Bluejay. Good night.
-Bluejay (a.k.a. Mantis, Thylacosmilus)
Darwin loves you.
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