Wednesday, November 20, 2013

how, if, and why species form?

thescientist | Evolution is not concerned with species, but with individuals. The survival and reproduction of those individuals that are best adapted to their environment determine the characteristics of subsequent populations, but neither the process nor the theory requires that these populations be organized into species. The formation of species, when it occurs, is a phenomenon that needs to be explained.

On closer inspection, the very notion of a “species” is difficult to formally define. This has been a matter of debate since before Darwin, who himself concluded that “we shall have to treat species in the same manner as those naturalists treat genera, who admit that genera are merely artificial combinations made for convenience” (Origin of Species, Chapter XIV). Many subsequent authors have proposed more formal definitions, known as species concepts, each useful for particular applications but not without idiosyncrasies.

For example, in sexually reproducing populations, the biological species concept refers to distinct groups of organisms that can only mate successfully with other members of the same group. This definition at first seems reasonable, but situations have been observed where members of group A can mate with group B, and B with C, but not A with C. Formation of biological species is therefore not an evolutionary necessity: under some conditions it happens, under others it does not.

Two other species concepts that are frequently employed are ecological species and genetic species.


ken said...

Actually I thought you were going to bridge gaps, gaps being considered plural and would include gaps in the link. However what you tried to "bridge" from what I posted was already discussed.."As more and more genes were sequenced, it became clear that the patterns of relatedness could only be explained if bacteria and archaea were routinely swapping genetic material with other species - often across huge taxonomic distances"....Isn't this the "gap" you bridged? And nobody would consider this significant enough to throw the tree idea out. But I guess, from my 5th grade perspective this was the gap...""A team at the University of Texas at Arlington found a peculiar chunk of DNA in the genomes of eight animals - the mouse, rat, bushbaby, little brown bat, tenrec, opossum, anole lizard and African clawed frog - but not in 25 others, including humans, elephants, chickens and fish. This patchy distribution suggests that the sequence must have entered each genome independently by horizontal transfer."

Of course in reality, all those articles you assigned, I really expected you to attack and give me doubt not just about the text I posted, but would go after the link.

CNu said...

The link was pure garbage, not worth even a few keystrokes. Rescuing you and BD from the artificial boondoggle of the 19th century trees seemed a more than sufficient goal in and of itself.

Symbiogenesis OTOH - has been one of the foundational concepts undergirding the subrealist oeuvre from its inception. I wouldn't even pretend to summarize in a comment the grand thesis the singular Dr. Margulis set forth over an entire career.

CNu said...

lol, but what would that leave the hobby enthusiasts who make it not only their life's work, but the singular font of their individual meaning, to engage in endless theological disputes over whose just-so story is best?

Nakajima Kikka said...

The idea that organisms must be a certain minimum size in order to speciate is intriguing, but the money shot of the article is in the last paragraph, as it may have profound implications for future environmental policy:

Just as evolution does not critically depend on species formation,
ecology as a science does not critically depend on it either. Species
richness as a predictor for ecosystem functioning, for example, can be
replaced by other measures of biodiversity, such as functional or
phylogenetic diversity, that do not depend on the species concept...

The neo-environmental movement of Stewart Brand et al. has been seeking a theoretical foundation for eliminating "wildness" (and the emphasis on its importance in natural maintenance of species richness for ecosystem functioning) as a driving force in ecology and environmental policy and replacing it with "managed development" of the environment using biotechnology, synthetic biology and nanotechnology to modulate the type, complexity and number of existing species for human benefit. The issues brought up in the article could prove to be just what they're looking for.