Science Forums 2

[CraigD]

Originally Posted by Michaelangelica

What about the very promiscuous bacteria? (most of this planet's life)
How do they choose which bits of another's geonome to appropriate?
The "Natural Selection" model just does not work here.

Organisms like bacteria do appear to confound our usual definitions of “species”, “offspring”, and “individual”.

They don’t reproduce sexually, but, as Michaelangelica notes, swap DNA nearly or perhaps even more effectively than organisms that do. Some have suggested that bacterial exchanges of DNA is more analogous to a sort of “spoken language” than the kind of gene-swapping we and other animals perform via reproduction.

The distinction between a bacterial species and individual is vague. Since they reproduce clonally, the descendent of a dead ancestor bacterium is arguably the same individual. Alternately, since they incorporate genes from other individuals, the same bacterium is arguably no more the same individual after the exchange than a child of a sexually reproducing organism is the same individual as either of its parents. The analogy of “bacterial DNA exchange = sexual reproduction”, however, is inexact, as a recipient bacterium gains relatively much less genetic information from the donor than the nearly 50% that a sexually reproduced child gains from either parent.

When Darwin wrote “The Origin of Species” from about 1840 to 1859, I don’t think he anticipated how unlike the beasts, birds, bugs, and plants he was able to study were organisms like bacteria. Nonetheless, bacteria appear to compete for resources – to “fight for survivial” - as or more intensely than other organisms, so the “survivial of the fittest” idea, though an imprecise one, appears to apply as well to them as to the organisms with which Darwin was familiar.

Why do some species (in all senses of the word) decide to die?

I’m unable to think of an example of an entire species “deciding to die.” Can you expand on this idea, Michaelangelica?