On 11/01/2011 07:56 PM, Patrick Elliott wrote:

> Seen at least one statement to the effect that "tree" isn't an accurate
> description at all, but rather the complex braiding you see at a river
> delta. It might split off in totally different directions at some
> points, but a lot of stuff close together is prone to flow back and
> forth between channels, maybe even "drifting" back together, when
> previously separate (though, so far we don't see any obvious examples of
> that).

The tree metaphor doesn't account for "horizontal gene transfer".

Bacteria reproduce asexually. However, they sometimes two cells will 
hook up and swap genes with each other (without producing offspring).

Viruses, plasmids and other "transposable elements" can move genes from 
cell to cell. (This is how genetic engineering works.)

The human genome actually contains several (mostly broken) viral genomes 
within it. Usually a virus infects a cell, gets copied, and the cell 
dies. At some point, an egg or sperm cell was infected, and the 
infection became permanent. (And, presumably, not too detrimental.)

There's even some suggestion that these virii's ability to evade the 
immune system might be how viviparous animals were able to evolve. 
(I.e., how an embryo evades the mother's immune system.)

Then of course, the dynamic, ever-changing face of geology and geography 
is such that there is an almost never-ending stream of habitats 
appearing and disappearing all the time. Lakes dry out and become 
multiple lakes, only to later reflood and become a single lake again. 
Hydrothermal sea vents spring up, develop their own local tribe of 
organisms, and then shut down, while new nearby vents appear.

Heck, black people and white people marrying, anyone?

It must surely happen all the time. It doesn't even require physical 
separation. Just any time one group happens to not interact with another 
group, and then later starts interacting again.

Post a reply to this message