Evolution, Part Two

[rowyn]

I found an article on the theory of punctuated equilibrium, which it turns out I massively mangled in my previous post on evolution. Or, rather, didn't address at all. What I described as "leap from one species to brand-new species in a single generation" is known as "macromutationism," and has little, if any, following. "Punctuated equilibrium" theorizes that new species evolve from previous species 'quickly' only in the geological sense. "Quick" in this case means mere millenia, five to ten thousand years. Darwin's original theory offered "gradualism", or change in species over millions of years.

Puntuctuated equilibrium fits the facts of the fossil record pretty well, and isn't as unbelieveable as macromutationism. Haven't read enough on it to say whether it's provable or disprovable based on evidence, but it seems to be the basis for useful research, so I'm happier with it. :)

Comments

[prester-scott.livejournal.com]

I have to admit the evidence you present is persuasive, even though I really still don't understand the science behind it.

In particular, I have this question:

And mutations (the same mutation, anyway) don't generally occur simultaneously with a population; that's not necessary at all. Once you realize that, the "odds" change dramatically.

Why isn't this necessary? I can see why the "chances" would be reduced in asexual or hermaphroditic organisms, but sexual reproduction requires at least two...

Re:

[level-head.livejournal.com]

Sexual reproduction mixes two genomes, certainly. But to take eye color as a well-known example; you might have a parent with brown eyes, and the other parent with blue eyes. Yours will be one or the other, but as brown eyes are "dominant", you would have needed to inherit a recessive (and hidden) blue eye gene from the brown eyed parent.

In other words, for one parent to have blue eyes, both genes she carries (I'll just pick a gender here) must be for blue eyes. If either one was brown, she'd have brown eyes instead.

The other parent [i]has[/i] brown eyes, but this means either that both genes code for brown eyes, or that one of them is a hidden blue.

Offspring get one gene from each parent.

Offsping in the first case can only be "brown-blue", which means that they will ALL carry the recessive blue-eyed gene (and can pass it on) but all will have brown eyes.

However, if the brown-eyed parent is "mixed", theoretically half of the offspring with a blue eyed other parent will have blue eyes.

Side note: Genetic odds don't really work with small numbers; there could be ten brown eyed children or ten blue eyed or any combination. Now if they had [i]lots[/i] of kids, it'd work out. But their finances wouldn't. ];)

I've over-simplified the eye color business, but this is how it works in principle. Throw green eyes and hazel eyes in the mix and it gets more difficult to see clearly.

In any event, picture a useful trait such as a longer than usual neck, or a slower metabolism, or a whatever might be useful in the circumstances happening to occur. (Or, a neutral trait such as brown eyes.) If this is associated with a dominant gene, it will take only one parent to pass it on.

Make sense?

===|==============/ Level Head