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populations vs individuals

One of the things I expect my students to understand, when we're talking about evolution, is that populations evolve, & not individuals.

PZ has said it rather well: Populations evolve, not individuals, and male and female elephants evolved from populations of pre-elephants that contained males and females. Species do not arise from single new mutant males that then have to find a corresponding mutant female — they arise by the diffusion of variation through a whole population, male and female.

Well worth remembering.

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3 Comments

It's a good point to bring up.

You're getting this from a discussion about that "Banana man" New Zealand "exported", right? (Or rather that he deported from here.) His ideas are so bizarre it's amazing that anyone believes what the guy is saying. His notion that man couldn't have evolved because females are needed is bizarre (not to mention sexist in his own way).

But more "on topic", it reminds me that one of the things being discussed about the work on the Neanderthal man genome is that because evolution works on populations, comparing an individual from Homo sapiens with an individual Homo neanderthalensis may not be that meaningful in terms of working out what genetic differences are really characteristic of the two (almost certainly it will be very limited), and that what will be needed is a collection of genome sequences from several or many individuals from both.

In a thread about the-NZ-export-who-should-not-be-named's conspiracy theory (http://scienceblogs.com/dispatches/2009/03/ray_comfort_conspiracy_victim.php), DingoJack gives a nice snapshot explanation of the origin of sexes, followed by a little Aussie humour:

DingoJack writes:
Greg Reich - You'll will no doubt be interested to know that males and females (at least in humans) are controlled by a 'master' gene. When the SRY gene (found on the Y chromosome) produces proteins it kick-starts a developmental cascade throughout the growing embryo. This normally pushes it into becoming male (female is the 'default' position)*.
Genetically similar genes to SRY called SEXP & SEXM (?) are found in fungi. Evidently this was a gene that doubled up and then one mutated to lose some functionality (SEXM - M for minus). Thus it was fungi that 'invented' sex, sometime before the fungi and animal lines diverged, but after the line of slime-molds diverged from the animal/fungi line.
Consequently males and females didn't evolve separately (as Ray seems to think), since genetically they are the same kind of organism, just with differing developmental paths. -DJ
*For example, Androgen Intolerance Syndrome produces individuals that are genetically male (XY) but functionally female. This is because the androgens that flood the developing embryo are not recognized and so the body continues to develop into the 'default' mode, female.

democommie writes:
Hey, wait just a goldurned minnit! RU sayin' that I was a woman, before I was a man. No way, I ain't no flip-flopper!

DingoJack writes:
Demo - Yep, you were a big girl's blouse - before you had anything worth either flipping or flopping :) - DJ

Just as well I wasn't drinking anything when I got to Dingo Jack's final comment :-)

Well... the humour is Australian...

In a more recent thread DingoJack adds (for the timid: no lewd humour this time):

PS The pa[r]thogenic lizards are believed to be the result of t[w]o closely related species interbreeding. The offspring of the two species is larger and so have larger eggs and offspring, which have a better chance of surviving. The two females in the breeding pair take turns biting the neck of the 'female', just like a male lizard would, to stimulate her to lay her eggs. These hatch without the intervention of any sperm (yep, that's right Ray, just like your 'virgin' Mary). There are species that even have three and five 'sexes' (due to mutations in the X chromosome). Ray would also be amazed that some birds have homozygous males, and some insects have haploid males. Nature isn't just stranger than you imagine, it's stranger than you can imagine. And all can be explained by evolution better than your pathetic belief in Bruce the big sky-fairy.

(Corrections in square brackets are mine.)

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