Bubba

Pardon my ignorance as a non scientist please, but I have an evolution question.

How does natural selection work if there is no dieback and no natural advantadge? I'm thining of two specific examples.

1. Humans in North America seem to be getting physicall taller over the last 150 years and I've read that there has been a genetic shift that actually makes us grow taller. In other words, not just due to diet.

2. Many aquarium reared ciclid (sp?) fish seem to loose coloration and robustness with passing generations, and again the shift seems to be genetic. e.g. reintroducing these fish to the wild doesn't seem to bring back vivid coloration. How does the gene pool shift dramatically to a non-advantage over what is a few (maybe 20?) generations?

Thanks in advance for your replies!

Bubba

pz

Natural selection doesn't require death -- it requires differential reproduction. There are lots of different ways you can achieve that.
I doubt that there is a change in a genetic component at play here.
That one's pretty easy to explain -- I raise fishies, too. Most fish have a tremendous overcapacity for reproduction. My fish, Danio rerio, have the potential to produce 50-100,000 progeny each over their lifetime. Little things that we barely appreciate can have effects on which tiny few of that multitude actually make it to adulthood. For instance, I've got one strain I'm trying to keep going that exhibit natural feeding behaviors. Unlike the strains that have been raised in aquaria and commercial breeding pools for generations, they don't wallow at the surface when you feed them; they tend to lurk at the bottom and dart to the surface for quick bites. It's a real struggle to keep that behavior, because in the absence of predators it's a major advantage for a growing fish to be very, very stupid and hang out near where food is introduced.

Basically, the answer is that you've removed any selection for color in the growing broods, and have instead put them in a different selection regime.

[ November 29, 2002: Message edited by: pz ]</p>

Bubba

Thanks!

Bubba