6 gill sharks and evolution...

Factual Questions
1

According to a NatGeo program about the deep ocean, 6 gill sharks are virtual unchanged for the last 190 million years.

How is this possible? Is it conceivable that something as complicated as a shark could have hit its evolutionary peak that long ago? Or because of its habitat, its never had a need to adapt?

When I think of evolution, I often wonder why some species stop evolving completely, like the 6 gill. I find it hard to believe that the composition of the earths oceans were the same as they are today, and yet I don’t know how much things may have changed at the depths the 6 gill live. Surely, the oceans would have been impacted by the meteor that supposedly wiped out the 80% (give or take) of the living things on the planet, but perhaps the impact didn’t go all the way to the sea floor.

From what I understand, naked mole rats are virtually the same genetically. Their are two mole rats, one male and one female… Other than that, they have the same DNA. I don’t understand how this is possible, but I will concede I watch too much TV at night to unwind. :slight_smile:

Can anyone help me out here? Isn’t evolution always searching for adaptations to better each and every species? Or is this just a general rule?

And as a follow-up, has man stopped evolving?

2

Evolution isn’t searching for anything, nor does it have a goal. It’s a mechanism by which change can occur.

3

Nope

Evolution is how species change over time. Better is a purely subjective value judgement.

Living things reproduce. There is variation among the offspring. Those that are most suited to the environment survive to have offspring of their own.

Even Darwin knew that smaller, less complex, and less intelligent could be better adapted to the environment that big, complex, and smart.

Nope.

The rules for what genes are selected have changed (for example, an out of shape nerd may have more kids than a big, strong, aerobically fit man) but we’re still changing genetically.

4

IOW, it’s not purely subjective. Instead, it has everything to do with producing more successful offspring.

5

At best we have fossilized imprints of six gill sharks from 190 million years ago, so the claim of *virtually unchanged *is based simply on superficial appearance.

6

Actually, you humans have stopped evolving. The essential trigger for that was the new-found ability (back then) of humans to manipulate the environment. You learned to build shelters (much better than the simple homes of other animals, like beaver lodges) that kept you warm and dry. You learned to use fire, and tools, and rudimentary medical procedures.

As these adaptations progressed, humans had less and less “need” (that is, less evolutionary pressure) to adapt to the environment. Humans could live in a wide variety of environments, from jungle to igloos, and be reproductively successful.

One very noticeable example is the difficulty human females have with childbirth. By nearly universal agreement among females who’ve done it, it is an ordeal, and dangerous. Death during childbirth is common – or was, more so, particularly before medical practices made it safer. And this is all because God punished Eve for listening to a talking snake? It’s because humans “learned” (evolved) to walk upright on their hind legs, requiring changes in the skeletal configuration, especially in the pelvis and surrounding joints. Because childbirth gradually became safer, due to medical practices (however primitive), females who would probably have died, lived instead. This removed the evolutionary pressure for them to continue adapting their pelvic structure to deal with childbirth, while still walking on their hind legs. (I learned all this from an anthropology class I took.)

That’s horribly harsh, but that’s how evolution works. If females who have trouble with childbirth were left to die in agony, then the ones with slightly better adaptations would have taken over the species, gradually over the eons, and the species would have adapted.

The loss of body hair can arguably be considered even worse: A mal-adaptation. Maybe. It’s easy to suppose that, with the taming of fire and building of houses, that the humans lost their need for body hair, and it gradually evolved away. (But I vaguely recall, however, learning that the loss of body hair didn’t coincide in time with the development of fire. I’m thinking that the hair got lost long before that. So I’m not sure if this is a good example.)

7

I find your phrasing vaguely disturbing :).

8

The loss of body hair enabled humans to cool their bodies more easily. Since man is arguably the best long-distance runner among the animal kingdom, the ability to cool our bodies meant we could hunt much larger animals but running them to exhaustion.

9

This is not correct. The idea that humans had largely stopped evolving because cultural and technological advances had largely removed selection pressures on them used to be the conventional scientific wisdom some time ago, when you and I were in high school and college, maybe, and originally learned about this stuff, but since then, especially since it has become possible to study evolution by looking at changes in the genome rather than just at the level of gross anatomy, it has been discovered that humans are still evolving, and quite rapidly by the standards of evolutionary biology (and considering our long generational time). Most of the selection pressures may be more at the stage of finding a mate and actually reproducing, rather than at the level of mere survival, but the genetic evidence implies that they are still most certainly there.

10

What’s surprising about that? We too have stopped.