Saturday, October 17, 2009

All around us, all the time

Ok, one more on the subject, and then I'll move on.

One of the interesting points in discussing evolution is that people tend to think of it as something that happened long ago. Evolution 'set' living things the way they are and that's it. And thus any evidence for evolution is to be found in the fossil record, and only in the fossil record.
Not so, not so!

Plenty of evidence is found in the fossil record, but that's not the only place to find it. Even back in my own university days, there was the classic story of moths in London. Used to be they had light-colored wings. As pollution turned the tree trunks on which the moths rested all black, the moths stood out and were easy prey. Over time, darker moths survived and eventually matched the tree trunks. Then people started coming out of the industrial revolution with a wish for clean air, the pollution was cleaned up, and London tree trunks are no longer black as coal. Dark moths, finding themselves easy prey like their light predecessors, disappeared, while lighter ones survived. Today moths in London have light coloring again.

It's easy to see how an animal or plant that is better at surviving and reproducing than its brethren gradually comes to dominate its ecological niche. This is true in the wild, and it's true for domesticated species. Just take dogs. Dogs we like the look of get special opportunities to breed. We force their evolution into various strange forms by selecting individuals. It's the very same thing as frogs evolving in a pond, only speeded up by the heavy hand of human dog-breeders and with endpoints that apply (naturally) only to the special case of domesticated dogs.

Thing is, selective pressure applies to humans too. We might like to think of ourselves as exempt, but not at all! There's a lot of time involved in natural selection. You have to pass your genes on to children, who grow up and have children of their own, so for people it takes 15-40 years for a single round of selection. In the modern age, we change our environment much faster than that.

You can see the effects of being poorly adapted to 21st century life in the type 2 diabetes that is rampant in many first-world countries, notably America. But this doesn't affect all groups equally. People who come from places that were more recently similar to an older way of life, where periods of feast and famine were regular and severe are harder hit by diabetes today. Their metabolism hasn't had as much time to adapt. It used to be advantageous to be able to eat huge amounts of food and store that energy as fat that would be consumed metabolically during times of famine. The fatties could survive, for example, the harsh Arctic winter, whereas thinner people could not. Eventually developing diabetes wasn't much of an issue compared with a serious annual risk of starvation. Now that food is abundant all the time, the craving to eat is still there, the ability to store fat is still there, but the crisis never comes and the diabetes does.*
So evolution goes on all over the world, every day, for every species. The selective pressures may be different, and often man-made, but there will always be pressure from somewhere, and living organisms will always respond to it.**
*the selective pressure against people vulnerable to type 2 diabetes may seem irrelevant to reproduction, because it generally occurs after childbearing is finished. However, it is probably not irrelevant. First, it has been shown that women who live withing 30km of their mothers have more children than their sisters who live farther away, an effect likely explained by the help that grandparents, and grandmothers in particular, give in raising the families of their offspring. If grandmothers are not available, through distance or death, women appear to hesitate more in having larger families. Also, having a parent of either sex die young hinders families economically and socially. Remember, in reproductive success, it's the number of fertile children you have that counts, not the proximal reasons why you have number of children you do - whether you conciously choose to limit your family or not.
**there is some argument that modern medical care is putting humans beyond the reach of evolution, since people who would otherwise not survive do now go on to have families. This is certainly true in some respects, but overall evolution still has its say in our future.


Barry said...

And what adaptive impulse gives rise to pink bunnies like Maurice?

Or maybe we will have to wait for an answer to that question until we see what happens with the offspring of his offspring?

Fascinating stuff Nancy.

steven said...

hi nanu - thanks for this. it explained some things that i have puzzled about, particularly with respect to diabetes. i wonder if the same effect is the root cause of breathing difficulties, and the astonishing rise in anyphalactic attacks. steven

shabby girl said...

Interesting to think about. You make it very easy to understand.

GingerV said...

yes! Not only does plant and animal life (including humans) evolve but our earth is still evolving. The change during our life time is not aparant but over billions of years it can be seen. We have mud slides here. Usually every year some hillside or another comes down. I have been ask why they come down? For millions of years the soil has been erroding off the granite underbelly of our mountains, unfortunately now humans live on those hillsides and are killed when they slide. In most cases humans aren't the cause are just victums of earth's evolution

NanU said...

I'm not sure about the rise of asthma, Steven, unless it comes in with allergies in general. There's a theory about that and our pretty-clean modern society: Your immune system has to learn to be really effective. So as young children are exposed to all sorts of ordinary antigens like those in dirt etc, their immune systems learn what can be ignored. In an environment with not much to react to, the immune system doesn't get any exercise and doesn't learn. So it attacks whatever comes along, which are usually things it isn't useful to react to.

And YES Ginger! Geography is not forever! Wearing away over here and building up over there are normal processes that have gone on since the earth was made, and will resist all the house-building and dike-building and dredging and levees and whathaveyou that we can throw up! Floods are normal (and essential for the long-term fertility of the soil)! Cliffs fall down - that's how they got to be cliffs in the first place!

Reya Mellicker said...

The bunny banner rocks!

And thanks for your thoughts about diabetes. Overeating is bad for everything.

You're so smart. Thanks!