Yet another beneficial mutation in humans uncovered

[Wally]

That this was not a new mutation in response to the environment, but a natural variation that happens in humans all over the world.

This is a fundamental misunderstanding. DNA does not mutate in response to the environment. It mutates randomly, and this mutation may have occurred independently all over the world at different times and not survived in the genome.

In this particular case, there were selection pressures that made it more likely to be passed on.

The environment does not create, it filters.

Basically, we're the leftovers.

[seer]

DNA does not mutate in response to the environment.

How can you know that? That that never happened? So in this case we have an arsenic-laden environment and a mutation just happens to come along to help them metabolize arsenic?

[Wally]

Let me rephrase that.

Specific mutations aren't caused by the environment. Certain factors in the environment (like radiation) can trigger a mutation, but it's going to be random.

[rogue06]

OK, so they live in an arsenic-laden environment and a mutation just happens to come around to help them metabolize arsenic?

Actually the mutation is almost always already present in a tiny percentage of people and not noticed until environmental pressure or something similar starts selecting for it because it provides an advantage.

For instance, if you have a lizard that is usually a solid color but a small percentage turn out to be variegated and some of those lizards migrate to a broken up rocky terrain the environment might start selecting for the piebald lizards because this could well provide a distinct camouflage advantage. After numerous generations the majority of these lizards living in this region will no longer be a single color.

[rogue06]

Let me rephrase that.

Specific mutations aren't caused by the environment. Certain factors in the environment (like radiation) can trigger a mutation, but it's going to be random.

It is often simply a case of genetic drift.

[Adrift]

Actually the mutation is almost always already present in a tiny percentage of people and not noticed until environmental pressure or something similar starts selecting for it because it provides an advantage.

For instance, if you have a lizard that is usually a solid color but a small percentage turn out to be variegated and some of those lizards migrate to a broken up rocky terrain the environment might start selecting for the piebald lizards because this could well provide a distinct camouflage advantage. After numerous generations the majority of these lizards living in this region will no longer be a single color.

I mean, that's how I always understood evolution, but isn't selective breeding just a form of this in some way? Rather than the environment doing the selecting, you have humans doing it, but the results are similar, aren't they?

[rogue06]

I mean, that's how I always understood evolution, but isn't selective breeding just a form of this in some way? Rather than the environment doing the selecting, you have humans doing it, but the results are similar, aren't they?

IIRC Darwin cited selective breeding (a.k.a. artificial selection) several times as doing the same thing that natural selection did (but much faster) in On the Origin of Species. It has been several years since I've read it though.

[seer]

Actually the mutation is almost always already present in a tiny percentage of people and not noticed until environmental pressure or something similar starts selecting for it because it provides an advantage.

For instance, if you have a lizard that is usually a solid color but a small percentage turn out to be variegated and some of those lizards migrate to a broken up rocky terrain the environment might start selecting for the piebald lizards because this could well provide a distinct camouflage advantage. After numerous generations the majority of these lizards living in this region will no longer be a single color.

So you are saying that this mutation to metabolize arsenic was in the population before the population was exposed to arsenic? Do we have any evidence of this? We know from your OP link that near by populations did not have these specific protective variants.

[seer]

Let me rephrase that.

Specific mutations aren't caused by the environment. Certain factors in the environment (like radiation) can trigger a mutation, but it's going to be random.

So this population just happened to get a mutation that allows for the metabolizing of arsenic in a highly arsenic rich environment?

[Wally]

So this population just happened to get a mutation that allows for the metabolizing of arsenic in a highly arsenic rich environment?

Incredulity is not an argument.

[rogue06]

So you are saying that this mutation to metabolize arsenic was in the population before the population was exposed to arsenic? Do we have any evidence of this? We know from your OP link that near by populations did not have these specific protective variants.

If it was the result of genetic drift it is no surprise that it wasn't retained in anyone in surrounding areas since there was no environmental pressure that would select for it.

[TheLurch]

So this population just happened to get a mutation that allows for the metabolizing of arsenic in a highly arsenic rich environment?

We've tested this sort of thing with bacteria. Grow a plate full of bacteria, and then make two copies of that plate. Stick one in the fridge to stop its growth, and pour virus over the second. By chance some of the bacteria will end up having mutations that make them resistant to the virus, and so you see little spots where their descendants grow.

Now take the second plate out of the fridge, and pour the virus on that. The spots almost all end up in the same places. That's because a large population will experience a lot of mutations, and always have a variety of genetic variants present. Many of these aren't useful for survival in the present environment, but can be useful if the environment changes.

The same thing is true of a large population that's human, and happens to live near sources of arsenic rich water.

[rogue06]

We've tested this sort of thing with bacteria.

As an aside, last week was the 29th Anniversary of Richard Lenski's long-term evolution experiment (LTEE).

[TheLurch]

As an aside, last week was the 29th Anniversary of Richard Lenski's long-term evolution experiment (LTEE).

And the 30th anniversary of supernova 1987a. Despite studying biochemistry at the time, i was only aware of the supernova. Lenski's work didn't cross my radar until much later.

[Adrift]

Maybe I'm missing something, but it doesn't really sound like anyone is saying anything much different from what Sparko already suggested. In my totally un-sciencey and bare bones way of putting it, evolution occurs (maybe "occurs" is not the right word) when environmental factors highlight random mutations in a gene pool that present a survival benefit. Not taking into consideration later mutation, migration, and genetic drift, in a fashion, this is selective breeding, except, that there is no intelligence (necessarily, and perhaps that's debatable) doing the selecting. Rather the unintelligent environment is doing the selecting...if you will.

I find discussions on this subject can be complicated sometimes because it seems to me that people on the evolution side of the debate (which I count myself in) get very...defensive...about exact word usage and concepts. Perhaps that's for good reason. They feel a need to be exacting because they've seen words and concepts that were more colloquial in nature taken and used against the theory of evolution. I once majored in Bio-Anthropology, and I'm certain I've forgotten more than I remember, but I find when I read threads like this that there's sometimes an unnecessary level of tension that seems unhelpful when explaining what evolution does. Evolution, on its surface, is not that complicated of a subject, but the quibbling over terms can sometimes lead to confusion I think. At least it does for me.