Is there a minimum time period over which human evolution can occur?

[JWerner]

I once read that humans haven't adapted to the agricultural revolution because it's only been about 10,000 years and it takes 200,000 years for humans to evolve traits in response to environment. Is this 200,000 year number nonsense? Is it roughly correct? I believed it until I considered catastrophic events like the plague. Theoretically, if a disease killed off all people without gene X, evolution could have occurred over one generation.

[j_p]

For your scenario the disease would have to have 100% morbidity and mortality AND there would need to be a specific genetic resistance to the disease. I don't think that's likely.

 

However, I have never heard that it takes humans 200,000 years to evolve a trait in response to the environment.

 

It seems to me that a smaller population would evolve more rapidly than a larger one, because any adaptive or maladaptive change would effect a larger proportion of the population. Didn't the AR lead to an increase in population? And didn't it mitigate humans' response to the environment in general?

[swansont]

I once read that humans haven't adapted to the agricultural revolution because it's only been about 10,000 years and it takes 200,000 years for humans to evolve traits in response to environment. Is this 200,000 year number nonsense? Is it roughly correct? I believed it until I considered catastrophic events like the plague. Theoretically, if a disease killed off all people without gene X, evolution could have occurred over one generation.

 

But how long did it take for gene X to spread through the population once it appeared? You have to count that, too. What you've done is ratchet up the selection pressure, and under some circumstances that leads to rapid change.

 

Evolution is the change in the genetic makeup of a population. It happens every generation - it's just a matter of how much happens in that time.

[alibabba]

Since we have caused adaptations in animals by selective breeding, isn't it pretty well known how many generations it takes for a wolf to be turned into a Chi wa wa? (and yes, I know that chi wa wa is not spelled that way)

 

In any event, that knowledge should help to answer the question in terms of generations required for a specific adaptation.

[□h=-16πT]

delete please.

[ecoli]

Theorhetically, it would only take one generation for humans to evolve. Obviously this is not realistic. But if some environmental stress knocked out everyone except for Blacks (lets say they're the only that could protect against UV emmision) as a whole, the human population would be qute different.

[Ophiolite]

Theorhetically, it would only take one generation for humans to evolve.

Drat, I was going to say that!

Obviously this is not realistic.

Ah, but it is. Evolution can only be observed when there is a large, that is, visible change in the phenotype. That does not mean that changes are not occuring. And these changes have to occur between generations. You can't have a gene mutating by a quarter in each of four generations. It has either mutated or it has not.

if some environmental stress knocked out everyone except for Blacks (lets say they're the only that could protect against UV emmision)

And coal miners.

[swansont]

Theorhetically, it would only take one generation for humans to evolve. Obviously this is not realistic. But if some environmental stress knocked out everyone except for Blacks (lets say they're the only that could protect against UV emmision) as a whole, the human population would be qute different.

 

 

I disagree. What is unrealistic is to see the results of the evolution in one generation. Humans, as well as any other population, evolve on the timescale of a generation. As Ophiolite has implied, you are redefining evolution to mean a change in the phenotype, and JWerner appears to have made that same, fairly common, mistake.

[Mokele]

Technically, the human population is evolving every day. Evolution = change in allele frequency in a population over time. Every time a new individual is added to a population (by birth or immigration) or an existing individual is removed from a population (by death or emigration), the gene frequency changes.

 

Now, for most genes, most of the time, this basically balances out and there's no long term change. However, if there is a continuous selective pressure, there can be change in both the short and long term.

 

How fast any change can occur depends on two things: size of the population and selective pressure. If we had a small population of humans under intense selection pressure, evolution would proceed very fast. For a large population (like now), selective pressure would have to be large to produce any sort of advantage at all.

 

Anyhow, for direct evidence that humans *have* evolved since the agricultural revolution, look at our CCR5 receptors. Currently, they're used by HIV, but some individuals lack them, making them very resistant to most HIV infections. Why? Because a bacteria (Yersinia pestis) used that same receptor to impose strong selective pressure about 800 years ago. The selective pressure is more commonly called The Black Death. Individuals who lacked the receptor were immune, so their genes propagated the most. Even now, centuries after the Plague, we still see large numbers of people carrying the genes for faulty CCR5s in Europe, where the plague was worst. So there's empirical proof that humans *can* and *do* evolve on a shorter time scale.

 

Mokele