Replies to This Discussion

Permalink Reply by Jo Jerome on July 25, 2010 at 11:21am

Interesting! Especially as I keep hearing lately that most of us are 'allergic' to wheat to some degree or another; which seems counter-intuitive given human agricultural dependence on wheat worldwide. But the reason given is that we've only grown and eaten wheat regularly for about 10,000 years, which isn't enough time to 'evolve' a tolerance for it.

This study would seem to contradict that.

Permalink Reply by Rudy Ruddell on July 25, 2010 at 11:29pm

Since evolution relies on random chance that out of millions of bad mutation, only one might be good, I do not think there is a timetable for an acceptable duration for evolution of a good trait. On trait may take 100,000 years to occur while another may take only 3000 years, like this one. The point of it all is that it is evolution happening since the invention of writing.

Permalink Reply by Jason Spicer on July 26, 2010 at 6:38pm

I think it's important to keep in mind that this adaptation to high-altitude living did not, in fact, require any new mutations. Here's the key section of the article:

"Many genes exist in a population in alternative versions. The biologists found about 30 genes in which a version rare among the Han had become common among the Tibetans. The most striking instance was a version of a gene possessed by 9 percent of Han but 87 percent of Tibetans."

Since the Han also possess the versions of the genes for high-altitude living, but in a much lower percentage of the population, I think it's safe to assume that the parent population of both groups contained at least some people with the high-altitude version of the 30 genes in question. And since altitude sickness is detrimental to fertility, as mentioned elsewhere in the article, that would be an accelerator in favor of the genes that allow high-altitude living, though just being sick all the time would probably eliminate many chances to pass on one's genes. Those with the high-altitude adaptations would simply have out-bred those without.

This is clearly a case of evolution in action, since it represents natural selection operating on the variation of a fitness trait or group of fitness traits. This case is very similar to the peppered moth changing color in England during the Industrial Revolution. But since no new mutations were required, the spread of an extremely beneficial adaptation in a population could happen quite quickly. Waiting for a mutation can take a long time, and may never happen. Nothing guarantees that any particular mutation will come along. These mutations probably arose hundreds of thousands or maybe millions of years ago, and possibly prior to humans becoming their own species. Adapting to high-altitude living is something that mammals have been doing for a long time.

Permalink Reply by Dale on July 26, 2010 at 12:15am

That is pretty interesting, I know there have been recent studies showing the evolution of the brain in the last few thousand years, but the real question is if there is ever a definitive cut off for that kind of evolution. Lactose tolerance is interesting, especially considering how some cultures in east Asia still have lactose intolerance on a large scale.

Permalink Reply by Rudy Ruddell on July 26, 2010 at 4:57pm

The following site shows a map of lactose intolerant regions. http://en.wikipedia.org/wiki/Lactose_intolerance

Here is a good site for learning about the evolution of the human brain. http://www.nytimes.com/2005/09/08/science/08cnd-brain.html They talk a lot about new alleles that have developed over the last 60,000 years, but not much about the last 10,000 years. They talk mostly about alleles and resistance to disease.

I think you may be referring to humans becoming smarter over time. For something like IQ to improve over time, there would need to be something in the environment that prevented low IQ people from reaching reproductive age. For example in the ice age, only the smartest people could figure out how to survive in Scandinavia.

I do not think average IQ has been improving over time. If anything, the average IQ is decreasing over time because these days we allow mentally retarded people to reproduce (not that there is anything wrong with that) whereas not so long ago mentally retarded people were institutionalized or allowed to die. I would like reiterate so that I am not misquoted: I do not think we should go back to those backward days; I am only applying evolutionary principles to the evolution of the human brain.

Permalink Reply by Jezzy on July 26, 2010 at 5:17pm

Interesting.
What counts as an "evolution"? Forgive the ignorance, but I'm curious. Humans are getting taller in further generations, we have many more genetic pass-ons than lactose tolerance, and presumably a lot of random mutations could be passed on... There are tigers with webbed toes, chickens are fatter, we've practically invented new dogs. Yet I understand the "theory of evolution" as it applies to humans was millions of years in the making. When do we call it evolution?

Permalink Reply by Rudy Ruddell on July 26, 2010 at 5:36pm

Every day there are millions of genetic mutations, most of which are bad, such as 12 fingers or two noses. However, every once in a great while a mutation occurs that enables a species to survive while others perish. For example, lactose intolerance could have developed at a time in which there was a great famine, but one person had a mutation that enable him/her to drink cow's milk, which he/she did and survived. Many other people died except that the lactose tolerant managed to reproduce and pass on the gene, thus creating a lactose tolerant group of people.

In answer to your question, we call it evolution when a mutation helps a living thing to survive while others die.

Permalink Reply by Jason Spicer on July 26, 2010 at 6:59pm

Mmm, I'd say it's more nuanced than that, Rudy. Evolution is the overall process of natural selection favoring adaptive mutations and discouraging maladaptive mutations in succeeding generations. I think technically, a mutation is a mistake in copying genes from one generation to the next. This is, as you note, almost always very bad for the organism with the copy errors, if not rapidly lethal, but sometimes provides an important edge. I'm not sure mutations are even required for actual evolution to occur, though. I think all you need is sufficient variation in a species such that dividing into two groups (say into two different altitudes) favors one end of the variation continuum over the other.

I think most people think of evolution in terms of one species evolving into another, but the boundaries between species are extremely fuzzy. The common definition is that organisms are considered to be members of different species if they can't interbreed, but it's actually not that clearcut. Some species can interbreed and produce sterile hybrids (like the mule, which is a cross between a donkey and a horse). On the other hand, a cross between a Great Dane and a Chihuahua will be a fertile dog, but it's not really possible for the two animals to even have sex, so the cross would have to be done artificially. Are Great Danes and Chihuahuas therefore different species or the same species? Neanderthal and Cro Magnon are typically considered separate species, but there is genetic evidence that they interbred. So basically, evolution is considered to happen when one species is separated into two groups long enough for significant physical differences to occur between the groups, usually including the inability to interbreed, but not always. It's not like the new species just pops into being with a huge difference all at once. There's a gradual accumulation of traits at one end of a variation spectrum that confers an advantage over generations.

Permalink Reply by Rudy Ruddell on July 26, 2010 at 7:31pm

Okay, I stand corrected:
"Two main processes cause variants to become more common or rare in a population. One is natural selection, which causes traits that aid survival and reproduction to become more common, and traits that hinder survival and reproduction to become more rare.[1][5] Natural selection occurs because only a few individuals in each generation will survive, since resources are limited and organisms produce many more offspring than their environment can support. Over many generations, mutations produce successive, small, random changes in traits, which are then filtered by natural selection and the beneficial changes retained. This adjusts traits so they become suited to an organism's environment: these adjustments are called adaptations.[6] Not every trait, however, is an adaptation. Another cause of evolution is genetic drift, which produces entirely random changes in how common traits are in a population. Genetic drift comes from the role that chance plays in whether a trait will be passed on to the next generation." http://en.wikipedia.org/wiki/Evolution

This does not say which factor, natural selection or genetic drift is important, but by the number of words used for natural selection and the fact natural selection was listed first, I would say natural selection is what they mean is the heaviest factor.

Permalink Reply by Jason Spicer on July 26, 2010 at 8:09pm

Interesting. Yeah, I'm not sure which is more important either, Rudy. I think genetic drift is the evolution you'd get over time if the environment didn't change at all. It's a lot easier to see the dramatic adaptation to relatively sudden environmental changes. Particularly in a species with a rapid generational turnover, like the Peppered moth, which probably only lives a year or less. Natural selection can work like wildfire in a population like that.

Now that I think about it, mutations have to enter the picture somewhere along the line in order for natural variation to be possible in the first place. But once you've got that, a species can switch from a dominant group of existing traits to a rare group in a hurry if the environment changes radically.