"Nobody 10,000 years ago had blue eyes," Hawks said. "Why is it that blue-eyed people had a 5% advantage in reproducing compared to non-blue-eyed people? I have no idea."
The theory I've heard is that a blue iris makes it easier to see pupil dilation, which is an indication of attraction. People are more likely to hook up when they can tell the other person is attracted to them, so...
That is possible, but the gene for blue eyes may also be linked with some other characteristic (biologically more relevant than attraction - like resistance to cancer) that might provide selective advantage. Linkage (close enough genes travel together) among genes plays a huge role in selection but often, and understandably, we regard the the feature that is easily visible to us as essential.
While it is irrelevant to your point, I'd like to make a note about your example.
Resistance to cancer would likely have little evolutionary value. Most mating and child rearing is done before the average age of cancer, particularly in past societies. I would similarly wager that cancer would not a be a strong enough force (it would usually hit people randomly rather than the entire group simultaneously) to ruin the ability of a tribe to defend itself.
If anything, cancer resistance (which would probably mean less cell mutation ability) would be disadvantageous from an evolution standpoint because you would have less variation and consequently may have trouble adapting.
Cancer may simply have been an example of kind, rather than specific to the case at hand; however, I wouldn't disregard it as quickly as you do.
The grandmother hypothesis [http://well.blogs.nytimes.com/2007/10/05/evolutions-secret-w...] supports cancer resistance as an evolutionarily beneficial gene. You also miss the obvious unstated point that cancer resistance itself may just be a side effect of another characteristic, such as more efficient mitochondria.
Your third paragraph fails to support any of its assertions; cancer resistance takes many forms, and most mutations are negative in nature: some math would likely be necessary to support a (carefully worded) argument in either direction.
I agree about the child bearing age point..resistance to infectious disease may have been a better example.
but re your last point, being prone to cancer could speed up evolution but at the same time could wipe out a sub population? infact- that (probably) holds for anything that speeds up evolution - but again math models would be needed to prove that.
"If anything, cancer resistance (which would probably mean less cell mutation ability) would be disadvantageous from an evolution standpoint because you would have less variation and consequently may have trouble adapting."
Evolution doesn't work that way. It doesn't favor mutation because mutation is "good" for evolution. You have to look at it from individual genes, and there the story is just the opposite.
Evolution happens in spite of, not because of genetic predisposition to mutation, because it's vastly more likely for a mutation to be pointless or harmful than beneficial. If you have a gene that makes mutation in the genepool overall less likely, that gene will be more successful at spreading itself, because the mutants have, on the whole, far less chance of success than the originals (which have already proven their worth in a long chain of ancestor individuals carrying them). Of course every so often a mutant gets lucky and is more successful (or at least not less successful) than the original -- this is what selection is all about -- but statistics are against them.
To elaborate your scenario: suppose the environment changed very rapidly, and adaptation in some direction were necessary to survive it. If by some stroke of luck a gene that increased the mutation rate happened to be there at that moment, defying the odds, it would find a favorable environment, but only for as long as the rapid change is required. Generalizing this: a successful genepool is one where the mutation rate is "just right" for adapting to the environment. Too much mutation and the genepool isn't stable and will eliminate itself, too little mutation and the genepool will be eliminated by the environment. In this balance, the odds are stacked in favor of avoiding mutation.
And all this is orthogonal to the discussion of how cancer (the uncontrolled reproduction of cells) is related to the capacity for mutations (infidelity in the copying process). Cancer resistance and mutation resistance are related, but by no means the same thing. To borrow a computer image: your computer has copy processes with very high fidelity (only the occasional alpha particle to spoil the fun) but this doesn't protect it against worms, which copy themselves unwantedly but with the same high fidelity. This analogy is badly flawed in obvious ways (regular programs are not designed to copy themselves, cells are), but I hope it gets the point across.
(1) Perhaps less pigment in the eyes improves vision in certain conditions (especially those in colder latitudes).
(2) As a recessive trait, blue-eyed mating limited a woman's ability to pass off offspring from other (dark-eyed) fathers as that of a blue-eyed father. This greater confidence in paternity won greater fatherly support, and in some eras/places (inheritable property?) this dominates the advantages of promiscuity. (This effect may fade or even reverse depending on proportion of eye colors.)
(3) Handicap principle -- even if blue-eyes are a disadvantage in some dimensions (sun-robustness, alien look), sometimes a conspicuous disadvantage is effective as a signal that fitness in other harder-to-measure dimensions is better. ( http://en.wikipedia.org/wiki/Handicap_principle )
(4) I suspect just about any unique visible characteristic, advantageous or mildly disadvantageous, can find some reinforcement as a quick signal of genetic kinship against outside competitive groups that look different. So just, "different enough to tell closer-cousins from distant-cousins" could be a sufficient explanation.
Novelty? I have red hair, which I'm not sure is adaptive (eg it puts me at greater risk for skin cancer) but which partners have rated highly as an attractive feature specifically because it's unusual. Then again I have a compulsive draw towards partners from outside my own ethnic group, so there's some selection bias going on with that interpretation.
Except that in practice, it hardly ever happened until very recently. Ethnic groups lived far apart, and those folks who lived near a boundary between two different ethnic groups would hardly ever interbreed with the others (whether that's mostly cultural or a lack of attraction, though, I'm not sure). Even now, it happens surprisingly infrequently.
They have studied violence and tribal group's have an insane level of homicide relative to the US average. When you look at children from spouse infidelity in modern times the numbers are something like 10 to 30%. So, I don't think the average family tree is as correct as people think. Add in rape / conquest and I expect most tribes where constantly exchanging DNA. The only real limitations where probably geographic.
Although in past times (pre 60s), excepting cases of wartime, it would probably have been harder to cheat and get away with without serious consequence. As parental testing gets easier/more affordable (perhaps even mandatory at birth or at least for child maintenance collection) this may change.
As it stands, culture encourages promiscuity under the guide of empowerment (whether this is positive or negative is a longer argument) and legislation certainly doesn't discourage cheating (e.g. fault-free divorce, child maintenance to support the female partner even in cases where the male partner ends up not being the actual father, alimony in the U.S.).
I was just guessing anyway - but I think it does not have to be a fully different ethnic group, maybe often people are attracted to someone who looks quite different. Of course there are those pysch experiments were people seem to rate the average face the highest, but I have heard the "attracted to exotic" variant too often, so I am a bit skeptic of that research.
As I've heard it, the development of both blue eyes and blond hair is thought of as mainly being driven by sexual preferences, i.e. status of novelty.
Sexual preferences are pretty strong drivers and combined with periods of harsh environments (e.g. where either of the sexes die off early in life) can create really fast evolution.
You could just attribute it to the attractiveness of blue eyes. Most people consider blue (and green) eyes more beautiful than eyes with a different color. But this will get you only as far as the next inevitable question: why are blue eyes attractive?
Beats me. I married someone with brown eyes (and black hair). On the other hand, she married a man with blue eyes (and blond hair), and my genes have been replicated into four children. My dad's genes for red hair have passed on to be expressed in two of my children.
Blue eyes and blonde/red hair are recessive traits, while brown eyes and hair are dominant. You having blue eyes means both of the gene pairs that control eye color have the recessive blue, while your wifes brown eyes can be caused by having a set of blue and a set of brown genes, and as brown is the dominant one, it is what was actually expressed in here eye color. The fact that your children have blue eyes means she does have genes for blue eyes, and they are inherited into your children as well as your blue genes, hence their blue eyes. The same goes for blonde/red vs brown hair.
Either that, or consult with your milkman/gardener.
You having blue eyes means both of the gene pairs that control eye color have the recessive blue, while your wifes brown eyes can be caused by having a set of blue and a set of brown genes, and as brown is the dominant one, it is what was actually expressed in here eye color.
My wife is from a part of China that is not very likely to have any genes for blue eyes (or red hair) in the indigenous population. The overwhelming probability is that she is homozygotic for both black hair and brown eyes.
The fact that your children have blue eyes means she does have genes for blue eyes
There is a reading problem here, because I never said anywhere in my post that any of my children have blue eyes. (In fact, these days I am startled whenever I see a child with blue eyes, even though I grew up with siblings with blue eyes, because all my children and my wife look at me with brown eyes. I see blue eyes and ask myself, "Do they make eyes in that color too?")
You also are well advised to do more reading about the genetics of human eye color and hair color
and human genetics in general. Genes can recombine from one generation to the next. My red-haired dad, by the usual assumption that you made in your reply, was homozygotic for red hair, making me presumptively heterozygotic for red hair, while my wife presumptively is not a carrier of that trait at all, on population genetics probabilities. But two of my children have hair that is "brown" at a glance but also includes red pigment (as can be seen when their hair is backlit by sunlight or when strands of their hair are observed under a microscope). Sometimes children can inherit a double copy on one gene from just one parent, as anyone who has carefully studied human genetics knows.
My reaction is that he misspoke here or he overstated his claim to make a point.
I know nothing about the proportion of people with blue eyes back then or right now for that matter. But I think at the very least, you could only make that claim with a tiny, tiny, tiny amount of confidence.
Maybe the proportion of humans with blue eyes was smaller back then, maybe it was larger, or maybe it was the same. I don't know. But to claim nobody 10,000 years ago had blue eyes is an impossible point to prove unless you have DNA samples from every human alive 10,000 years ago. We might be able to say that all the people alive today with blue eyes descended from one ancestor, but we can't claim to know about the population of people with blue eyes back then. For all I know, half the population 10,000 years ago could have had blue eyes but then got wiped out by swine blue.
That's like saying no one 100 years ago was over 7'6" tall. I know a bit more about height and think that this statement may be true. But it would be real hard to prove. Now shift the timespan back by 2 orders of magnitude, and I think it'd be harder to prove.
I'm not saying that the general idea is wrong, but I'm just it would be a good idea to question that claim a lot before thinking about reasons why that might be the case.
What I don't understand is how they can say the blue-eye mutation occurred in one single individual. I would think it is just as possible that the mutation could have occurred multiple times, and thus there would be multiple origins to those with blue eyes.
I did find a different source that would tend to support the randomness of mutations, and that also indicates that there are two different mutations that can lead to blue eyes, and as such, it is unlikely there is only one ancestor.
http://www.thetech.org/genetics/ask.php?id=160
How do we know that nobody 10,000 years ago had blue eyes? Er, well, of course it's impossible to _know_, but what leads us to conclude that nobody 10,000 years ago had blue eyes? Anyone know?
Don't only Caucasians have blue eyes? And aren't they (full disclosure "we" in my case) also the only ones with the mutated version of the gene which controls how much melanin is deposited in skill, hair and... I think also irises? Asians and Africans both have the normal version of the same gene.
And melanin has many roles, sun protection being just one, the other is as a structural protein. Just compare how black skin ages vs. how a redhead of the same (advanced) age looks.
And why would Caucasians have a mutation which deposits less of such a useful protein? Vitamin D.
It is produced when UV light hits the skin. In northern climates with less sun, and skin being covered or you die of exposure, often even when the sun is up, people get a lot less vitamin D.
Inuit get more due to their diet, and modern man also gets much more again because of diet. And yet most people living in the north even today lack vitamin D.
Also, I thought all of the above is common knowledge which makes me question the whole article.
Also, this is neat:
A 2002 study found the prevalence of blue eye color among Caucasians in the United States to be 33.8 percent for those born from 1936 through 1951 compared with 57.4 percent for those born from 1899 through 1905.[10] Blue eyes have become increasingly rare among American children with only 1 out of every 6 – 16.6 percent which is 49.8 million out of 300 million (22.4% of white Americans) of the total United States population having blue eyes.[33][34] The plunge in the past few decades has taken place at a remarkable rate. A century ago, 80 percent of people married within their ethnic group. Blue eyes, a genetically recessive trait, were routinely passed down, especially among people of Scottish, English, Irish, Welsh, Western and Northern Slavic, and Northern European ancestry.[33][34][35] In the 1930s, eugenicists[citation needed] used the disappearance of blue eyes as a rallying cry to support immigration restrictions. They went so far as to map the parts of the country with the highest and lowest percentage of blue-eyed people.[citation needed]
From your wikipedia link: Blue eyes contain low amounts of melanin...
Blue eyes are most common in Northern Europe and Central Europe and to a lesser degree in Southern Europe,North America and southern Central Asia; Afghanistan is a notable example.[30] They're also found in parts of North Africa,[31] West Asia, and South Asia[32], in particular the northern areas of India and Pakistan. It can rarely occur as far south as Sri Lanka. However blue eyes are not found within the population of East Asia, due to the major pre-dominance of the brown eye gene in the area.
Central Asians, people from the Caucasus, Afghans, Pakistanis, and even Indians darker then many an African are considered Caucasian. They are Caucasians. And North Africa is full of Caucasians, hell even German tribes, Goths if I recall correctly, settled there during Roman times.
So only Caucasians have Blue eyes. Again because of a gene mutation which control how much melanin is deposited in hair, skin, and irises.
Someone with a lot of melanin could have blue eyes, but they wouldn't appear blue do the the melanin. That's why blue eyes contain low amounts of melanin.
And low amounts of melanin are related to vitamin D, which is related to living in northern climates.
Thanks for posting the link to the published study, as I was about to. I see both the study and the submitted news article about it are more than two years old.
After edit: Here is a link to a more recent article on a closely related subject:
Races as we know them today didn't exist until fewer than 20,000 years ago, when genes involved in skin pigmentation emerged, Hawks said.
1) This blows my mind -- am I reading it right that there was virtually no variation in skin color 20,000 years ago? I assumed there was always variation in skin pigmentation, with darker skin colors predominating until we expanded into northern latitudes where lighter colors made sense.
2) What about Neandertals? I always imagined them being light-skinned, since they were adapted to northern climates. I wonder if they evolved genes for light skin tens of thousands of years before modern humans did. If so, that must have made them look even more freakish to modern human eyes, and vice-versa.
am I reading it right that there was virtually no variation in skin color 20,000 years ago?
I think the correct statement is as you say in another part of your post: there has always been variation in skin color in the human population. It was geographically segregated (forming "races" in the biological sense) only very recently. And even today there is a lot of variation among individuals in skin color within each continental subpopulation of human beings.
The usual view of evolution of skin color is that the ancestral condition was white skin under dark hair (as we still see in chimpanzees). Then at some unknown time, human ancestors became less hairy, and darker skin pigmentation became necessary. Then as human beings (Homo sapiens) migrated to latitudes with less sunlight (VERY recently) gene frequencies changed again in favor of lighter skin in some areas. (Inuit people are quite dark skinned for people who live near the North Pole and usually wear heavy clothing.)
As I remember the explanation: Dark skin means more melanin in the skin. Melanin blocks the UV light that the body uses to synthesize D vitamin. So white people in north are better suited for utilizing the scarce sunlight for D vitamin production and black people in the south are better protected against the skin cancer risk caused by the UV radiation.
I wouldn't dismiss this so quickly. It is widely accepted and is also part of what is evaluated when the doctor recommends or not that you give extra vitamin D to your child, having white skin means you need to spend less time in the sun to have sufficient vitamin D and not require supplements.
Perhaps the question is more complex because sunlight is not all in the visible wavelengths and skin is actually translucent and light reaches different level through the skin, melanin prevents parts of the light to reach deeper levels in the skin and also converts parts of light.
UV-B sunlight strikes a substance on the skin called
7-dehydrocholesterol converting it into vitamin D3. The vitamin D created by this reaction is then reabsorbed by the skin and enters the bloodstream. Apparently some new research indicates reabsorption may take up to 48 hours!
Melanin inhibits the above reaction, so blacks need more sun to get the same amount of vitamin D.
Anyone has real details on how they actually date the origin of the presence of DNA sequences? I sure have my own uneducated guesses but I'd be curious to know. Or even better find a reference to the explanation.
>Dawkins, with his gene-centered view of Darwinian evolution, refutes this, explaining that evolution by natural selection is gradual.
People say he refutes this. According to him, he never said anything to refute this. In either case, you have to be specific about what "gradual" means. Dawkin's evolution is more gradual than intelligent design, but not so gradual that it is inconsistent with Stephen Gould's claim.
Dawkins is skeptical of non-adaptive processes in evolution and of natural selection above that of the gene (i.e. at the organism or even species level).
I'm not implying that they have a hostile personal relationship, but their academic disagreements were significant. Examples include the gradual view of evolution, and also Gould's claim of NOMA, which Dawkins (detests).
(I have studied some related subjects but not evolutionary biology, so I don't really know the research papers. But I do know that political/religious idealists are often dishonest to influence public opinion.)
Now that's interesting. Any theories?