This can’t possibly be true. This would mean that the blue-eye mutation happened only ONCE in all of the history of homo sapiens.
What am I missing here?
From the Science article:
Geneticist Richard Sturm of the University of Queensland in Brisbane, Australia, an author of one of the papers says that someday scientists may find additional mutations that cause blue eyes but for now, the signs point to a single change.
We just don’t have enough data yet.
Why not? Remember that we are diploid (two copies of every gene), and we have sexual recombination. The fact that all copies of a gene are descended from a single copy of that gene does not imply that one individual is the sole ancestor of everyone who carries that trait. That person is just one of their many ancestors.
Isn’t this where logic steps in? “We haven’t yet tracked down evidence of a single other example of this mutation” = “It never happened in any of billions of homo sapiens” and not “We haven’t found one yet”?
“One individual” is how I’ve always seen this presented.
As all living humans share a common ancestor there’s nothing new here. The question is did this one mutation happen only once much later than mitochondrial Eve. And how would we ever know?
A gene is obviously in one individual when a mutation occurs. But my point is that the number of ancestors we have doubles with every generation we look back (until it starts saturating). So although all people who have the gene apparently inherited that gene from one individual, that doesn’t imply that this individual is their only ancestor.
Don’t see how that logically follows from the title premise.
Since nobody has done so, I’ve linked to what I assume is the article in question.
No, I’m sure the evidence is better than just “we haven’t found it yet”. I haven’t looked at the paper, but I expect that every allele that they have sampled carries not only the same functional mutation, but also other neutral mutations that imply identity by descent. And that the sample size is large and wide enough to tentatively draw the conclusion that they would have found a copy of any other allele unless it were a recent de novo mutation.
Yeah, this.
Relevant prior thread:
The data doesn’t show that none of these folks other ancestors had blue eyes. It says that all of these folks are related to this one common ancestor.
I’m trying to imagine what happened those thousands of years ago when the first blue-eyed baby was born, and whether people thought this was a good or bad omen. My guess is that his/her blue eyes weren’t seen as a sign of evil because he/she might not have been allowed to get old enough to reproduce if that was the case. Perhaps the blue eyes made the person popular for baby making?
We don’t have evidence that any of this happened. A mutation for blue eyes may have happened many times before and since in human history, and at the time this particular mutation occurred maybe half the population already had blue eyes.
The fact that every person alive today with blue eyes has this same allele might be just chance, genetic drift - essentially the same phenomenon as sampling error. The human effective population size has been quite small at times, which makes this kind of loss of diversity through drift more likely.
I’m far from expert, but isn’t it supposed that some very early developments/mutations may have only occurred once, such that all cellular life has a single ancestor?
Many babies have blue eyes and the color doesn’t darken until a year or so later. So a baby with blue eyes probably wasn’t seen as much of an omen.
But if it happened once, why are we sure it never happened again?
I did not know that.
Yep. My understanding is that this is standard among Australian Aboriginals. And looking for a cite about it found some hits about a tribe in Indonesia where some members have blue eyes into adulthood. It’s unlikely that this tribe is descended from the same person that other blue-eyed people are. Other people with blue eyes mostly don’t have this Waardenburg syndrome.
Nobody is claiming that it never happened again. We just have fairly good evidence that all instances of blue eyes alive today are descended from one occurrence. Other alleles that may have carried a similar mutation were lost from the population.
We can’t prove that with absolute certainty without sequencing every single individual with blue eyes. A de novo mutation could have occurred a year ago and only be present in one baby. But to get to a high probability we don’t have to sample a huge number of people.
It’s possible that the mutation occurred many times, but that all of the other instances died out.
Also, the first person to have this mutation wouldn’t have had blue eyes, and the gene was probably already fairly widespread before the first person to have blue eyes as a result of it. Remember that blue eyes are recessive, so you need two copies of the blue gene to have blue eyes. So the earliest it could actually be seen would be once two descendants of that original mutant mated with each other and had children. It’s even possible that the first blue-eyed person was lynched for being a bad omen before reaching adulthood, because that one lynching wouldn’t have wiped out the gene in their relatives (though blue-eye-lynching probably wasn’t common, or the gene wouldn’t have spread as widely as it has).