# All blue-eyed people share one common ancestor **URL:** \ **Category:** Factual Questions\ **Created:** [January 30, 2023, 7:07pm UTC](https://boards.straightdope.com/t/all-blue-eyed-people-share-one-common-ancestor/979066 "2023-01-30T19:07:10Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![lissener](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lissener/32/6139_2.png) [@lissener](https://boards.straightdope.com/u/lissener)\ **Post date:** [January 30, 2023, 7:07pm UTC](https://boards.straightdope.com/t/all-blue-eyed-people-share-one-common-ancestor/979066/1 "2023-01-30T19:07:10Z")
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? ---
**Author:** ![silenus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/silenus/32/166_2.png) [@silenus](https://boards.straightdope.com/u/silenus)\ **Post date:** [January 30, 2023, 7:12pm UTC](https://boards.straightdope.com/t/all-blue-eyed-people-share-one-common-ancestor/979066/2 "2023-01-30T19:12:06Z")
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. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [January 30, 2023, 7:25pm UTC](https://boards.straightdope.com/t/all-blue-eyed-people-share-one-common-ancestor/979066/3 "2023-01-30T19:25:46Z")
> [@lissener](#): > > This can’t possibly be true. 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. ---
**Author:** ![lissener](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lissener/32/6139_2.png) [@lissener](https://boards.straightdope.com/u/lissener)\ **Post date:** [January 30, 2023, 7:26pm UTC](https://boards.straightdope.com/t/all-blue-eyed-people-share-one-common-ancestor/979066/4 "2023-01-30T19:26:05Z")
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”? ---
**Author:** ![lissener](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lissener/32/6139_2.png) [@lissener](https://boards.straightdope.com/u/lissener)\ **Post date:** [January 30, 2023, 7:27pm UTC](https://boards.straightdope.com/t/all-blue-eyed-people-share-one-common-ancestor/979066/5 "2023-01-30T19:27:07Z")
“One individual” is how I’ve always seen this presented. ---
**Author:** ![OldGuy](https://avatars.discourse-cdn.com/v4/letter/o/3bc359/32.png) [@OldGuy](https://boards.straightdope.com/u/OldGuy)\ **Post date:** [January 30, 2023, 7:27pm UTC](https://boards.straightdope.com/t/all-blue-eyed-people-share-one-common-ancestor/979066/6 "2023-01-30T19:27:20Z")
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? ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [January 30, 2023, 7:28pm UTC](https://boards.straightdope.com/t/all-blue-eyed-people-share-one-common-ancestor/979066/7 "2023-01-30T19:28:57Z")
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. ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [January 30, 2023, 7:29pm UTC](https://boards.straightdope.com/t/all-blue-eyed-people-share-one-common-ancestor/979066/8 "2023-01-30T19:29:02Z")
> [@lissener](#): > > This would mean that the blue-eye mutation happened only ONCE in all of the history of homo sapiens. Don’t see how that logically follows from the title premise. ---
**Author:** ![Atamasama](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/atamasama/32/12961_2.png) [@Atamasama](https://boards.straightdope.com/u/Atamasama)\ **Post date:** [January 30, 2023, 7:36pm UTC](https://boards.straightdope.com/t/all-blue-eyed-people-share-one-common-ancestor/979066/9 "2023-01-30T19:36:09Z")
Since nobody has done so, I’ve linked to what I assume is the article in question. > **[Blue-eyed humans have a single, common ancestor](https://www.sciencedaily.com/releases/2008/01/080130170343.htm)** > > New research shows that people with blue eyes have a single, common ancestor. Scientists have tracked down a genetic mutation which took place 6,000-10,000 years ago and is the cause of the eye color of all blue-eyed humans alive on the planet today. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [January 30, 2023, 7:37pm UTC](https://boards.straightdope.com/t/all-blue-eyed-people-share-one-common-ancestor/979066/10 "2023-01-30T19:37:38Z")
> [@lissener](#): > > “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”? 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. ---
**Author:** ![AHunter3](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ahunter3/32/368_2.png) [@AHunter3](https://boards.straightdope.com/u/AHunter3)\ **Post date:** [January 30, 2023, 8:07pm UTC](https://boards.straightdope.com/t/all-blue-eyed-people-share-one-common-ancestor/979066/11 "2023-01-30T20:07:05Z")
> [@Riemann](#): > > 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. Yeah, this. Relevant prior thread: > [@Single Common Ancestor doesn't mean the others died!](https://boards.straightdope.com/t/single-common-ancestor-doesnt-mean-the-others-died/435870): > > A recurrent misconception cropping up over and over again. Some news report comes out to the effect “Every human on the face of the earth had an ancestor in common x, xxx, xxx years ago, says scientist”. Gee, say various and sun-dried people, imagine that, just think of all the other people on the face of the earth back then, and only this dude’s progeny made it! :smack: :smack: :smack: a) It’s not so amazing\*. I have 2 parents, had 4 grandparents, 8 gread-grandparents, 16 ancestors in t… 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. ---
**Author:** ![Dewey\_Finn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dewey_finn/32/4222_2.png) [@Dewey\_Finn](https://boards.straightdope.com/u/Dewey_Finn)\ **Post date:** [January 30, 2023, 8:13pm UTC](https://boards.straightdope.com/t/all-blue-eyed-people-share-one-common-ancestor/979066/12 "2023-01-30T20:13:09Z")
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? ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [January 30, 2023, 8:23pm UTC](https://boards.straightdope.com/t/all-blue-eyed-people-share-one-common-ancestor/979066/13 "2023-01-30T20:23:18Z")
> [@Dewey\_Finn](#): > > I’m trying to imagine what happened those thousands of years ago… 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. ---
**Author:** ![Dinsdale](https://avatars.discourse-cdn.com/v4/letter/d/97f17d/32.png) [@Dinsdale](https://boards.straightdope.com/u/Dinsdale)\ **Post date:** [January 30, 2023, 9:10pm UTC](https://boards.straightdope.com/t/all-blue-eyed-people-share-one-common-ancestor/979066/14 "2023-01-30T21:10:56Z")
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? ---
**Author:** ![OldGuy](https://avatars.discourse-cdn.com/v4/letter/o/3bc359/32.png) [@OldGuy](https://boards.straightdope.com/u/OldGuy)\ **Post date:** [January 30, 2023, 9:13pm UTC](https://boards.straightdope.com/t/all-blue-eyed-people-share-one-common-ancestor/979066/15 "2023-01-30T21:13:08Z")
> [@Dewey\_Finn](#): > > 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? 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. ---
**Author:** ![lissener](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lissener/32/6139_2.png) [@lissener](https://boards.straightdope.com/u/lissener)\ **Post date:** [January 30, 2023, 9:20pm UTC](https://boards.straightdope.com/t/all-blue-eyed-people-share-one-common-ancestor/979066/16 "2023-01-30T21:20:31Z")
But if it happened once, why are we sure it never happened again? ---
**Author:** ![Dewey\_Finn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dewey_finn/32/4222_2.png) [@Dewey\_Finn](https://boards.straightdope.com/u/Dewey_Finn)\ **Post date:** [January 30, 2023, 9:21pm UTC](https://boards.straightdope.com/t/all-blue-eyed-people-share-one-common-ancestor/979066/17 "2023-01-30T21:21:47Z")
I did not know that. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [January 30, 2023, 9:25pm UTC](https://boards.straightdope.com/t/all-blue-eyed-people-share-one-common-ancestor/979066/18 "2023-01-30T21:25:46Z")
> [@OldGuy](#): > > 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. 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. > **[Here’s why this Indonesian Tribe has dazzling blue eyes](https://telanganatoday.com/heres-why-this-indonesian-tribe-has-dazzling-blue-eyes)** > > This is because of a rare genetic disorder called Waardenburg syndrome which causes congenital hearing loss and pigmentation deficiencies, which can include bright blue eyes. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [January 30, 2023, 10:29pm UTC](https://boards.straightdope.com/t/all-blue-eyed-people-share-one-common-ancestor/979066/19 "2023-01-30T22:29:45Z")
> [@lissener](#): > > But if it happened once, why are we sure it never happened again? 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. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 30, 2023, 10:33pm UTC](https://boards.straightdope.com/t/all-blue-eyed-people-share-one-common-ancestor/979066/20 "2023-01-30T22:33:12Z")
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). [Next page](https://boards.straightdope.com/t/all-blue-eyed-people-share-one-common-ancestor/979066.md?page=2)