Fascinating read on the origin of blue eyes, tracing it back to a single ancestor. It's remarkable how a single genetic mutation can have such a profound impact on a visible trait in a population. This reminds me of another genetic trait, lactase persistence, which also arose from a single mutation event. The ability to digest lactose in adulthood, common in populations with a history of dairy farming, is another example of how a small genetic change can lead to significant shifts in human adaptation and cultural practices. It makes one wonder what other hidden genetic changes we might shaer with specific groups of people.
> Deemed a neutral mutation, Eiberg says the eye-color example "simply shows that nature is constantly shuffling the human genome, creating a genetic cocktail of human chromosomes and trying out different changes as it does so."
Blue eyes tends to make people seem more attractive and the evolutionary reason is that they end up being a good quality in a mate because it's easier to see pupil dilation. Thus making it easier to perceive their emotional states better than of someone with black/brown eyes.
This is also true for pale eye colors in general(non-black and non-brown) which are perceived as more attractive, another reason being that they're rare and exclusive. This not just helps in finding better mates but also helps with survival, like how attractive or taller people are helped more in society or are promoted more. Like how almost all US presidents are tall.
Not sure what the technical defintion of a neutral mutation is, but I don't think this is one based on plain English, or I am just plain wrong.
When you analyze if attractiveness or height gives you a genetic/population advantage, you cannot stop at "they are promoted". They have to have more children, and the children have to also have genetic advantages.
For example, if you have a pale skin in Sweden 20.000 years ago, your vitamin D metabolism is better, so of your 5 children 4 reach adulthood healthy. Meanwhile, your black neighbor had 5 children and only 2 reached adulthood, and they have rickets. In a few generations, the skin gets white among the population.
But if you both lived in Africa, 4 of your 5 kids developed melanoma at young age. They either die or get horribly scarred. Meanwhile, your neighbor still has 4 healthy kids that never get sunburns. The amount of sunlight is so high that D vitamin is not an issue.
I saw this graphically when I was in the Namib desert. There was a family of Himba people who had an albino child. The boy had sores all over his body and had to stay under strong shade constantly. Poor kid was living a cursed life simply because he’d gotten a bad roll of the genetic dice.
Does it have to be beneficial? Another possibility is that the melanin production machinery just broke in a small population and the population was geographically isolated enough that the breakage wasn’t overwritten by neighbors (since there were no neighbors). I wonder if this has been ruled out somehow?
This is called genetic isolation, and it's the origin of many species. But when it happens you don't get a gradient. You get two populations separated by (usually) a geographic barrier.
The closest case I could imagine for this in humans are the australian aboriginals and papuans. You don't have a continuous gradient south-north between them and asian populations (assuming the Out Or Africa as true), but a sharp cut dated 50K years ago. Europeans are genetically closer to an asian than asians to papuans or australians.
Lets imagine a small group of engineers that develope a bad software pattern in full isolation. They don't know better, so they work in that way for years. Now suppose they get in contact again with the rest of the world. How could their bad pattern expand to the rest of the world engineers if it is inferior? The ones that addopt it would be selected against, the ones who doesn't would be selecter positively.
For it to expand it had to have at least something positive (unless you do a Chengis Khan). This is what happened to sickle cell disease, which is a bad mutation but gives you resistence to malaria, so the sickle cell disease is common in Africa. Meanwhile, African Americans have much less of the mutation, because in the USA there is no malaria, thus the gene is being slowly removed from the population.
I meant pale eye color, I edited the parent comment. It had nothing about skin color. And also eye color is just one dimension among hundreds, some of which you listed.
The first, second, and fourth links are about pupil dilation generally. They don’t say anything about eye color. They most certainly say nothing to support your assertions about the connection between eye color and the perception of pupil dilation.
The third link (the Reddit thread) does mention eye color but only in the context of the effects of dilating drugs (drops). This also is irrelevant to the topic at hand.
> They most certainly say nothing to support your assertions about the connection between eye color and the perception of pupil dilation
I would think this was common knowledge just from talking to a lot of people face to face but again this is HN with people of multiple backgrounds and people that don't like talking to people and spend a lot of time indoors, not to mention people who are not good at picking up emotional and social cues, so here's the reference from 1975.
> We also found that blue-eyed people have a stronger pupil response than brown-eyed people when they view a picture that causes pupil dilation or constriction. To be more precise, with respect to the total range of response from the smallest pupil size to the largest the range is greater for blue-eyed people than it is for brown-eyed people. (This statement applies, of course, only to changes in pupil size resulting from emotions or attitudes.)
> It is of course easier to see a pupil surrounded by a blue iris than it is to see one surrounded by a brown iris.
I see you are more interested in hurling insults than arguing your case in good faith. That’s fine but it means I am done responding to you after this comment.
> It is of course easier to see a pupil surrounded by a blue iris than it is to see one surrounded by a brown iris.
Again this is an undefended assertion. It’s important to remember we’re talking about subconscious responses to pupil size. Just because you (and Eckhard Hess) believe it is “easier” to consciously perceivr pupils surrounded by blue irises does not mean your subconscious is any less aware of pupils in brown eyes. If it’s true that it’s easier to subconsciously decode pupils in blue eyes then it should be easy to verify experimentally. Similarly, if it is easier to be aware of the emotional state of blue-eyed people then that should be easy to prove experimentally. What’s harder is showing your assertions that blue-eyed people thus make better partners or that this makes blue eyes an evolutionary advantage.
> It’s important to remember we’re talking about subconscious responses to pupil size. Just because you (and Eckhard Hess) believe it is “easier” to consciously perceivr pupils surrounded by blue irises does not mean your subconscious is any less aware of pupils in brown eyes.
Subconscious responses are still limited by physical limitations. If you don't believe, you can win the James Randi one million dollar prize by demonstrating it with an experiment. Maybe you can show that someone can subconsciously identify the shapes of a very black object placed in front of another very black object in a dark room.
> If it’s true that it’s easier to subconsciously decode pupils in blue eyes then it should be easy to verify experimentally
It's a proven fact that features are easier or harder to discern based on their background. For example a white cat is easier to see when it's almost pitch dark compared to a dark cat. Maybe someone like you can pioneer research in an experiment to formally prove it.
One can start by asking people which pupils are easier to discern from the iris in this picture. Pupils are black or a very dark color btw.
Compare top row to the rest. Now think about all the lighting conditions and distances that occur when people talk to or interact with other people. Of course there are people with vision impairments who won't notice the differences and may think they might all look the same. Scientists don't waste time trying to prove things already proven just because some internet troll debater may question things.
Hess' paper is quite well cited, so it should be easy to find any counter assertion to something that he stated with such high confidence: "It is of course". Maybe you can try finding one, but from this thread so far it seems like you're more interested in dismissing things for arguments' sake rather than try sourcing information like I have been doing.
> I see you are more interested in hurling insults than arguing your case in good faith. That’s fine but it means I am done responding to you after this comment.
You're the one that hasn't put in any research and just dismissing any scientific source I post. It's a pain and a waste of time to respond to low effort argumentative folks.
> You're the one that hasn't put in any research and just dismissing any scientific source I post. It's a pain and a waste of time to respond to low effort argumentative folks.
That's because your scientific sources are of questionable quality and don't support your hypothesis.
> so it should be easy to find any counter assertion to something that he stated with such high confidence: "It is of course".
More specifically Hess wrote "It is of course easier to see a pupil surrounded by a blue iris than it is to see one surrounded by a brown iris. Perhaps it is not unwarranted to assume that the response has been favored by evolutionary selection more in blue-eyed people than in brown-eyed people." (Emphasis mine.)
"Perhaps it is not unwarranted to assume" does not suggest high confidence.
> so it should be easy to find any counter assertion
I did a Google Scholar search for: "The Role of Pupil Size in Communication" blue brown
] As a means of clarifying certain of Hess' (1975) unsubstantiated conclusions concerning the role of pupil size in nonverbal communication, the relationship between eye color and the pupillary attributions of college students to Hess' happy-angry face task was measured. The results supported Hess' claim that eye color is related to sensitivity to pupillary cues but were incongruent with his notion that blue-eyed people are especially sensitive due to some selective evolutionary process.
The text describes issues with Hess's work, and how others at the time viewed Hess's conclusion:
] Hess offered no other evidence for this conclusion. That is, he did not bother to report any statistical evaluation of the differences between these means, nor did he provide the sample sizes and the standard deviations that would have permitted others to do so. Perhaps it is this lack of concern for relevant detail on Hess' part that led Ianisse (1977) to conclude, "it is difficult to seriously entertain the notion that the pupil plays a major role in nonverbal communication, for no convincing research has shown the proposed phenomenon to be veridical" (p.170). Ianisses's point is well taken, and perhaps even charitable, for Hess' apparent disdain for statistical evaluation of his data invites the speculation that possibly the obvious statistical tests were computed but were not reported because these results proved to be not significant.
and their attempt at replication showed that hazel-eyed people were more sensitive than blue-eyed people, but write that such an interpretation "would strain credibility":
] These results seem to be incongruent with Hess' conclusion that blue-eyed people have had some selective evolutionary advantage with respect to sensitivity to pupillary cues. While our data suggest that hazel-eyed people seem to be more sensitive to pupillary cues, we feel that it would strain credibility to attempt to explain these differences in terms of a selective evolutionary process as Hess did. In fact, any explanation of the processes that might have led to the differential sensitivity of browne, blue-, and hazel-eyed people to pupillary cues seems premature. For, as Janisse (1977) has correctly pointed out, it remains to be demonstrated that results such as these are veridical. Thus, subsequent research should focus on determining whether the apparent sensitivity advantages enjoyed by hazel- and perhaps blue-eyed individuals translate to more effective interpersonal skills.
It's hard to get much easier than that.
That part of Hess's research failed replication, just like how https://www.sciencedirect.com/science/article/pii/S016787602... ("Replicating five pupillometry studies of Eckhard Hess") showed how some (though not all) of Hess's work could not be replicated, and pointed out how "Hess mostly used small sample sizes and undocumented luminance control".
Why are you so certain of Hess's hypothesis when it seems to have been shot down over 40 years ago? If you know of any follow-up studies which showed the replication attempt could not be replicated, while the original could, please provide it.
Perhaps you can point to something more substantial than 50 year old research containing documented questionable accuracy?
Did you not find these follow-up papers in your attempts to understand this research? They were quite easy to find, while you seemed very certain they did not exist. What formed the basis of your confidence that Hess's hypothesis had not been challenged?
And remember, your claim is "the evolutionary reason is that [blue-eyed people] end up being a good quality in a mate because it's easier to see ... their emotional states", so supporting evidence must "focus on determining whether the apparent sensitivity advantages enjoyed by ... blue-eyed individuals translate to more effective interpersonal skills."
Which you have failed to do, preferring to make chains of correlations to support your argument.
But correlations are not generally transitive, so that argument is invalid.
>Blue eyes tends to make people seem more attractive and the evolutionary reason is that they end up being a good quality in a mate because it's easier to see pupil dilation. Thus making it easier to perceive their emotional states better than of someone with black/brown eyes.
I'm sure there are evolutionary disadvantages to not being able to hide your emotional states.
also the attractiveness of the color is probably taught and culturally defined.
Is this supposed to be some kind of subconscious thing? Because I’ve never noticed what anyone’s pupils are doing - and the majority of my family friends and light colored eyes, so, if this was actually a thing, I’d have lots of opportunities to experience it.
> The study found that the openness of the eye was most closely related to our ability to read others' mental states based on their eye expressions.
which is where you probably drew your conclusion. However, the actual paper goes into more details, and reading it show that conclusion is wrong. It says:
> For these analyses, we extracted seven eye features from each exemplar: vertical eye aperture, eyebrow distance, eyebrow slope, eyebrow curvature, nasal wrinkles, temporal wrinkles, and wrinkles below the eyes (Fig. 1). Euclidean coordinates from the appearance models were used to compute eye aperture (distance from top to bottom of eye), eyebrow distance (distance from top of eye to eyebrow), eyebrow slope (slope from start to end of eyebrow), and eyebrow curvature (angular change from start to end of eyebrow).
Fig. 1 in shows example of how they define eye aperture, and it is NOT the pupil size, but the size from the bottom to top of the center of the eye.
Further, their analysis suggests that eye pupil size is either strongly correlated with the seven components they analyzed, or has relatively small contribution to expressing mental state. They say aperture had the strongest correlation with mental-state, "explaining 61.7% of the variance; the valence dimension was the secondary component, explaining 26.8% of the variance. ... Together, these [seven] components captured 88.8% of the total variance."
That is, your claim about pupil size being an evolutionary benefit due to the increased ability to perceive mental state, appear to be contradicted by the very paper you say supports your hypothesis.
There's a long history where defenders of pseudoscience, including Young Earth Creationism and "scientific racism", of citing papers which supposedly support their claim, only to find that either they are irrelevant or say quite the opposites. If you want to make a solid claim, you need to avoid that style, otherwise you'll draw their pseudoscience stink onto you.
> We also found that blue-eyed people have a stronger pupil response than brown-eyed people when they view a picture that causes pupil dilation or constriction. To be more precise, with respect to the total range of response from the smallest pupil size to the largest the range is greater for blue-eyed people than it is for brown-eyed people. (This statement applies, of course, only to changes in pupil size resulting from emotions or attitudes.)
> It is of course easier to see a pupil surrounded by a blue iris than it is to see one surrounded by a brown iris.
That is the press release for the primary article, which is listed at the bottom of the page: Daniel H. Lee, Adam K. Anderson. Reading What the Mind Thinks From How the Eye Sees. Psychological Science, 2017; 28 (4): 494 DOI: 10.1177/0956797616687364
Lee and Anderson DO NOT talk about pupils. That's why irrational replied to your link with "Did you even read what you linked? The linked article has nothing to do with pupils."
I confirmed that irrational's observation is correct, despite your denial.
Your quote now comes from The Role of Pupil Size in Communication, Eckhard H. Hess, Scientific American, Vol. 233, No. 5 (November 1975), pp. 110-119.
The Lee and Anderson (2017), doesn't contradict Hess (1975). Rather, it says that any effect of pupil dilation size on the ability to perceive mental state is significantly smaller than several other factors related to the eye.
The Hess paper is a woefully inadequate source for your claim that blue eyes are not evolutionarily neutral. How many people were studied? How much stronger was the response? What is the statistical significance and how was it calculated? How does it compare to other ways the eyes signal mood like in Lee and Anderson? Were there conflating social factors, like the blue-eye subjects being from a higher social class on average than the brown-eyed subjects?
The paper doesn't give any of those numbers, which makes sense as Scientific American was on the border between an academic publication and a popular science magazine.
Furthermore, the author characterizes the evolutionary hypothesis as "perhaps it is not unwarranted" - a far more tentative claim than you are trying to push.
You need to fill in the missing steps. How do you get from "perhaps not unwarranted" to "substantive enough to advocate on HN"? Because you appear to be advocating an hypothesis with very little evidence.
There's been 50 years of research since Hess. My sampling of the recent papers citing Hess are completely silent of a blue/brown-eyed distinction, which suggests to me it did not play out.
How did you find the Lee and Anderson paper? When did you read it? Why did you cite it when it doesn't even mention the word "pupil"? Do you understand how it seems to strongly diminish the significance of your evolutionary hypothesis?
You definitely notice body language subconsciously, our scleras being visible is well known to play a role in determining where the other is looking for example.
yeah and there are already plenty of comments explaining how these are irrelevant- you can’t just connect adjacent studies by assumption and have those assumptions be true
gaganyaan, see also the followup where the presented citations doesn't support the claim for evolutionary benefit.
See also my comment at https://news.ycombinator.com/item?id=35679767 showing the 1975 hypothesis could not be validated in a 1979 paper, and how even at the time it was "difficult to seriously entertain the notion" Hess proposed.
See also the thread at https://news.ycombinator.com/item?id=35667066 where one of belltaco's citations actually demonstrates that total vertical eye aperture - not pupil size - is the biggest predictor of mental state. Pupil size wasn't even considered, but the remaining variance is too small for pupil size to be a significant predictor. Total aperture is even easier to see than pupil size.
In other words, there's a bunch of citations, but no convincing support presented for the evolutionary hypothesis.
Another take I’ve heard is that lighter eyes allow you to see the dark ring around the iris (limbic rings), which apparently fades as you age, becoming progressively lighter, forming a sort of proxy for age.
All this talk about pupil dilation being more obvious with blue eyes (and thus an attractive trait to possess), yet I haven't seen anyone comment on darker eyes tending to nearly always look dilated, and therefore less of a threat.
For a couple of animal-world examples, take the black Labrador Retriever - the ones with black eyes look more playful than the ones with intense looking brown eyes, when outside in the sun.
Blue eyes in the sun would look piercing (and therefore more threatening) compared to dark brown eyes. This is super easy to see in Siamese cats, both because of eye colour, and the extent that their eyes can dilate.
You can also see how blue eyes are often savagely played up in Viking imagery.
So while there are arguments to be made, there are also counter points that should be taken into account.
I'm not convinced. Assume it is accurate, there was one single blue eyed mutant that lived 10K years ago. Maybe the blue eyes were attractive and this individual was sexually prolific. Since blue eyes are recessive, none of their children would have had blue eyes. For more blue eyes to appear, there would have had to be lots of incest among the mutant's children. But what would have made the blue-eyed mutant's children more likely to pass on the recessive blue eyed genes if they didn't have blue eyes? For there to be so many blue-eyed individuals today, I think it is far more likely the blue-eyed mutation occurred many times.
This is probably true for almost any other phenotype attribute. Not just blue eyes. From epicanthic folds to the structure of the nose or lactose sensitivity. It all originated from a single mutation on any one individual.
Since blue eyes are recessive, presumably that one ancestor had brown eyes and so did all their children. At some later point, some of that ancestor's descendents had children and they had blue eyes?
It reads to me as definitive according to the research so far, though the one sentence about green raises questions about rarer colors than blue, speculatively the other colors are polygenic.
Not necessarily true. All humans (Everyone with two legs) have a single ancestor 100k years ago, yet I'm pretty sure humans with two legs are older than that.
>All humans (Everyone with two legs) have a single ancestor 100k years ago
There was a black American that died in South Carolina somewhat recently that gained his Y chromosome from a man older than the common ancestor of most men, Y-Adam.
>Perry did not descend from the genetic Adam. In fact, his Y chromosome was so distinct that his male lineage probably separated from all others about 338,000 years ago [0]
This would actually be really surprising, wouldn’t it? I would think the default would be a pool of pre-human hominids which gradually changed over time and eventually crossed the arbitrary line we deem “human”. I suppose in theory one individual may have had the last teeny mutation to cross over that arbitrary line which then spread everywhere to cross the rest of the pool over, but it seems more likely that bits of the “human” features developed in different populations over time and eventually and gradually merged through cross breeding (after each mutation was already in multiple individuals). The linear view with a singleton seems overly simplistic for “humans” overall. For a single trait it still seems overly simplistic and unlikely, but not nearly as radically so.
EDIT I think there is some confusion here. I believe the article claim is that the feature "blue eyes" may have originated from a mutation in a single individual organism, or at least bottlenecked in a single individual organism. OP sounds like they are saying "yeah, now do humans", but the entire feature complex "human" is almost certainly not like that. If all OP is saying is that there is probably at least one tiny feature in humans which originated from a mutation in a single individual organism, then sure this is trivially true, but that situation is very, very different from the article situation.
I believe the article is claiming that the feature "blue eyes" has a single organism bottleneck (or origin) in the past. If this were also true for the feature complex "human", that would be very surprising. If all that is being claimed here is that humans all have at least one common ancestor among many non-common ancestors, then sure that is trivially very likely. It is also nothing like what is being claimed about blue eyes IIUC...
Right. Those are via different methods. "Mitochndrial eve" is via female line only - i.e. mother's mother's mother's mother etc. Similarly the Y-chromosome Adam is via male line only. If we use both sides (e.g. mother's father's mother's father), then it's much closer.
Well you have two parents, four grandparents, eight great-grandparents etc. Eventually inbreeding (if you can call it that when it's really distant relatives) starts becoming a factor so that some person may take up multiple "slots" in your family tree. But either way, it would seem that if you go far enough back every single human will be an ancestor of yours.
Edit: Just to clarify what I'm trying to get at is that there are probably quite a lot of Ancestors That Everyone Descend from.
My father researched a family tree; not rigorously, like Mormons do, but he spent about a decade tramping around the country, visiting graveyards and inspecting parish records. I have a bound volume of the tree. He claimed descent from (a) William The Conqueror, (b) Lady Godiva, and (c) Charlemagne.
I don't have his records, only the tree. The links are pretty ropey, especially when you reach further back. And he imported big chunks of it from trees built by others. His conclusions seem pretty implausible, but that article makes them seem a bit more plausible.
Well given that blue eyes is neither neither mt-dna or y-chromosome, I made an argument about the autosomal "normal dna" that is inherited from both sides.
Consider some arbitrary point far in the past and pick a random human, and consider their descendants. Human population was growing almost exponentially [1] and continued to do so for many thousands of years.
If you keep track of the number of descendants of that random human who are alive over time, what you'll find is that in almost all cases it either goes to 0 over a short number of generations or it increases almost exponentially until it hits some limit such as a physical barrier that stops growth in all the places their descendants live and prevents their descendants from leaving.
If a few of their descendants can travel, then in their new area their descendants either go to 0 or exponentially spread in the new area.
It doesn't take a super long time, in the case where the number of descendants doesn't go to 0 for the number of descendants to grow to the point where everyone is a descendant of that random human.
But note that the same is true for any other random human we might have picked at that time. Every person who was alive at that time either has no living descendants or everyone now alive is a descendant of theirs.
The same is true for any point farther back than the arbitrary point we picked, because anyone alive at that earlier point who has any descendant who reached the first point will be an ancestor of everyone now alive, because their descendant who reached the first point is.
The most recent point at which everyone then alive is either an ancestor of all now alive or of none now alive is called the "all common ancestors point" or the "genetic isopoint".
Most researchers think the genetic isopoint was somewhere in the range of 4000-15000 years ago.
There's also a point of interest that occurs between the genetic isopoint and the present called the "most recent common ancestor point". That is the point where any two people now alive have a common ancestor at that point, but there are groups of three people where there is no common ancestor of all three at that point.
There's also the "matrilineal most recent common ancestor" and "patrilineal most recent common ancestor", which are like the "most recent common ancestor" except you only counts female descendants or male descendants, respectively. These are also called the "Mitochondrial Eve" and "Y-chromosomal Adam", respectively. These are even farther back than the "all common ancestor point"
You can also look at this going backwards. As you go back the number of logical ancestors you have doubles each generation. But that exponentially growing number of logical ancestors has to map to the almost exponentially shrinking number of people, and so some distinct logical ancestors of yours are implemented by the same physical ancestor. The farther back you go the more people's ancestor trees each physical person then alive is in, unless they are in none. And so you again find the most recent common ancestor point, and the all common ancestor point, and the matrilineal and patrilineal most recent common ancestor points.
If the genetic isopoint really was less than 15000 years ago, you can make some interesting inferences. For instance the Neanderthals went extinct around 40000 years ago. That's farther back than the genetic isopoint. Since some people now alive are known to have Neanderthal ancestors (because they have some Neanderthal DNA) then everyone now alive must have Neanderthal ancestors.
Note that this doesn't mean everyone alive must have Neanderthal DNA. You only pass half your genes on to your kids so you can eventually end up with descendants who don't actually have any of your genes.
Same with the Denisovans. They went extinct before the genetic isopoint, and some modern humans are known to have Denisovan ancestors and we we can conclude that we all do.
[1] I say "almost" exponentially because instead of e^(at) where a is constant, a is variable and has long term been slowly decreasing.
I do wonder how many "single ancestor" bottlenecks humans and other species have evolved through.
That said, I do wonder how sound the research above is. It seems that lateral gene transfer resulting from, say, the first viral pandemic, could be responsible for a common snippet present in all surviving life billions of years later.
