I've a question - my siblings have varied eye color, 1 dark brown, 2 brown , 1 blue, 1 grey/blue and I'm hazel/green, however most started out life as blue - what causes these maturational changes in color, some age or development mediated gene expression, or epigenetic factors?
My daughter, by the way, started out with blue eyes, which became violet, then dark brown, now medium brown - so from light to dark and back to midway??

Many children of N. European descent start off blond and by their early teens have darkened to brown or auburn. In the Deep South this is called ''tow-headed blond'' (meaning he or she will only be blond until puberty). Southern girls, many once tow-headed, feel it is their birthright to revive this inner blondness with the aid of magical potions and hair technicians.

As these woman (and men) age, some grow hair in inconvenient places calling for even more potions and depilation technicians. Then, of course, there is male pattern baldness, hairy ear passages, and the like.

The culprit in all of this? Perhaps rising levels of testosterone (at least relative to estrogen).

Why not the same in early eye color?

Any ideas on what could be the advantage of blue eyes? Given that there are known disadvantages of blue eyes, there must be some counterbalancing force to explain its frequency.

For example:

[Macular degeneration] is twice as common in blue eyes

someone should look at the blue-eyed lemur. i don't have time right now....

Why do cats have different eye colors? Persians tend green, Black cats yellow, Siamese, blue. What did I leave out?

Dogs are reliably brown-eyed. Brown-eyed cats, none that I can find.

Can one have left and right eye of different colour?

yes. i've met someone like that.

Dogs are reliably brown-eyed. Brown-eyed cats, none that I can find.

But aren't there quite a few dogs with blue eyes? Huskies are the most famous example, but there are others, like this dalmatian:

http://www.thidwick.com/bluang.jpg

I thought the lack of brown-eyed cats could have something to do with the ancestors already being light-eyed, but then again, many wolves seem to have light eyes too.

Forgot about those northern Huskies -that pesky linkage between northern climates and blue eyes again. Perhaps there is an advantage during the dark winter months - perhaps better light gathering abilities - that offsets disadvantages during the summer months. People living nearer the equator would not have to adapt to such seasonal variations in daily sunlight.

Also interesting, cats are nocturnal hunters. How about dogs, coyotes, foxes and wolves? I'll bet blue-eyed lemurs do it in the dark.

william, most mammals are nocturnal, or dusk creatures. primates are strange in being most diurnal. and yes, i believe wolves are more active at night too....

Many children of N. European descent start off blond and by their early teens have darkened to brown or auburn.

Not many, most - practically all where I'm from. (I started out blonde too, now dark brown and if I'm following my father, my hair will eventually go black. It's the same with the other pigment - I had no red until teenage, but once I could grow a real beard, I had some red hairs.)

Why not the same in early eye color?

Eye and hair colour work very differently. Here, most people have changing hair colour until early adulthood but few people noticeably change eye colour after infancy. (Children clearly have much lighter hair, it's impossible to miss, but I haven't noticed them having lighter eyes.)

William:

Dogs are reliably brown-eyed. Brown-eyed cats, none that I can find.

Cats and dogs have otherwise very different-looking eyes, too. For example, dogs (IIRC - I'm a cat person) have circular pupils like humans, but cats' pupils look like... vaginas (flattened into vertical slits). I'm not sure what the shape of cat eyes is about, but it may be about controlling the amount of light (or it may be about a difference in horizontal/vertical resolution or...). Cat eyes have some anatomical differences to humans that aren't visible to the eye, too, I think. Their eye colour may have very different roots.

I am also a ''cat person'' and could never understand ''cat phobia'' - I don't mean disliking cats for their aloof, finicky ways, but actual fear and hatred of cats. I came to believe it was related to the cat's iris - resembling that of a snake. Pinker, in his book ''The Blank Slate'' claims we are hard-wire into having a fear of snakes. The trigger is not clear - is it the long wriggly body or maybe the mesmerizing slitted (and catlike) eyes? Thus, cat phobia is possibly a corollary to fear of snakes.

An (my) alternate theory of cat phobia (also called Ailurophobia, Elurophobia, and Felinophobia, among other things) is that early man often served as breakfast for some primordial cat. Even scarier than packs of wolves, these stealthy feline carnivores stuck at night - adding even more terror to that stretch of darkness where our senses and defenses were impared.

For a really scary cat, who only seems missing a pair of saber teeth see

http://www.snopes.com/photos/ ani...liger.asp#photo

What gets me is that (1) he's still growing and (2) he can run at 50 mph.

jaakkeli,

That's interesting about your beard, because I have exactly the same thing, except about 40% of beard hair is red, the rest dark brown. One of my mother's brothers is the same.

I've seen the same things in New York in Punjabis and some Ashkenazi Jews - except here it is black and red.

As regards hair color, one of my sisters had hair so blonde it was almost white as a child, then about 3 yo it started to turn darker, eventually light brown by 7 yo, but by 12 or so it was auburn (red/brown)...

William:

I came to believe it was related to the cat's iris - resembling that of a snake. Pinker, in his book ''The Blank Slate'' claims we are hard-wire into having a fear of snakes.

Well, I'm not... (the local snakes are not dangerous to adults, BTW)

An (my) alternate theory of cat phobia (also called Ailurophobia, Elurophobia, and Felinophobia, among other things) is that early man often served as breakfast for some primordial cat.

But big cats have round pupils! From the first Google image links...

http://www.exzooberance.com/virt...er% 20471057.jpg

http://www.vetmed.wisc.edu/dms/f...b/2004- lion.jpg

http://www.avon.k12.ma.us/midhig...M% 20Panther.jpg

Their pupils seem to constrict into tiny spheres, just like ours. Of course that doesn't necessarily mean that saber-tooths didn't have "cat-like" eyes, but if so, their scaredness wouldn't have come from saber-tooths. (Well, of course there's also the easy argument that if you're close enough to a saber-tooth to freak out over the details in its iris, IT'S TOO LATE!!! :-D)

When it comes to grouping hunters (lone or group hunt? nocturnal or also daytime? long chases or short chases?), I think we're actually more likely to be in the same group with big cats (and wolves) and small cats in the same group as snakes and roundness/slit-shaped follows that. (But then, cats have great low-light vision while AFAIK snakes tend to have crappy vision...)

(Of course, cats might simply be imitating snake eyes to scare people. Tigers don't need to imitate!)

Oh, William, never mind, I should read posts I'm replying to - you said an *alternative* theory to the snake eyes. Argh I feel stupid.

pconroy:

That's interesting about your beard, because I have exactly the same thing, except about 40% of beard hair is red, the rest dark brown. One of my mother's brothers is the same.

Hmm, what I meant by some hairs was that I have a mostly brown beard (when I have a beard, it grows as a sparse mess, so the only semi-reasonable style available to me is "hi, I recently joined the Taliban" and I'm not too fond of that) with some red hairs. I think the issue is that there are two pigments, red and brown, and I have both of them, the red just usually doesn't show (perhaps it modifies the shade of brown, but not enough that it would look at all red). Sometimes the brown fails to show up in beard hairs and then they look red - sort of like grey hairs, except red. I don't think it's uncommon at all, most people just interpret any lighter hairs as "greying" unless there's so much red that it shows very clearly.

jaakkeli

You left out this guy:

http://www.iceagemovie.com/ image...esktop_3_lg.jpg

jaakkeli,

Oh OK, for me individual hairs are either dark-brown or red-orange - with less of the latter - evenly dispersed with no patches, which you can see up close - from a distance it just looks like a dark gingery color. Overall beard is very thick and dense.

Yours sounds more like my brother, whose beard has blonde hair with a few red-orange hairs here and there, but is very thin and wispy, and can hardly classify as a beard at all... more like the way some Asian "beards" appear??

William:

The theory (cat=snake) makes even less sense when you realize, not only that most snakes are of harmless varieties but that snakes, both of the venomous and harmless species, may have either type of pupil. One of the large venomous divisions, Viperidae (including both vipers and pit vipers), has vertically elliptical pupils but the far more dangerous elapids (cobras, mambas, etc.) have round pupils (as do most, but not all, harmless types). Just not enough stuff there to go theorizing about.

That said, I do not think it unlikely that there is "hardwiredness" to snake-aversion. For one thing, the fact that some, even most, are harmless does little to offset the likelihood that snake-avoidance behavior would confer survival advantage in more primitive conditions of knowledge (such as recognition of species) or of therapy. It might even be conjectured that the relative abundance of harmless species and individuals vs poisonous may be inter-related in some way with mens'
knowledge of the two.

Yours sounds more like my brother, whose beard has blonde hair with a few red-orange hairs here and there, but is very thin and wispy, and can hardly classify as a beard at all... more like the way some Asian "beards" appear??

Not unless "Ainu" is your idea of Asian beards. My hairs are thick and grow length annoyingly fast, it's that there are too few of them per square cm, so it doesn't cover up the skin properly when not very long. It would not be a problem if the beard were more orange-red, since then the skin/beard contrast would be smaller, but with the brown it looks horribly stupid - I may have a huge mess of inch-long dark thick hair on my face, but you still see right through it. (So, at mid-length my face looks like an overgrown armpit.) The colour from a distance tends to look uniform or uniform with random light hairs that people interpret as grey - one of the fun parts of having a beard is to tell those people to look closer ("WTF?! Orange?!? When did you last wash it?").

Those

gene berman:

The theory (cat=snake) makes even less sense when you realize, not only that most snakes are of harmless varieties but that snakes, both of the venomous and harmless species, may have either type of pupil. One of the large venomous divisions, Viperidae (including both vipers and pit vipers), has vertically elliptical pupils but the far more dangerous elapids (cobras, mambas, etc.) have round pupils (as do most, but not all, harmless types).

But the populations have different ranges, like human populations. In northernmost Europe the only poisonous snake is the common adder, which does have "snake eyes"

http://www.kornnatterlexikon.de/ ..._berus_1600.jpg

I'm not sure where the northernmost range of the second most northerly poisonous snake would lie, but that's by far the northernmost snake at least in Europe (it can live in almost all of Finland), so probably not very close - cobras and others are very far. That is, the only really poisonous animal here has snake eyes and the only animal (besides cats) that has snake eyes (that I can think) of is poisonous. So, do northern Europeans have higher rates of snake-eye-phobia than tropical populations (who actually have a chance of seeing those really nasty round-eyed snakes)?

Of course, the common adder is not actually dangerous to (most) adults. A bite is easily lethal to small children, though, and instinctive phobias are good for kids. (But still, I think the better argument is that you should be scared of a snake before getting close enough to inspect its eye shape...)

Jaakkeli

I don't like the looks of that snake at all - and I'm surprised, it living so far north, that it doesn't have blue (snake) eyes.

heh.

Btw, my daughter has an intense snake phobia - she practically goes into convulsions, even when she see a common garden snake. This really ticks me off as she sounds like she's dying, I come running at full throttle, and all I see is this poor frightened little green snake thinking WTF? But get this, she adores cats; and her cat has brought live snakes into the house several times (to the amusment of all - save one).

Also, I have asked people with cat phobia what it is that makes them dislike cats so much. A common response is ''the way they look at you, they look so evil''. Recall also that during the great witch hunts of the middle ages, cats were often considered part of the witch's black magic and joined the poor women in the flames. Just google: witches cats burned

>Children clearly have much lighter hair, it's impossible to miss, but I haven't noticed them having lighter eyes.

- Dunno about *lighter* eyes, but I think kids often have *clearer* blue eyes - the iris somehow gets duller or cloudier with age.

jaakkeli:

Around the globe, in more northerly latitudes the poisonous snakes are all relatively few and all of the elliptically-pupilled type. The widespread European species is a true viper; except for the elapid coral snake of the extreme south, the North American species are pit vipers (rattlesnakes, water moccasins, and copperheads--the latter two closely related) and N.E. Asia has, to my knowledge, only the Mamushi, a pit viper very similar to the American moccasin and copperhead.

But that's not what has been determinative of snake-avoidance, which, in the main, would seem to have predated the bulk of the settling of such more northerly places. The places where humans seem to have longer-established population are in tropical and subtropical climates--lands whose poisonous snakes are certainly not so easily distinguished by shape of pupil. Besides--if you're close enough to notice the shape of the pupil, you're too close!

Somehow, snakes seem to inspire legends and more ordinary misconceptions, even among those living in the same place and presumably, most familiar. In 1980, with a group of natives in the Guayana Highlands of Venezuela, a bright yellow snake between 7 and 8 feet was seen streaking into some tall grass. The Indians were all scared, declaring that that particular snake was extremely deadly--fatal in a few minutes. But I knew otherwise, recognizing from certain characteristics of form, that it was a variant of a snake found in the southern U.S., the Indigo Snake (entirely black). I thrashed around in the grass and caught it. All were scared and amazed but, after I had goaded it into biting me a few times and had only a few scratches to show, all became convinced and actually wanted to handle the thing that they had formerly believed so deadly. One even expressed the wish that he had a picture so they could convince
folks from other villages. Further, they seemed to understand, in an ordinary, everyday way, when I opened its mouth to show that it did not have the elongated, hollow teeth--fangs--characteristic of venomous varieties. And, best of all, none offered any objection when I released it.

We seem to agree that snake-avoidance, especially of a reflexive, "hard-wired" variety, would have distinct survival value in the remote past (or even now).