The skin colour dilemma...

[Inquisitor]

I have this problem:

 

When two people of differing skin colour have offspring, the kids will have uniform skin colour and also their hair is of uniform consistency.

 

The kids might be light skinned or dark skinned, robust haired or flaxen haired. This does not matter.

 

What matter is that their skin is uniformly coloured all over, and so is their hair uniformly curly/flaxen all over.

 

Now, consider horses of different colours. If they mate, the resulting offspring will have spotty skin. they have a base colour, and over it, huge splots of different colour. So in them, their colour will come from both parents.

 

So why does this not happen with humans? When, say, senegalian female marries a norweigean bloke, why does not their children have spotty skins? Why are they not white with huge black splashes all over the place.

 

Also, why the kids would have uniform hair? Why not white hair with patches of dark hair thrown into the mix???

 

This is quite puzzling to me, especially as evolution would not have time to delete spotty skins, as marriages of different races have been very uncommon all along human history.

 

Is there some explanation to this, ie why have not mixed race humans splochy skins, like other animals tend to have if their parents are of different colours???

[YT2095]

because there`s no gene to determine where these spots or even stripes should be, let alone that there Should be any in the 1`st place.

[Moontanman]

I think that wild horses are much more genetically diverse than humans as well. Wild horses (not the kind in cowboy movies) that haven't been inbred to get the different characteristics we see in domesticated horses do not show the white and black spots and other variations we see in domestic horses.

[GDG]

I'm not sure about horses, but in tortiseshell cats the color variation occurs due to mosaicism. The genes for the enzymes responsible for the skin/fur pigmentation are carried on the X chromosomes: in females, the genes on one of the two X's must be "silenced" so that they don't have a "double dose" of those genes (otherwise, males would only have a half dose). The silencing occurs during development, but essentially at random, with the result that patches of skin express the allele from one X (from one parent), and other patches express the allele from the other X (from the other parent). Perhaps horses have a similar system.

[john5746]

http://www.gmilburn.ca/2009/03/20/clever-as-a-fox/

 

This reminds me of the domesticated fox experiment in the above link. Selecting for less aggressive foxes resulted in several physical changes, including pigmentation.

[John Cuthber]

I'm not sure this "When two people of differing skin colour have offspring, the kids will have uniform skin colour and also their hair is of uniform consistency." is strictly true.

I'm sure there are pairs of siblings who are differeent colours because they happened to get a different mix of genes from their parents.

Also, skin colour isn't generally identical across the whole body; at the very least you have to accept that dark skinned people's palms are generally paler than the rest of them.

 

Anyway, to the extent that it is true (and to a fair degreee it is) I think the simple answer is that in any one body there's generally only one set of genes and your skin is the colour that that set codes for. Same with hair. The relation between genes and colour is complicated but if there's only 1 set of genes then there's only one colur.

[Inquisitor]

I do not see one gene could set the tone, as here are a lot of different skin tones seen in mixed marriages. One kid might be very dark, one very light, one totally white and so on. This is really weird and not seen in animals.

 

Note that in pigs, dogs, and cows we see the same spottyness when the parents are of different colour. This should happen with humans also.

 

Also, I should think different races have a slightly different genes for skin colour, and therefore they could not just mix, so that dark+white gene would produce light brown as it would in a colour palette. But seeminly they do, in real life. I find this deeply miraculous as it does not happen with other animals, just us humans...

[iNow]

This is really weird and not seen in animals.

 

<...>

 

I find this deeply miraculous as it does not happen with other animals, just us humans...

I strongly suspect that this is where you're mistaken, and a large source of your confusion.

[zule]

I have this problem:

 

When two people of differing skin colour have offspring, the kids will have uniform skin colour and also their hair is of uniform consistency.

 

The kids might be light skinned or dark skinned, robust haired or flaxen haired. This does not matter.

 

What matter is that their skin is uniformly coloured all over, and so is their hair uniformly curly/flaxen all over.

 

Now, consider horses of different colours. If they mate, the resulting offspring will have spotty skin. they have a base colour, and over it, huge splots of different colour. So in them, their colour will come from both parents.

 

 

I think you are wrong: If you crossbreed a cream-colored horse with a black one, you will get a brown colt, the same which occur in humans.

 

If you want a black with white spots colt, the horse or/and the mare parents will have to be spotty. The difference is that we don’t have spotted human father or mother in order to get a spotty baby.

 

 

As far as I know, the only animal where you can get a spotty cub from two plain parents is the cat, as GDG has explained.

Edited April 8, 2009 by zule
problems with quotation

[Inquisitor]

I believe the skin colour solution was of Divine origin.

 

God did not want crossbreed humans to look like zebras. Thar would have been bad for the individuals in question. But more than that, it would have fuelled racism all over the globe, with humans of diff races not being capable of having normal children togeter.

 

Oooh, this topic is so locked now I mentioned God. It's like a red cloth to some so called open minded people here...

[iNow]

It's also against the rules of discussion, and has absolutely nothing whatsoever to do with science (unless perhaps you are studying mental illness, social grouping, or anthropology). Since the god concept is ill defined, non measurable, and based on conjecture... it has no place in a discussion about scientific study. That, on top of the fact that people are often hypersensitive to all criticisms of their faith, is why it's not allowed here at SFN.

[Moontanman]

I believe the skin colour solution was of Divine origin.

 

God did not want crossbreed humans to look like zebras. Thar would have been bad for the individuals in question. But more than that, it would have fuelled racism all over the globe, with humans of diff races not being capable of having normal children togeter.

 

Oooh, this topic is so locked now I mentioned God. It's like a red cloth to some so called open minded people here...

 

Do you have any evidence to support that contention?

[lucaspa]

I do not see one gene could set the tone, as here are a lot of different skin tones seen in mixed marriages.

 

What matters is the melanin content of the skin. Our skin "tone" is determined by the amount of two different types of melanin in the skin.

http://anthro.palomar.edu/adapt/adapt_4.htm

 

Melanin is made by special cells called "melanocytes" in the skin. Because the genes for each type of melanin content are expressed the same in every melanocyte, there is no "spottiness" the way you are using the term.

 

Also, I should think different races have a slightly different genes for skin colour, and therefore they could not just mix, so that dark+white gene would produce light brown as it would in a colour palette.

 

But it's not one gene, it's two: pheomelanin and eumelanin. Skin color depends on the proportion of these two melanins and on the number and size of the melanin granules in the skin. Remember, people do "tan" and change skin color by increasing the number and size of the melanin granules with stimulation of melanin synthesis by UV radiation (all this is in the website).

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I believe the skin colour solution was of Divine origin.

 

God did not want crossbreed humans to look like zebras.

 

Sorry, but the data denies that. Melanin content evolved to protect the breakdown of folic acid by UV radiation. If humans have too little folic acid, neural tube birth defects and lack of sperm result. If humans evolved like zebras, too much UV would get thru the "white" parts of the skin to break down folic acid. So the skin had to be black all over (except for palms of the hand and soles of the feet that do not get irradiated by the sun much). Lighter colored skin evolved as people migrated out of Africa into areas where there was less UV light. It turns out that UV is necessary to make vitamin D from cholesterol in the blood vessels in the skin. In northern latitudes, black skin (lots of melanin) blocked too much UV light and resulted in vitamin D deficiency -- rickets. So those individuals with less melanin content and more pheomelanin were selected. G Kirchwager, Black and white: the biology of skin color. Discover 22: 32-33, Feb. 2001.

 

For those people who believe in God, evolution is the secondary cause by which God created humans. "Secondary cause" is a theological term. You might want to look it up.

[Kyrisch]

I believe the skin colour solution was of Divine origin.

 

Good so far. Topic sentence, leading into explanation...

 

God

 

Which?

 

did not want crossbreed humans to look like zebras. Thar would have been bad for the individuals in question.

 

'Bad'? For some reason, I'm doubtful that adjective that might appear in any Biology texts written for non-elementary grades. If you're positing an explanation, then do so. "Bad" is no more a scientific word than "sort of," "tall," or "big" is.

 

But more than that, it would have fuelled racism all over the globe,

 

Hah. Ha-ha. Like that isn't the case now?! Really? If stopping racism was such a high priority, then your 'God' figure really sucks at achieving what it's set out for, doesn't it?

 

with humans of diff races not being capable of having normal children togeter.

 

Add 'normal' to my list of completely un-scientific words (i.e. meaningless words of varying shades that really gives no information).

 

Oooh, this topic is so locked now I mentioned God. It's like a red cloth to some so called open minded people here...

 

No. Fail. Epic, epoch, e-pooch phale. 'God' discussion is not allowed because whenever it comes up, posts like the above happen, which, as I have pointed out quite clearly, are not scientific. As this happens to be a science forum, they are not pertinent nor conducive to the cause of the Board and are thus locked.

 

Nice try though. Good day.

Edited April 16, 2009 by Kyrisch

[Mr Skeptic]

I know someone with freckles.

[lucaspa]

I know someone with freckles.

 

So do I. My father had them all over his body. If you read the website I posted, you find that freckles result from concentrations of granules of pheomelanin.