Help re: evolution

[Mystman]

A lot of the dinosaurs became bipeds. It clearly worked for them. (alligatoars are descended from bipeds... kind of funny, went back to four legs and went back to the water)

Wait what?

 

[sfs]

Could you briefly describe the evidence?

Positive selection for a new trait leaves characteristic signatures in the distribution of genetic diversity around the selected locus. This is because, as the trait spreads in the population, individuals with the beneficial allele will also share a segment of DNA around the allele, since they are inherited together. The signatures include things like reduced diversity (because most of the population has the same DNA in that region), large differences in frequency between populations (if the selection is only occurring in one of the populations), and a long, unbroken haplotype at high frequency (i.e., if you have a particular allele in that region, you will probably also have a set of nearby alleles -- because they are all being inherited together).

Searches in the human genome for long haplotypes have produced the strongest evidence for positive selection in humans, although other signatures have also been used. If you go through the lists of candidate regions, you will find something like a dozen genes associated with lighter pigmentation in Europeans and Asians. The list of genes is different for the two continents, although there is some overlap between them. The only other target of selection with anything like that many likely instances is resistance to malaria, so skin color does seem to have been under strong selection throughout the northern latitudes.

 

[Hespera]

Wait what?

That is my understanding, taking into account that I may be disremembering what I read. They are archosaurs.. and they definitely went back to the water.

 

[peadar1987]

The advantage of light skin / hair / blue eyes is related to the low light and vit D requirements for northern people.

As for the heavy skull, well, if that was the deal then we'd probably have bipedal rhinos and triceratops!

A lot of the dinosaurs became bipeds. It clearly worked for them. (alligatoars are descended from bipeds... kind of funny, went back to four legs and went back to the water)

Any notion why dinosaurs went bipedal, would it be in any way comparable to why people did?

Well I got the references from National Geographic, one of the issues last year I think. Can't remember exactly when, so I can't give you a reference unfotunately. However, you seem to know your science, judging by your other posts, so I'm happy to take your word for it.

I should have said that relatively speaking our skull is heavier. Rhinos etc. probably have stronger back muscles anyway, helping restrain the bending moment from the head. I'm no biologist though, I'm really just saying what I've read elsewhere.

 

[juvenissun]

Positive selection for a new trait leaves characteristic signatures in the distribution of genetic diversity around the selected locus. This is because, as the trait spreads in the population, individuals with the beneficial allele will also share a segment of DNA around the allele, since they are inherited together. The signatures include things like reduced diversity (because most of the population has the same DNA in that region), large differences in frequency between populations (if the selection is only occurring in one of the populations), and a long, unbroken haplotype at high frequency (i.e., if you have a particular allele in that region, you will probably also have a set of nearby alleles -- because they are all being inherited together).

Searches in the human genome for long haplotypes have produced the strongest evidence for positive selection in humans, although other signatures have also been used. If you go through the lists of candidate regions, you will find something like a dozen genes associated with lighter pigmentation in Europeans and Asians. The list of genes is different for the two continents, although there is some overlap between them. The only other target of selection with anything like that many likely instances is resistance to malaria, so skin color does seem to have been under strong selection throughout the northern latitudes.

So the evidence illustrated that people over geographic regions are characterized by special gene characters. To make it more simple, gene differences echo racial differences. Is it right? Does the evidence say anything more than that?

 

[sfs]

So the evidence illustrated that people over geographic regions are characterized by special gene characters. To make it more simple, gene differences echo racial differences. Is it right? Does the evidence say anything more than that?

The important point is not that people in different geographic regions have different genetic traits, but that those traits were selected for. That is, people in particular regions are characterized by special genetic variants that have behaved differently than variants in the rest of the genome. For example, if you look at genes throughout the genome, you will find very few that have large differences in allele frequency between different populations. Around a few genes, however, you will find chunks of DNA where frequency differences are larger than normal for a whole string of variants, which is a sign that selection has been operating there. Probably only one of those variants actually causes any kind of phenotypic difference between the populations, but the rest have changed in frequency along with it.

Some of these selected differences distinguish races, as they are conventionally defined (which helps explain why the conventional definitions exist). Some do not. Lactose tolerance, for example, occurs in humans because of positive selection. It can be found in northern Europeans and east Africans, but not (usually) in southern Europeans or west Africans.

 

[sfs]

The advantage of light skin / hair / blue eyes is related to the low light and vit D requirements for northern people.

That's a plausible hypothesis, and may very well be correct, but no one has demonstrated that the difference in vitamin D production would provide a strong selective advantage. Reconstructing the selective agent can be difficult or impossible in some cases of historical selection.

 

[Hespera]

sfs sez

Originally Posted by Hespera

The advantage of light skin / hair / blue eyes is related to the low light and vit D requirements for northern people.
​

That's a plausible hypothesis, and may very well be correct, but no one has demonstrated that the difference in vitamin D production would provide a strong selective advantage. Reconstructing the selective agent can be difficult or impossible in some cases of historical selection.QUOTE///



H sez...

I dont think I can prove it, about Vit D, but, we do find a skin pigment gradient from north to south, even allowing for all the mobility of people in the last couple three hundred years especially. I dont think red heads would have done well trying to live as bush men, loin cloth in the desert and all..

Also we note the eskimo who are perhaps relative newcomers to the far north, but definitely not blue eyed blondes. so its far from exact. But I think there is something to it.

 

[Gracchus]

Also we note the eskimo who are perhaps relative newcomers to the far north, but definitely not blue eyed blondes. so its far from exact. But I think there is something to it.

Remember that for half the year the Inuit (or eskimo) have very long days, and during the summer the sun may not set at all. Lots of sunlight and a highly reflective environment would favor darker irises. This would usually entail a darker skin. Even so, the Inuit used to make "sunglasses", strips of bone or horn worn over the eyes with only a narrow slit to see through.

The Laps, native to northern Scandinavia are also a dark people. Light skin would be advantageous only in the temperate zones.

 

[juvenissun]

The important point is not that people in different geographic regions have different genetic traits, but that those traits were selected for. That is, people in particular regions are characterized by special genetic variants that have behaved differently than variants in the rest of the genome. For example, if you look at genes throughout the genome, you will find very few that have large differences in allele frequency between different populations. Around a few genes, however, you will find chunks of DNA where frequency differences are larger than normal for a whole string of variants, which is a sign that selection has been operating there. Probably only one of those variants actually causes any kind of phenotypic difference between the populations, but the rest have changed in frequency along with it.

Some of these selected differences distinguish races, as they are conventionally defined (which helps explain why the conventional definitions exist). Some do not. Lactose tolerance, for example, occurs in humans because of positive selection. It can be found in northern Europeans and east Africans, but not (usually) in southern Europeans or west Africans.

Thank you very much. I will have to study what you said. Hope you would still see my next question when I come back to this.

 

[Gracchus]

Consider also that there is more genetic diversity within Africa than without, because Asians and Europeans are descended from populations of one small area in eastern Africa.

Consider the bushman, the Bantu, the Nilotic peoples and the pygmies.

 

[Wiccan_Child]

She's one of the things that sparked off my question actually! Though I forgot all of her details. But I'm confused about why you say her peers didn't fail to breed. Surely none of her female peers have descendents alive today?

Oh, most definitely. The son of one of these women would be unable to spread her mitochondrial DNA (since it comes soley from the mother), but the lineage itself would remain.

So, if I had kids, they would never have the mtDNA of my mother. So although her mitochondrial DNA can never be spread through me, the rest of her DNA can, so she could very well have descendants with foreign mtDNA.

Mitochondrial Eve, then, is the woman from whom all mitochondrial DNA is derived. She's the woman who just so happened to luck out.

Also, how was the ~170,000 worked out? Did they take into account the fact that mitoch DNA mutate much more quickly than nuclear DNA?

Yes. Using population dynamics, one arrives at a figure of 140,000. Using genetics to trace back mitochondrial lineage, we get a figure of ~170,000.

 

[sfs]

Thank you very much. I will have to study what you said. Hope you would still see my next question when I come back to this.

If you want to read more about how positive selection is detected, you could look at this. It's from 2006 and therefore predates most of the results on skin pigmentation (but look at the part about the gene SLC24A5), but it has more information about genetic signatures of selection. It's supposed to be readable by a broad audience.

 

[juvenissun]

If you want to read more about how positive selection is detected, you could look at this. It's from 2006 and therefore predates most of the results on skin pigmentation (but look at the part about the gene SLC24A5), but it has more information about genetic signatures of selection. It's supposed to be readable by a broad audience.

Thanks.

 

[mpok1519]

I attended a seminar last semester regarding laughter in chimps in humans. It was very interesting and he shared a few interesting observations.
1. We can't make ourselves laugh, but other people laughing does make us laugh
2. Males are funnier. They make females laugh at a higher rate, and is one quality that many women listed as desirable in his pole. Also males tend to laugh less than females.
3. We are the only species that "laughs out loud."

Chimpanzees also have the ability to laugh, however they can not do it "out loud" since they do not have a well developed larynx (voice box). He showed a video of someone tickling a young chimp and it was making a sound like a panting dog, but it was more exaggerated.

We are also the only biped species. The ability to walk upright has reduced the pressure on our diaphragm. As a result we are only only species that does not breath in unison with our running stride. This reduced pressure has allowed for the selection to be more permissive on our voice box, because our diaphragm is no longer forced to breath at a certain rate when we run. As a result, humans with more developed voice boxes we able to be selected for.

So I make the assertion that our ancestors probably learned to walk upright first, and then they developed the ability to communicate with speech.

The adaptation of the pronounced chin is also a reason why humans are able to talk; the muscle attachments shifted in a way that allowed for more versatility to move the mouth, making complex speech patterns avaliable. somewhere around 120,000 years ago, people began to form language.

 

[mpok1519]

So the evidence illustrated that people over geographic regions are characterized by special gene characters. To make it more simple, gene differences echo racial differences. Is it right? Does the evidence say anything more than that?

did you know that there is more variation within a race than there is without?

Me (white guy) actually has more shared DNA with a person from Ghana than any white guy living in Nebraska. There is more genetic variation within a race than there is without; scientists actually state that there is no real reason why race should even be apart of any real biological classification. Race is a cultural construct which actually many think should be uncreated.

 

[plindboe]

Aha. I get it. Mitochondrial Eve's female peers may have had sons, who didn't pass on their mitochondrial DNA...

Hence she wasn't even a real bottleneck Arrrgh!! Too many new concepts to cope with!

Indeed. It may sound confusing at first, but it might make it easier to absorb when you see it as a drawing.

Peter

 

[juvenissun]

did you know that there is more variation within a race than there is without?

Me (white guy) actually has more shared DNA with a person from Ghana than any white guy living in Nebraska. There is more genetic variation within a race than there is without; scientists actually state that there is no real reason why race should even be apart of any real biological classification. Race is a cultural construct which actually many think should be uncreated.

What you said sounds interesting. But I do not understand.

 

[mpok1519]

What you said sounds interesting. But I do not understand.

what do you mean? How this applies to evolution?

 

[R3quiem]

Can you provide evidence (such as a scientific paper or something) that states that the genetic differences in a single race are more than the genetic differences between races?

My immediate response to such a claim is doubt, but if you can provide a link or something from an established source, I'd like to read it.

What you may be thinking of is the fact that various races across the world are more alike than some humans of African descent, because all races of the world outside of Africa arose from a specific area within Africa. That, however, does not imply that all people within a race are less alike than with people of a different race. I hear that the populations within some east-Asian countries are the most homogeneous on the planet.