The fact of that matter is that there wasn't free intermingling between modern humans and Neanderthals. That's why we are able to tell modern human and Neanderthal DNA apart.
Well, no, perhaps there wasn't a huge amount of intermingling, but there was some.
There was as much intermingling as we would expect from separate species who occasionally produce a hybrid.
There is also growing evidence that human/Neanderthal hybrids may have suffered from infertility. It is still way to early to call this conclusive, but it is an interesting bit of information.
"Some of the genes, meanwhile, appear to have led to fertility problems. For instance, Sankararaman found that the X chromosome is almost devoid of Neanderthal DNA. This suggests that most Neanderthal DNA that wound up on the X chromosome made the bearer less fertile – a common occurrence when related but distinct species interbreed – and so it quickly disappeared from the human gene pool. “Neanderthal alleles were swept away,” says Sankararaman."
Neanderthal-human sex bred light skins and infertility
In northern climes they are more likely to suffer the effects of vitamin D deficiency. This could lead to soft bones and improper skeletal development. This has two implications: firstly they may be more prone to accidental death before having an opportunity to reproduce; secondly, the impact on their physical and mental wellbeing may render then less attractive as a mate.But why would darker skinned people be at a disadvantage when it comes to reproduction?
I have no idea, but the option is available, which was not the case when the ancestors of the Swedes, for example, were losing much of their melanin and developing long noses to warm the cold air before it hit their lungs.Also, do present-day Africans living in the west (countries such as Britain or ones where there is a lot less sun) take vitamin supplements generally speaking?
Correct, but I am not sure in what way it is relevant.Obviously when a black person marries a white person, then their children tend to have paler skin. However, I have read that occasionally someone has given birth to a black person totally unexpectedly, as there was some (perhaps unbeknownst to them) black ancestry in their family.
In northern climes they are more likely to suffer the effects of vitamin D deficiency. This could lead to soft bones and improper skeletal development. This has two implications: firstly they may be more prone to accidental death before having an opportunity to reproduce; secondly, the impact on their physical and mental wellbeing may render then less attractive as a mate.
I have no idea, but the option is available, which was not the case when the ancestors of the Swedes, for example, were losing much of their melanin and developing long noses to warm the cold air before it hit their lungs.
Correct, but I am not sure in what way it is relevant.
I assume that modern day pygmies and a masai could have children? Or maybe not?
Supposing for example, half the people in a particular population had blond hair and half had black hair, but for some reason for decades or centuries or millennia, no-one was born with black hair...would it be possible for someone to suddenly be born with black hair, and everyone would be completely taken by surprise?
Masai aren't particularly tall. You're probably thinking of Dinka.
If no one had been born for centuries without blond hair this would indicate that the allele is gone from the population. If the allele is recessive and still present in the population then it is highly probable that two people with the recessive allele would have children with blond hair. If both parents are heterozygous (i.e. have the black and blond allele) then 25% of their children will be homozygous (two of the same allele) for the blond allele, on average. It goes back to the old Punnett squares that we were taught in grade school:
If the capital Y is dominant black hair and the little y is recessive blonde hair, then 3 in 4 children will have black hair and 1 in 4 will have blond hair. Also, 2 out of 4 children will be carriers of the blond allele.
Thanks, that's interesting (Afraid I don't know anything about Punnett squares,never came across them either in primary or secondary school..not called that anyway LOL..perhaps they call them something else in the UK). I also only did any kind of science until age just about 14 and was never really taught anything about evolution, genetics or anything, hence my very unknowledgeable questions.
I know I could get a book out of the library or research some of this stuff on the web. However, then one ends up either reading TOO simplistic stuff (like for 5 year olds or something) or it gets too complicated and one ends up having to find out what every other technical word means. Having a back and forth question and answer thing like this helps me wrap my head around stuff a bit better. Thanks
Well, both yes and no. Random mutation could always have a chance of reintroducing a trait (hence why certain deadly conditions that are carried by dominant genes and kill before reproductive age can persist), though it will be unlikely to ever become as prevalent as it once was through natural selection if all the people that expressed the trait suddenly died.I'm trying to understand how these things work...it only may be relevant in that if there is gradual change in people according to their environment, eventually certain traits may be completely eliminated?
Technically, yes, and you are thinking of recessive genes. It would be unusual for a freely breeding population to need that much time, even with the long human generations, but it could happen, hypothetically.As long as there is a particular gene still lingering about so to speak (is it recessive genes I'm thinking about, rather than dominant?), could that rematerialise even thousands of years after it was more common?
Well, black hair is the dominant gene of the two, but if you applied this situation as the people with blond hair dying out, it would still be possible for a blond haired child to be born, even after generations of it not happening. It'd just be unlikely to take that long, unless the majority of black haired carriers of the blond hair genes also died. Furthermore, thanks to random mutation, it would be possible for a blond haired person to be born even if all people with the genes for that hair color died out some time before, it certainly wouldn't be guaranteed, though.Supposing for example, half the people in a particular population had blond hair and half had black hair, but for some reason for decades or centuries or millennia, no-one was born with black hair...would it be possible for someone to suddenly be born with black hair, and everyone would be completely taken by surprise? Could that gene remain dormant, so to speak, for that long?
The only genes that almost never change are the hox genes, which control how developing embryos grow and develop their bodies in the womb or egg. This is because most changes to these genes would result in nonviable embryos that would die. Thanks to that, they are very much retained and similar even between species that aren't closely related, such as humans and sharks.Sorry, not explaining my question well, but am trying to understand the relationship between what is inherently present in genetic material and what might actually gradually change (mutate?) or be lost, but without other human contact from another population, so that certain traits would become more or less 'fixed'..the new 'normal' if you like.
Well, both yes and no. Random mutation could always have a chance of reintroducing a trait (hence why certain deadly conditions that are carried by dominant genes and kill before reproductive age can persist), though it will be unlikely to ever become as prevalent as it once was through natural selection if all the people that expressed the trait suddenly died.
Whenever a population is brought near extinction, genetic variety suffers, and certain genes are lost to the population. However, in natural selection, there is no intent, so the genes lost could be benign or harmful or neutral, just by chance of what parts of the population die. Over time, populations can and do recover from these genetic bottlenecks if they survive long enough, and genetic variation will increase back to what it used to be. This, however, takes many, many generations. Cheetahs went through an extreme genetic bottleneck about 10,000 years ago, such that all modern cheetahs are descended from fewer than a dozen survivors. To this day, all cheetahs are compatible organ donors with each other, because they lack genetic diversity to such an extent.
Technically, yes, and you are thinking of recessive genes. It would be unusual for a freely breeding population to need that much time, even with the long human generations, but it could happen, hypothetically.
Well, black hair is the dominant gene of the two, but if you applied this situation as the people with blond hair dying out, it would still be possible for a blond haired child to be born, even after generations of it not happening. It'd just be unlikely to take that long, unless the majority of black haired carriers of the blond hair genes also died. Furthermore, thanks to random mutation, it would be possible for a blond haired person to be born even if all people with the genes for that hair color died out some time before, it certainly wouldn't be guaranteed, though.
The only genes that almost never change are the hox genes, which control how developing embryos grow and develop their bodies in the womb or egg. This is because most changes to these genes would result in nonviable embryos that would die. Thanks to that, they are very much retained and similar even between species that aren't closely related, such as humans and sharks.
However, no gene is immutable, for even a mutation in a hox gene can be neutral or benign, it's just relatively uncommon. How likely a gene is to experience a mutation has much more to do with it's position on the DNA strand than it's role, with genes located more towards the center being more protected and mutating less than those more towards the ends. No trait is fixed. Nothing is inherent either, not even the nucleotide bases of DNA itself, as there are a number of conditions associated with one of the usual 4 bases being replaced by a nucleotide not usually associated with DNA, such as uracil, which is a typical component of RNA.
Furthermore, so many codons (units of base pairs that code for an amino acid) are redundant and do the same thing that I could artificially cause mutations in more than a tenth of the genes of a developing human embryo and still have said embryo grow up to appear as a normal human, and even be capable of reproduction. Most mutations do pretty much nothing, because most occur on parts of DNA that aren't even genes or are redundant changes to genes.
Thanks very much for that info
Sort of related to all that, how does one decide what is 'abnormal' and maybe not desirable, that is, something has gone wrong at some stage of development.
Oh, and I've just remembered, you know these cases of children ending up living all by themselves in jungles and things? I saw a documentary a long while back where a small child had ended up living in the forest or jungle (perhaps in India?). The monkeys I think helped look after him. Anyhow, what was interesting was, that he had actually grown longer hair all over his body. I wondered why that would happen. Would it happen to anyone living long enough in those conditions? That doesn't appear to happen to small tribes that live in fores/jungle situations.
The ultimate arbiter of what is and isn't desirable is how successful your descendants are at making more descendants. It all comes down to good ol' natural selection. What helps your grandchildren and descendants be successful is what gets passed on.
However, the opposite is not necessarily true. Just because something is passed on does not mean that it is inherently desirable from a fitness standpoint. This is actually part of a very entertaining and interesting metadebate in biology right now called the Adaptionist Bias. Some biologists have fallen into the trap of assuming all physical features in any organism must increase fitness because they have been passed on. The problem is that neutral changes can also be passed on, meaning that just because a feature is kept does not necessarily mean it is helpful.
I'm not aware of that example, sorry to say.
Yup, we are playing some part in preserving people and allowing them to have kids when, without our intervention, they would die long before that point. Were we to actively, say, encourage these people to have more kids, that could be considered artificial selection, but since we are just changing the environment to allow it, we're just lessening the natural selection pressures on our species as a whole.Hm, yes. But of course, nowadays with modern technology, medicines, blood transfusions, transplants etc, people can still be successful at reproducing and perhaps passing on certain undesirable things, perhaps through many generations. And those with certain genetic disabilities or flaws, for want of a better word, can survive a lot longer and lead far more fulfilling and quality lives than they could maybe even a century ago. So perhaps human intervention can play a part. (But then, that wouldn't be natural selection or adaptation of course, rather that humans have the capability of overcoming or curing many things).
A valid question with no concise answer, unfortunately. Is it moral to change the genetics of a developing infant to prevent them from inheriting, say, Huntington's disease? Is it immoral not to do it? Will this impact the preservation of our species in the case of pandemics? There's no universally accepted answer to those questions, and it is unlikely that there will ever be one.Of course, that is actually also a scary thing, what scientists are now starting to be able to do with genetic engineering. How far should it be taken?
The idea that any given "race" of humans is universally superior to any other is garbage, especially any European ones, which have some of the lowest genetic diversity. Also, there are laws in place in many countries that prevent discrimination on the basis of genes, so, there are some protections that keep possible future practices in mind.Just as well they weren't quite so advanced a few decades ago...Hitler (or his henchmen) would have had a field day getting his scientists to create the perfect Aryan race with blue eyes and blond hair, and eliminating in one way or another anyone else he thought substandard or subhuman.
Hm, yes. But of course, nowadays with modern technology, medicines, blood transfusions, transplants etc, people can still be successful at reproducing and perhaps passing on certain undesirable things, perhaps through many generations. And those with certain genetic disabilities or flaws, for want of a better word, can survive a lot longer and lead far more fulfilling and quality lives than they could maybe even a century ago. So perhaps human intervention can play a part. (But then, that wouldn't be natural selection or adaptation of course, rather that humans have the capability of overcoming or curing many things).
Of course, that is actually also a scary thing, what scientists are now starting to be able to do with genetic engineering. How far should it be taken? Just as well they weren't quite so advanced a few decades ago...Hitler (or his henchmen) would have had a field day getting his scientists to create the perfect Aryan race with blue eyes and blond hair, and eliminating in one way or another anyone else he thought substandard or subhuman.
I tried to find that instance of the feral child on the web, but couldn't find the specific one I was looking for...but no matter. Can't even remember what channel the documentary was on.
Yup, we are playing some part in preserving people and allowing them to have kids when, without our intervention, they would die long before that point. Were we to actively, say, encourage these people to have more kids, that could be considered artificial selection, but since we are just changing the environment to allow it, we're just lessening the natural selection pressures on our species as a whole.
A valid question with no concise answer, unfortunately. Is it moral to change the genetics of a developing infant to prevent them from inheriting, say, Huntington's disease? Is it immoral not to do it? Will this impact the preservation of our species in the case of pandemics? There's no universally accepted answer to those questions, and it is unlikely that there will ever be one.
You might think that, from a practical standpoint, it should be obvious that we should actively prevent these diseases as much as we can, but it isn't that simple. Doing so reduces genetic diversity; something we depend on so that we don't all die out from one disease. Certain negative conditions, such as Sickle Cell Anemia, have benefits to the carriers of the gene that don't suffer the symptoms; in this case, an increased resistance to malaria. So, actively removing all genetic diseases from our species has risks.
Sorry, Haven't been able to figure out how to do the multi-quote thing, so have replied in this font.
That is interesting about the malaria resistance. Of course, I suppose if they could somehow stop mosquitos infecting people, then perhaps it would be OK to eradicate sickle cell anemia...but I can see that it must be a very difficult balancing act to do the right thing. It would seem that whatever humans do to improve things (not just disease prevention, but other things), we unwittingly introduce other problems that need resolving.
The idea that any given "race" of humans is universally superior to any other is garbage, especially any European ones, which have some of the lowest genetic diversity. Also, there are laws in place in many countries that prevent discrimination on the basis of genes, so, there are some protections that keep possible future practices in mind.
Oh yes, I quite agree, I certainly wasn't advocating those ideas!! Heaven forbid! But let's just hope that countries continue to scrutinise scientific advances and make sure laws are passed to prevent any abuses or doing anything that might lead to untold damage.
The difference between natural and artificial is a metaphysical or philosophical one, so I won't delve too deeply into that one.
What I can say is that mutations can compensate for one another. In our case, mutations conferring intelligence can lessen the impact that other mutations we have. Ultimately, fitness is determined by how well an allele is spread through a population, despite our aesthetic judgments.
We always need to be careful of the naturalistic fallacy. Just because something is natural does not necessarily mean it is morally good. It is natural for bacteria to infect human beings, but we happen to think it is morally good to treat that infection and get rid of the naturally occurring infection.
On top of that, nowhere in the theory of evolution does it state that we should kill any less fit individuals. No scientific theory tells us what we should do, they can only tell us what the consequences of our actions will be.
The thing about feral children that always fascinated me was the development of their cognitive function. Children who did not grow up around other human beings and experience using language and social skills at a young age often lacked certain cognitive abilities. They couldn't use language at an older age, or solve complex puzzles. Being human and being part of a human society is actually a requirement for our brain to develop properly. Pretty interesting stuff.
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