Interesting thought

Every species in our lineage tells us something about ourselves, because the hominoids (humans, apes and everything in between) are genetically extremely tight. We have had far less time to diverge than the members of many other animal families, like the equids (horses, zebras, donkeys) or canids (wolves, dogs, jackals). If it hadn’t been for the human ego, taxonomists would long ago have squeezed all hominoids into a single genus.

If that’s true then why aren’t we cross fertile (or are we?)

46 thoughts on “Interesting thought”

  1. To the extent to which the biological species concept is valid, it is the species level where fertilization can take place. Two species even in the same genus are not supposed to be able to cross-fertilize and produce viable, non-sterile offspring.

  2. Not sure it is true. Evolution seems to happen very quickly, with long stable periods between rapid spurts of genetic change.

    Humans seem to have evolved rapidly in the last few hundred thousand years, not sure that we are any longer ‘close’ relatives of the apes in comparison to the relatedness of equid or canids to each other.

    I’ve never heard of cross fertilisation between humans and apes, and a quick google reveals that apes have 24 chromosome pairs whereas we have 23, which would suggest there can be no interbreeding. Other bloggers may know more about this sort of thing than me, I look forward to many expert comments.

  3. On the speed of evolution – consider blue eyes, which are the norm across northern Europe but not the norm elsewhere. People have only been living in northern Europe for a few thousand years (afaik !), so the spread of blue eyes to become the dominant gene must have taken only a couple of hundred generations. If blue eyes are a side effect of fair skin/hair which are adaptations to low light (do we know that for sure?) – then we see genuine evolution happening in just several dozen generations.

    I spout here only amateur genetics, others may burn me down with actual learning and knowledge, no offence will be taken.

  4. People have only been living in northern Europe for a few thousand years (afaik !)

    There are relics in Scandinavia going back nearly 10,000 years – about 170 grandfathers in Pratchett-counting – double that, obviously, in generations.

  5. Aren’t blue eyes, fair hair and skin simply the absence of melanin, said substance being fairly unnecessary in the far north of Europe?

  6. Blue eyes are not dominant – the gene is recessive, and in Germany you can get to 51% of the population if you lump in green with blue. Blue alone is about 36%.

    It’s just there’s enough people around with the recessive gene

  7. The aptly named Mr Bonk is on the right lines. Different chromosome number makes viable offspring (or in fact any offspring) vanishingly unlikely, and it can also diverge extremely rapidly. In fact rapid chromosome number shifts are thought to be a potential driver of speciation where you don’t have geographical separation.

  8. I understood that the introduction of aids to humans was due to people attempting to experiment in this field.

    It seems without success.

  9. there’s quite a lot of evidence that homo sapiens and neanderthals interbred, despite fairly marked differences in things like cranial capacity. There’s a very obvious gag set up there.

  10. ‘I understood that the introduction of aids to humans was due to people attempting to experiment in this field.
    It seems without success.’

    Isn’t it actually thought to have come from bushmeat? Anyone attempting to shag a chimp would probably not enjoy it. They’re not docile or weak creatures.

  11. @abacab – “dominant” was an unfortunate choice of word of my part as you rightly point out that it has a specific meaning in genetics and the blue gene is not dominant. Please read “preponderant” for dominant.

  12. Interested/BiI:
    Necrophiliac hunters, shagging a freshly killed female chimp? Particularly if the tribe valued virginity and the young men were desperate. – James I would apparently slip his erection into a freshly killed stag, but then he was a Scot…

  13. I have blue eyes but was widely referred to as the “indiscretion in the Raj” in my university days for reasons not unrelated to my epidermal pigmentation.

  14. In terms of species definition, the separation is being able to produce offspring that can be fertile with another of the offspring.

    For instance, horse and a donkey can breed to produce a mule (or hinny). But a mule cannot breed with another mule to produce a mule (although they can—occasionally—produce offspring with a pure horse or donkey). One of the main reasons, as it happens (and sort off alluded to above), is because horses and donkeys have different numbers of chromosome pairs.

    But anyway, a genus is above species in the hierarchy. A horse is, for example, a species in the genus equid.

    DK

  15. Fair skin in the North has been explained by the shortage of vitamin D in the diet. Their cereals were poor in it. The skin can make vitamin D, but to make enough of it you need the sunlight to penetrate a mm or so. Hence fair skin.

    I should add that this is a breeding issue, maybe not an evolutionary issue. The fair skinned survive because the dark skinned don’t. Not so much the survival of the fittest but the elimination of the unfit, as any plant breeder will tell you.

    As a theory, the fair-skin is weak, in my view. Scandinavian diet would include a lot of fish, chock full of vitamin D. Cod liver oil, anyone? Also it’s easy to store. If you eat a polar bear’s liver you will overdose and maybe die.

  16. Nobody really knows why white skin evolved, nor blue eyes. As for breeding with our late cousins: not only Neanderthals, also Denisovans.

  17. So Much For Subtlety

    Tibetans are probably genetically adapted to life on the Tibetan plateau. All of which is odd because they and Europeans should not have been where they are to have had much chance of evolving separately.

    Which, again, suggests that it is possible different populations have different IQs for actual real genetic reasons. We have had time to evolve blue eyes. We have had time to evolve some other things too.

    Bloke in Germany – “Different chromosome number makes viable offspring (or in fact any offspring) vanishingly unlikely”

    Although Down’s Syndrome is caused by the replication of Chromosome 21. So they do have different chromosome numbers, sort of. And yet they are distressingly fertile.

  18. Umm, yeah, but no. Down’s is diploid (triploid? yes, triploid) on 21. That’s not the same at all as having a different number of chromosome pairs, which is what we’re saying about some equids and apes. And at least as far as I know, they’re less fertile (very much less so) than the general population. Although Wiki does indicate that might be opportunity rather than fertility itself.

  19. The best explanation of widespread blond hair, fair skin and blue eyes is probably kin selection. The aboriginal inhabitants of the boreal regions (the Lapps, the Eskimos…) have dark skin, and they were there before the blondies. They have survived rather well. It’s hard to see how a blondie could survive in hot, sunny regions, but it might have been a neutral mutation in polar climes. It seems not to have conferred an evolutionary advantage.

  20. DK,

    > In terms of species definition, the separation is being able to produce offspring that can be fertile with another of the offspring.

    I thought that too, but looked it up last time this discussion happened round here, and turns out that’s only a rough approximation. Apparently, “species” is not well defined, and there are various exceptions to any rule anyone comes up with.

    On the original topic: I agree. Humans are obviously the same genus as chimpanzees. There’s a lot less difference between us than between a gorilla and an orang-utan.

  21. “It’s hard to see how a blondie could survive in hot, sunny regions”

    Not only do they survive, they become much better at sport than those left in the drizzling north.

    Geneticists will be, or should be, glued to the Rugby World Cup .

  22. de Waal is posing an interesting question: how we define culture.
    If simple bereavement is a metric, then chimps and elephants have culture.
    If culture is defined as transmission of learning, then we are unique.
    If the cave includes grave goods, then perhaps we can conclude that a culture can be made by a creature with a brain the size of an orange.

  23. Johnny Bonk: “apes have 24 chromosome pairs whereas we have 23, which would suggest there can be no interbreeding”.

    Not so. Consider: at some point an ancestor of humans produced an egg, or sperm, with a chromosomal fusion: the chimpanzee-style chromosomes 12 and 13 became joined end to end to generate human chromosome 2. Now, this egg or sperm must have combined with a sperm, or egg, that had the original chromosome set, since the chance of the same fusion happening at the same time in the same place in two individuals of opposite sexes is vanishingly small. But the resulting offspring, wit one human chromosome 2, was obviously viable, and its subsequent mating with other individuals that did not have the reduced chromosome number were obviously fertile, otherwise it would have had no descendants. See?

  24. Though apparently Northern Europeans have a small percentage of Neantherthal DNA. The BBC did a reconstruction of a Neanderthal man from archaeological sources. Bore a striking resemblance to a Highland Scot – large, stocky, fair skin, red hair. All he needed was the plaid and the claymore. Hmm.

  25. BIF,

    > If culture is defined as transmission of learning, then we are unique.

    No, transmission of learning is common in primates, and has also been observed in dolphins. There’s even one family of cheetahs that has started hunting in packs — if they raise another generation doing the same, they’ll have done it too.

    In primates, the rise of culture is a side-effect of climbing trees. Babies cling onto their mothers’ backs in order not to fall, and therefore see everything their mothers do. Amazingly, breast-feeding — which one would certainly think was instinctive — is learned behaviour in chimpanzees and other primates: if a female chimp is taken away from her mother before her mother has another child, she doesn’t see her mother breast-feed, and will not know how to do it when she has her own offspring.

  26. You need to remember most of this stuff (especially skin colour, IQ), is multifactorial. It ain’t “black and white” [sic] like blood group and eye colour. It’s just that the population frequency of “white tendency” alleles is far higher in Europeans than Africans, and has been shifted that way by some form of selection acting on the African populations that settled Europe back in the day.

    In other words, you could probably breed Europeans with sub-Saharan style black skin if you cared to. Just as you could take pretty much any population on earth and breed darker or lighter, cleverer or thicker, whatever takes your fancy. For obvious ethical reasons we don’t do this with humans, but you could. The only starting material you would need is a sufficiently large starting population to make sure you have that diversity of alleles from which you can produce a Generation n+x with the characteristics you are selecting for.

  27. It will be interesting if on subsequent expeditions they find grave goods. So far, it looks like merely dignified disposal.

  28. I should add that this is a breeding issue, maybe not an evolutionary issue.
    Selective breeding IS evolution.
    If culture is defined as transmission of learning, then we are unique.
    Bollocks. Watch e.g. birds teaching their offspring to fish.

  29. @JeremyT, selective breeding isn’t quite evolution. However “pure-blooded” you make mastiffs or Staffies you generally don’t completely eliminate the variability which would allow you to go back at least partway in the direction from which you came, or ever totally eliminate the ability to interbreed with other varieties.

    Human skin colour is easier. Imagine there are 50 genes determining the degree of melanification, each of which has two alleles, either “black” or” white”. No dominance, purely additive effects. In your totally black population the average person actually has 45 of those genes set to “black” and 5 to white. Different people however will have “white” at different loci, so throughout the population you have enough genetic diversity to breed white humans (with, for the sake of argument, on average 45 genes set to white and 5 to black) within just a few generations. And you can go back from there, back and forth, as much as you want, if sufficient selective pressure is added, and you haven’t bottlenecked the population such that some of your 50 genes lose all the “black” or “white” alleles at the population level.

  30. re: ‘Polar Bear livers’. That’s vitamin ‘A’ not ‘D’. There was a ‘New Tricks’ episode where Richard Briers tried to poison James Bolam with a broth made from the livers of old dogs. So, that makes it a fact! The vitamin A accumulates in some carnovores’ livers over time. Search for hypervitaminosis A.

  31. BiG. ‘Selective’ doesn’t (only) mean a conscious programme conducted by humans, but the tendency of people with advantageous mutations to produce more descendants. Here their partners may do the selecting by opting for healthier mates. In some cultures they may also have multiple mates.
    Thus e.g the allele granting lactose intolerance (which in cattle herding groups confers higher nutrition levels) gives its owners a better chance of surviving, mating and propagating the allele.

Leave a Reply

Your email address will not be published. Required fields are marked *