Advertisement
If you have a new account but are having problems posting or verifying your account, please email us on hello@boards.ie for help. Thanks :)
Hello all! Please ensure that you are posting a new thread or question in the appropriate forum. The Feedback forum is overwhelmed with questions that are having to be moved elsewhere. If you need help to verify your account contact hello@boards.ie

Human Evolution

Options
  • 26-04-2008 2:08pm
    #1
    Closed Accounts Posts: 1,553 ✭✭✭


    I am reading Jared Diamonds 'Guns, Germs and Steel' at the moment and he is referring to the debate about the path of human evolution. At the time of writing he says that there were two opposing debates. An excerpt from the book:

    '...skulls of humans living in China and Indonesia hundreds of thousands of years ago are considered by some physical anthropologists to exhibit features still found in modern Chinese and Aboriginal Australians, respectively. If true, that finding would suggest parallel evolution and multiregiional origins of modern humans, rather than origins in a single Garden of Eden. The issue remains unresolved.'

    The emphasis added was mine, and he isn't referring to the 'actual' Garden of Eden, merely a symbolic metaphor.

    Has the above issue been resolved?


Comments

  • Moderators, Science, Health & Environment Moderators, Society & Culture Moderators Posts: 60,153 Mod ✭✭✭✭Wibbs


    Fascinating stuff human evolution. Hot potato too. I reckon we've only begun to scratch the surface.

    The out of Africa theory has a lot of support from the genetic evidence. We're all very closely related as a species. Among the lowest diversity of any primate. Africans have the most diversity which suggests the origin of modern humans started there.

    The problem comes with the hard fossil evidence as you point out. Morphology in modern human populations follows archaic humans in those areas which suggests evolution from those archaic humans. Teeth, skulls and other bones seem to show a progression in those populations. The other problem is that replacement by modern africans would have to be complete for the out of africa theory to hold. Possible though as there were genetic bottlenecks that sggest the human population dropped very close to extinction in the past due to environmental pressures.

    Tool technology is another one. Hand axes were a widespread technology in africa, yet they don't show up in asia until much later, well after the suggested takeover point by moderns out of africa. Humans always bring their technology with them, so that's a weird one. Makes no sense.

    The timing is a problem too. Both the suggested time for this replacement and the speed of same. The americas are an example. The accepted theory, sometimes vigourously defended is that the clovis culture represents the first americans. Problem being that there are very intriguing sites in the americas that humans were around from a much older time. Before the later dates for out of africa.

    http://www.sciencedaily.com/releases/2006/02/060209184558.htm Interesting link

    Personally I favour a more complex theory, than simple replacement. I reckon the dna evidence is only one part of the puzzle so I would be an out of africa person with back and forward mutliregional hanky panky going on.

    Me not being up on genetics. As a slight aside, but pertinent enough, I wonder could the more learned put me right here? It's about the diversity/age of population part of the out of africa theory. Africans have the most diversity so that's why they're an older population is the theory. I would have thought in an older population inter breeding between members of that population would reduce variation over time, not increase it. Naturally isolation would keep diversity high between certain populations, but again over time would the genes not head towards a more homogenous state?

    If we look at the modern day, air travel and the smaller world is likely to increase marrige between different populations so in the future would we not all become more the same over time, with variations dying out like red hair and blue eyes as examples? Should not the humans with the most variation be the newest as they haven't had time to go to the "average" so to speak?

    I can kinda see why the accepted theory holds, but I was just looking for better counsel.

    I'm probably not explaining myself well here. Apologies.

    Rejoice in the awareness of feeling stupid, for that’s how you end up learning new things. If you’re not aware you’re stupid, you probably are.



  • Closed Accounts Posts: 1,553 ✭✭✭Ekancone


    Wibbs wrote: »
    Me not being up on genetics. As a slight aside, but pertinent enough, I wonder could the more learned put me right here? It's about the diversity/age of population part of the out of africa theory. Africans have the most diversity so that's why they're an older population is the theory. I would have thought in an older population inter breeding between members of that population would reduce variation over time, not increase it. Naturally isolation would keep diversity high between certain populations, but again over time would the genes not head towards a more homogenous state?

    Im not a geneticist either, but i reckon that such a scenario would lead to homogeneity of active genes, but would greatly increase the level on redundant genes or DNA, which is why the gene pool would be more diverse. That's only my intuition though.


  • Moderators, Science, Health & Environment Moderators, Society & Culture Moderators Posts: 60,153 Mod ✭✭✭✭Wibbs


    Got ya.

    Another interesting blip for the out of Africa theory is Mungo Man http://www.abc.net.au/science/slab/mungoman/default.htm

    My take is that man evolved in africa to the point of homo erectus. These guys leave africa and spread across europe and asia. In those places they keep evolving into local populations of more advanced erectus. Neandertal being the obvious one. Indeed early neandertals are less gracile and less like us than later ones. They start to look similar to us, even before we appear to show up. Meanwhile back at the ranch in good oul africa, where erectus is also evolving it gets to archaic versions of us(wider eye spacing higher skulls, more robust etc) at around the 120,000 yrs ago mark. These boyos also reckon, "hey joe that europe place looks good for a laugh" and come over and either slightly out compete and/or bump uglies with the locals*. They do the same in Asia and beyond. Where a bottleneck springs up due to a natural disaster 30 odd thousand years ago, this reduces the apparent diversity to where we see it today.


    *Out competition could be based on something as simple as larger networks beyond the tribe. Neandertal sites throw up tools and other stuff that's almost always from the local area. In "our" sites stuff comes from much farther afield. Seashell jewelry 100's of miles away from the sea. Flints where no fint exists in the area. Stuff like that. Something as simple as that is a hell of an advantage as when the shít hits the fan, there's more options for support. Neandertals seem to not have that and are isolated. They get increasingly so when we come along. At the crossover point they do find tools and jewelry from neandertal sites that have been made by us. Which suggests trade. Neandertals also become less robust. That could be just due to their own evolutionary path or may be evidence of hanky panky during these trades. Another question for the genetic experts. If this interbreeding was say more likely neandertal men with sapien women due to cultural reasons, would that show up in the mitochondrial dna of us, given the mtdna is only passed on the ma's side IIRC? so you could have admixture of dna, but the mtdna would look like there was none. The reverse situation with neandertal women and sapient men would surely throw a different slant on the results.

    Throw our abstract culture into the mix and our advantage would be complete.

    Poignantly they also have found some evidence of neandertals copying our jewelry. Necklaces of animal teeth in particular. We however drill the teeth for suspension, they tie them on.

    Rejoice in the awareness of feeling stupid, for that’s how you end up learning new things. If you’re not aware you’re stupid, you probably are.



  • Closed Accounts Posts: 923 ✭✭✭Chunky Monkey


    Not exactly related but Desmond Morris has this theory that the pattern of hair on our backs shows we used to live in water. I've never heard that before. Has anyone else?


  • Registered Users Posts: 4,381 ✭✭✭oblivious


    daithifleming , Wibbs a very good read is bryan sykes seven daughters of eve

    Bryan sykes developed the fist assay to extract DNA from ancient bones and mitochondrial DNA profiling.

    mitochondrial DNA showed we all had a common ancestry around 150,000, strongly suggesting the out of African model. The unique thing about mitochondrial DNA is that it added a time dimension through mutation rate passed through the mother line


  • Advertisement
  • Moderators, Science, Health & Environment Moderators, Society & Culture Moderators Posts: 60,153 Mod ✭✭✭✭Wibbs


    Yep it's a good book that one. There are problems with the mitochondrial eve theory though. The mitochondrial "clock" for a start. There was an article in scientific american I read a while back where a researcher had while looking at families in Iceland IIRC found the rate of the mitochondrial clock was not consistent so was in serious doubt when it came to accuracy. It was much faster for a start. The other bit is that mitochondrial dna is not always just from the mothers side(which surprised me). mitochondrial dna could sometimes come from the paternal side. It was rare but it happened. That throws the mitochondrial eve into question. She existed of that I'm sure, but when she existed, how much other mixtures from other hominids came into it, even maybe where she existed is still an open debate I reckon.

    The water ape theory ahs been around for a while. We do seem to have some characteristics of water mammals not found in other primates. The diving reflex for a start, the distribution of sub cutaneous fat for another. The latter could be an adaptation that arose when we lost our fur though. Fur is an interesting one though. Thing I've noticed, if you look at apes they're hairier on the back and quite hairless on the chest. The reverse is true in humans.

    Rejoice in the awareness of feeling stupid, for that’s how you end up learning new things. If you’re not aware you’re stupid, you probably are.



Advertisement