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Thread: Hominid inbreeding left humans vulnerable to disease

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    Post Hominid inbreeding left humans vulnerable to disease

    Hominid inbreeding left humans vulnerable to disease


    • 12:48 25 January 2005
    • NewScientist.com news service
    • Will Knight
    A lack of mates among human ancestors that lived million years ago has left modern humans more vulnerable to genetic disease, a new study suggests.

    Researchers compared samples from the genomes of more than 1000 people with those of chimpanzees to see how much genetic mutation has occurred in the two species since they diverged from a common hominid ancestor, about six million years ago. They also made comparisons with another closely related pair of species, rats and mice.

    They focused on portions of DNA close to protein-coding genes. These segments are thought to regulate the activation of these genes.

    The researchers calculated that these stretches of human and chimp DNA contained approximately 140,000 non-advantageous mutations, higher than expected and well above the number of retained genetic mutations seen in rats and mice. The mutations occur naturally but make both chimps and humans more susceptible to diseases with a genetic basis, such as cancer.

    Evolutionary bottleneck

    The researchers believe the high rate of mutations is seen because the hominid ancestor to both species went through an evolutionary bottleneck, when its breeding population was limited to only about 10,000 individuals.

    This meant that the process of pruning out damaging mutations via natural selection of the fittest mates was more difficult and slower. In contrast, rats and mice have descended from a much larger population, leaving them less susceptible to genetic diseases.

    Adam Eyre-Walker, a member of the research team at the University of Sussex, UK, says the phenomenon is comparable to the genetic problems experienced by severely endangered species, in which inbreeding can accelerate extinction.

    "The process happens in all species with fairly small populations," he told New Scientist. "But we've probably escaped our genetic fate by having a few advantageous mutations that have been functionally so successful," such as those that led to large brains and the development of language.

    Eyre-Walker adds that humans have since halted the genetic deterioration by huge expansion of the global population, although selective pressures are less severe due to better healthcare.

    Pinnacle of evolution

    Martin Leecher, a member of the team based at the University of Bath, UK, adds that the results show the relative fragility of the human evolutionary line. "We're used to viewing us as the pinnacle of evolution," he says. "Seeing that rodents control their genes much more precisely is somewhat sobering."

    Hendrik Poinar, a molecular evolutionary geneticist at McMaster University, Canada, says that the results are intriguing. But he adds that it is difficult to draw firm conclusions about the evolution of the human genome, as there may be other factors involved.

    "It is hard to estimate the effect a bottleneck would have had on our populations in the past as we have poor knowledge of how large or small the populations were, and how they expanded and contracted," he told New Scientist.

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    Post Re: Hominid inbreeding left humans vulnerable to disease

    OK, interesting thoughts but does it say when this bottleneck happened? If it is present in both man and chimps then it has nothing to do with hominid evolution and could have happened 12 million years ago. Or are my eyes finally failing me.

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    Post Re: Hominid inbreeding left humans vulnerable to disease

    It's not clear from the article, but some logical deduction might dictate a timeframe of 4 - 2.75 million years ago, whiwh warp us back right into the era of the australopithecines, or much mater in a proto-human phase before the Homo erectus.

    Freeman in Cultural Developments in the Paleolithic assumes that hominids survived extinction thanks to a loophole offered by an unprecedent adaptative edge of socio-cultural kind:
    greater efficient organisation, sex-based division of labour, observing of regularities/patterns in nature and its food resources, more complex linguistic and signalisation systems...

    Painstaking, dangerous situations require improvisation, the beginning of laying out a plan to collect the best material and the sharpest minds to contrive strategies and methods for survival and stimulating endurance linked to loyalty and group's coherence, while some notion of segmentation are institutionalize not longer just for reproductive ends, but to pick up individuals conform merits, qualities and aptness to certain skills and lock them into a position to unfold them to their best possibilities and hence saveguard them for the benifit of the group in stead of wasting them out in e.g. the hunt or the defence line where, where they might perish or be a hindrance in the action...acknowledging the existence of unique individuals with special and not easy to interchange properties...

    Interestingly, the time factor seems to play a role in this development.
    The concept of time, patterned, visible in and around the group, seizable at last, whereas animals follow time instinctive, without digesting information from it, no real apprehension that allows to predict and therefore making a mental image of a hypothetical case that might or might not be there.
    This new faculty imo must have stimulated creativity and cognitive endowments of the hominids, their survival kit to overcome biological failure.

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    Post Re: Hominid inbreeding left humans vulnerable to disease

    Interesting... Evolution has shown us that a small population under pressure by environmental factors evolves the quickest. So this bottleneck would explain why humans evolved so FAST.
    In particular the larger brain made of billions of more neurons, and the simultaneous increase in pelvis size of females, allowing them to birth such larger brained infants. A process that took hundreds of thousands of years, and not millions as would be expected.
    Last edited by Bismark; Thursday, January 27th, 2005 at 03:04 AM.
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    Post Re: Hominid inbreeding left humans vulnerable to disease

    Australopithecines were variable in brain size, though mostly ape-sized. It took roughly two millions years with the appearance of the habilines that the brain took up volume.

    An increase of the neocortex might have helped the hominids to outmaneuver the platitudes of a merciless and haunting existence, finally avenging themself for being nature's whipping boy.

    However, some studies recorded surprising promptitude among microcephalic persons, notwithstanding that their brain size are even less in volume than chimps', to develop some rudimentary form of higher communication in using linguistic faculties and arbitrary symbolic systems.
    Pre-humans could despite biological restrictions have adopted higher skills in tool working and group-related organisation, shown gradually greater cognitive resourcefulness and intensified enculturation, so the neocortex thesis is not sufficient enough to explain our complex brain structure and functions.

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