The Loom

This Week in Human Evolution

Tiny%20skull.jpgI’ve been in low-blogging mode for a few days as I try to fire off a few dead-tree articles. But I wanted to write up a quick post to draw your attention to threetwo very interesting pieces of human evolution in the news.

1. Modern evolution. A new paper presents the results of a systematic scan for human genes that have experienced natural selection in the past few thousand years. An impressive 700 regions turned up. The fact that humans have been evolving during recorded history is not new. The ability to digest lactose in milk as an adult, resistance to malaria, and other traits have long been recognized as having experienced strong natural selection after the dawn of agriculture. But this new study certainly sets the standard for all future work in this area, because it is so thorough. (Gene Expression takes you through the steps. The original paper is here.) The next logical step would be to add new populations to the database. The new study compares only three populations–Yorubans from Nigeria, Chinese and Japanese, and people of European descent in Utah. I wonder how different the evolutionary pressures are in other groups. Inuits get no benefit from malaria resistance, for example. Lactase digestion turns up in people descended from cattle herders. Are there adaptations for eating rice, cassava, or blubber?

Adaptations for drinking milk are not the stuff of racial controversy, but brain genes certainly are. Last year there was quite a hullabaloo over findings that a couple brain genes were also evolving quickly over the past few thousand years. The fact that natural selection appeared to be occurring in those genes in Europeans and Asians generated a fair amount of commentary that at least had a whiff of racism to it. Those particular findings seem to dissipate in the new study, perhaps because it looks at a bigger sample of people. On the other hand, there are other brain genes that the new study identifies as evolving. Some are found only in one or two samples, and one is in all three. These results show no simple pattern that can be exploited for blithe generalizations. So I expect silence from pundits.

2. The Evolutionary Volume Knob. While working on my Smithsonian Intimate Guide to Human Origins, I was particularly struck by a visionary paper published in 1975. Mary King and Alan Wilson argued that the evolution of humans might have been dominated not by the emergence of new genes, but by new uses for old genes. At the time, scientists knew precious little about human DNA. They had yet to sequence a single human gene.

In Nature today, scientists published a study that investigates their proposal with all the tools biotechnology has to offer today. The scientists set up devices known as microarrays that can measure the activity of genes in cells. They measured the activity of over 1,000 genes in liver cells from four species of primates–humans, chimpanzees, orangutans, and rhesus monkeys. About sixty percent of the genes show the same levels of expression in all four species, suggesting that they have changed little since the common ancestor of monkeys and apes. But they found 14 genes in humans that buck that conservative trend, showing significantly higher or lower activity than in other primates. Interestingly, five of these genes encode proteins that turn on and off other genes (transcription factors). The authors note that in studies on closely related fruit flies, transcription factors don’t seem to have evolved very quickly. So it’s possible that the patterns found in the new study offer some clues as to why we humans are so different from chimpanzees compared to fruit flies separated by the same amount of evolutionary history.

3. [Update 3.11.06: I've decided to delete this last entry. I've explained why here]

Comments

  1. #1 HS
    March 8, 2006

    Surprised to hear that efficient bipedalism didn’t occur until 2 million years ago. I remember some controversy when Lucy was discovered, but I’d thought it was resolved that she was fully bipedal. Besides, I have trouble accepting that a. afarensis and their contemporaries were shuffling around like a movie version of cave people.

  2. #2 Henry
    March 8, 2006

    In regards to the Turkish family, I actually found some pictures of them, and it’s not really that impressive. In fact, I tried to do what it appeared they were doing in the pictures and suceeded, though I didn’t do it for very many strides because it was quite uncomfortable (and I didn’t want to fall on my face, as if I had much dignity left after trying this).

  3. #3 SkookumPlanet
    March 8, 2006

    The earliest hominids show some hints of bipedalism six million years ago, but hominids didn’t walk efficiently upright like we do for another four million years

    This threw me in that it bypasses australopithecines as efficient bipeds. My layman’s understanding is —

    Australopithecines — our basic body plan, including all the major equipment of our bidpedal locomotion, but under 4 feet tall with a chimp-size head with a chimp-size brain.

    Homo Erectus — same body plan, but our size [maybe slightly taller] with larger, still chimp-like head and intermediate brain size.

    Archaic Homo Sapien — like us, but experimenting with getting our brain size out of females. so there are “non-conforming” skulls in a variety of ways.

    Modern Homo Sapien — arises from a small, geographically integrated population in East Africa, of less than 10,000, between 100,000 to 150,000 years ago.

    Is this picture wrong in a major way?

  4. #4 Carl Zimmer
    March 8, 2006

    The latest work I’ve seen shows australopithicenes as bipedal but inefficient and slow. Plus, they couldn’t run. It’s not until Homo ergaster that you see long limbs and other adaptations for long-distance walking (and maybe running).

  5. #5 Marco Ferrari
    March 9, 2006

    Thanks Carl for the brilliant criticism to the “turkish hypothesis”. I really doubt that just one gene could rearrange the whole body to make us a two legged creature, from a four legged ape, but there are indeed genes that apparentely singlehandedly changed our behaviour and mind. Of course Foxp2, but also, if I recall, a gene for the structure of the jaw muscles. Any other gene that you remember can restructure whole body part?

    Marco

  6. #6 Bruce Wright
    March 9, 2006

    HS, Carl also writes in his latest book that australiopiticenes had long arms and hook-like fingers, like arboreal apes.

    So maybe they brachiated as well as walked.

  7. #7 Nicholas Humphrey
    March 9, 2006

    As a distinguished science journalist, you should know better than to spread empty gossip about the “unsavory” conduct of the British scientists involved in studying the Turkish quadrupeds. There is simply no truth in the allegation that we “paid off” the family not to collaborate with other researchers.

    The BBC film, airing on 17 March, provides a responsible, intelligent, and enthralling account of the science and the human story that lies behind it. I am proud to be associated with it.

    We have published a preliminary report of our findings at

    http://eprints.lse.ac.uk/archive/00000463/

    Nicholas Humphrey

  8. #8 Steve Sailer
    March 9, 2006

    Assuming this isn’t a hoax (which is certainly possible), it looks like another case of Middle Eastern cousin marriage in action:

    “The siblings, who live with their parents and 13 other brothers and sisters, are mentally retarded, as a result of a form of cerebellar ataxia — an underdevelopment of the brain similar to that in cystic fibrosis. Their mother and father, who are themselves closely related, are believed to have passed down a unique combination of genes resulting in the behaviour.”

    A quick check of the invaluable http://www.Consang.net finds that the three studies of Kurdish populations all show that about 3/8ths of their marriages are between first or second cousins. So, it’s likely a birth defect caused by inbreeding.

  9. #9 Steve Sailer
    March 9, 2006

    Re: Modern Evolution. A top population geneticist just emailed me:

    “The new papers out of Bob Moyzis’ lab and Jonathan
    Pritchard’s lab at Chicago, written up by Nick Wade monday in the New
    York Times, have to be the final nail in the coffin of the “race is a
    social construct” crew. They show that evolution is happening very
    rapidly in our species, and different things are being selected in
    Africans, Asians, and Europeans. Selection is making us more unlike
    each other.”

  10. #10 Theodore Price
    March 9, 2006

    Nicholas,

    Thanks for posting your preprint. With all due respect I found the “evolutionary implications” to be far over speculative and I doubt a referee would let it pass. These family members have obviously severe cerebellar developmental and/or atrophy problems. It seems that the obvious hypothesis would be that they have severe problems with balance leading them to walk on all fours. You do address this in the manuscript, but — were any tests performed to see how impaired their balance and/or eye coordination is? There is a bit about family history and some comments from a local doctor, and an MRI????? How about a simple neurological screen (with ratings that can be compared to a normal population)? You do rattle off a list of cerebellar tests in which they performed poorly, but then state that their cerebellar problems were mild. I find this more than a little odd.

    What is the justification for publishing the genetic data seperately? Which gene is disrupted/mutated? What does this tell you about the speculative comments in your discussion? Seeing that you know what the genetic findings are, the rampant speculation in the discussion seems unjustified.

  11. #11 Carl Zimmer
    March 9, 2006

    Steve, I don’t think you should be using my forum for passing on anonymous remarks. How do I know you’re quoting a top population geneticist? How can I follow up on that? Perhaps you feel that it gives more weight to this remark than if you were to say it in your own words, but that doesn’t justifiy a blind quote.

  12. #12 HS
    March 9, 2006

    I read the pdf about the quadrupedal humans (it seemed strange to hear them referred to as quadrupeds). I’m interested in the suggestion of an historical existence of this gait in our ancestors. As to australapicethines, wouldn’t the fossil bipedal footprints from these would tend to rule out this gait in hominids?

  13. #13 Steve Sailer
    March 9, 2006

    “Steve, I don’t think you should be using my forum for passing on anonymous remarks. How do I know you’re quoting a top population geneticist? How can I follow up on that? Perhaps you feel that it gives more weight to this remark than if you were to say it in your own words, but that doesn’t justifiy a blind quote.”

    I’m sorry, Carl, I was under the impression that you were a science reporter and thus would appreciate a tip on what’s going to turn into a Big, Big Story in your field.

    You ask, “How can I follow up on that?” Well, you could email me and ask me and I could ask the top population geneticist if he’d want to talk to you, on or off the record, about the implications of the HapMap research.

    But I guess you’d just rather not think about this topic.

  14. #14 Carl Zimmer
    March 9, 2006

    Steve–

    In case you didn’t notice, I invite people to email me tips. Comment threads are for discussion, and quotes from nameless authorities do not further it. Please show some consideration to other readers.

  15. #15 HS
    March 9, 2006

    Thanks for feedback on the ‘efficient’ bipedality question. But I have trouble getting my head around the idea that upright hominids were somehow not good at walking (and apparently couldn’t run at all).

    Carl mentions short limbs as a barrier to efficiency, but short limbed homo saps do just fine (children, dwarves, pygmies, for example).

    Noone could have guessed from skeletal evidence that homo saps would have an efficient quadrupedal gait, and yet the Kurdish quadrupeds clearly do. Why do think that early hominids were inefficient bipeds?

  16. #16 Dan Cabacungan
    March 9, 2006

    I’m not sure that there is a clear link between the wrist-walking family and our evolutionary past.

    Here’s where I see the disjoint:

    Page 8: “Without the cerebellar problem, these infividuals would surely have learned to walk bipedally, like their unaffected siblings.”

    So, it’s a cerebellum issue…right?

    Page 11 (Evolutionary Implications): “Given that all five individuals developed the same adult gait, as if following the same developmental programme, there are grounds for asking: where could the ‘memory’ for such a programme come from?”

    As noted in the paper, there’s an observed predisposition in the family toward doing the “bear crawl” in before learning how to walk even among the bipedal children. If it’s hard to balance and walk upright, and one can get around easily without doing so, is it really implausible that the muscles, bones, and joints of the affected family members would grow to accommodate this? I remember doing the “bear crawl” as an exercise in gym class in elementary school. Not exactly easy to do, but definitely more comfortable than crawling on hands and knees across a wood floor. Certainly it would get easier with practice–possibly easier than walking with a cerebellum problem.

    I think that even more “resilient” than bipedalism is the ability for humans to retain locomotion. It just so happens that, in most cases (as the article observes), we default to bipedalism because that’s how our bodies are built. In cases of paralysis, birth defects, missing limbs, etc. where it’s impossible or very difficult, we find other solutions. Given the link that the researchers acknowledge between the cerebellar problem and the difficulty walking upright in the affected family members, the question seems to be “Why wrist-walking and not some other locomotion solution?” Not “Is this an expression of a set of genes that once determined how our ancestors might have walked?”

    The latter is more fun to think about, but the former seems a much more legitimate question in this case.

  17. #17 Bill Hooker
    March 10, 2006

    I think that even more “resilient” than bipedalism is the ability for humans to retain locomotion.

    I think Dan has it exactly right. Tan’s (and to a lesser extent Humphrey’s) enthusiastic flogging of the “reverse evolution” nonsense — and I’ll eat crow if it’s not, but I say it’s nonsense — is distinctly sleazy.

  18. #18 HP
    March 10, 2006

    As near as I can tell, the “big, big story” that Steve Sailor is talking about is in fact the story about recent evolution you write about at the beginning of this very post. At least, the fake quote that Steve extracted from his bowel seems to be derived from this ignorant bilge that spilled out of “top population geneticist” Andrew Sullivan. Via The Poor Man.

    Remember, it doesn’t have to be true, as long as it’s “truthy.”

  19. #19 Gerry L
    March 11, 2006

    From time to time, stories flourish about Oliver, a chimpanzee who had disconcertingly human features and routinely walked upright. I seem to recall they even did some DNA testing on him. It is apparently much more exciting for public consumption to suggest a breakthrough in the search for a genetic “missing link” than to plod through some of the more mundane explanations. At least it makes for better television.

    At our zoo we have a former carnival chimp who, in her late 30s, still walks upright when it serves her purpose. I just met a 44-year-old retired circus chimp in Florida who walks bipedally — but only on tip-toe. Maybe some TV producers will want to feature Chloe and Marco in a special about apes hopping the evolutionary chasm. (I hope not.)

  20. #20 triticale
    March 13, 2006

    There has in fact been a little bit of racial controversy regarding lactose tolerance. Those who thrive on racial controversy raised one a while back regarding the insensitivity of including dairy products in the “official government” food pyramid.

  21. #21 Paul Evitts
    March 26, 2006

    Can someone help me with this? Human crawling is a stage in human development that as far as I’ve been able to find isn’t replicated in any other species. Knuckle walking (NOT crawling) is, as far as I can tell, NOT a developmental stage (in humans or any other species) but rather an optional alternative to bipedal walking that became (e.g.) a preferred general locomotion strategy for other primates (e.g. gorillas and chimpanzees) that may have emerged about the same time that ‘efficient bipedalism’ emerged as a successful (more successful??) locomotion strategy for human ancestors.

    So, a study that indicates mentally and physically and maybe genetically challenged humans engaged in knuckle walking seems to have no bearing on the real issue: how humans evolved to incorporate real crawling into a locomotion strategy that ends up with efficient bipedalism.

    The Kurdish material is, surely, a red herring.