jump to navigation

Human Nature Decoded–No Whiskers, and No Penile Spines! March 10, 2011

Posted by Nina Rosenstand in Nina Rosenstand's Posts, Philosophy of Human Nature, Science.
Tags: , , , ,
add a comment

I’ve written a book about the Philosophy of Human Nature, The Human Condition. I’ve given talks, and written papers and blogs, and tweeted about the subject. I’ve been devouring every morsel of information about human evolution I could get my hands on since I was 13 years old. I teach two classes per year focusing on Phil of Human Nature. And what do I read this morning in the CNN online Health section? Brand new research about a significant difference between apes and humans: Ape males have penile spines and human males don’t. First thing I thought was, “And a good thing, too!” Now wipe the smirks off your faces—this finding turns out to have seriously philosophical consequences:

We know that humans have larger brains and, within the brain, a larger angular gyrus, a region associated with abstract concepts. Also, male chimpanzees have smaller penises than humans, and their penises have spines. Not like porcupine needles or anything, but small pointy projections on the surface that basically make the organ bumpy.

Gill Bejerano, a biologist at Stanford University School of Medicine, and colleagues wanted to further investigate why humans and chimpanzees have such differences. They analyzed the genomes of humans and closely related primates and discovered more than 500 regulatory regions — sequences in the genome responsible for controlling genes — that chimpanzees and other mammals have, but humans do not. In other words, they are making a list of DNA that has been lost from the human genome during millions of years of evolution. Results from their study are published in the journal Nature.

…[The scientists] found that in one case, a switch that had been lost in humans normally turns on an androgen receptor at the sites where sensory whiskers develop on the face and spines develop on the penis. Mice and many other animals have both of these characteristics, and humans do not.

“This switch controls the expression of a key gene that’s required for the formation of these structures,” said David Kingsley, a study co-author at Stanford University. “If you kill that gene — smash the lightbulb — which has been done previously in mouse genetics, the whiskers don’t grow as much and the penile spines fail to form at all.”

To sum up: Humans lack a switch in the genome that would “turn on” penile spines and sensory whiskers. But our primate relatives, such as chimpanzees, have the switch, and that’s why they differ from us in these two ways.

So what does it matter, other than, presumably,  a different female sexual experience, and a lack of ability to sense things a few inches from our faces?

The other “switch” examined in this study probably has to do with the expansion of brain regions in humans. Kingsley and colleagues believe they have found a place in their genome comparisons where the loss of DNA in humans may have contributed to the gain of neurons in the brain. That is to say, when humans evolved without a particular switch, the absence of that switch allowed the brain to grow further.

The earliest human ancestors probably had sensory whiskers, penile spines and small brains, Kingsley said. Evolutionary events to remove the whiskers and spines and enlarge the brain probably took place after humans and chimpanzees split apart as separate species (Some 5 million to 7 million years ago), but before Neanderthals and humans diverged (about 600,000 years ago), Kingsley said.

So there you have it: We were on the fast track to becoming Homo Sapiens when the switch for sensory whiskers and penile spines was turned off! Make of that what you want, in this Women’s History Month! For me, that story made my day!

(I thought of calling this blog post “Of Mice and Men”, but that would be unfair to Steinbeck.)

Advertisements

They Are Us? News from the Primate Research Front May 11, 2010

Posted by Nina Rosenstand in Nina Rosenstand's Posts, Philosophy of Human Nature, Science.
Tags: , , , , ,
2 comments

Time for an update on our ongoing reevaluation of our primate cousins: here’s story #1, from the New York Times. In brief, we’ve known for fifty years that humans aren’t the only tool users, or even tool makers. Now it turns out that humans aren’t the only ones using, well, sex tools, either! One group of chimps in Tanzania does, too (which, by the way, makes it a culture, rather than instinct):

After noting that chimpanzees’ “tool kits” are now known to include 20 items, Dr. McGrew casually mentions that they’re used for “various functions in daily life, including subsistence, sociality, sex, and self-maintenance.”…

…The tool for sex, he explained, is a leaf. Ideally a dead leaf, because that makes the most noise when the chimp clips it with his hand or his mouth.

“Males basically have to attract and maintain the attention of females,” Dr. McGrew said. “One way to do this is leaf clipping. It makes a rasping sound. Imagine tearing a piece of paper that’s brittle or dry. The sound is nothing spectacular, but it’s distinctive.”

The NYT science piece by John Tierney is on the flippant side, but that doesn’t detract from the power of the report: sexual practices among apes can be local, non-inherited, taught, and culture-driven in addition to being biological. Sounds rather familiar.

And here’s story #2: Europeans and Asians are related to Neandertals, after all! Now we’ve heard for ten years that Neandertal DNA hasn’t been found in the human population, but that turns out to be false: Discover Magazine reports that, according to  a study published in Science ,

Researchers from Germany’s Max Planck Institute for Evolutionary Anthropology first sequenced the entire Neanderthal genome from powdered bone fragments found in Europe and dating from 40,000 years ago–a marvelous accomplishment in itself. Then, they compared the Neanderthal genome to that of five modern humans, including Africans, Europeans, and Asians. The researchers found that between 1 percent and 4 percent of the DNA in modern Europeans and Asians was inherited from Neanderthals, which suggests that the interbreeding took place after the first groups of humans left Africa.

Anthropologists have long speculated that early humans may have mated with Neanderthals, but the latest study provides the strongest evidence so far, suggesting that such encounters took place around 60,000 years ago in the Fertile Crescent region of the Middle East [The Guardian].

So does that mean that Homo Sapiens, just having wandered out of Africa, and the waning Neandertal populations found each other attractive, dated, and intermarried? This is an issue some of us have been wondering about for decades, and what the research apparently shows is that Neandertal male DNA is present in the human population, but not female DNA. A variety of explanations have been posted on various science websites (see the links in the Discover article quoted above) , such as the very good idea that a pregnant Neandertal female would give birth with her own family, while the human mother would raise her hybrid child with the other humans, where the Neandertal genetic material would show up later. That would mean that both species adhered to the ancient matrilocal custom of the family living with the wife’s maternal relatives. But we can’t possibly know about such customs, at least at this stage.

I have another idea which I will float here: evidence of Neandertal DNA in the human population after their move out of Africa doesn’t mean that Neandertals and humans liked each other, or that they lived together as families, or that they had hybrid human-Neandertal societies. As Hemingway says in The Sun Also Rises, “Wouldn’t it be pretty to think so…” But the real story may be less friendly, and more realistic: human females may simply have been raped by male Neandertals, as part of warfare, or chance encounters. Let’s remember that rape is not a sexual phenomenon per se, but also a power manifestation. And the human females may have made it back to their home village, to raise hybrid children, or may have raised them in Neandertal captivity if we’re going to go all-out with speculations. Certainly it is also possible that Neandertal women were raped by human males (which would be somewhat harder to imagine, since those Neandertal ladies would be many times stronger than a human male, but gang rape or rendering the woman unconscious would solve that problem…), and raised human hybrid children back with their Neandertal community. But apparently there is no DNA evidence of that, if I understand the results correctly.

So is there a moral to these two stories? I think so… You decide…

The Human Condition? Here’s Ardi! October 2, 2009

Posted by Nina Rosenstand in Current Events, Nina Rosenstand's Posts, Science.
Tags: , , , , , , , , , , ,
4 comments

 This is a good day for those of us who like to hear, and tell, stories of Human Origins: The current story in the scientific world has been told for a while now, ever since Don Johanson found Lucy, the Australopithecus afarensis, in Hadar, East Africa in 1974: We are the children of small-brained, upright-walking primates who lived some 3 million years ago—primates with insignificant canine teeth, and almost-human hands with opposable thumbs. A creature living on the savannah, enforcing the perception that it was the loss of woodlands that made our early ancestors get up on two legs and look around.

But now we have a brand new chapter in our Story of Origin. Ardi is being introduced to the world, in today’s issue of Science Magazine and all over the newsmedia: Ardipithecus ramidus, a new ancestor (perhaps), at least another traveler on the road that lead to Homo sapiens. The painstaking assembly and interpretation of Ardi’s fractured bones (skull, teeth, pelvis, hands, feet) took 17 years, but now the researchers, including Gen Suwa, Tim White, Yohannes Haile-Selassie, C. Owen Lovejoy and others,  have made their findings public. Ardi’s species predates Lucy by more than a million years, and it lived not far from that very same region. You can explore the details yourself if you are so inclined; personally, I am so excited that I can barely contain myself—this is the story I have been waiting for ever since the news of Lucy broke. What came before Lucy? Since 1974 we have known that the previous picture of early hominids as knuckle-walking, big-brained apes was wrong. We didn’t first develop the big brain, and then get up and walk. It was the other way around. But how far back in time did we diverge from the apes, and when did our hands leave the ground for good? We know that there were medium-sized monkey-type creatures dating back some 8 million years, and even dating back to the first early mammals, 60 million years ago, there were little mouse-sized mammals with some primate characteristics. But where the question gets interesting for most of us who are not paleontologists is, when did we start out on the road to becoming “Human”?

Of course this is one of the primary reasons why Darwin’s theory (The Descent of Man, 1871) met with such massive resistance which can still be felt whenever the debate swings in the direction of Creationism and Intelligent Design: Did we descend from chimpanzees? The Darwinist answer has, usually, been No, not exactly: We and the apes we know today descended from a common ape-like ancestor—we just had to look around for a “missing link” that could show us the intermediary version. Since then, the entire concept of a “missing link” has been discredited: Evolution doesn’t work that way—we don’t have links in a straight chain, but rather a multitude of branches that arise and die out, with some branches ending up being more successful than others. And besides, so few fossils are ever found that it would be astonishing to find an exact Happy-Medium form in-between two distinct species. Well, perhaps that’s what we have now. While Ardi is not a “missing link” (because we should stop using that terminology), she is so old that she represents a hominid (or hominim which is the new and more exact term) who is not even as “human” as Lucy who was truly not very human except for her manner of walking, and her hands. So is she more like an ape? And this is where the surprise comes in: Not really, even if her feet look like ape feet. If ever we humans were ape-like, it must be even further back in time, because Ardi seems to have (1) been upright, judging from the position of her head and pelvis, and (2) had smaller canine teeth than apes. Furthermore, this is the end of the fantasy that we evolved bipedalism on the savannah: Ardi lived in and among the trees, judging from other fossil finds in the area! But even so, she was already upright and bipedal at least some of the time. So was she Lucy’s ancestor? They don’t know yet for certain, but there’s a good chance that her species gave rise to Lucy’s species. And if that is the case, then she is also our ancestor. And she was not typically ape-like. Now that has got to please those who have a problem with the notion that we are “descendants of apes,” but that would be a premature celebration—it doesn’t mean we are not related to primates, it just means that some typical ape-like features were lost in the human line much earlier that we thought, and perhaps the human line never had them, such as chimp-style knuckle-walking. And the chimps and the Bonobos are still our closest living cousins on the planet. That hasn’t changed.

Now all this is factual as well as interpretative science. Why am I so excited? For one thing, I’ve always been fascinated by paleoanthropology. But more importantly for a philosopher, I have also for many years thought that our human origin is at least to some degree a determinant for our “human condition.” That’s what today is known as evolutionary psychology, but in more philosophical terms it means that our physical interface with the world (to borrow an expression from Merleau-Ponty) is an integral part of who we are, and how we interact with the world. Our Lebenswelt includes our physical being, and our physical being has an evolutionary history. If there’s anything that unites us as human beings, aside from our DNA, across the lines of politics, religion, race, gender, and so forth, it is this common history, the physical triggers that become the emotional and cognitive triggers. This is not to say that I discount the existence of “free will,” whatever that is—but our immense array of mental choices and possibilities is grounded in our physical abilities, limitations, and history.

Photo: Before â??Lucy,â?? There Was â??Ardi:â?? First Major Analysis of One of Earliest Known Hominids

[From ABC News: Artist’s conception of what Ardipithecus ramidus would have looked like 4.4 million years ago.
(J.H. Matternes/Science/ABC News Photo Illustration)]

So what can Ardi tell us, if the scientists are right? (1) We were upright, in the trees, long before we had the brains to make plans what to do with our freed-up hands, and comfortable being face-to-face with each other, close and personal, as well as probably capable of identifying each other at a distance; (2) we did not have massive canine teeth, meaning that the males probably didn’t fight over the females, meaning that we are perhaps looking at pair bonding and a semblance of gender cooperation (if not downright gender equality) dating back 4 million years—much more like the Bonobos than the Chimps, by the way. Does this mean that we were non-aggressive creatures, food for the predators rather than predators ourselves? Some of us would probably like to think so, but we can’t make that assumption. Look at Ardi’s eyes: Perfect stereoscopic vision, looking forward. Those are the eyes of a hunter, at least potentially, perhaps part-time if not full-time—opportunistic, like chimps. Besides, Ardi was omnivorous, like we are—she was not a vegetarian. The “killer ape” theory probably shouldn’t be declared totally dead yet.

In addition, National Geographic Magazine comes out with this spin: Why did we start walking upright? What can you do with free hands? Some of us would immediately say, You can hunt. But others would add, And you can gather. And bring what you have gathered to—your mate. Or the one you want to become your mate. Jamie Shreeve suggests just that scenario: We began embarking on the road to humanity by realizing that there was a sexual advantage to being able to bring food to one’s potential partner, in our freed-up grasping hands. And the upright female has another advantage: When she’s in estrus (heat) it doesn’t show. Which, according to Shreeve, would mean that she could string along the food-bringing male, even when she wasn’t ovulating, and even play around if she was so inclined. Now that opens up new vistas for the pair-bonding theory…