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June 5, 2011Posted by on
I have a few suggestions for you:
Eric Michael Johnson has a habit of writing about some of the most important, fascinating topics in anthropology, and two of his posts are up for consideration: Sacrifice on the Serengeti, about female life history, and Penis Spines, Pearly Papules, and Pope Benedict’s Balls, about, well, all of that stuff.
May 19, 2011Posted by on
A new paper published in PLoS ONE by David Carrier tests the hypothesis that bipedalism in humans evolved because it helps them to fight better. The first fatal flaw lies in the first sentence:
Many quadrupedal animals stand on their hindlimbs to fight.
How then, does this explain human uniqueness?
“… it is illogical to invoke the behaviour of living apes to explain the origins of something that they themselves have not developed…”
and I think it would be great if we could ask ourselves why all of these bipedal aggression postures haven’t resulted in bipedal anteaters, felids, or canids, but were so important in human evolution. My dog does a cute little thing where she stands up on her hind legs to pounce a squeaky toy. Perhaps if I hadn’t had her spayed, her descendants would have been bipedal? (She also stands up to get food from low-hanging branches….er… coffee tables.)
A second flaw lies in their methodologies, in which they had humans stand bipedally to strike a force transducer, and then had them get down on their hands and knees and do the same thing. What ancestral state does this posture approximate? Forget bent-knee, bent-hip- let’s go with knee-crawling! The authors themselves admit,
The fact that humans are habitual bipeds reduces the relevance of humans as a model organism for this study.
but add that using chimpanzees or bonobos would increase the “relevancy” of this particular experiment. I don’t think it would. Chimpanzees and bonobos don’t represent an ancestral hominid, either. You’d want to get a sample that included a bunch of different species- monkeys, anteaters, felids (why not?). But I still don’t know that a protocol like that would support the hypothesis that humans evolved to be bipedal because that particular aggressive posture was important to their ability to secure a mate.
Carrier, D. (2011). The Advantage of Standing Up to Fight and the Evolution of Habitual Bipedalism in Hominins PLoS ONE, 6 (5) DOI: 10.1371/journal.pone.0019630
March 11, 2011Posted by on
The following guest post by Eric Michael Johnson is part of the Primate Diaries in Exile blog tour. You can follow other stops on this tour through his RSS feed or by following him on Twitter. If this is your first time visiting A Primate of Modern Aspect make sure to browse some of the other posts on the blog. Thanks. – EMJ
Do Nature‘s penis spines really separate humans and chimpanzees?
There is very little known about the reign of Pope Benedict III except that clerics were generally satisfied with his testicles. Upon his coronation in 855 AD God’s chosen messenger on Earth sat in a special chair resembling an ancient commode while the Holy See checked to make sure that the papacy was indeed infallible.
Two reliable clerics touched his testicles; witnesses who presented legal evidence of his maleness. . . At this the priest and the people responded, “Deo gratias” [Thanks be to God].
After all, you couldn’t be too careful. The Bible was very clear that, “He whose testicles are crushed or whose male member is cut off shall not enter the assembly of the LORD.” Healthy genitalia was a sign of spiritual purity and the Church made a point to check beneath the mantum of every Pope until up through the fifteenth century.
Of course, Christianity wasn’t alone in this respect. The ancient Greeks saw the penis as a gauge to their proximity with the Gods, the Hindu god Shiva is worshipped primarily by paying homage to his penis, or linga, and the Sumerian god Enki was thought to have brought life to the Tigris Valley when he “lifted (his) penis [and] brought the bridal gift.” The Pope seems to have merely been the latest in a long line of devout men who were dropping their pants for the Lord.
Now, scientists have gotten in on the act and have sought to understand human origins by studying our own little Bishop. From the standpoint of evolutionary biology this male obsession with their own genitalia makes perfect sense. Every animal alive today is able to stand and be counted because of a long line of ancestors who successfully reproduced. The natural world is a living erotic museum filled with variations in male genitalia, illustrating how natural selection has paid nearly as much attention to the male member as Catholic priests have.
But there’s a sinister side to this obsession, by which of course I mean penis spines. Throughout the Order Primates, as well as in many other mammal species, males have developed small (and sometimes not so small) keratinized structures along the head and/or shaft of their penis that have been adapted to maximize reproductive success. According to the, rather appropriately named, primatologist Alan Dixson in his book Primate Sexuality, these spines can be simple, single-pointed structures like in macaques or complex ones with two or three points per spine like in the prosimians (lemurs and lorises). These different forms of penis spine therefore suggest different mating strategies that various species have adopted during their evolution.
Examples of penile morphologies in primates. Note the obvious spines on I and K and the dots on N. Top row: Eulemur fulvus, Saimiri boliviensis, Macaca arctoides (stump-tailed macaque). Bottom row: Macaca fuscicularis (long-tailed macaque), Papio cynocephalus (baboon), Pan troglodytes (chimpanzee).
However, a new study in the journal Nature has generated a great deal of titillation this week as Cory McLean and colleagues have revealed a sequence of DNA that promotes these penis spines, a sequence that humans appear to have lost. The genetic mechanism involved has already been explained extremely well by Ed Yong and John Hawks. However, the interpretation of what the loss of this DNA reveals about human evolution is perhaps the most provocative claim and has resulted in a flurry of media attention.
“Simplified penile morphology tends to be associated with monogamous reproductive strategies in primates,” write the authors. According to their study, the loss of these spines would have resulted in a reduction in sexual sensation (because the spines are thought to be connected to nerve endings) and would therefore have allowed our ancestors to engage in more prolonged sexual activity that the authors associate with pairbonding and the evolution of social monogamy (citing Owen Lovejoy’s Ardipithecus ramidus paper from 2009 as a model).
As Nature News wrote in their summary of these results:
It has long been believed that humans evolved smooth penises as a result of adopting a more monogamous reproductive strategy than their early human ancestors. Those ancestors may have used penile spines to remove the sperm of competitors when they mated with females. However, exactly how this change came about is not known.
This is where it’s important to know precisely what it is that we’re talking about. Nature News referred to these structures in chimpanzees as “penis spikes” when the reality is more akin to goose bumps. Scicurious has posted a review of the only study that seems to have been done on these structures (published by W.C. Osman Hill in 1946) that found these “spines” to be only about 0.35mm wide, or the thickness of a human hair. Hardly a structure that would be useful for removing sperm.
Another problem is McLean et al.‘s argument that loss of penis spines would result in reduced sensitivity and longer bouts of sexual activity. As Dixson points out in Primate Sexuality (p. 118), orangutans have more elaborate penis spines than chimpanzees do and yet their average duration of sexual activity is significantly longer than either chimpanzees or humans. Chimps engage in sexual activity for an average of 8.2 seconds while the average for humans (based on Kinsey’s data) is less than 120 seconds. In contrast, orangutans range between a median of 840 seconds and a maximum of 2,760 seconds. Humans actually rank 14th in the duration of sexual activity (also falling behind macaques).
However, there’s a more serious problem with the argument presented in this study. The source the authors cite in support of their argument for smooth penis monogamy is Dixson’s Primate Sexuality, however he doesn’t discuss what penis spines indicate about primate mating systems in that book. That’s in his later book Sexual Selection and the Origins of Human Mating Systems, where his conclusions are somewhat different.
Four penile morphologies in single-partner or multi-partner primate mating systems (including humans). All categories show a significant difference except for penis spines.
As Dixson’s graph indicates, there are significant differences between a single-partner mating system (monogamy or polygyny) and a multi-partner mating system on three of the four categories: penile length, baculum length, and distal complexity. The only penis morphology type that isn’t significant are penis spines. This doesn’t necessarily invalidate McLean et al.’s argument for increased pairbonding, but it doesn’t support it either. It shows that there is no correlation between penis spines and primate mating systems, the correlation that McLean et al. is arguing for. In contrast, Dixson concludes that Homo sapiens is a polygynous species. However, other factors suggest that a multi-male multi-female system is more accurate given the diversity of human sexuality.
There’s also one final thing. Not all humans have lost their penis spines. Dating back to 1700 anatomists have identified what have now become known as pearly papules (also called Hirsuties coronae glandis). As reported by Denniston, Hodges, and Milos in 2009:
We have shown that, in the chimpanzee, these papules are a normal feature (spine-like) and are associated with nervous structures. It seemed to us that, in man, they may be a return to an earlier morphology.
To see a picture of these human “penis spines” click here [NSFW].
Five studies have been done involving nearly 2,000 patients in three separate countries, with an estimate that about 30% of all men develop these papules. In contrast, only four chimpanzees were studied in Hill’s 1946 paper on penis spines so it’s unknown how prevalent these structures are even within genus Pan. As Hill notes in his study:
The spines of the Chimpanzee are simpler structures than those of any of the other Primates, and the question arises as to whether they are degenerate remnants of a once powerful armature or a new product of evolution.
While the genetics of these pearly papules have yet to be studied, it doesn’t seem that a strong case can be made yet for significant differences between our two species on this point. John Hawks goes on to note that the chimpanzee version can even be implanted into transgenic human foreskin fibroblasts:
That indicates that the overall genetic system to make penile spines is still there lurking in our genomes. If we could turn on the gene at the right time, replacing the function of the enhancer, we can still grow penile spines.
I’m confident that the bulk of this week’s Nature paper will offer a host of tantalizing insights into the ways that humans and chimpanzees have travelled down different evolutionary paths since our common ancestry. At the same time, our evolutionary history has primed some members of our species to seek firm answers by looking to their respective, er, members. As we sit and try not to think about Pope Benedict’s balls, we can muse on how potential revelations may indeed develop from these investigations. But it’s also possible that we’ll only be greeted with a cold hand and a cheap thrill before moving on to the next study.
Image: Chimpanzee Pope by Nathaniel Gold.
McLean, C., Reno, P., Pollen, A., Bassan, A., Capellini, T., Guenther, C., Indjeian, V., Lim, X., Menke, D., Schaar, B., Wenger, A., Bejerano, G., & Kingsley, D. (2011). Human-specific loss of regulatory DNA and the evolution of human-specific traits Nature, 471 (7337), 216-219 DOI: 10.1038/nature09774
February 4, 2011Posted by on
As Scicurious’ mom points out, penises are funny lookin’. As long as humans have been humans, men and women have looked down and thought, “now what could be the possible reason for that?” The question no doubt vexed our early ancestors so much that they simply had to evolve larger brains to think about it more.
We’ve even looked at the penises of other species and pondered their functional anatomy. The chimpanzee penis, for example, is long, skinny, and kind of pointy at the end. Chimpanzee penises are designed to dislodge hard little plugs of semen left in the vaginal canal by a previous male. When a chimpanzee female comes into estrus, she will mate pretty much non-stop until she comes out of it. Lines will form at the base of a tree in which she dwells, and the chimpanzee males will simply wait their turn, ascend the tree, and rely on their penis and sperm to do all the competitive work. Their copulatory plugs form and basically seal off the cervix from the incoming sperm of later males, and may also help to keep their own sperm in there, so that when ovulation actually occurs your sperm is right there and ready. Copulatory plugs are pretty common in primates, and if they work, they obviously have a pretty big effect on an individual male’s fitness. Males who have pluggy semen and pointy penises have sons with pluggy semen and pointy penises, and a pointy little arms race is born.
I suspect that the above hypothesis (Which I call The Crowbar Hypothesis) for chimpanzee penis shape was the inspiration for one of the most-often discussed hypotheses for Human penis shape: The Plunger Hypothesis (TPH). TPH is basically the idea that the bulbous shape of the glans in humans acts as a plunger which scoops a previous male’s sperm out of the vaginal canal, while at the same time delivering his own sperm to an optimal position for insemination. At least, until the next competitor’s plunger penis scoops it out. Some insects actually do exactly this.
So, what should we expect from such a hypothesis? First and foremost, we have to have evolved in a society in which there is a lot of sperm competition. Chimpanzees have tons of it, and since their troops are primarily composed of related males, there is little to no outward signs of competition for females. They’re certainly not thumping their chests or doing other threat displays to get their brothers to lay off their female. Instead, they’re politely lining up and waiting their turn.
We should also expect that the shape of the “plunger” actually affects how much semen is scooped out. Males with better plungers should have more offspring, and there should be some variation in penis shape, glans to shaft ratio, all that stuff. Does this criterion apply? Maybe, but no one’s looked at it. All we have is the infamous dildo experiment.
And now we have the Glans-as-Hormone-Sponge Hypothesis. The GHSH suggests that the human penis is plunger-shaped in order to scoop, but instead of scooping out the competitor’s sperm, it’s scooping up vaginal secretions filled with love-inducing hormones. The foreskin, he states, is particularly sponge-like, and will soak up her hormones, be absorbed into his blood stream, and induce the release of more hormones from his brain.
Okay, that’s an interesting idea, too. And he’s not saying he has evidence for it; he’s just suggesting it.
Here’s the problem with both of them, though: The glans begins life as the genital tubercle. In males, the base of the tubercle grows out to become the shaft of the penis, while the glans becomes demarcated from the shaft by the coronary sulcus- the ring around the plunger, if you will.
The shaft of the penis gets a little groove down the middle of it which will eventually fold around itself to become the urethra. This groove does not extend into the glans. In the glans, a little pit develops at the tip and moves inward until it meets up with the future urethra. The two adult structures are distinct because they’re formed from from distinct embryonic structures.
And here’s the part that will blow your mind: Females also have a coronary sulcus around their glans (of the clitoris). Her coronary sulcus separates the glans from the rest of the phallus. The main difference between the male glans and the female glans is that the male glans had to extend out from the body so it could get to the vagina, and did so by growing a larger phallus.
So my question is, why do females have vaguely plunger-shaped clitorises? Or are we perhaps trying to ascribe function to a simple relict of an embryonic event? Do females have a coronary sulcus because males have a coronary sulcus, or might it be the other way around? Do males have a ledge around their glans for a reason, or is it simply because the clitoral glans is a distinct structure from the rest of it?
Bowman EA (2010). An explanation for the shape of the human penis. Archives of sexual behavior, 39 (2) PMID: 19851854
BIRKHEAD, T., & HUNTER, F. (1990). Mechanisms of sperm competition Trends in Ecology & Evolution, 5 (2), 48-52 DOI: 10.1016/0169-5347(90)90047-H
H/T to Scicurious, where you can go to see all sorts of penis pictures.
January 25, 2011Posted by on
Hey there blogland. I’m preparing for the “reboot” of A Primate of Modern Aspect, and I’d like to get to know my readers a little better. Take a second and vote in the poll over there in the sidebar. Thanks!
And while you’re at it, go check out this post about why we all blog at This is Serious Monkey Business.
October 24, 2010Posted by on
I know, I know. Another non-science post. My classes are taking up a lot of brain space this semester, and this blog is being neglected. It’s okay. I’ll be back in regular form soon.
But, in the mean time, Scicurious is hosting a grad student eating carnival, and, well, I’m a grad student, and I love cooking. It’s soup weather where I am, and I’ve been making up a big crock of soup every weekend to last me until at least mid-week. Homemade soup is so easy to make, and sooo much better and cheaper than canned. It’s comfort food at its best.
A few soup tips:
It’s okay to use bouillon cubes. These are pretty much just dried cubes of broth, and they stay good forever. You can buy boxes of broth, too, but those are more expensive and I often find that the taste is kind of… meh. The taste is unmistakably “canned soup,” whereas the bouillon cubes are a more neutral backdrop. You can also save all of your bones from everything (well… since we’re dealing with anthro people, best not use your people bones…) and keep them in your freezer, but I don’t eat meat enough to accumulate enough soup base. So use bouillon cubes.
Now that you’ve got your bouillon cubes, you can spice them up. Get some herbs and spices. I’ve got a few that I keep around the apartment as houseplants, and they cost about $3.99. I usually make a “bouquet garni” out of a sprig of rosemary, some thyme, and a bay leaf. You throw these in and then fish them out before serving. It sounds fancy, and it tastes fancy, but it’s really not hard or fussy at all. If you don’t have a green thumb, you can buy these herbs dried for anywhere from $1.99 and up, or omit them if you must.
Last week I bought a bunch of “cheese rinds for soup” for 2 bucks. I think it adds some depth of flavor, but I’m not really sure. I haven’t done any double blind randomized control studies.
Okay, on to the soup! This is my recipe for Mushroom Barley Soup.
You will need:5 Bouillon cubes, one smallish onion, one or two cloves of garlic, 1/2 cup pearl barley, and about a pound of mushrooms. You can choose your mushrooms to suit your tastes, but I use one package of cremini (which are actually small portabellos!) and a few shitake out of the bulk section, just for variety. If you want, you can use cheapie button mushrooms.
- First, chop up an onion and a clove of garlic or two and sautee until translucent and aromatic.
- In the meantime, bring a pot of about 5 cups of water to a boil. Add five bouillon cubes. I use beef, but you can use chicken or vegetable. Throw in your aromatic herbs, if using.
- Add your 1/2 cup barley. This will need to boil for about 35-40 minutes, and will swell to about 4 times its original volume.
- Add the onions to your broth.
- Slice your mushrooms and then sautee until they’re giving off some liquid. Add to the pot.
- Walk away for about 30 minutes. You can use this time to toast a nice crusty french bread with some cheese on it if you want, or make a nice salad, or watch an episode of Futurama. When you come back to your soup, check to make sure the barley is done. When it is, enjoy!
- Bouillon cubes are $1.99 for a jar of 25. You’ll be using $.40 worth of bouillon for this recipe.
- My onion cost $.39, but your price may vary. I’ll round up to $1.
- A bulb of garlic cost me $.42. Again, I’ll round up to a dollar.
- Mushrooms will also vary based on how which variety you get. My creminis cost $3.99, and I got $.78 worth of shitake. Total mushroom cost: $5.
- Barley is about $1 for a bag, and you’ll only be using 1/2 cup. That’s $.25 cents worth of barley.
Total for stocking up on essentials: $10. This pot of soup cost me $7.04 to make, and will feed me 4 or 5 times, so about $1.75-$2 per serving. Pack it up and take it to school for lunch, or just keep it at home for a good, hearty dinner after a day of lab work. If you want to get fancy about it:
- Splurge and buy yourself a baguette from the bakery section for $2.50
- I think this soup could handle a splash of fish sauce, worcestershire sauce, or soy sauce if so inclined.
- If you want to go for some beef instead of mushrooms, go crazy. Ground beef should work, or even some short ribs if you leave your soup on the burner or in the crockpot for a few hours. You can get a pack of “stew beef” for $2-4, depending on the size.
- If you need to buy your herbs, it will cost anywhere between $6-15, but these will last you until you graduate!
Another tip that I have: If you have some veggies which are about to go bad, make them into some minestrone! Basically, start with your standard soup base (bouillon, aromatics, and for this one add some sort of little pasta instead of barley). Add whatever veggies you have (carrots, green beans, celery, spinach, kale, eggplant, zucchini, tomatoes… etc. etc. etc…. ) and a can of beans. I can’t offer a price breakdown for this one, because it’s basically a fridge-cleaning recipe. You’ve already bought these veggies for other purposes, but for whatever reason didn’t use them up. Have an extra chicken breast? Throw it in the soup. Bacon? Sautee an onion with it and throw it in the soup. There’s nothing sadder than letting produce go bad, so throw it in the soup! You’ll never make two minestrones that taste the same, which, I think, is the beauty of minestrone!
Finally, a lot of times I’ll find some sort of beautiful produce, bring it home, and realize that I have no idea what to do with it. When this happens, I browse the archives at the Smitten Kitchen and always find something delicious.
October 9, 2010Posted by on
Like many/most biological anthropology graduate students have to do at some point in their careers, I’m taking gross anatomy and histology with the first year medical students this fall. What a culture shock!
A few observations that make me chuckle:
- Medical students begin all of their questions with “What exactly…” What exactly does the gluteus maximus do? Why exactly do mitochondria stain darker? What exactly do we have to know about the brachial plexus in order to pass the test?
- The one class that I don’t have to take that they do have to take is a “personality” class where they learn that wearing too much perfume is unprofessional. Instead of that class, I take a research ethics class where we learn that feeding radioactive oatmeal to children is wrong.
- “Do non-medical doctors get to be called ‘doctor’ when I e-mail them to ask for help?”
- The look of astonishment on their faces when I know what I’m talking about or am able to teach them something that they didn’t know, Like bony landmarks, or who John Lennon was.
- “I thought most grad students were medical school drop-outs.”
- How impatient they get when someone asks a question and I say, “Well let’s think this through…”
- “It’s cute that you are actually interested in this.”
- When I go back to normal anthropology school, fellow students say, “I bet they don’t even know what an australopithecine is!”
- “I’m so bad at coming up with research ideas. Maybe I should just go to medical school and do rote memorization for the rest of my life.”
It’s funny to observe what the different groups of students find important and desirable and “smart.” For medical students, the fact that I study “monkey bones” makes me a much less serious student than they perceive themselves to be. Even though I keep up with them when we do drills or study together, they assume I’m not as smart because if I were, I’d be in medical school. They require answers and need to know how to do things, not why we do things, or how we learned to do things, or that there may be two or three ways to do things that give equally good results. They are very goal-oriented, and have no time for things that have nothing to do with achieving that goal.
On the other hand, the graduate students have an attitude that they are more intellectually curious and therefore smarter than kids who went to medical school. They seem a lot more comfortable with uncertainty, to the point where they probably don’t study as hard as they could. They have tunnel vision in that they sometimes get so focused on what they are interested in that they can’t grasp that other people might be interested in other things. And that tunnel vision has the unfortunate property of having no end in sight. You can never know EVERYTHING about what you are trying to learn about, so goals are harder to define and “finished” is almost impossible.
I’m sure both groups will mature into wonderfully smart and perceptive doctors (medical or otherwise), but it’s funny how distinctive the two personality types seem to be at this early point in their careers. I wonder if it’s learned through four years of undergrad, or if the two careers just naturally attract two different personality types. One piece of advice that was passed down to me, and that I think applies to both groups, is this: You are both not as smart as you think you are, and smarter than you think you are.
September 16, 2010Posted by on
I found a new paper in my reader this morning from the crew who published the first description and taxonomic statements about Darwinius massillae, Phillip Gingerich and his colleagues. This paper is a reply to Williams et al. (2010), which called into question a lot of the conclusions about the place of Darwinius in the greater scheme of primate evolution. For a quick re-cap of where we are in the debate today, you can read this, this, this, or Brian Switek’s paper here.
They open their newest paper with a statement that everyone can agree on:
A forty-seven-million-year-old primate Darwinius masillae from the middle Eocene of Messel in Germany is worthy of attention because it is one of the most complete fossil primates found to date.
That, it certainly is. Beautiful, too. Ida helps us paint a picture of what life was like for primates in the Eocene.
For many paleontologists, that would be good enough. But other paleontologists live and breathe in order to make taxonomic statements (ie, This is related to That). Consider these two species of paleontologists the Morphologist and the Cladist.
The Cladist needs to rely on the Morphologist, though. When the Cladist wants to make a phylogenetic tree or cladogram, he or she needs to compile a list of character states, or traits, that are going to be used. An important point that Gingerich et al make in this paper is that those traits have to be independent traits- developmentally, functionally, and evolutionarily. If they are not, you are going to have a lot of redundancies in your phylogenetic tree, and you may end up showing that a certain group is more closely related than it actually is. One developmental character shift can affect many different aspects of anatomy. A good Morphologist will understand the origins of different anatomical traits, and should be able to tell which traits are meaningful, and which are redundant.
Gingerich et al. re-state the traits which they found in Darwinius massilae which they interpreted as derived toward the Haplorrhine clade, as a result of shared ancestry. Let’s review:
- A cranium with a short rostrum (Or a head with a short nose). This trait evolved in Haplorrhines after lemurs and lorises split off to form their own branch. Darwinius doesn’t simply have a short snout because it is a young individual, because size of the premolars, as well as the number of them, is reduced. However, there are strepsirrhines with “short” snouts, and Haplorrhines with “long” snouts. My main question is, when does a snout go from “longish short” to “short,” or “shortish long” to “long”? Maybe “most” haplorrhines have a short snout and “most” strepsirrhines have a long snout, but does that make it a reliable trait?
- A Mandible with a Deep ramus (or a “tall” jawbone). The mandible became “deep” after tarsiers split from the rest of the haplorrhine clade, and Darwinius shares this trait. Again, there are strepsirrhines with deep rami and haplorrhines with shallow rami.
- A fused mandible. Most mammals have a mandible that exists in two halves, a right and a left. Anthropoid primates (monkeys and apes) have a fused mandible, so that it exists as one solid entity. Darwinius has a “partially” fused mandible, which is fused on the bottom (the ventral side) and open at the top (the dorsal side, where the teeth are). This trait is also a “generalization with exceptions.” However, the exceptions are spread out throughout the primate tree, which indicates that this trait probably evolves very “easily.” It may even be related to loading during life, so that it’s not a trait that is under selection and can pop up in any primate who subjects its jaws to heavy stresses.
- Spatulate incisors (Spoon-shaped incisors, as opposed to pointy incisors). Many strepsirrhines (and tarsiers, too) have pointy incisors. Williams et al. contended that the primitive state was to be more blunted and spoon-shaped, and that the pointy incisors were the ones that were derived. Gingerich et al. counter that they “cannot imagine” that, although they can conceive of the fact that spatulate incisors are convergently derived in the taxa which display them (Darwinius, eosimiids, and some omomyids).
- Absence of claws or grooming claws. Lemurs, lorises, and tarsiers all have a grooming claw on their second digit. Monkeys and apes do not, except for the callitrichines. Tarsiers have a claw on the third digit, as well. As for fossil adapiforms or omomyiforms? Nobody knows. Fossil lemurs have been found without grooming claws, but none of have been found with a conclusive claw. Again, Gingerich et al. “cannot imagine” that nails on all digits could be primitive for primates.
What the hell? Since when has “I can’t imagine!” been a valid scientific argument? Especially since Williams et al. traced their line of reasoning so clearly in their paper! Compare this exerpt from Williams et al.:
However, the polarity of this feature is unclear. Extant lemurs, lorises, and Tarsius have a claw on the distal phalanx of digit II of the foot, whereas non-callitrichine anthropoids do not (Soligo and Muller, 1999). Tarsiers also have an additional claw on digit III of the foot. Gunnell and Rose (2002) note that there is no clear evidence for the presence of a digit II claw in adapiforms and omomyiforms. A toilet claw has been reported for Europolemur kelleri ([van Koenigswald, 1979] and [Franzen, 1994]), although from our own observations of high-resolution casts of the specimen in question (HLD-Me7430) we remain unsure. Its congenerEuropolemur koenigswaldi lacks a toilet claw (Franzen et al., 2009). Thus, it is plausible that the presence of flattened nails on all digits is the primitive condition for euprimates and that toilet claws evolved independently in extant strepsirrhines, tarsiers, and callitrichines. Accordingly, the presence of a nail on digit II supports neither haplorhine nor anthropoid status for Darwinius.
with this exerpt from Gingerich et al.:
Claws or grooming claws on the pes change from present to absent between nodes 13 and 12 in the phylogram of Figure 2. Thus the loss of grooming claws and acquisition of nails on all digits in Darwinius is appropriately counted as a derived characteristic shared with Haplorhini.
Asserting something does not make it so! Yes, based on the taxa that they used to construct their tree (mainly living taxa), there is a split between tarsiers and the rest of the haplorrhines. But did they use the right traits? Or the right taxa? Make intelligent choices. Don’t be bound by your “imagination.” You can plug a bunch of living taxa into a computer program and then figure out where your fossil fits, but is that really making a sound scientific choice? Don’t those other fossils count for something?
Two more traits which Gingerich et al. consider to be derived are inclued in their article, but they are discussed as simply occurring between nodes and “thus” “appropriately counted” as derived features.
Gingerich et al. say that the Williams crew did not find any traits which were derived toward Strepsirrhines, but I think that may miss the point that Seiffert (2009) made with Afradapis- adapiforms are a sister clade to modern Strepsirrhines, and are derived in their own direction.
Am I missing something? Why was this article so disappointing?
Gingerich, P., Franzen, J., Habersetzer, J., Hurum, J., & Smith, B. (2010). Darwinius masillae is a Haplorhine — Reply to Williams et al. (2010) Journal of Human Evolution DOI: 10.1016/j.jhevol.2010.07.013
Williams, B., Kay, R., Christopher Kirk, E., & Ross, C. (2010). Darwinius masillae is a strepsirrhine—a reply to Franzen et al. (2009) Journal of Human Evolution DOI: 10.1016/j.jhevol.2010.01.003
Seiffert, E., Perry, J., Simons, E., & Boyer, D. (2009). Convergent evolution of anthropoid-like adaptations in Eocene adapiform primates Nature, 461 (7267), 1118-1121 DOI: 10.1038/nature08429
September 6, 2010Posted by on
I thought I was going to enjoy this op-ed piece. Massimo Pigliucci said it was “tongue-in-cheek” and was going to be critical of evolutionary psychology, and from a female perspective. Hey, I’m a female who is skeptical of a lot of evolutionary psychology, and I love internet snark! Sounds good!
But then I clicked over and noticed that it was from Wendy Shalit. Her female perspective- that women are miserable because we’re immodest- is not my female perspective. As it turns out, she is not only critical of evolutionary psychology, but seems to view apes themselves with the kind of disdain that I usually only see coming from creationists.
Shalit apparently read a previous op-ed by Christopher Ryan of Sex at Dawn (and co-author of a book by the same name, which I have unfortunately not had a chance to read yet). I’ve disagreed with Ryan in the past about fossils, and I take issue with comparing bonobo behavior to modern human behavior to the exclusion of chimps, or really any other primate. Chimps and bonobos are much more closely related to each other than either are to humans, and both display extremely derived social and sexual behavior. I don’t think either can serve as an analog for early human/hominid behavior. But even if it could, it would say nothing about modern human behavior, because humans have evolved quite a bit in the past 6 million years. We have faced evolutionary pressures which differentiated us from the common ancestor that we share with chimps, and so have chimps and bonobos.
But, I generally agree with him that modern humans display a wide variety of what primatologists would call “mating systems,” from the pair-bond to polygyny to multi-male/multi-female. I think a lot of it is cultural rather than biological, but I’m also willing to admit that it’s hard to tease the two apart in this debate.
Shalit, however, seems to have a problem with the very idea that studies of ape behavior can teach us about ourselves. After a healthy dose of scare quotes around phrases like “pair-bond,” she says, “Let’s face it — the new ‘science’ of infidelity is just not very scientific.” Part of being a scientist is actually doing some legwork to evaluate claims which you find dubious. You either think that human behavior has evolved, or you don’t. If you do, it isn’t an inherently offensive idea that humans are a promiscuous species. You may evaluate the evidence and come to a different conclusion, but that’s different from taking offense to it.
Here’s the thing that gets me all riled up when I read these sorts of op-eds: Lots of people study primate sexuality. It’s a fascinating field. And who the primates are having sex with is only part of the fun. We know about stress, group dynamics, cognition, and general evolutionary theory because of the good, hard work of these people who are driven by curiosity. But for some reason, the only time primate sexuality gets any attention is when we turn it into a debate about how humans should be having sex.
We never say, “Hey, those muriquis are too promiscuous. Don’t they know that all of their close evolutionary cousins are polygynous? If they just did what came naturally to them, they’d have a lot less psychological stress.” Or, “Those gibbons are so sexually repressed. If they just gave in to their natural predilection for promiscuity, I bet those nasty gibbons would have fewer territorial disputes and gibbon society would be much more peaceful.”
No, we recognize that in those primates, their behavior has been shaped by different ecological and social pressures. Sometimes, we accept that those pressures occurred very recently, and are probably very specific to a certain environment which that species occupies. We recognize that they have a unique evolutionary history. But as soon as we introduce humans into the equation, we change our descriptions of behavior into prescriptions, and our supported hypotheses into capital T Truths about human nature. We try to figure out THE. NATURAL. WAY., so that we can start doing it ourselves, and shaming those around of us who haven’t caught on yet.
I’ve talked before about how behavior is sometimes given a “special status” in evolutionary studies. Researchers assume that it is so labile that it is virtually meaningless. Current behaviors, according to these researchers, can tell us nothing about past behaviors or evolutionary relationships, and so we should focus entirely on anatomy. And yet, in the popular press, we are led to believe that human behavior has been unchanged for millions of years, while our bodies have undergone complete restructuring and our brains have increased in size to an unparalleled degree. It’s the dreaded paleo-nostalgia.
Either that, or we’re supposed to be so repulsed by our primate cousins and their raunchy sex lives that we cast aside all possible science which may or may not illuminate our own condition.
I guess there really aren’t that many people who would read an op-ed about primate behavior unless it made a bombastic conclusions about human behavior. It’s telling, then, that there aren’t very many primate behaviorists writing op-eds about human sexuality.
August 31, 2010Posted by on
It’s the beginning of the academic year, and many budding young biological anthropologists are beginning their first semester as graduate students! With that in mind, it’s probably a good time to talk about one of the most important aspects of our graduate education: The Thesis. I received an e-mail from a reader in which he asked a few questions about choosing a thesis topic. The reader is currently working on an MA and wants to study primate morphology when he applies to different PhD programs, and had this question to ask:
Can I still apply for Grad schools which have an emphasis on morphological aspects on primate and human evolution even with a thesis which is barely related to it?
Now, all I have to go on is my own experience, but one piece of advice which has been given to me over and over again by advisors, mentors, and my senior colleagues is this: Your thesis is not your life’s work.
It’s actually quite a liberating statement, I think. It takes the pressure off of choosing the “perfect” thesis topic, because you can always change which direction you want to go later. The important thing is to pick a topic which you know you can complete and do a good job with. And honestly, how many “famous” scientists got to be that way because of their thesis or dissertation? None that I can think of… You want to be putting the bricks in place for an entire career of brilliant work- not working on your magnum opus.
I think that there are many subjects in biology which inform our knowledge of morphology, and a background in a different subject may end up being to your advantage. While you’re working on your MA thesis, I think there is some wiggle room. As long as you are learning something that you enjoy, I don’t think any graduate school will penalize you for working on something which has made you a better biologist.
Another catchphrase that we grad students here use as motivation is this: The only good thesis is a finished thesis. We all want to complete a ground-breaking thesis that will get us into the pages of Science or Nature, but the point of your graduate education is to learn how to be a scientist. You want to complete your education as quickly as you can, so you can go on to actually be a scientist. Being scientists-in-training, we are all perfectionists to one degree or another, but it’s more important to have a finished product than it is to have a perfect product. We all know people who have spent the better part of a decade working on their dissertation, but grad school should not be a career. Chances are that all of that extra time you spend agonizing over tiny details won’t end up making a difference anyway.
This is the kind of stuff that we hear from our advisors all the time, but it helps to hear it from other students sometimes, too.
And, since it’s the beginning of the semester, I’ll pass along a link to Kenny’s roundup of 8 tools no graduate student should go without. Check out the Monkey Matters Blog while you’re over there. It’s fun stuff!