According to a study just coming out in the Journal of Sexual Medicine, “variations in emotional intelligence–the ability to identify and manage emotions of one’s self and others–are associated with orgasmic frequency during intercourse and masturbation.”
Tag Archives: Behavioral Biology
Grasping the function of the human penis
Gallup has taken on the task of explaining, in ultimate terms, the evolutionarily designed features of the human penis. He works this as an engineering problem from the perspective of evolutionary psychology, which is always a little bit dangerious, but gallup isn’t quite the arm waiver that a lot of other EP’s are, so he may be doing it right.
Gallup’s work is written up an an all-too-sophomoric Scientific American article by Jesse Bering which just barely falls short of explaining this important biological phenomenon in terms of a pair of headlights, a flashlight, and a little red waagon.
Here’s the money quote:
Magnetic imaging studies of heterosexual couples having sex reveal that, during coitus, the typical penis completely expands and occupies the vaginal tract, and with full penetration can even reach the woman’s cervix and lift her uterus. This combined with the fact that human ejaculate is expelled with great force and considerable distance (up to two feet if not contained), suggests that men are designed to release sperm into the uppermost portion of the vagina possible. Thus… “A longer penis would not only have been an advantage for leaving semen in a less accessible part of the vagina, but by filling and expanding the vagina it also would aid and abet the displacement of semen left by other males as a means of maximizing the likelihood of paternity.”
The other component of the work is the intriguing possibility that penises have evolved to carry semen previously left in one female’s vagina from another male to be deposited hours later in the vagina of a second female. Which I suppose could be called facilitated cuckoldry.
I’ve not read the original paper yet. I’m not quite up to it. But if I do, I’ll let you know if it is truly a seminal work, or if Gallup is just jerking us around.
Finches Determine Sex of Offspring
As you know if you read my blog, Trivers Willard is an important theoretical construct which has been tested numerous times. TW works in some species, not in others, and overall, that should be predictable (accroding to TW).
It turns out that finches control the sex of their offspring, and do so in a way that TW would predict, apparently. There is a paper in Science that I’ll probably eventually get to writing up for you, and in the mean time, here’s a quick news report from Scientific American.
See if you can figure out how Trivers Willard is working here, and why the important theoretical aspect of this research is glossed in this news report.
The curious case of penile vaginal intercourse and depression in women
I’m starting to worry that the last few Friday Weird Science write-ups by Scicurious (who seems, these days, to be the primary blogger at Neurotopia) have been of papers that I happen to have read. Just so you know: Thousands of papers are published per week across the diverse sciences, and although Scicurious tends to deal with life science and I tend to read life science, the chances of this particular harmonic convergence across bloggers regarding papers published over the last decade is statistically almost zero. More likely, Scicurious and I just have similar taste … or lack thereof.
The latest paper written up by Sci is on the relationship between certain kinds of sexual intercourse and reduction of depression in women, suggested by a study by Gordon Gallup and others.
Continue reading The curious case of penile vaginal intercourse and depression in women
Male vs. Female Brains
The male and female human brains are different. Some of the better documented differences are similar to differences seen in other mammals. They are hard to find, very small, and may or may not be of great significance. Obviously, some are very important because they probably relate to such things as the ability … or lack thereof … to bear offspring. But this is hardly ever considered in the parodies we see of these differences.
[Repost from Gregladen.com]
Continue reading Male vs. Female Brains
Topi or not Topi …
Go to any bar and you’ll see a lot of males standing and sitting around not mating. I’ll bet you would have guessed that the reason they are not mating is that no females will mate with them for one reason or another. But there is the distinct possibility that they are very inconspicuously resisting mating opportunities. It turns out that males can do this …. avoid mating without conspicuous resistance … more easily than females. For obvious reasons.
This could be why what has become (inappropriately) known as “reversed sexual aggression” often goes unnoticed, and a recent study of the African antelope Damaliscus lunatus (a.k.a. “topi”) explores this possibility.
Why is There no Birth Control Pill for Men?
Why is there no Birth Control Pill for men?
The answer I’d like to propose can be summed up in two closely linked words pilfered from the question itself:
Continue reading Why is There no Birth Control Pill for Men?
Chimpanzee Food Sharing
Is chimpanzee food sharing an example of food for sex?
One of the most important transitions in human evolution may have been the incorporation of regular food sharing into the day to day ecology of our species or our ancestors. Although this has been recognized as potentially significant for some time, it was probably the Africanist archaeologist Glynn Isaac who impressed on the academic community the importance of the origins of food sharing as a key evolutionary moment. At that time, food sharing among apes was thought to be very rare, outside of mother-infant dyads. Further research has shown that it is in fact rare … the vast majority of calories consumed by human foragers in certain societies and at certain times of the year comes from a sharing system, while the fast majority of calories consumed by chimpanzees is hand to mouth without sharing.
Continue reading Chimpanzee Food Sharing
Marta’s (good) questions, … fur
Why did humans evolve hairlessness? Hair (fur) protects mammals from heat and cold, what would be the benefit from losing this asset?
I think the most commonly held theory is that fur works on quadrupeds, but once you stand upright, it is less effective, and less fur works better. For later time periods, clothing works better than fur because it is more adaptable. Consider that whatever fur-based system human ancestors had was based on needs in the tropics where it does not get that cold, so it is not hard to imagine that clothing is much more effective.
Recent studies of body parasites suggest that body lice unique to humans differentiated genetically only fairly recently, in the range of several tens of thousands of years. This body lice requires clothing … human clothing on human bodies is the habitat for these lice. This suggests there may have been a reduction from a certain level of furriness only with modern humans living in a wide range of environments and using controlled fire, clothing, and some kind of shelter (hut/house) to deal with the elements. So it is possible that the immediate ancestors to modern humans (perhaps Homo erectus?) were actually fairly furry.
As for details of the body hair, this is also interesting. Why do humans have pubic hair but not a lot of other hair? Why to males have more body hair than females in many cases? Why to human males have facial hair? The African Apes have much less facial hair than most modern human males. It has been suggested that this has to do with sexual selection. It is important to distinguish between the idea that the starting condition is a lot of fur and that females may have lost more than males, vs. the starting condition was very little hair and males have added more. The amount of fur, it’s appearance, etc. may be related to testosterone (this is true in males and females but more obvious in males) so facial hair may be a signal of “quality” in males.
Marta’s (good) questions, … continued
Why did the evolution of a large brain happen only once (among mammals, and in particular, primates?)
Larger brains have evolved a number of times. It seems that there has been a trend over several tens of millions of years of evolution of larger brains in various clades, such as carnivores and primates. There is probably a kind of arms race going on among various species in which a larger brain is an asset.
However, as you imply, a really large brain (like the extraordinarily large human brain) seems to be very rare. One of the reasons for this is that there are at least two major kinds of costs of a large brain that outweigh the benefits. One kind of cost is the energetic expense of having this large brain. Over 10% of the day to day energy demands of an adult human go to the brain. The total energy requirement of an infant can be over 60% while the brain is both a relatively large proportion of the infant’s body, and is undergoing a great deal of growth. The brain tissue is very picky about things like the temperature it requires for normal function and the kind of nutrient it needs.
Marta’s (good) questions, Greg’s (oft’ lame) answers: Bonobos?
My student, Marta, exploded the other day.
She was sitting there in class two weeks ago and exploded. She does not know that I know this, but I noticed it happen. Since she was sitting, as usual, in the front row, and it was all in her face, the other students did not see it but I definitely did.
By “exploding” in this case I mean that her brain suddenly filled with unanswered questions, which she then started sending me in frantic emails. Many of these questions are about things we will eventually get to in class, but some are on issues that we won’t touch on at all. I decided, and I received her kind permission to do this, to answer her questions by blogging them. This way I get to kill two birds with one stone, which is usually a good thing (unless of course you are the second bird).
In some cases I’ve re-written the question a little, but in all cases, they are good questions. I cannot guarantee that all of my answers will be good. But I do appreciate Marta’s inspiration, and find it inspiring myself. My only concern is that Marta gets interested enough in this material to become a biological anthropologist and thus wastes an otherwise potentially productive life. I’m hoping she becomes a doctor or a world leader instead, but we’ll see…
OK, on to the first question (I’ll deal with others in later posts):
Continue reading Marta’s (good) questions, Greg’s (oft’ lame) answers: Bonobos?
Great Moments in Human Evolution: The Invention of Chipped Stone Tools
Or not.
Much is made of the early use of stone tools by human ancestors. Darwin saw the freeing of the hands ad co-evolving with the use of the hands to make and use tools which co-evolved with the big brain. And that would make the initial appearance of stone tools in the archaeological record a great and momentous thing. However, things did not work out that way.
Continue reading Great Moments in Human Evolution: The Invention of Chipped Stone Tools
Delay of childbirth and cesarean section: There may be a link.
A study just out in PLoS Medicine suggests that an increasing trend of delaying childbirth is associated wiht a rising rate of the use of cesarean delivery. The explanation appears to be impared uterine function.From the editor’s summary:
Though it was not studied here, the researchers hypothesize that impaired uterine contractility may be a consequence of prolonged stimulation of the uterus by estrogen and progesterone, resulting from a prolonged interval between menarche and first birth. Further research is needed to understand the determinants and management of dysfunctional labor in older women to help design strategies for reducing population cesarean delivery rates without adversely affecting maternal and infant outcomes.
Continue reading Delay of childbirth and cesarean section: There may be a link.
Morning Sickness is an Adaptation, not a … Sickness
There is new information from an older idea (from about 2000) by Paul Sherman and colleagues. The idea underlying this research is simple: Symptoms of illnesses may be adaptive. Indeed, this may be true to the extent that we should not call certain things illnesses. Like “morning sickness.”
Broadly speaking, there are two different kinds of reasons that a woman may experience nausea in association with pregnancy. 1) This pregnancy thing is a complicated mess with all kinds of hormonal (and other) things going on, so you puke; or 2) a woman who is pregnant feels nauseous for good evolutionary reasons. Continue reading Morning Sickness is an Adaptation, not a … Sickness
Sex Ratio Bias in India
Sometimes boys are worth more, sometimes girls are worth more. In an evolutionary sense. Or, more correctly, the value of a certain sex … as an offspring … can be measured in fitness terms. Fisher noted this and hypothesized this was the explanation for the 50-50 sex ratio we usually see. As one sex becomes more rare, it becomes more valuable, and thus parents (mothers, perhaps, usually) bias towards that sex. Then the disparity goes away and thus the differential value goes away.Of course, the truth is that we don’t actually see the 50-50 sex ratio all the time … many species of organisms have a highly biased sex ratio. Many have a highly biased ratio in adults, much more biased than in offspring. This sort of thing varies quite a bit. But what about humans, and what about the report that Indian girl-boy ratios at ‘all-time low’ … Continue reading Sex Ratio Bias in India