Sex-volution
This week I have spent some of my time (a lot, really) reading and replying to posts on the TWIS forum relating to evolution and religion. It is amazing how fast the discussion turns into mudslinging as soon as a creationist steps into the fray. It’s mean on both sides; the evolution proponents who berate the short-sightedness of the creationists, and the creationists, who defensively attack evolution like cornered animals. It eventually turns into name calling if no one steps in to create rules for the discussion. I hope that I can foster the forum to be based on open inquiry of science, not dogma, with a focus on observable, testable, and repeatable evidence.
Anyway, with all this evolution talk on my brain, I can’t help but look for evidence in everything I read. Recently, it seems to be all about love and sex in the science headlines, and the stories raise some interesting questions about the evolution of human sexuality and love. Are we hard-wired to experience love and romance? Is this wiring something that developed in an ancestor of most modern-day mammals? What controls the ability to experience these intense feelings? Are some individuals better able maintain close relationships simply as a result of their genes? While these questions may not have been answered, there is some interesting evidence and debate on the topic.
Tags: Science, Radio, technology, Podcast, Podcasting, News, Media, Sex
One scientist doesn’t believe that the female orgasm is an evolutionarily adapted trait, while others have found evidence that it may just be in a woman’s genes. A team out of Emory University have shown that bits of “junk” DNA may be responsible for our ability to feel compassion. Another research team suggests that romantic love is controlled by areas of the brain involved in reward and motivation, and there are other findings that orgasms turn off emotional centers in the female brain.
The female orgasm may or may not be a direct result of evolution. That is to say that we don’t really know whether the ability to orgasm confers improved reproductive capacity onto a female. Does a woman who orgasms reproduce more successfully than those who don’t, and are those genes passed on to her offspring? Elizabeth Lloyd thinks that the female orgasm is simply a by-product of evolution that has molded humans into two sexes. She argues in her new book, The Case of the Female Orgasm, that the female orgasm is a “happy accident” based on the fact that men and women derive their sexual characteristics from the same embryonic tissue. Sexual hormones in the developing emryo cause men to go on to develop a penis, and women a clitoris. Men depend on climax to reproduce, while the jury is still out for women.
Lloyd argues against all current scientific evidence that suggests the female orgasm is evolved, producing solid scientific evidence to the contrary. However, recent evidence from a twins study might add more evidence to the pile supporting an evolutionary purpose. Researchers in London calculated that “35-45% of the variation in ability to orgasm can be explained by… genetic variation.” The rest of the variation relies on other biological, societal, and pychological factors.
Now, one could argue that even though there is genetic variation underlying the trait, the proportion of those genes in the population may not be changing if there is no selection pressure acting upon them. We have genes for many traits that are not being acted upon by selection pressures, but only the genes that confer survival advantages will increase in the population. Obviously, still more evidence needs to be brought to bear on this issue before a decision can be made. If, for instance, it was shown that levels of the hormone oxytocin, the release of which has been linked with orgasm and which stimulates lactation and uterine contractions related to pregnancy, increased in the body during orgasm, that those increases were related to improved movement of sperm toward the egg, and the combination of oxytocin and sperm motility led to a higher rate of reproduction, we could be reasonably certain that, yes, the female orgasm has an evolutionary purpose.
Oxytocin is also thought to increase the ability of mammals to form pair-bonds. In human terms, it might make us more capable of forming emotional bonds and maintaining long-term relationships. It has been shown to directly affect the ability of rats and sheep to bond with their offspring, and for prairie voles to pair-bond with mates as adults. Might oxytocin be responsible for love and romance?
Well, oxytocin can only be responsible in part as it has an important partner in crime called vasopressin, which has also been shown to affect the ability of adult prarie voles to form lasting relationships. In more recent prairie vole research, scientists Larry Young and Elizabeth Hammock at Emory University have discovered that variation in portions of the genetic sequence for the brain receptors that bind with vasopressin may be responsible for individual variation in monogamy and other similar social behaviors. The regions of DNA responsible are contained within control regions of the vasopressin receptor gene, and are called microsatellites. These interloping segments of DNA consist of repeating sequences of genetic information, but were once considered junk since they seemed to have no particular function.
Now, though, the researchers have determined that individuals with longer microsatellites have more vasopressin receptors in areas of the brain responsible for sociality. Those animals with shorter microsatellites have fewer receptors for vasopressing in the same brain areas. A finite number of receptors can only interact with a similar amount of hormone. A larger number of receptors would make an animal able to respond to more vasopressin. Therfore, creating a larger response to the hormone. Logically, it follows that the voles with longer microsatellites would be more social and nurturing to their young, due to an enhanced ability to respond to vasopressin release.
The implications of the prairie vole study have a long reach. The researchers have also shown that bonobos have longer microsatellites than chimpanzees. This difference translates behaviorally, and could eventually be used to explain variation in human social behaviors. For example, human familial microsatellite lengths have been linked to the social disorder of autism. Consequently, behaviors such as monogamy and sociality could be evolving in humans based upon the selection pressures affecting the microsatellites within our genes.
In addition to pinning down the genetic basis to our sexual and romantic proclivities, researchers have begun to determine the areas of the brain that are responsible for the way we feel when so in love. An fMRI study of people madly in love showed that romantic love has more to do with rewards and motivation than with sex. The areas of the brain that were activated when the people saw pictures of their partner in love were the ventral tegmental area and the dorsal caudate body, both of which are involved in the motivation to achieve a reward, and the activation was mainly on the right side of the brain. Whereas, the left side was activated when the subjects were shown pictures of attractive people they were not in love with. Additionally, this study supports the view that we have three separate systems within our brains that separately control our sex drive, romantic love, and long-term attachments.
Romantic love, while may be derived from motivational brain areas rich in dopamine, over time will develop into long-term attachment with a partner. The researchers showed an increase in activity in vasopressin rich areas of the brain in those subjects who had been in longer relationships. Once the reward has been won, in a monogamous species the brain must find a way to maintain the relationship indefinitely. The evidence suggests that vasopressin may be the key to that maintenance. Additionally, sex with an established partner may also allow oxytocin to play a part in strengthening that bond even more.
To bring the story full circle, while oxytocin is released during orgasm and stimulating areas of the brain implicated in social bonding, other areas of the brain are being told to quiet down. Researchers in the Netherlands recently used PET scanning technology to demonstrate that the amygdala and hippocampus (areas involved in anxiety, fear, and alertness) were turned off in women experiencing orgasm. The scientists think that the brain may turn off emotions that would normally be used to maintain awareness of surroundings in order to allow reproduction to ensue more effectively. In a sense a woman must trust her partner enough to be at ease with him and feel protected, in order to allow herself to completely relax during the sexual act.
It seems there may be more evidence for the evolutionary purpose of the female orgasm after all. If a woman is able to relax enough to orgasm, the orgasm may improve chances of reproducing and allow further bonding with the partner to ensure future mating and help rearing young. Along those lines, if a woman is threatened by a male, say a rapist, she will not relax or experience orgasm, possibly decreasing her chances of conceiving from the unwanted mating. Who knows? The variation in our genes, may play a massive role determining our sexual and romantic social behaviors. The jury is still out, but if these studies are any indication, we may yet figure ourselves out.
Who’s in for trying to genetically select for a super-race of females capable of multiple orgasms? It might just be easier than we think.
Here are all my sources of information:
http://mypage.iu.edu/~ealloyd/
http://www.alertnet.org/thenews/newsdesk/L06270721.htm
http://slate.msn.com/id/2119551/
http://www.eurekalert.org/pub_releases/2005-06/niom-rsb060805.php
http://www.medicalnewstoday.com/medicalnews.php?newsid=25393
http://www.oxytocin.org/oxytoc/
http://www.sciencedaily.com/upi/index.php?feed=Science&article=UPI-1-20050621-16371100-bc-netherlands-sex.xml
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