Sunday, March 21, 2010

Genes for everything

To what extent our genes represent the totality of our behavior? There are many sociobiologists out there stating that many genes- including homosexual genes, human universal genes, depression genes, even rape genes- are included in human's genetic make up in order to survive the crucial natural selection. Although these are not Coyne's ideas, stated on page 228, these genes seem to be logical in some way. The survival of the parental genes, the passing of the genes, is one of the strong focus of natural selection, according to some scientists. Are these gene behavior representation idea true to the six evolutionary theory points? If so, how and in what way? If not, why are these behavioral "genes" a misrepresentation of the evolutionary theory?


  1. This prompt is almost more of a psychology question than a biology question, as the study of human behavior spans both fields. However, it appears as though behavioral genes may be at least partially a product of evolution. For example, the Homeobox gene (Hox), which regulates development in humans, originated in cnidarians hundreds of millions of years ago, and was evidently a successful genetic change, because Hox genes are found in all animals that descended from cnidarians (Wikipedia). The way a human develops as an embryo can affect how it behaves as it grows older, if for example a malfunction in the genetic development creates a disorder such as cystic fibrosis, autism, or ADHD. In addition, some human behaviors such as eating, sleeping, and sex are definitely adaptive, helping us to survive and reproduce (230). In these cases, natural selection would have selected for individuals who performed these activities most efficiently, and over evolutionary history the typical three meal per day, nine hours of sleep "natural" behavior probably emerged as the combination best suited to our survival. However, other behaviors, such as homosexuality, religion, and even a tendency to rape are more affected by the environment than by genes. While homosexuality is probably more acceptable in our society today than it was a few hundred years ago, there were undoubtedly gays back then. One speculation as to the evolutionary advantage of homosexuality is extra help in child care, ensuring more brothers and sisters for the gay individual (230). This show of altruism may have worked when humans were hard-pressed to survive, but over time, it became unacceptable in society, and thus the evolutionary advantage of being gay disappeared. Yet somehow, through all those years, homosexuals have continued to exist. This would seem to contradict evolutionary theory, which is based on the fact that nature is always choosing individuals with advantageous traits to survive, and eventually myriad small and beneficial changes in the genes create new species and cause certain traits to disappear. However, the unacceptability of homosexuality may be the very reason it has survived. Because gays were not accepted, many of them probably acted "normal" and married women and reproduced, keep the "gay" gene alive. Overall, it seems as though the environment probably regulates expression of these behaviors more so than the genes which code for them.

  2. In addition to Blumy’s comment about how “it appears as though behavioral genes may be at least partially a product of evolution” in the case of them being “more affected by the environment than by genes” as expressed in the phenotype, I must mention a very important evolutionary subtopic that is directly linked to behavior being dictated genetically. To say that behaviors such as depression, homosexuality, and even rape are 100% genetically inherited in origin would be wrong. Jerry Coyne states that it is dangerous to “Darwinize every aspect of human behavior, turning its study into a scientific parlor game” (Coyne 228) because much of human behavior is dictated by the environment.

    However, drawing upon past knowledge from the AP Biology course, it becomes evident that much of the environmental impact on human behavior can change the PHENOTYPE, not the GENOTYPE, of certain traits through the means of epigenetics, thus providing a link between behavior and genetics. True, there is not a sequence of letters for every single thing in the human body, but the expression of these letters as determined by the epigenome (expression being the phenotype) can be interpreted as an inheritance of certain behaviors. Take the example of Jesus and Celso Cardenas, who are identical twins. They were both born with the exact same DNA, but Celso is gay and Jesus is not. This phenomenon is explored in a National Geographic video on YouTube, which goes on to explore the inheritance of one’s sexual orientation. But wait, because one is homosexual and the other is heterosexual and yet have the same DNA, that must mean that sexual orientation is based on environmental conditions rather than genes, right!? Well, the video goes on to state that the normal chance of someone being gay is 5%. However, the probability increases, based on study, to about 50% in the case of identical twins. Clearly the inheritance is not 100% genetic nor 100% environmental, but the important thing to realize is that many COMPLEX behavioral patterns are not black or white. Instead, they are in the gray area, a balance between true genetics and pure environmental exposure.

    I think I can shed a bit more light on this with the example of how my family likes chocolate covered orange slices. My grandpa loves them, my dad loves them, and I love them. This means that there is probably a genetic element here, yet it is also evident that there is an environmental aspect as well because my sister hates them! If the orange slice loving gene got passed down, she obviously got it, but something environmental when she was growing up obviously put her off from chocolate covered orange slices. Remember, this is only a funny little metaphor and not a true study, only for the purpose of helping one understand a little application of epigenetics.

    Also, epigenetics is shown to play a part in rheumatoid arthritis and many other autoimmune diseases originally thought to be genetic in origin. In the journal article “What can we learn from epigenetics in the year 2009?” these points are discussed thoroughly. It just goes to show that it is imperative not to “Darwinize” (Coyne 228) everything because not everything is genetic in origin.

    Page 228 of the book

  3. I agree with Zach in that most of human behavior can be attributed mostly to psychology, but basic behaviors that directly affect one's individual fitness often are regulated by genes. Sleep, eating and sex, as zach mentioned, are behaviors that directly affect an animal's ability to survive and reproduce, and thus may be regulated by genes. On the other hand, more complicated animal behaviors like those displayed in humans can't be simply written off as a (gene Instead, complicated traits such as homosexuality and depression are most often by-products of genes coding for a more complex brain, which formed as a product of evolution. This is an increasingly heated issue, especially in the area of homosexuality, as some do say that these traits could be partly hereditary This brings up the question of why something like homosexuality would get passed on. Like Zach states, Coyne does say that homosexuality could indirectly help one pass its genes on by caring for siblings, nieces or nephews; this is called the "kin selection" hypothesis ( This, however, doesn't give a solid explanation for the persistence of "gay genes", meaning likely other biological factors contributed to the natural selection that has allowed homosexuality to persist; perhaps the homophobia that has persisted in society historically forced homosexuals to reproduce and pass on their genes. This is the area where some people believe that homosexuality is also heavily influenced by the environment, which means that in some cases, one could carry a homosexuality gene and still reproduce ( If this is so, then the persistence of the homosexuality gene could simply be a result of genetic drift, with the environment eventually causing one to become homosexual.