There has been a debate amongst the sciences since time immemorial. Artists of antiquity argued viciously over the source of inspiration. Some thought creativity was heritable, some thought it was a learned quality, and some thought it was the result of literal possession by spirits. Even in modern times, the humanities are split on the issue of ‘Nature vs. Nurture’; though the sciences call the debate ‘Genes vs. Environment’.
This debate is a bit archaic; we know that a combination of genes and environment are intricately entwined in human behavior. As Pinker explains in The Blank Slate, we can infer from common sense that genes do play a significant role in cognition. Parents can attest that their newborn children come into the world with different temperaments and talents. Children will learn human language when exposed to it, whereas pets will not. And most of us would say that the minds of men and women are not indistinguishable.
Contrariwise, it is also common sense that genes cannot be completely deterministic. Embryos still require a mother’s womb to develop in; and language acquisition still requires exposure to adult, native speakers. Our minds are preconditioned to develop certain ways, and at certain times. However, the structures and processes involved in cognition have a tremendous amount of complexity, leaving human behavior practically impossible to model. This paper will explore the extent to which genetic influences on behavior have been correlated.
Part of the problem in assessing genetic determinism is that a behavior which appears to be heritable does not mean that it is genetic, it could be tribal (learned within the family), or cultural (due to similar environmental experiences). Thus, conclusive studies typically must incorporate gene sequencing, though identical twin studies bypass this need. This produces another issue. We know from genetic studies with physiological traits that it is simple to find genes for traits when only one or two variations exist in the gene. But for neurology, many more genes can contribute to the expression of singular traits.
According to the Human Genome Project website, the genetic basis of many traits have been uncovered: right and left handedness, hand clasping pattern, arm folding preference, ability to move ears, recognition of pitch, stuttering, ability to curl, fold, or roll the tongue; anxiety, risk-taking, and novelty-seeking. Many diseases have simple genetic profiles. Some studies corroborate genetic influences in susceptibility to cancer, diabetes, other diseases, addiction, and alcoholism. There is also genetic evidence surrounding violence, intelligence, and sexual orientation. These issues tend to provoke controversy over social justice, therapy, eugenics, and legal defense. Are criminals responsible for their actions if their genes ‘made them do it’? Is it ethical to ‘cure’ sexual predispositions, or is it immoral? Do parents have a right to ‘engineer’ their children? The ethical extent of these considerations depends largely on the technology at hand, and the quality of the science conducted. As our technology grows faster, our understanding of the world grows with it. An inevitable increase in choices forces the development of new ethical questions about their use, and their effects. However, such ethical considerations are beyond the scope of this paper.
According to a study in Samoa, one evolutionary explanation for homosexuality is that a gene increases a sexual orientation towards men, regardless of the individual’s gender. Females with the gene have more children than women without the gene. This compensates for the men who choose to be celibate or homosexual, and eliminate themselves from the gene pool (VanderLaan et al p. 4). Theoretically, there is no reason for an opposite gene to not exist as well. Other explanations exist but have not yet been corroborated.
Genes correlated to violence have been sought for a long time, but whenever a study comes out the results are almost always debated. There are many small genetic correlations to violence, but each only composes a small fraction of the criminal population. It is known that men with XYY genes tend to be more aggressive and masculine. People with a particular variation of the monoamine oxidase A (MAOA) gene have decreased dopamine levels and increased likelihood of criminal and delinquent behavior (Fox).
A ‘smart gene’ was purported to be found in rats in a study in 1942, conducted by Robert Tryon. He selectively bred his rats into groups which solved mazes more quickly and made fewer mistakes, and those that made more mistakes and solved mazes less quickly. After 21 generations, he claimed to have generated a ‘bright’ and a ‘dull’ strain of lab rats. However, while he showed that their performance was genetic, he was wrong to conclude that intelligence was genetic. As was pointed out by many critics, the behavior could have physiological roots rather than neurological ones, such as bad vision or weaker leg muscle.
Since then, genetic studies with ‘smart rats’ reveal that a variant of the NR2B gene increases memory capacity or speed in the hippocampus. This gene produces CaMKII protein, opening synapses for milliseconds longer, significantly improving short term and long term memory formation (ScienceDaily). However, learning does not necessarily equate to intelligence. The precise definition of intelligence is still widely debated in the scientific community.
The ‘staggerer’ mutation is a point deletion in the ROR gene, found in rats. It is responsible in cerebellum development and function (Steinmayr). It is a highly conserved region of DNA. This would make sense evolutionarily, because movement is a crucial survival component in phylum chordata.
One of the most helpful kinds of studies are identical twins separated at birth. This eliminates the need to conduct gene sequencing. However, this likewise still presents a challenge in sifting out genetic causes from environmental stimulus. James Springer and James Lewis (separated at birth) had each married women named Linda, and then divorced and married women named Betty. They both became sheriffs, and both had skills in mechanical drawing and carpentry. They both had sons whom one named James Alan and the other named James Allan with two L’s. They both had a dog and named it Toy. Both drove pale blue Chevrolets. They both smoked Salem cigarettes, and drank Miller Lite. They were prone to migraines and were chronic nail biters (Never Say Always). Every study of identical twins separated at birth show some remarkable similarities.
What identical twin studies show in general is that style and preference are largely rooted in genetics. It was commonly thought that such emotional dispositions were more individualized and environmental, and is still thought to be so by many scholars. Twins themselves say that while they share eerie similarities, they still have different life stories, and unique identities. Twins express the same posture and dance the same way because of their physiological similarities. Monozygotic twins (fraternal) share 50% of their genes, but their behavioral similarities are commonly thought to be associated with conditions in the womb of the mother.
Clones offer the same advantages as twin studies, though less feasible. A herd of genetically identical, cloned cows still developed a distinct social hierarchy. Cloned animals exhibit the full spectrum of behavioral traits, from curious and inquisitive, to timid and shy (Singer).
Mutations of the FOXP2 gene creates significant language impairment. The majority of mental retardation syndromes are the result of genetic mutations (microcephaly, Down’s, PKU, cretinism, x-linked, and more). Mutations in the AMT (10%) and GLDC (80%) genes cause glycine encephalopathy. Mutations in the SLC25A19 gene cause Amish lethal microcephaly. Besides genetic inheritance and random mutation, such syndromes can also be generated from mutagenic substances. Similar disorders can arise from poison or malnutrition during pregnancy or childhood.
Then there are the cases of feral children. A schizophrenic father locked his daughter, Genie, in a closet for the first 13 years of her life. She was strapped to a potty trainer, and forced to wear diapers. She was rescued by police in 1970, and had dramatically impaired mental capacity and no language capability. She eventually learned many words, but never learned proper syntax, or complex abstract ideas. This lead to the formation of the “critical period hypothesis”, that exposure to language is required before the age of 12 (Kasper).
In addition to the prominent roles of various environmental stimuli in language acquisition, other genetic factors must be involved. In Pinker’s The Stuff of Thought, he explains the ‘verb-learning paradox’: “learning locative constructions in English is nearly impossible. Yet somehow children can hold back applying the wrong rules to words they have never heard. Their uncanny application of rules is something of a linguistic paradox, that children can learn the un-learnable” (41). Pinker goes on to dispute complete linguistic determinism, on the basis that it would require a near-infinite gene pool, and secondly because the abstract notions of things would have to exist prior to their invention. However, “there must be some innate concepts, like the keys on a piano, from which others meanings are constructed” (p. 92).
The Human Genome Project website lists some reasons why behaviors in general are in principle linked to genetics. Behaviors are often species-specific, behaviors often breed true, behaviors run in the family, and behaviors change in response to drugs that alter brain chemistry. The highly social primates share qualities of nurturing, cooperation, altruism, and facial expressions. Altruism can have advantages within societal contracts, making it’s net survival worth evolutionarily viable. Insect altruism is highly genetic. Though both insect and primate altruism are most highly emphasized in terms of kin selection. Acts of radical altruism in certain human individuals do not appear to have any evolutionary advantage, and this remains a puzzle for geneticists, but it might not be a genetically rooted phenomenon.
In Quantitative Genetic Studies, Christine Boake overviews many of the interconnectedness of environment and genes. She provides a whole chapter on how the size of an animal limits its expressive capacity. For instance, a large bird may have a more impressive display, but has less endurance in his courtship dances. Theoretically, this can create an evolutionary divergence which is accentuated by sexual selection, or by life strategies (185-186).
Migration has a wide diversity of environmental factors, as species often are moving north to south (or vise versa), across varied habitats, temperatures, and food sources. However there are prominent genetic effects on migration. Insects which can have wing mutations will obviously have impaired or nonexistent flight capacity. In Acrythosiphon pisum, the pea aphid, a lower population of grandmothers will reduce the number of offspring (161). In closely related species, one may show sensitivity to certain environmental conditions while others do not, and it is safe to assume that genetic mechanisms are at play. In garter snakes, and some mammalian species, antivenom capability sacrifices locomotor skill.
Territoriality in Drosophila melanogaster has been shown to have genetic bases. Individuals will be better at defending territories if they are born on richer food mediums, and they are more aggressive if they hatch with denser larvae populations. Sometimes territoriality interferes with performance. Territoriality requires high metabolic function, meaning that environments will naturally select for more or less aggressive populations depending on various conditions (191,194). There are strains of cannibalism in Tribolium confusum, the common flour beetle.
Science now knows that it is the interaction of biological mechanisms and their environment which is responsible for much of the complexity in the human and animal worlds. Advances in our understanding of human genetics are particularly troubling, not only because the results increasingly seem to narrow our sense of control in the world, but oppositely because the results remain baffling. Despite all of this empirical data which shows correlations between behaviors and genetics, biology has yet to develop a remotely satisfactory physiological model of transduction.
We are a puzzle-solving creature, and we are ourselves the most difficult puzzle we’ve encountered. To solve ourselves is initially depressing, but then we learn to manipulate that theory, and become something metatheory, the next piece to solve. This paradox is essential to the human condition and it surfaces in all worldviews as ontological explanations (in order to be consistent with the observed world).
Boake, Christine. (1994). Quantitative Genetic Studies of Behavioral Evolution. (Ed.). University Chicago Press.
Fox, Maggie. (2008). Study finds genetic link to violence, delinquency. http://www.reuters.com/article/2008/07/14/us-delinquents-genes-idUSN1444872420080714
Kasper, Loretta. (1998). SAMPLE FINAL EXAMINATION IN READING. http://kccesl.tripod.com/readingmatrix/samplereadingfinal.html
Never Say Always (2009). Identical twins who were separated at birth: Amazing similarities. http://lornareiko.wordpress.com/2009/10/08/identical-twins-who-were-separated-at-birth-what-are-they-like/
Pinker, Steven. (2002). The Blank Slate: The Modern Denial of Human Nature, Penguin Group.
Pinker, Steven. (2007). The Stuff of Thought, Penguin Group.
ScienceDaily (2009). Smart Rat ‘Hobbie-J’ Produced By Over-Expressing A Gene That Helps Brain Cells Communicate. http://www.sciencedaily.com/releases/2009/10/091019122647.htm
Singer, Emily. (2009). The Dark Side of Pet Cloning. http://www.technologyreview.com/view/411834/the-dark-side-of-pet-cloning/
Steinmayr, Markus. Elisabeth Andre, Franc Ois Conquet, Laure Rondi-reig, Nicole Delhaye-Bouchaud, Nathalie Auclair, Herve Daniel, Francis Cre Pel, Jean Mariani, Constantino Sotelo, and Michael Becker-Andre. (1998). Staggerer phenotype in retinoid-related orphan receptor ⍺-deficient mice. Proceedings of the National Academy of Sciences, USA. Vol. 95, pp. 3960–3965. Neurobiology http://www.pnas.org/content/95/7/3960.full.pdf
U.S. Department of Energy Genome Program’s Biological and Environmental Research Information System (BERIS). (2008) Human Genome Project Information. http://www.ornl.gov/sci/techresources/Human_Genome/elsi/behavior.shtml
VanderLaan DP, Forrester DL, Petterson LJ, Vasey PL (2012) Offspring Production among the Extended Relatives of Samoan Men and Fa’afafine. PLoS ONE 7(4): e36088. doi:10.1371/journal.pone.0036088 http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0036088