The logic seems simple. Our brains control our behaviour and our brains are built and maintained by our genomes. We KNOW that there are certain genes that produce proteins essential for the perfect construction of our nervous systems. A developing pile of neurons is formed into perceptive input lines and cognitive output lines by the guidance of specific proteins in specific quantities. Millions of years of evolution has made this process relatively flawless.
But the big question is: what about our behaviours? What about our thoughts, emotions, instincts and consequential (if you're inclined to a reductionist philosophy) actions? If the neurons are controlling all of these, and proteins are controlling the neurons, and genes are behind the proteins-- isn't it obvious that genes are behind behaviours?
This works out easily in theory. Sometimes its deceivingly simple-- Prairie volescan be made to be more monogamous (a clear and measurable behaviour) by increasing dopamine levels (or, presumably, by regulating [read: selecting or mutating] the genes that control dopamine).
But in the past, biology has had a terrible time trying to find actual BEHAVIOUR genes. First, the scope was too narrow. In retrospect, it's obvious that there aren't simple behaviour controlling genes, as the genomes interact with a complex system that's interacting with a complex environment. There's no one sequence of DNA alone that's going to make a person invent a faster toaster or be good at baseball.
These scientific oversights, although somewhat humorous in retrospect (jokes about the simple geneticists of the 1950s and before are similar to laughing at the Dark Age idea of heliocentrismor mythological Apolloand his sun-chariot), they had tragic complications. Many primitive geneticists sought the forced sterilization of those with "weak" genes. Although Hitler jumps to mind first, many scientists held similar (if less extreme) ideas in England and the North America. Thousands of mentally handicapped or otherwise undesirable people (ex. low IQ) were sterilized by state programs that got AHEAD of good science.
In many places of the world (including, say,the South) these ignorances are still held as a form of "popular" science shorthand. How many times have you heard something along the lines of: 'He's got the genes to be a good pianist because his father was..."?
Modern science, everywhereexcept Kansas, has moved on.
The next step for behavioural genetics was understanding how complicated the state of affairs really was. If there aren't simple behaviour controlling genes, then what are there? Enter the idea of a "genetic predisposition". Once biologists had a chance to actually study these behaviour genes, they realized that for the most part, they merely added to one's chances of having a certain trait. There are no INTELLIGENCE genes, but there are some genes that when coupled with a supportive, educational, stimulating environment can lead one to probably be an "intelligent" person.
This leads immediately to the problem of classifying traits. How do you test whether someone is intelligent, aggressive, depressed? For psychiatric disorders, a scale of "Does the person have 5 of the following 10 symptoms?" is often applied. This works for clinicians, but for a behavioural geneticist, one has to assume that those symptoms could likely be different genes or gene-gene interactions or gene-environment interactions. The messy web of "could" becomes almost impossible to untangle-- and certainly not in any statistically significant or HELPFUL way.
Some thought it might be easier to start with actual observable complications. Certain types of mental retardation results also in misshapen body types that might be classifiable in terms of genetics. In this case, although the phenotypes might be easier classified, there are still environmental interactions.
Simply put, everyone is different. Two people sharing the same genomic sequence (even if it likely results in a classifiable phenotype) still have unique psychological development (biologically and, say, perceptively. They have unique protein production as well as different perceptions of the world.)
Twin studies, lead by those revolutionaries such as the University of Minnesota, have been looking at how much control genes have relative to the environment in producing a behavioural phenotype. For example, if Jim and John are identical twins, but were raised in completely different environments-- how are they similar and how are they different? Often, its astounding to see that one growing up in a poverty-stricken D.C. ghetto is equally neurotic, obsessive, aggressive and intelligent as the one that grows up in a wealthy Jewish community in Connecticut. These comparisons can give a statistical likelihood of how strong "genetic predispositions" might be. Often their compiled results are worded like "Intelligence is found to be 62% heritable. Schizophrenia is found to be 35% heritable."
Another interesting personality psychology idea is that these predispositions for a trait are themselves predispositions for actions. Even when a person is classified as neurotic or aggressive or obsessive or intelligent-- clearly, they're not acting that way ALL of the time. A gene might give a person a 20% increase in the odds that they're going to be neurotic, which, as a classification simply means that in a given situation the chance is reasonable that they are going to act neurotically (or rather, act in a way that would pass the test for neuroticism).
This lack of concrete ideas is a daunting spectre to the field, obviously. If our classifications are based on "probably" and our discoveries of the roots of these classifications are also based on "probably" how likely are our results going to be in reality? We're compounding our error. It feels rather like we're trying to build a major scientific advancement on a soupy, muddy riverbank. I'd say its "probably" going to sink unless we can find more concrete intellectual footing--more actual, firm, concrete scientific ideas.
And there's the rub. We know that genes are involved with behaviour. They control neuron development and maintenance and produce the proteins that actually interact with the brain to cause thoughts, feelings and actions. But we can't even classify the behaviours, let alone explain how genes are involved in their expression. We can prove likelihoods and statistical probabilities all that we want, but behavioural genetics is far removed from actually saying, "Neuroticism is THIS and I'm neurotic because of gene A and B interacting with my environmental factors C and D and E which also interact with genes C and D-- D, which was enhanced by environmental factor F and gene X." We don't know what neuroticism really IS, so how can we try to find genes and complex interactions that lead to it.
immediately and obviously the complications seem too overwhelming for good science.
Even if we thought that we had identified a genomic sequence (gene allele) that caused a certain phenotype-- how are we going to test that? Setting aside all ethical concerns-- which, obviously, we could never do, we'd have 2 choices: we can block the gene from acting and see what happens or we can enhance it-- stimulate it-- and see what happens. But WHEN we do these two things developmentally might make a big difference. A person's behaviours occur on a time-scale. For example, if a gene is supposed only to turn on at puberty and we stimulate it at some embryo stage, it might interact with other genes and proteins prematurely and not give us a clear picture of what the gene is actually doing in normal development. OR, let's say that the gene makes a protein that functions in one way at some concentration, but by altering the gene's function we change that concentration and so change the function of the protein. Far from being contingencies, these scenarios and others are plausible and sometimes probable in developmental Biology.
Hopefully, there might be a homologof our new gene in a related species. Humans and mice are relatively closely related (we're both mammals-- which is a unique evolutionary branch of animals). For example, hemoglobingenes in mice are extremely similar to hemoglobin genes in humans-- parts of them are actually interchangeable. (incidentally, this is often how the evolutionary relationship of different organisms is determined-- by genomic comparisons: more similar genome sequences indicate a closer common ancestor in evolutionary history--for example, chimps and humanshave 99% similar genomes). If the mouse has a genethat is similar to our gene of interest, that doesn't mean that it acts the same way or that we could classify the phenotype in the mouse to begin with. How do you tell if a mouse is neurotic? How do you tell if a mouse is intelligent? Often the comparisons are impossible: mice don't use language or have as complex social interactions as we have.
Given all of these daunting hurdles in the way of the science its amazing that we don't give up and study something easier. But, as I said before, the connection seems to tantalizingly obvious: Genes control neurons and neurons control behaviour. It's so simple!
For now, it seems we shall just have to be content to refute eugenicsand accept behavioural genetics' small place in the world (exemplified by the tiny space afforded to it by wikipedia).
But that's just my opinion. Zac.
Ps. Speaking of refuting eugenics: Eugenicists are always striving for "purity" or "cleanliness" in the gene pool, but biology has proven, again and again, that large population sizes with great genetic diversity are the healthiest in terms of evolution. If we were all the same, one environmental change or genetic disorder could wipe us off out of existence.
