Behavior Genetics Essay, Research Paper
Human Behavior Genetics
To illustrate a point concerning the inheritance of gestures, Charles
Darwin quoted an interesting case that had been brought to his attention by
A gentleman of considerable position was found by his wife to
have the curious trick, when he lay fast asleep on his back in
bed, of raising his right arm slowly in front of his face, up to his
forehead, and then dropping it with a jerk so that the wrist fell
heavily on the bridge of this nose. The trick did not occur every
night but occasionally. Many years after his death, his son
married a lady who had never heard of the family incident. She,
however, observed precisely the same peculiarity in her
husband…One of his children, a girl, has inherited the same
trick.? (Darwin, 1872: 33-34)
Probably everyone could cite some examples, perhaps not as quaint as
Galton?s, in which some peculiarity of gait, quality of temper, degree of
talent, or other trait is characteristic of a family, and such phrases as ?a chip
off the old block?, ?like father, like son,? and ?it runs in the family? give
ample evidence of the general acceptance of the idea that behavioral traits
may be inherited, as are physical ones.
What Is Behavioral Genetics:
Behavioral genetics is simply the intersection between genetics and the
behavioral sciences. Behavioral geneticists are currently applying the various
techniques of genetic analysis to various behavioral characters in order to
learn more about them. The characters under study are diverse, varying in
subject from homosexuality, IQ, and even hostility.
Many theories have been presented to explain homosexuality behavior
in humans. Two of these such theories are E. Slater?s Birth order and
maternal age of homosexuals theory and hormonal differences.
Birth Order and Maternal Age of Homosexuals:
E. Slater?s studies in homosexuality led him to the finding that male
homosexuals tend to be born late in sibling order. He found an increase in
mean birth order, and increase in maternal age at birth, and a variance of
maternal age as great as that of patients with Down?s syndrome (mongolism)
This increase approached the figure obtained in the small series of Turner?s
and Klinefelter?s cases in the literature and differed widely from that of the
general population. Slater regarded these findings as supporting a hypotheses
of heterogeneity in the etiology of homosexuality in the male and as
suggesting that a chromosomal anomaly such as might be associated with late
maternal age may play a part in causation in some instances. To be sure, this
information was reinvestigated and found that a shift in paternal age was
primary; this finding would rule out a chromosomal theory and suggest a
genetically predisposition to sexual deviance manifesting in the fathers
(Kaplan, 1976: 301-304).
Another theory on the subject of homosexuality deals with hormonal
differences in adult homosexuals. Low urinary testosterone levels have been
noted in male homosexuals and, likewise, female homosexuals have been
reported as excreting low levels of estrogen.
IQ and Behavioral Genetics:
Human intelligence can be usefully construed as a single trait which is
largely under genetic control. The influence of different genetic and
environmental factors have been estimated, but only crudely.
A study of foster children by Skodak and Skeels showed that both the
rate of increasing resemblance to true parents and the final level achieved is
the same regardless of whether children are raised by their true parents or not.
This is extremely strong evidence in support of genetic control of
intelligence. However, that same study also revealed evidence that the
children?s? IQ levels were in fact, higher on average than the mothers. These
differences can be attributed to adoption (Barker,1995: 74-79).
There is interesting evidence that societies which reward on the basis
of individual ability are becoming stratified in such a way that differences in
intelligence have a genetic component. Earlier studies of family size and IQ
led to the prediction of a decline in the intelligence of the populations studied.
These predictors were shown to be due to an error, and natural selection for
IQ was shown to be positive in the same populations. Nevertheless, the
relationship is a dynamic one, changing with different social conditions, and
it should be a topic of constant scrutiny (Barker, 1995: 74-79).
Alcoholism, regarded by the early eugenicists as part of a syndrome of
hereditary degeneration including also criminality, insanity, and epilepsy, has
remained a social issue of great importance. Indeed, alcoholism is one of the
principal public health problems in the United States today, with estimates of
the number of those dependent upon alcohol in the country ranging as high as
10 million. The tendency for alcoholism to ?run in families? has been long
noted in folklore, and is upheld by a number of investigations into the
distribution of alcoholism within families. A particularly extensive
investigation was made by Amark, who studied several large samples of
alcoholics and their relatives in the Swedish population. One feature of this
study is particularly clear. The incidence of the condition is higher in males
than in females, and is also higher among relatives of probands than in the
population at large (Ehrman, 1976: 285-291).
Within the last several decades, a specific sex-chromosome anomaly in
phenotypic males has received considerable publicity. In 1965, Jacobs and
so-workers reported that the incidence of chromosomal anomalies among
individuals institutionalized because of ?dangerous, violent, or criminal
behavior? was higher than that in the population at large. Of 197
institutionalized volunteers who were karyotyped, 12 were found to have a
chromosomal anomaly of some kind. One was a 46, XY/47, XXY mosaic,
one as 48, XXYY, and seven were 47, XYY. Three had no sex-chromosome
differences, but only minor autosomal defects. The average height of the 47,
XXY males was 73 inches, in contrast to an average height of 67 inches for
the males of normal karyotypes in the institution (Dawkins, 1973: 301-304).
The possibility of a genetic component in criminality has raised a
number of interesting legal problems. In 1968, the defense attorney for a man
on trial for murder in Paris presented an unusual defense. He claimed that his
client possessed an extra Y chromosome and, thus, was not criminally
responsible for this act. Although convicted, a reduced sentence was
imposed. At about the same time in Australia, a jury acquitted a man charged
with murder on the grounds of legal insanity after a defense witness testified
that the man had an extra Y chromosome. As it stands, there now appears to
be some precedent for diminished responsibility before the law of XYY
individuals (McClearn, 1973: 301-304).
Although history has long attributed some actions to ?like father, like
son? or ?it runs in the family?, the quickly expanding field of behavioral
genetics is finally offering some proof to those claims. After determining the
cause of starting point of such problems as alcoholism, sleep problems,
schizophrenia, and certain types of antisocial behavior, the field of behavioral
genetics may begin to shed some light upon possible solutions with the use of
genetic engineering for eliminating these problems. The only remaining
thought would be whether or not we have the right to start eliminating and
changing human characteristics.