Реферат: Behavior Genetics Essay Research Paper Human Behavior

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).

Hormonal Differences:

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).

Antisocial Behavior:

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.

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