Kevin MacDonald, Ph.D.
CSULB, Department of Psychology
PSYCHOLOGY 361
BEHAVIOR GENETICS
Behavior genetics challenges the behaviorist perspective of John Watson who famously wrote:
"Give me a dozen healthy infants, well-formed, and my own specific world to bring them up in and I'll guarantee to take any one at random and train him to become any type of specialist I might select -- a doctor, lawyer, artist, merchant-chief and, yes, even into beggar-man and thief, regardless of his talents, penchants, tendencies, abilities, vocations and race of his ancestors."
1.) BEHAVIOR GENETICS STUDIES IDIOGRAPHIC DEVELOPMENT
2.) BASIC CONCEPTS:
PHENOTYPE = OBSERVABLE OR MEASURABLE CHARACTERISTICS (E. G.,
HAIR COLOR, IQ)
GENOTYPE = GENETIC COMPLEMENT OF PERSON (E. G., HAVING A
RECESSIVE GENE FOR COLOR BLINDNESS)
POLYGENY: MANY GENES INFLUENCE A TRAIT BUT NO ONE GENE HAS A
MAJOR EFFECT (E. G., HUNDREDS OF GENES INFLUENCE IQ AND
PERSONALITY)
BEHAVIOR GENETIC CONCEPTS
GENOTYPE -- ENVIRONMENT CORRELATIONS:
WAYS THAT GENETIC TENDENCIES BECOME CORRELATED WITH PARTICULAR ENVIROMENTS.
ACTIVE GENOTYPE -- ENVIRONMENT CORRELATION (NICHE-PICKING):
CHILD SEEKS OUT ENVIRONMENTS AS A RESULT OF GENETIC INFLUENCES (E. G., CHILD WITH A SENSATION SEEKING TEMPERAMENT)
EVOCATIVE GENOTYPE-ENVIRONMENT CORRELATION: CHILD EVOKES
ENVIRONMENTS AS A RESULT OF GENETIC INFLUENCES (E. G., CHILD WITH
A DIFFICULT TEMPERAMENT EVOKES NEGATIVE RESPONSES IN CAREGIVERS; CHILD WITH A SUNNY DISPOSITION GETS POSITIVE RESPONSES.)
Another example: Children with violent natural parents and children with non-violent natural parents are adopted into separate families, and the adoptive families are compared. Children with violent natural parents have adoptive parents who use harsh discipline. Chidlren with non-violent natural parents have adoptive parents who use mild discipline. This "environmental" effect is the result of an evocative genotype--environment effect: Aggressive, difficult children evoke harsh parenting.
PASSIVE GENOTYPE -- ENVIRONMENT CORRELATION: CHILD IS PASSIVE RECIPIENT OF ENVIRONMENTS WHICH FIT WITH HIS/HER GENOTYPE. (E. G.,
INTELLIGENT PARENTS HAVE CHILD WITH GENETIC POTENTIAL FOR
INTELLIGENCE; PARENTS ALSO PROVIDE A GREAT DEALOF
INTELLECTUAL STIMULATION WHICH MESHES WITH THE CHILD'S GENETIC
POTENTIAL)
SHARED ENVIRONMENTAL INFLUENCES: ENVIRONMENTAL INFLUENCES
SHARED BY CHILDREN IN THE SAME FAMILY.
EXAMPLE: CHILDREN IN SAME FAMILY GO TO SAME SCHOOL, HAVE SAME
ALCOHOLIC MOTHER, ETC
UNSHARED ENVIRONMENTAL INFLUENCES: DIFFERENT CHILDREN RECEIVE
DIFFERENT ENVIRONMENTS; OR DIFFERENT CHILDREN RESPOND TO THE
SAME ENVIRONMENT DIFFERENTLY;
EXAMPLE: DIFFERENT BIRTH ORDER, SEX DIFFERENCES
Reaction Range: The range of phenotypic expression depending on different
environments of different quality. Different people have differerent reaction ranges; i.e.,
they respond differently to the same environments.
IQ score
_____________________________________________
Abusive Poor Average Enriched
Quality of Environment
CANALIZATION: THE GENETIC RESTRICTION OF A PHENOTYPE TO A SMALL NUMBER OF DEVELOPMENTAL OUTCOMES, PERMITTING ENVIRONMENTAL INFLUENCES TO PLAY ONLY A SMALL ROLE IN THESE OUTCOMES; In other words, genes restrict the extent to which the environment can influence the phenotype. A highly canalized phenotype is not much influenced by environmental influences; a weakly canalized phenotype is open to environmental influences.
THE DEGREE OF GENETIC INFLUENCE INCREASES AS CHILDREN APPROACH ADULTHOOD; I.E. GENETIC INFLUENCES ARE STRONGER IN ADULTHOOD THAN AMONG CHILDREN.
1.) CORRELATIONS OF MZ TWINS STAY HIGH WHILE
CORRELATIONS FOR DZ TWINS DECLINE
IQ CORRELATIONS FOR MZ AND DZ TWINS
AGE MZ DZ
6 MO .75 .72
12 MO .68 .63
24 MO .81 .73
36 MO .88 .79
4 YR .83 .71
6 YR .86 .59
8 YR .83 .66
15 YR .88 .54
2.) ADOPTION STUDIES
a.) CORRELATION BETWEEN ADOPTIVE PARENTS AND ADOPTED CHILDREN
DECLINES FROM .35 TO ZERO
AGE 7: r=0.35 AGE 17: r=0.00
b.) IQ OF ADOPTED CHILDREN DECLINES TO CLOSE TO
THE IQ OF NATURAL PARENTS
AGE 7: IQ OF ADOPTED CHILDREN = 110
AGE 17: IQ OF ADOPTED CHILDREN = 95
EXPLANATION:
ACTIVE GENOTYPE--ENVIRONMENT CORRELATION (NICHE-PICKING)
BECOMES MORE IMPORTANT AS CHILDREN GET OLDER
CONCLUSION: DIFFERENT ENVIRONMENTS WITHIN THE "NORMAL" OR
"AVERAGE" RANGE DO NOT HAVE MUCH INFLUENCE ON IQ.
HOWEVER, ABUSIVE ENVIRONMENTS CAN AND DO AFFECT IQ.
AVERAGE VS ABUSIVE ENVIRONMENTS
IQ
________________________________________________________________________
ABUSIVE NORMAL ENRICHED
TYPE OF ENVIRONMENT
A recent study by Turkheimer suggests less heritability (genetic influence) at the lower end of the socioeconomic scale, and much higher heritability at the higher ends. The idea is that in better environments, the vast majority of variation is caused by genetic variation. But in poor environments, more variation is caused by bad environments. However, other studies have not found this effect except in clearly abusive environments.
Rank Order versus Average Effects of Adoption (textbook, p. 92):
One classic adoption study showed that adopted children often averaged 20 or more IQ points higher than their biological mothers. Because in this study the adoptive parents tended to be more highly educated and more socially and economically advantaged than the biological parents, this result was probably due to the more stimulating home environment that the adoptive parents provided. But note also that, despite this environmental influence on development, individual differences seemed still to be substantially influenced by genetic inheritance. The rank ordering of the children's IQ scores more closely resembled that of their biological mothers than that of their adoptive parents. The children whose biological mothers had the lowest IQ scores were likely to have lower IQ scores than the children whose biological mothers scored higher. Thus, although the absolute level of intellectual development was apparently boosted by the environmental influences provided by the adoptive parents, individual differences among the adopted children in intellectual performance--that is, their relative standings in this regard--appeared to stem more from their biological inheritance than from the increased intellectual stimulation provided in their adoptive homes.ADOPTION STUDYTHE FOLLOWING ILLUSTRATES THESE FINDINGS
NP = NATURAL PARENTS;
AP = ADOPTIVE PARENTS
AC = ADOPTIVE CHILDREN
CHILDREN ADOPTED NEAR BIRTH
120
111
115
129
125
AP: X= 120
114
112
110
108
106
AC: X = 110
94
92
90
88
86
NP: X = 90
TESTED AT AGE 7:
ENVIRONMENTAL VARIATION IS IMPORTANT:
AVERAGE OF AC (110) > AVERAGE OF NP (90); THIS IS AN AVERAGE EFFECT OF ADOPTION OF 20 IQ POINTS. STUDIES TEND TO SHOW THAT THIS AVERAGE EFFECT WASHES OUT AS THE CHILDREN APPROACH ADULTHOOD.
GENETIC VARIATION IS IMPORTANT:
1.) AVERAGE OF AC (110) < AVERAGE OF AP (120)
2.) POSITIVE CORRELATION BETWEEN AC AND NP
