Unit 9: Nature and Nurture

Chromosomes: threadlike structures made of DNA molecules that contain the genes.
Genes: the biochemical units of heredity that make up the chromosomes; a segment of DNA capable of synthesizing a protein.
DNA: (deoxyribonucleic acid) a complex molecule that makes up the chromosomes. (A DNA molecule has two strands-forming a "double helix").
Genome: the complete instructions for making an organism, consisting of all the genetic material in its chromosomes.
                       Evolutionary Psychology
Natural Selection:
the principle that, among the range  of all inherited traits, those that lead to increased reproduction and survival will most likely be passed on to future generations.
Mutation: a random error in gene replication which is the source of all genetic diversity.
Evolutionary Psychology: the study of the evolution of behavior and the mind using the principles of natural selection.
Behavior Genetics: the study of the relative power and limits of genetic and environmental influences on behavior.
Environment: every nongenetic influence, from prenatal nutrition to the people and things around us.

*Behavior geneticists try to determine the relative impact of nature (genetics) and nurture (environment) by doing twin and adoption studies.

Identical Twins: twins who develop from a single fertilized egg that splits in two, creating two genetically identical individuals.
Fraternal Twins: twins who develop from separate eggs.  They are no more similar, genetically, than brothers and sisters, but they share the same fetal environment.
a person's characteristic emotional reactivity and intensity.

*Thomas & Chess identified three distinct temperament styles in babies as young as 2 months old. 
10%--Difficult babies: irregular rhythmicity, withdraw from new situations, slow-to-adapt to new situations, & intense reactions
15%--Slow-to-warm-up babies: low activity level, withdraw from new situations, slow-to-adapt, low intensity of reactions, & negative mood.
40%--Easy babies: Opposite of difficult babies.

Temperament seems quite stable throughout life and the same percentages are found in other cultures.  Thus, it is believed that temperament is genetically based.

Heritability: the amount of variation among individuals that we can attribute to the differences in their genes.
*For example:  if identical twins are found to be different in some way, the heritability of that trait is 0%.  The difference can't be due to their genes, because they have identical genes.  Any differences between them must be due to their non-shared environments.

the enduring behaviors, ideas, attitudes, and traditions shared by a large group of people and transmitted from one generation to the next.
Norm: the understood rules for accepted and expected behavior.
Personal Space: the buffer zone we like to maintain around our bodies.
Memes: self-replicating ideas, fashions, and innovations passed from person to person.

X- chromosome:
the sex chromosome found in both males and females.  Women have two, men have one.
Y-chromosome: the sex chromosome found only in males. When paired with an X-chromosome from the mother, it produces a male child.                         NEXT PAGE

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