Monday, September 12^th

I wanted to start today by discussing the Ohman and Mineka article…we’re now in the beginning stages of the material that pits nature against nurture, learning vs. instinct. I wanted to discuss this paper in the beginning of this section, because I think it will help us get over our urge to dichotomize.

What did they do?

Described the results of a few different studies conducted in their lab over a number of years—

Previous observations:

-snake phobia highly prevalent in humans and non-human primates

-captive primates not as fearful

-individual differences exist—2 possibilities: individual differences are due to genetic differences, individual differences are due to differential ability to learn to fear snakes. Implies that one can learn to fear snakes..this is the hypothesis tested in the study

-previous results supported this notion—captive monkeys can learn snake fear vicariously, by watching another animal’s fearful behavior. Can they learn to be fearful of just anything??

When model monkeys exhibited fear of flowers or rabbits, a vicarious fear was not learned.

More evidence…conditioning paradigm:

CS—snakes or flowers

US—shock

UR—sweating (SCR) to anticipation of shock

CR—sweating to snakes or flowers

CR to snakes was far more pronounced than it was to flowers

Most interesting finding is that when a gun was used as the CS, the response of the snake was still stronger, suggesting that it is not that we learn that snakes are harmful and that’s why we are afraid of them…we are capable of being afraid of them before we learn they’re harmful.

And…don’t need conscious perception in order to have a strong aversive response to snakes…masking studiess

Now…let’s turn our discussion back to the more familiar argument of nature vs. nurture in determining our personalities.

Remember from last time that nature and nurture influences cannot be separated when determining the traits of any individual. Now, with that having been said, that all individuals are a product of the gene-environment interaction, there are some kinds of nature-nurture questions that CAN be asked.

One can ask whether differences between any two individuals are due to their genes or their environments. Requires very special circumstances to be able to do so, and we also have to be careful about asking questions appropriately. The most controversial application of this legitimate “nature-nurture” question is when questions of differences between racial groups are asked. I just want to say at the outset that this application should always be called into question, and here’s why. There’s a very special circumstance that allows us to ask this kind of question…

Genetically identical plants. Plant them in different soil. Differences between them are due to the different soil.

Genetically different plants. Plant them in the same soil. Differences between them are due to their genes.

If we start off with genetically different plants, and put them in different soil (largely the case with racial differences), and then observe differences between them, we are unable to ask answer any questions about them. People can argue all they want that the cause of the difference is environmental, or genetic, but they will never be able to parse out the different influences unless one is held constant. That’s one reason.

Another reason is the assumption that races differ on genes that are relevant to the trait in question. No one would argue that there are genes relevant to physical appearance, or susceptibility to some diseases that vary among ethnic or racial groups. But finding genetic explanations for these group differences is not what gets people irate. It’s when genetic differences are claimed for behavioral traits that gets people angry.

Lastly—as Turkheimer points out…the relationship between genes and complex human behavior takes a very torturous path during the course of development, where environments affect genes, and genes affect environments. It is only for a very few behavioral traits that we can make any direct connection between individual genes and behavior. So we’re going to try to not get too carried away when we find genetic basis for behavior—Turkheimer points out that this is not surprising. It’s not surprising to psychologists who study behavior, but since it may be surprising to those of you that have never taken psychology before, we’ll spend some time talking about the evidence to suggest turkheimer’s 1^st law of behavior genetics:

-all human behavioral traits are heritable. What does heritability mean??

Not the same as genetic inheritance!

Heritability literally means the proportion of variability in trait that is attributable to differences in genes.

We are able to determine heritability for human traits when we have the equivalent of the identical plants potted in different soil. Monozygotic twins reared apart.

Useful comparisons for determining heritability:

Compare concordance rate (degree of similarity between 2 individuals) among:

· MZ twins and DZ twins

· MZ twins reared apart and together

· Non-related members of same household (adopted siblings)