Mad Kally

Could I be the Tooth Fairy?

ps418

Yes, but Lewontin is not accurately describing the state of the field. There is a firm concensus amongst behvaior geneticists that many personality traits and cognitive abilities are substantially heritable, and that the measures used to demonstrate this are in fact 'convincing.'

I'm glad you find it hilarious. But I dont know what this has to do with our discussion. No researcher says that, for instance, 80% of intelligence is the product of the genes. That wouldnt make any sense. What they say is that a given amount (e.g. 80%) of the variance between individuals in specific types of intelligence (e.g. pattern completion tasks such as progressive matrices) or personality traits (or whatever) is accounted for by genetic variance, which is a different thing.

I agree that nature and nurture can not be partitioned, or exist independently. But the amount of variance in a trait that is accounted for by genes, versus that amount of variance that can be accounted for by environment, can be determined.

Also, your Lewontin quote discussing Cyril Burt has nothing to do with Cricket's question about which environmental effects are responsible for the significant correlations in personality traits amongst monozygotic twins reared apart. Burt was one of the first to study the issue using twins, but a mountain of evidence has accumulated since Burt's day. Plomin and Kosslyn (2001) "[d]ozens of studies, including more than 8,000 parent-offspring pairs, 25,000 pairs of siblings, 10,000 twin pairs and hundreds of adoptive families, all converge on the conclusion that genetic factors contribure substantially to 'g'" (Genes, brain and cognition, Nature neuroscience 4, p. 1154; references ommitted). The very same could be said about "human personality traits" rather than 'g,' except that the number of studies would be a bit smaller.

Lewontin casts doubt on Burt's results by claiming contact between supposedly raised-apart twins (among other things). Bouchard's et al's studies of twins reared apart specifically adresses contact. Some of the twin pairs had preassessment contact, andd some didnt- none of those considered in Bouchard et al had contact in childhood or adolescence), and concludes that degree of contact members of a reared-apart twin pair "accounts for virtually none of their similarity."

lpetrich

Here is <a href="http://www.psych.ucsb.edu/research/cep/primer.html" target="_blank">a primer of "evolutionary psychology"</a>. That article maintains that we have numerous instincts -- and that many of them are for behind-the-scenes operations like visual perception. We do not see objects directly; our primary perception is of light intensities from various directions, which are then interpreted unconsciously as coming from various objects.

Also, instinct and learning can be mixed in complicated ways; shared circumstances can induce learning that has the appearance of instinct.

One good illustration is the use of spoken natural language. It is universal in self-sustaining human societies; no example of one is known without it, however interesting such a society would be.

There are also brain adaptations to processing various aspects of language, such as Broca's area and so forth. There is also the interesting phenomenon that language learning is much easier in childhood than later; it is as if some parts of our brains have a plasticity that is rigidified at puberty. Thus, children easily learn large amounts of vocabulary and grammatical complexities that adults often have trouble with.

However, many of the details of natural language are learned; correspondence between sound and meaning only exists in sound-imitation words, and details of grammar vary widely. Though such grammatical categories as nouns and verbs are apparently universal, such details as word order vary widely. Though the default English order of subject-verb-object is very widespread, also very widespread is subject-object-verb and less widespread is verb-subject-object. Both noun-adjective and adjective-noun are widespread. The amount of word morphology is widely variable, with some languages having much more of it than others. Grammatical-gender systems vary widely, they include "natural" gender, male/female, common/neuter, and even a multitude of categories (Bantu prefixes, Chinese classifiers, ...). Etc.

[ December 07, 2002: Message edited by: lpetrich ]</p>

Tom Sawyer

I remember studying the twins studies in Psych class and the professor was going on about how they were invalid in showing anything. One of his main points (I forget most of them, it was a while ago) was that adoption agencies try to match adoptees to the same socio-economic background that the birth parents came from. That being the case, the environment between the two wouldn't be all that different, regardless of whether they were raise dtogether or apart.

Russell E. Rierson

Hello Mad Kally. Yes, could Wilson's theory have a ring of truth to it???

Like when perfectly normal people lose all logical reasoning and give away all of their worldly possesions to a "cult". Also they practically worship the cult leader, identifying him/her with a "messiah". The cult leader almost always has very irrational ideas, yet the cult followers consider every word from this individual to be "gospel" <img src="graemlins/notworthy.gif" border="0" alt="[Not Worthy]" />

Could our distant anscestors also have listened to irrational beliefs and abandoned rational questioning of the "leader"? Would natural selection have favored this?

Interesting...


Russ

[ December 07, 2002: Message edited by: Russell E. Rierson ]</p>

Vorkosigan

Unless there was a force to counteract this spreading chaos, intelligent individuals would leave the tribe, the tribe would fall apart, and all individuals would eventually die. Thus, according to Wilson, a selection pressure was placed on intelligent apes to suspend reason and, blindly obey the leader and his myths, since doing otherwise would challenge the tribe's cohesion. Survival favored the intelligent ape who could reason rationally about tools and food gathering, but also favored the one who could suspend that reason when it threatened the tribe's integrity. A mythology was needed to define and preserve the tribe.

Let's leave the cognitive aspects of this aside for the moment (although I think that they explain religious belief). Can we disqualify this proposal on the grounds that it is really a description of group selection, a process that is not known to occur in nature? In order for BELIEF to be directly selected for, there would have to be some advantage to individuals for being believers....what would that be?

Vorkosigan

atheist_in_foxhole

Wouldn't it be ironic (and hilarious) if the religion that the creationists cling to turns out to be nothing more than an evolutionary advantage?

ps418

Actually, socioeconomic status (SES) accounts for virtually none of the moderate to high positive correlation in IQ and some(!) personality dimensions between MZ twins reared apart (see the Bouchard et al paper I referenced above), and does not explain why the correlations in IQ and some(!) personality dimensions between MZ twins reared apart are typically much greater than for fraternal twins reared together, or why adoptive siblings reared in the very same (thus SES-equivalent) home show little or no correlation as adults with their adoptive parents.

pz

However, genetics also fails to adequately explain these results and others. We also have to remember that these are people, not experimental animals, and these succinct summaries of the experiments do not adequately convey the complexities that compromise the work. For instance, when you say "adoptive siblings reared in the very same (thus SES-equivalent) home", you are implying that there is no other difference between these adopted and natural children other than their genetic inheritance...and we know that that is not true.

ps418

What a glaring nonsequiter. I most certainly did not state, imply, or suggest that "there is no other difference between these adopted and natural children other than their genetic inheritance," nor does this follow in any logical way from what I did say. My point, which I thought I made fairly clearly, was that SES does not explain much if any of the observed correlations in IQ and some personality traits in studies of twins reared apart.