Nature vs. Nurture: Identical Twins & Free Will

[SteveRives]

A study was printed in Psychology Today (maybe six years ago), that followed identical twins separated at birth.

It turns out that their "chosen" professions, their wives and husbands, their pets, the timing of significant events, etc. all matched up like a pre-programmed sequence. So, for example, with one set of twins, they both became fire fighters, dressed alike, had the same kind of glasses, same kind of home life, etc.

I think the article was titled Nature vs. Nurture. The conclusion was that we are not as free as we like to think. Who knows of some follow-up articles or resources along those lines? And does anyone know the original publication data of the article from PT?

 

[selfAdjoint]

I think that idea may have referenced the big U. Minnesota study of separated identical twins, based on the record of adoption agencies which for years had the practice of splitting a pair of newborn twins and putting the babies out for adoption separately. I remember one case, two boy babies had been put with Catholic families; one of the families then returned to their ancestral Italy. There was a photon of the two, grown, shaking hands. Both were Bishops in the Catholic Church, one had risen to that state in the US and the other in Italy, and neither knew about the other till the study brought them together. Another photo showed two women, also separated twins. Both were loaded with costuume jewelery including the oddity in both cases of wearing two rings on several fingers. That study found the heritabiility of many personality traits, "from IQ to religiosity" to be well above 50%.

 

[neurocomp2003]

i wonder if they do analysis of the upbringing. because perhaps these cases were a result of similar upbringing(not just social class...but strictness, parental interaction, friend interaction etc.)

 

[loseyourname]

If it were just upbringing, wouldn't we expect regular siblings, who are not genetically identical, to be very similar to each other? Although I probably share many opinions and perspectives with my sisters, I find that our personalities and aspirations are widely divergent. As Adjoint points out, though, the finding was about 50% heritability. That is certainly a big number, but it still leaves plenty of room for difference between genetically identical siblings.

As far as the question of freedom goes, I'd say we're free enough, or at least it feels that way. Even if both brothers grew up to be firefighters, that shouldn't bother anyone. That's what they enjoy, that's what they have a natural talent for, and they had the freedom to pursue a career that they enjoyed and had a natural talent for. That's good enough for me. I have no desire to go against my genes and do something I'm terrible at and don't enjoy.

 

[neurocomp2003]

...no siblings don't share the similar upbringing...unless your parents were truly unbiased to all aspects...you went to the same schools, and had the same teachers...had similar type of friends...and similar extracurricular activity and much much more properties. Sibllings dont' usually get the same upbringing because there's also that sibling relationship...unless you were bore quite some years apart.

 

[loseyourname]

Okay, then if you think two people raised by the same parents will have significantly different enough upbringings to make it so that they will not grow up to be the same, what makes you think two people raised on different continents will have a more similar upbringing than two people raised by the same parents?

 

[hitssquad]

The Minnesota Twin Registry

I think that idea may have referenced the big U. Minnesota study of separated identical twins

It is a registry of twins. Studies are still being performed using it. Here is one of the latest of those studies:
ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15351771


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Arch Gen Psychiatry. 2004 Sep;61(9):922-8.

Family transmission and heritability of externalizing disorders: a twin-family study.
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The registry is described here:
ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15351771


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Twin Res. 2002 Oct;5(5):488-92.
The Minnesota Twin Registry: current status and future directions.
Krueger RF, Johnson W.
Minnesota Twin Registry, Department of Psychology, University of Minnesota, Twin Cities Campus, Minneapolis 55455-0344, USA. krueg038@umn.edu

The Minnesota Twin Registry is a birth-record-based twin registry. Begun in 1983, it includes data for 4307 surviving intact pairs born in Minnesota between 1936 and 1955. In addition, the Registry includes 901 twin pairs born in Minnesota from 1904 to 1934, as well as 391 male pairs born in Minnesota from 1961 to 1964. The research focus is primarily on human individual differences assessed by self-report. Questionnaires completed by the participants include measures of personality, occupational interests, demographics, and leisure-time activities. We outline major contributions that have resulted from Registry research, as well as current and future research directions.

PMID: 12537882
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[selfAdjoint]

i wonder if they do analysis of the upbringing. because perhaps these cases were a result of similar upbringing(not just social class...but strictness, parental interaction, friend interaction etc.)

The original study, which was reported in Science also studied nonidentical twins and non-twin siblings at the same time. This enabled them to evaluate the contributions of being raised as siblings, being raised with a same-age sibling, etc. Thus their statistics weren't JUST based on separated, monozygotic twins but were a general study of the various child raising environments on the personality factors they were studying.

But if your argument is that the similarity of the separated identical twins was due to the similarity of their (separated) home environments, then consider that one would expect as much variation in the home environments as exists in the general population, and the probability that two twins would be raised in sufficiently close environments to produce high similarities in personality variable is no higher than for two randomly chosen individuals. If a large proportion of the many twin pairs studied showed similarities between their members, the probability of that being due to similar environments becomes very small.