Right, I forgot all about this thread. I said I was going to post papers. Here we go:
The best tool we have for separating heredity from environment is the twin study. The idea is simple; identical twins have identical DNA, so when reared apart, their DNA will be the same while their environments will be different.
Perhaps the most commonly tested trait (because people both for and against the proposition of the primacy of genetics are interested) is IQ. Without getting too par out into the weeds of the debates (Stephen Jay Gould wrote a very fashionable book about how hereditary didn't matter that has been lampooned by most scientists in the field ever since), most geneticists agree that IQ tests measure something, however imperfectly. Here are the correlations between scores on IQ tests:
The same person tested twice= .87
Identical twins reared together= .86
Identical twins reared apart= .76
fraternal twins reared together= .55
Biological siblings= .47
Parents and children living together= .40
Parents and children living apart= .31
Adopted children living together= 0
Unrelated people living apart= 0
Citation: Genome by Matt Ridley, also Neisser, I. et al (1996) Intelligence: knowns and unknowns, American Psychologist 51: 77-101
Here's Ridley a little bit later in the book:
Quote:
"The conclusion that all these studies [multiple replicated IQ/heredity studies] converge upon is that about half of your IQ was inherited, and less than a fifth was due to the environment you shared with your siblings - the family. The rest came from the womb, the school and outside influences such as peer groups. But even this is misleading. Not only does your IQ change with age, but so does heritability. As you grow up and accumulate experiences, the influences of your genes increases (emphasis his). [...] the heritability of childhood IQ is about 45%, whereas in late adolescence it rises to 75%.
Remember, these findings are utterly uncontroversial, and can be applied to a whole bunch of different human pheonomena. Your penchant for change and daringness is very largely influenced by a gene found on Chromosome 11, the D4DR, studied in depth by Dean Hamer (his book, Living with our Genes, is a classic in this field.) Of course, that gene, like all genes, is genetically determined. Professor Ira Carmen at Illinois has done a whole slew of research on genetics and political affiliation (
http://ann.sagepub.com/cgi/content/refs/614/1/34). Think of a trait- any trait at all- and I'll bet you that it will be about 40-50% genetic, at least. Some are much more, such as certain diseases, and the obvious stuff such as hair and eye color, which follow basic Mendelian principles. The only one I can think of is what language you speak, but even there, your ability to comprehend language is very largely biological and genetically determined.
There's much, much more (this time I'm fighting on my home turf- this is like safety stuff for you Coast.) If you'd like more citations, I'll bring more citations, but I'm late for my workout.