I had an argument yesterday with someone about the heritability of IQ. I said it was obviously largely heritable. She countered with statements about the importance of education, and family background, and teacher expectations, and nutrition. I agreed that all of those could have an influence, but pointed out that all of the evidence suggested roughly 85% of the variance between people is due to genetic factors, with 15% due to environmental factors. I mentioned the separated siblings studies, which show how much closer adopted children are to their biological families than to their adoptive ones.
She then repeated her arguments about education, etc.
I then asked her, is there any sense in which some people are just smarter than others, even if they come from similar backgrounds? She replied, "Oh, well backgrounds are never exactly the same. How can you think that two families are exactly alike?"
I then asked, are you unwilling to admit that genetics have any role at all in determining IQ? She replied, "I'm willing to admit that IQ has a lot to do with nutrition, and early childhood education." And so on.
In other words, she refused to answer the question.
Whenever people refuse to answer a question, it's because they know how ludicrous they would sound if they answered the way they'd like.
Which is just a straightforward admission that they're wrong -- much as "straightforward" seems like the wrong adjective for their style of argument.