I have conducted a few studies on this. It seems that co-residence has not effect per se and does not play a causal role in generating father-child incest aversion. Co-residence (and care-taking activities that some scholars have taken as a similar measure) and incest aversion do indeed correlate. This is why some studies claim to have found support for a westermarckian effect also in this case. However, recent data shows that both co-residence and incest aversion are caused by the same background factor: paternity certainty. The more certain a father is that he is the biological father of a child, the more likely he also is to live with that child during its childhood, and the more certain he is that he is the biological father, the stronger is also the aversion to have sex with a child. In our latest study of more than 400 men, co-residence has no effect at all after controlling for paternity certainty.

Thanks, Jan.   How do you separate the cultural taboo factor affecting the father's attitudes/feelings from inherited/evolved predispositions toward father-daughter incest aversion?   And how would your theory work with respect to earlier hominins who would not have had the cognitive ability to draw an cause-and-effect connection between mating and paternity?