>>18
Lol, because animals are just like humans, only dumber, amirite? Because it's not like "simple" animals such as bats or rats have developed complex brain structures to solve specific problems relevant to their lifestyle, like interpreting echolocation or chemical data, right?
Most animals do recognize members of their own litter, if nothing else. The more socially-inclined an animal is, the more likely it is to keep a reference of information on familial relationships. (The more social primates and other mammals, i particular, have lives that sound like soap operas.)
And you think it's hard to program an animal to differentiate members of its species? How easily do you recognize faces? Compared to the problems of mechanics, optics, etc, coding a few brain cells to remember faces, smells, or other data on individuals is a walk in the park.
Incidentally, >7 was correct- there is some part of the human brain that suppresses sexual desire towards those it codes as "family members." This has very little to do with what your mind 'knows' to be family and a lot to do with who you spent most of your time with when you were a small child (up to ~8 seems to be the breaking point, or so I'm told). Incestuous desires within the immediate family are most common- hello, Dr Freud!- among those who saw very little of their siblings/parent/child during that initial period. There is even some interesting examples of failed attempts to raise children together from birth when they are betrothed in an effort to strengthen family bonds- such marriages are inevitably failures to the Nth degree.
Oh? You were talking about incest between cousins and other, more distantly-related members of family? The genetic math is complex and boring, but it comes down to "some cousins are okay and others aren't," at least as far as inbreeding, etc go. And yes, first-generation inbreeding does significantly increase the chances of genetic defects- but the change from 1-in-50,000 to 1-in-25,000, say, is not terribly noticable with one couple. You need a few hundred years of that kind of nonsense (re: the Royal family, Alabama) to see a noticable trend.