Probably a result of the environment, at least, if you follow Darwinian theory. Personally, I think that genes were already present, but weren't fully developed and so they had to adapt and change to suit the environment they were in. So, I think it is a little of both. In fact, mostly the environment is what cause behavioural changes in certain species, especially those of isolated species, like on the Galapagos islands.

From a purely scientific standpoint, the answer is both, and more. We know that genetics can contribute to the way a person behaves because we know they have an effect on brain chemistry and many other characteristics that contribute to our psyche. But to say we can completely inherit our dispositions from our parents would, of course, ignore much of the environmental pressures that act on a person's mental propensities. We know that a child growing up in a poor environment will have very different selective pressures on them than one in a rich environment. The mindset of the parents imprints on the child in different ways, depending upon how receptive the child is and how active the parents are in the child's life. What one learns over the course of one's life definitely can have an affect on how they live their lives.

The only other thing I'll mention here is that genetic traits aren't the only heritable elements we receive. There are also epigenetic factors, and these can greatly modify how much of a role the genetic factors play in our lives. For example, one can have a gene that causes the increased production of serotonin, but is never expressed, making it completely unimportant. Our genetic composition only truly matters if it expresses as physical (or physiological) characteristics.