Instincts are so powerful that we lose ourselves in them–they compel us, control us, and drive our desires without the requirement for any modicum of conscious awareness. They make us feel most alive, most “right”; in many ways, they make up the foundations upon which our identities are built, the center to which our personalities are relative.
Instincts are coded in our genes; they originate from past behaviors that guaranteed the preservation of those genes by driving us to survive and procreate.
Behavior in practice has changed over time, insofar as genes have continued to evolve due to sexual selective pressures as well as the effects of changes in our cultures. Cultural evolution is very similar to genetic evolution, with its analogous ‘meme’ behavior, a term coined by Richard Dawkins, representing cultural analogues to genes in that they self-replicate, mutate, and respond to selective pressures.
Research in the fields of genetics, neuropsychology, and paleobiology yields evidence that, despite drastic changes in our environments, cultures, technology, knowledge, and general realities, our deepest, instinctual genes have remained largely unchanged from the emergence of homo sapiens 200,000 years ago. People today still behave in ways that aided our survival during the Stone Age.
You can take the person out of the Stone Age, evolutionary psychologists contend, but you can’t take the Stone Age out of the person.
Sexual selection is the only genetic selection left in the modern world, as selective pressures for survival are no longer relevant in our society. Intelligence, physical attractiveness, and economic advantage still effect our sexual choices, although in the first world it is a growing trend that the more educated people are having fewer children and the least educated are having more, but that is beside the point.
What culture and social conditioning tend to do is not change instincts and emotions, but redirect, suppress, channel, and otherwise control the expression of them.
A good example of this is found in human sexuality. Sex is one of the most deeply ingrained instincts we have, short of our basic instinct to stay alive. But the impact that culture and individual psychology have on sexuality is quite extensive. I am not speaking of sexual orientation, but the ways in which sexuality gets channeled, directed, and expressed.
One theory for sexual ‘deviancy’, or abnormal sexual preferences and fantasies is that instincts, as strong and powerful as they are, must be channeled and compartmentalized to preserve the integrity of one’s social conditioning as well as one’s own ego and personal identity. A team of researchers in Canada recently found that, interestingly, nearly half of people surveyed were found to have at least one type of sexual perversion.  Perversion may just be a way instincts get channeled and expressed in a way that can be compartmentalized as a ‘game’, where behavior is reserved for certain roles that are kept at a distance from the participants’ primary identities.
In short, it seems instincts, at the core, are impossible to change.
To continue on the example of sexuality, in the Victorian era, there was widespread sexual repression, which is what likely caused the boom in the “hysteria” diagnosis, which doctors treated with handjobs, leading them to invent the first vibrators to save their hands from fatigue. 
Japan is seeing an unprecedented decline in sexual activity, coined the “celibacy syndrome”.  It is an open question whether sexuality is getting channeled and expressed in other ways, in a Freudian sense within Japanese careers or online in Japan’s ever-growing online and virtual reality communities. And if it is not found elsewhere, it could manifest in the negative sense: as loneliness, despair, and feelings of alienation. However, if that is not the case, it is also possible that, after Japan’s economic and natural disaster history and its increasing urban development and cultural futurism, Japanese people could be seeing a decline in the sexual instinct itself.
Japanese people could be seeing a decline in the sexual instinct itself.
What is interesting to note is that we have already seen a drastic change in human behavior. It happened during the development of the first cities. For hundreds of thousands of years, humans engaged in incessant tribal warfare until the development of the first cities, which was necessary for the development of civilizations. Cities allowed for more specialized activities to develop, but they required strangers to get along. People had to learn to extend courtesy and empathy to people that weren’t a part of their inner circle; they had to project their group mentality onto a much larger circle, which required humans to suppress their hostile natures.
It seems that humans can change their instincts. It takes a very, very long time, and it requires significant social and circumstantial pressures–significant enough to override the very behaviors that allowed us to stay alive until this point.
This is good news, because human nature is horrible in many ways. We still exhibit tribal mentalities to the extent that war and racism are still very much alive. It is the hope of many of us that future generations will live in a world one day without destructive hatred, inspired by instincts no longer appropriate to the world we live in.