Some disciplines are too focused on either nature or nurture when it comes to human behavior—biologists are not trained in how culture can affect behavior, and anthropologists, sociologists and cultural studies scholars are not trained in how genes work. These fields get exposed to work that supports nature or nurture, and then they tend to be more dismissive of the other.
My cognitive psychology professor at Georgia Tech said that the nature-nurture debate kind of defined psychology. That's not a bad thing. One of the great qualities of psychology, as a scholarly field, is that it can actually address the nature/nurture question. Not that it's easy.
It's hard. Some people I know will reject a genetic explanation if a plausible cultural explanation can be brought to mind. Genetic explanations are thought to be ad-hoc. They don't realize that their own cultural explanations are just as ad-hoc. The question of why a particular cultural item is in place is often not thought to be answerable—or it is thought that each one was subject to non-generalizable historical context.
The problem is that culture will often conform to what our genes predispose us to. A simple example is in food preferences, which nobody doubts has a cultural component. However, it is striking that cuisines worldwide conform to tastes that indicate nutrition—sugars, fats, and proteins. This is not to say that American fast food culture conforms to nutrition, only that it conforms to the taste of nutrition. In the wild, sugar, fat, protein and salt were rare commodities that we evolved to find delicious. McDonald's french fries taste more nutritious than they are.
What we have in this case are genetic predispositions for food preference, and then cultures conform to them. If an idea came up in a society that strongly opposed a genetic predisposition, such as starving your children, it would probably have a very difficult time catching on and ending up being considered a part of a culture.
Culture can also affect genes! For example, Northern Europeans drank more milk, where the Mediterraneans ate more cheese. Over the years, the Northern Europeans evolved to be more likely to be able to digest lactose into adulthood.
The best way, experimentally, to determine the influence of genes and culture is with separated twin studies. When genetically identical children are raised in different cultures, we can, to some extent, control for the effects of culture. But these studies are expensive and difficult to do.
It would be great to be able to look at genes and cultures themselves and come up with good guesses for hypotheses, but how is that possible when genes can affect culture, and culture can affect genes?
We can look at genes as causing a predisposition for a behavior (making it more likely), causing no relevant predisposition, or actively inhibiting a behavior. Similarly, we can look at culture as supporting, being irrelevant to, or inhibiting a behavior. These can be crossed, giving us these combinations:
genetic predisposition, cultural support: behavior present
genetic predisposition, no cultural support: behavior present
genetic predisposition, cultural inhibition: behavior not present, or in struggle
no genetic predisposition, cultural support: behavior present
no genetic predisposition, no cultural support: behavior not present
no genetic predisposition, cultural inhibition: behavior not present
genetic inhibition, cultural support: behavior present or struggle
genetic inhibition, no cultural support: behavior not present
genetic inhibition, cultural inhibition: behavior not present
So if a behavior is present, it must be encouraged by genes or culture or both.
How do we know if there is a genetic predisposition for something? It's hard. We can sequence the genetic code of people, but we need behavioral data to know if they are behaving in a particular way, and nobody is devoid of culture. But another way to winnow the list down is to know if the culture supports or inhibits something. If we knew that a culture either does not support a behavior, or actively tries to inhibit it, yet that behavior is still present, it is a good candidate for being predisposed for genetically.
The question then becomes this: how do we know if a culture supports or inhibits a behavior? We can look at explicit cultural artifacts, such as laws, social norms, mores, and manners. For example, American law clearly encourages monogamy, and inhibits murder. We can also look at implicit cultural influences, such as media portrayals.
Here is where my knowledge is spare. Cultural scholars might have already solved this problem (if so, please put some information for me in the comments), but those are some thoughts I have.
To summarize, though, we should not be quick to conclude that a behavior either has a cultural or genetic cause. Both could be at play in complicated ways, and finding out the relative contributions of them require careful science, not commonsense reasoning. Don't jump to a purely genetic explanation or a purely cultural one just because it conforms to your intuitions about the nature of humankind. In fact, your intuitions about genetic or cultural factors might itself be a result of genetic or cultural factors.
Then again, maybe it's like a lot of things, and comes from neither, but is just a result of your personal experience with the world.
Pictured: An Inupiat family from the present-day Alaska region. Clothing is cultural, but our genetic predisposition to want to stay warm affects the clothing worn in different regions of the world. From Wikipedia.