What defines a Human being?

In the anthropology class we were asked -in your opinion, what is, and builds a human being? Well the teacher had told us a lot in the topic, that humans are the only ones who have culture, and that culture is not natural, it is something humans build. But I was a little sceptical. So, when she asked us to write what we think I wrote that:

From my point of view, the human being is built up throughout his life based on the genotype and phenotype. Genotype is the genetic information we got from our parents, in a way, untouchable for the individual or the environment around, but is changeable over time. Instead the phenotype, that is the agents that are influenced by the individual and the environment around him directly.

If we take an individual, for example, a newborn, we now we cannot change his eye or skin colour his programmed to be 175 cm tall, and he will. But we can modify his mental development beyond the basics, we can change his perception of the world around him. And this way we would be modifying part of him, and so to him.

Now, the newborn, has a identical twin, but right in the moment of the birth they are instantly separated and taken to two different places in the world. The ONE is going to live in a tropical rain jungle, the OTHER in a metropolis. One is going to have social and cultural values prepared to subsist in a society where the shaman, the oldest man in the tribe, is respected. He is going to learn about the earth gods and may be other divinities, he will be supposed to respect the shaman's decision of whom he married, he will protect his relatives (in this case: his tribe) and for this he will be able to sacrifice himself for them. 

The OTHER, the townsman, will learn to survive and win in a society where only one god is venerated unknown and omnipotent, the city's leader is relatively young and old people are  discarded. Other is going to marry the one he decides. But Other is also going to protect his relatives (in this case: family and friends), and he will sacrifice himself for them, but not for the ones that he does not have a "connection".

So, from the genetic point of view, the genotype, they are the same, but if we look at the phenotype, we discover that they are really different, the culture is different, because the cultural environment, the society, is different.

Both genetic and cultural information are natural components, the difference between both is that genetic information evolves in long periods of time and cultural information evolves differently in one generation.

Well the teacher did not like this that much, she wrote that the work itself is good, but there is a conceptual error, she said that culture is a social construction, and that means it is not a natural thing. Well, I still think that is her point of view. So we discussed it in class extensively and we did not reach a concluding point, so I wrote an other work just to argue the first one. I based my argumentation in works of White, Steward and Rappaport. She said he will read it, so when she give it back to me I tell you what she said.