@student2,
Hi Student.
Be very careful when you say "certain things are general.... humans have the same basic nature". It is very easy for you to assume that things you take for granted based on the culture you grew up in are general, when people in other cultures have a very different view. Marriage customs are a perfectly good example of this.
In college I was assigned Kenneth's Good's controversial book called
Into the Heart: One Man’s Pursuit of Love and Knowledge Among the Yanomama.
Good is an American anthropologist. As a adult man he went to live with this hunter-gatherer tribe which still follows traditional customs including child marriage. The tribal elder in the community in which he was living offered him a 9 year old girl to marry, a custom that is perfectly acceptable, even expected in the local culture. He accepted the offer (he claims he didn't consummate the marriage until she was 14 or so).
Obviously this type of marriage between an adult man and a 9 year old girl is deeply troubling in any Western cultural context. For the record... I think that what he did as a Western researcher was exploitative and immoral. However his insights on this culture are pretty important to the field, and the fact that child marriage worked so well in the context of this traditional culture raises important questions for anyone ready to question the meaning of their own culture.
If you have the chance to live (or even travel extensively) in another culture ... and I mean living in the culture accepting their lifestyle and point of view, I highly recommend it. It is the most educational thing a person can do. I was lucky to be born in one culture, and marry into another (with some time in a third).