Seeing there is know consensus on when one becomes human, how can abortion be legal ?

There is not concensus, that's the problem. Some believe human life starts at conception. Others believe it begins when brain activity can be detected. Others believe that life begins when the fetus (referring to a level of development) can survive independent from the mother. A few believe life begins at birth. A very small number believe life begin after a completed birth.

What consensus are you talking about?

*EDIT* - "I googled to see what was the answer to when life begins." This is EXACTLY why the Supreme Court said states laws that banned abortions were unconstitutional (Roe v Wade).

From the Court opinion written by Justice Blackmun: "We need not resolve the difficult question of when life begins. When those trained in the respective disciplines of medicine, philosophy, and theology are unable to arrive at any consensus, the judiciary, at this point in the development of man's knowledge, is not in a position to speculate as to the answer."

Because the time at which a fetus becomes viable is a state interest counter balanced by an individual's constitutionally guaranteed right to privacy, the constitution acts to protect the individual from an overly intrusive state entity which as you said does not have consensus to carry its own argument while the issue of freedom of privacy is fairly clear cut.

Because the law says it's legal. This law could be overturned immediately if the five Republican Supreme Court Judges would overrule Roe v. Wade. They have a majority right now. I can't understand why people keep voting Republican when they don't change the abortion laws either.

The legal definition of a baby is when it takes it's first breath outside of it's mother. Before then it's a fetus. That's all there is to it.

Because it is a women's right to privacy and freedom of choice. Roe v Wade will never be overturned, so all you pro lifers should put on your big girl panties and deal with it.

if there is 'no' consensus, how can it be illegal ?

too many people believe different things, that is why it should be up to individuals.

edit.. i don't have it backward, i just don't agree with your statement... since you're missing half of your own point.

with out a consensus on the definition .. who are you arbitrarily claim your belief is the correct one?

"know"? Don't you mean "now"?

I'm not sure you are human.