I can't speak to the theological basis for the Christian dogma on abortion, but I can say that in pre-Christian antiquity it was kind of a non-issue. Aside from numerous abortifacient medicines available to women, many ancient cultures, including the Greeks and Romans, practiced a kind of "fourth-term abortion" called exposure. Basically, if a baby was unhealthy or unwanted, the parents would take it out to a secluded spot and leave it to die. It was also not uncommon for couples who couldn't conceive to visit these spots and rescue a child, which is one common theory about the "she-wolf" that nursed Romulus and Remus.

I at least can tell you for sure that there were/are times and cultures with different definitions for when the human life was deemed to have begun and the ending of a pregnancy was deemed acceptable.

While, as already said, many cultures practized the exposure of unwanted children, infanticide of already born and viable children got forbidden by Mohammed in the Quran. On the other hand there is no explicit prohibition of abortion in neither the Quran nor the Sunnah.

We do find two passages in these texts that show how the beginning of human life was considered in the time of Muhammad:

Though the Sunnah does not report a case where the Prophet Muhammad directly discusses intentional abortion, on one occasion Muhammad makes a ruling on forced miscarriages. In a case whereby a woman killed her pregnant co-wife, Muhammad requires the murderer’s kin to play blood money (diya) for the co-wife and a payment (ghurra) for the unborn foetus (Katz 2003). This case provides an understanding of the legal position of the foetus. As the value of the ghurra is usually one-twentieth of the diya, it appears that the foetus has some legal protections but is not a ‘full-fledged human being’ (Katz 2003, p. 28).

One central passage in the Quran furthermore describes explicitly that in the first stages of gestation the foetus is not yet human.

And certainly did We create man from an extract of clay. Then We placed him as a sperm-drop in a firm lodging. Then We made the sperm-drop into a clinging clot, and We made the clot into a lump [of flesh], and We made [from] the lump, bones, and We covered the bones with flesh; then We developed him into another creation. So blessed is Allah, the best of creators (23: 12–4).

http://heapol.oxfordjournals.org/content/early/2013/06/08/heapol.czt040.long

In the ancient world there really wasn't much of a stigma against abortion (supposedly the Romans had an arbortificant plant that they used to extinction). The problem was, abortion carried a great risk (as, of course, did pregnancy) and there weren't really any effective methods. For women who were prostitutes, whose livelihood depended on them not being pregnant, sometimes abortion was worth the risk. If you want information straight from the horse's mouth: here is a poem by Ovid describing his girlfriend's abortion. His response is angry, but not about the loss of the child, just the risk to the woman.