Everything Shane said is correct, but I believe the true meaning of the birth is an answer to one of the biggest questions of the movie. Whatmovie; what caused the chaos on LV-223 that occurred 2000 years prior to the Prometheus expedition? We know it had something to do with the black goo because of how the engineer's decapitated-head reacted when its nervous system was revived by Ford (The head shows symptoms similar to the ones experienced by Holloway after being infected with the goo). Well remember when David first activates the engineer holo-record-log-thingy? If you listen closely during the opening moments of the log, you can hear a faint screech right before the engineers appear fleeing from an unknown threat. TheI noticed that the screech is extremely similar to the screech of the new-born xenomorph at the end of the film. So it is possible that the problem that led to the disruption of the engineer's plan to exterminate humanity was caused by an engineer-born xenomorph. If my thesis is correct then the writers of Prometheus outdid themselves in a very odd way.