The title does not refer to a 'gift' from Earth as I thought it would, but instead to a genetic 'gift' possessed by Teyla to link telepathically with the Wraith. It seems she can sense the Wraith presence and it has been causing her sleepless nights.
Apparently, the Ancients accidently created the Wraith when they allowed Humans to colonize the proto-Wraith-bug planet. Proto-Wraith-bugs that fed on the Humans incorporated Human DNA and became the humanoid Wraiths. The Wraith language is also an offshoot dialect of Ancient.
On another planet, home to Teyla's ancestors, a Wraith scientist carried out experiments on Humans in a secret lab, against the wishes of other Wraith, in an attempt to make Humans taste better to Wraith. He incoporated Wraith DNA into Humans. These Humans had the ability to link telepathically with the Wraith and could read the minds of the Wraith. They also became violent, presumably when the wraith took possession of them, and so they were outcast by the other Humans.
Some of the outcasts left the planet, including someone who was an ancestor of Teyla, hence her ability, though she has never used it before. The Wraith scientist had allowed his test subjects back out into the population because he thought that with interbreeding he could disperse and dilute the ability. The other Wraith found out what he had done, and came and wiped out the planets remaining population.
With less than a week before the Wraith Hive ships arrive at Atlantis, the team ask Teyla to link up telepathically, and attempt to gain useful knowledge of the Wraith plans. Teyla willingly does this several times, though she becomes possessed by a Wraith twice and violent.
The Alpha site is attacked and suspicion falls on Teyla for giving away it's position, but it appears that the Wraith already know much more about us than we ever thought. They have all the knowledge of Colonel Sumner. They are desperate for new rich feeding grounds, because they were never all supposed to wake up at once. They are coming to Atlantis, not for the city, but because they know that it is the only way to get to the Milky Way, and to Earth...
