Evolutionary:
Here is my take:
Since humans developed from Homo Erecti, there was still a diversity in the gene pool...The groups that were living together probably were related, however, they were not groups that were small enough to cause genetic defects to become prevalent.
Truth be told, marrying and having a child with your cousin would not, in the first generation cause any noticable defects...unless there were some major genetic defects already there. 3rd, 4th, 5th generation of inbreeding would definitely start to show problems. (i.e. cleft chins turning into major birth defects, minor flaws becoming major issues as the inbreeding continues.)
All in all, the gene pool still had enough diversity to deal with many defects...however, maybe some of the human frailty there is today and susceptibility to diseases is due to the fact that the gene pool was limited for a long time...
Aerodynamics:
This would be attributable to the same mechanism that airplanes use (i.e. flaps) to move upward and downward in their flight. The birds are jsut really damn good at it!!
By changing the airflow, as you stated, over their wings, they are able to change the pressure differences between the tops of their wings and the bottom...thereby either creating lift or destroying it.
great questions!!
