1.   Analysis at the genetic level also let him determine whether the Jurua acted like a species barrier, as Wallace had hypothesized.

2.   Attempts to bridge species barriers are often said to involve no little hubris.

3.   After all, society accepts drugs made by putting human genes in hamster cells, even though this crosses species barriers as much as agricultural biotechnology does.

4.   For instance, the influenza virus jumps the species barrier, frequently moving from pigs to people.

5.   One theory is that bovine spongiform encephalopathy can be traced to the disease of scrapie in sheep and that it somehow crossed the species barrier here.

6.   Since then, Gibbs and others have shown that the disease can be transmitted across several species barriers, into mice, monkeys, ferrets and other animals.

7.   Some have raised the specter of a slow-acting virus crossing species barriers to then spread among humans, perhaps via sexual transmission.

8.   The aim is to transfer the disease resistance to HIV-infected people, bridging the species barrier.

9.   The species barrier is gone.

10.   But how did the disease jump the species barrier to humans when scrapie never did, or just what agent causes it?