Biologists can infer the reason for these selective forces from the kinds of genes that are tagged by the genome scans.
Update: As many of you pointed out, there are multiple places to get your full genome scanned now for prices in the mere thousands of dollars. Pocket change, really.
Anyone who has forked out a few hundred dollars to have their genome scanned can decide whether to find out if their APOE gene puts them at increased risk of Alzheimer's.
