Speciation or what happened to the bears and their descendants when they went over the mountain Adventure Works The ultimate source for outdoor equipment The bear went over the mountain Our relationship to other life forms From what we know about the alleles we share with other life forms on earth we can see how we are related to them and descended from common ancestors Click here to see how http www pbs org wgbh evolution libr ary 04 4 l 044 02 html Once upon a time There were a lot of bears in one place They called themselves the Population of Bears There were over 10 000 of them But some of the bears were unhappy because the honey in their valley made them sick Some of the bears were unhappy because they were bald and others made fun of them And some were unhappy because they were snobs and thought all the other bears were not as attractive as they were Their valley was surrounded by 4 mountains So the first group of bears went over the mountain to the south And the second group of bears went over the mountain to the east And the third group of bears went over the mountain to the west However this did not turn out to be a good decision for all of them The first group of bears got stuck in heavy traffic The second group of bears was captured and all were put into zoos All of them died except for one male and one female Their offspring looked pretty strange and didn t survive But the third group of bears was contented and prosperous in its new valley Pretty soon there were lots of new little bears But some white bears and some others wanted to search for new prey so they left and went north And then from the south there came a great flood It flooded the great valley of the Bear Population and the territory of bear sample 3 but not the far north where the white bears had gone All the bears in Bear Valley drowned except for a few who happened to be on top of Old Smokey when the flood hit Meanwhile the climate changed in the north One type of bear had better fitness in this environment than did the others Eventually the cold environment warmed up and the white bears migrated back to the Ol Smokey Mountain bear population Guess what happened next Adventure Works The ultimate source for outdoor equipment The bear went over the mountain NOTHING Adventure Works The ultimate source for outdoor equipment And then one day the mountain blew up tossing all the bears back down into the valley which by now had dried up Volcanic ash covered everything Adventure Works The ultimate source for outdoor equipment A family tree of humans is based on analysis of shared and unshared alleles Adventure Works The ultimate source for outdoor equipment The bear went over the mountain Summary 1 All the 4 forces of evolution act upon modern humans but neither genetic drift nor natural selection has resulted in speciation 2 By comparison with the bears in this tale humans have never been isolated from each other long enough to speciate become different species We ve remained one species because of constant gene migration Adventure Works The ultimate source for outdoor equipment The bear went over the mountain