Slowly but surely, the next "great extinction" (the 6th) is in our midst.  Successive waves of species extinctions have followed since humans' spread out of Africa. Extinction rates for birds, mammals and amphibians are similar to those present of the five global mass-extinction events of the past 500 million years that resulted from meteorite impacts, volcanism and other forces. Threats to animal survival increase in step with a rise in human population. What does man do when overpopulation of wolves threatens caribou populations? The sooner man decides that conserving is more important than consuming, the species at the top of the food chain can save himself from impending doom.