"When people use the term extinction, they mean that many living species vanished. This is just part of the equation, however. Another side is that some species survived. In all past major extinctions, with ecosystems out of balance, many of the surviving species experienced explosive growth. This is what happened 13,000 years ago, when an unusual mix of conditions created favorable conditions for the human species.
First, there were new genes. Spurred by genetic mutations that produced a burst of creativity and technological resourcefulness, humans became even more efficient predators. The Event killed off many competing predators, and skilled hunters decimated many surviving ones, ensuring that more people survived. The same resourcefulness made humans better at finding food in every way, and consequently human populations expanded rapidly.
Second, a benign climate, due partly to the green house effect of the impacts, fostered larger human populations. The warmer climate, coupled with humans' newfound resourcefulness, fostered the invention of agriculture, freeing humans from a nomadic lifestyle. The development of better housing, clothing, and weapons all allowed human populations to increase.
Third, increasing populations led more people to live together in villages and towns, where the division of labor allowed a larger pool of skilled talent to develop. This fueled an almost constant technological boom in many fields, producing, among other things, pottery making, metalworking, and writing.
All that may seem positive, except that the burgeoning population, initially fostered by the extinction Event, contained the seeds of many of our current troubles. When overpopulation occurs in any species - whether it is rabbits, locusts, lemmings, or people - a host of problems comes along with it, including epidemics, starvation, extreme aggression, ecosystem destruction, and scarce resources, every one of which is a major pressing problem in our society today.
An extinction sequence comprises the following stages:
1) A major catastrophe leads to the disappearance of some species.
2) These disappearances lead to the overpopulation of some surviving species.
3) Overpopulation leads to devastating depopulation.
This equation has held true for every past extinction event. In the current sequence, we have passed through the first two stages as a species but not the last stage, depopulation..." (Richard Firestone, Allen West, Simon Warwick-Smith, The Cycle of Cosmic Catastrophes, Bear & Co., 2006.)