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The earliest direct and (this next part is very important) intentional influence humans had on the evolution was the result of selective breeding. Be it harvesting a certain grain, planting a certain fruit tree, humans have always used selection in which plants and animals we choose to eat or for company. Because of the way humans select which plants and which animals, we influence their evolution. In recent history, a group of Siberian scientists decided to see how rapidly selective breeding could tame the fox. The scientists used Siberian foxes that were most tolerant of humans and bred them. Over fifteen generations of breeding only the most human-tolerant foxes, the intent was to create a fox who was, and whose offspring would then be, tame. A five-point scale was used guage how tame individual foxes were. After three generations of selective breeding, 2s and 3s on the scale were common. Eventually, 5s (the most tame) were commonplace and many foxes actually craved human contact. A testament to the imperfect nature of selective breeding, though, all of the tame foxes barked. Adult foxes do not bark, it is a trait only infants and juveniles possess. It is impossible, though, to select a single trait with selective breeding and as a result of that, somewhere along the line, a fox selected for its tolerance of humans was also one that possessed some trait causing him to act, generally, more juvenile (barking, tail held high) throughout his life. Traits are attached to organisms and selective breeding is a single-trait litmus test (Palumbi). Selective breeding allows for the rapid evolutionary change of organisms (plants and animals) but the method is heavy handed and imperfect. Nature has it's own method of selective breeding, it's called adaptation. In the speculation of how dogs evolved from wolves, both the two prominent theories have everything to do with humans. Theory #1 One theory is that wolves domesticated themselves. They evolved into dogs of their own volition. Wolves that were naturally more tolerant of humans were able to live near human settlements or follow nomads, feasting on whatever scraps were left behind. Obviously eating humans' leftovers is the easy life compared to the typical wolf life. Of course, timid or fiercely territorial wolves were ill-suited to live near humans. Wolves able to live somewhat near humans were the first step in the road to doghood, as this theory stipulates. The more human-tolerant the wolf, the closer a wolf could get to human settlements (and humans) the greater the opportunity for scraps and (as wolves became more and more tame) possibly handouts. The trade off: domesticated wolves (more like dogs by this point) were vigilant guards, bed warmers and an emergency food source -- perfect for early man (OPB). Theory #2 This theory posits that wolves were domesticated by humans -- that humans initiated and directed wolves' evolution into dogs. The method would have been very similar, if not identical to the methods of taming/domestication employed by the Siberian scientists who tamed fox (OPB). Ultimately, both theories hinge on humanity. Humans caused the evolutionary change in wolves whether directly or indirectly. Theory two, however, suggests a much more rapid evolutionary change. Both theories attribute the evolutionary change, in some measure, to humans, but theory two indicates use of selective breeding. Selective breeding, the most primitive tool in humans' evolutionary arsenal, is also one of the greatest example of rapid evolutionary change at the hands of humans. The questions remains though, are humans necessary for rapid evolutionary change in plants and animals, or would they evolve as quickly, but perhaps in different ways, on their own? Another source of rapid evolutionary change is in transplantation. Plants or animals are gathered up and shipped off to strange new worlds where they and the natives wage an evolutionary war for supremacy of the land. This evolutionary war comes courtesy of humans and our gift of transportation. Humans have brought about rapid evolutionary change in animals by way of our ability to travel a great distance in a short while. Animals that stowed away on the ships that early explorers like Columbus traveled the world in, were introduced to countless ecosystems to which they were alien (Palumbi). Animals that had spent millions of years settling into a comfortable evolutionary niche suddenly found themselves displaced or hunted by newcomers that neither predator nor prey was equipped to deal with. To be contenders once again, animals had to evolve quickly. Fierce competition stoked the evolutionary flames but humans and their swift transportation sparked the blaze. Biologist Tom Schoener went about trying to prove that animals must (and do) evolve rapidly when shuffled about and dumped into unfamiliar surroundings by humans. He used lizards to prove his point. Schoener first located a small island chain full islands that were forested, lush, but devoid of the type of lizards he used in his experiment. He scattered his lizards about the islands, taking careful note who went where, what the lizards looked like, their measurements and such. Many years later, Schoener returned to the islands to study the lizard population. Lizards he had sent to island with typically squat, bush-like vegetation had evolved short, widely spaced legs, perfect for maneuvering about broad ferns and leaves. Lizards on island with typically tall, thin vegetation had evolved long legs for wrapping around branches and stems. In only 15 generations, widespread evolution had occurred. All of the lizards came from the same stock and all of the groups of lizards experience a rapid evolutionary change (Palumbi). This change could never have occurred were it not for humans ability to rapidly move animals about and in only a short time, introduce one species to an entirely new, otherwise unreachable surroundings. Ever since humans have traveled great distances with animals in stride, we have incited evolutionary change. Though at times it was not our intention, humans have constantly introduced alien species to self-contained environments -- often with devastating effects. There is, for example, the struggle of village weaver and the cowbird. Village weavers tend to inspect their eggs thoroughly, each day. There exist birds, nest parasites they are called, that lay their own eggs in Village weavers' nests in the hopes that the egg will pass the village weaver's inspection. If it passes, the weavers unwittingly raise the parasite egg and feed the chick when it hatches. The chicks of these nest parasites eat a great deal more than the weaver's chicks and so eventually, the weaver's young starve and die the parasite is all that remains. Village weavers know who their parasitic enemies are, though, and can spot their eggs most of the time. If a weaver spots a parasitic egg, it tosses it out of the nest. As a result, a real village weaver is killed now and again, but by and large, the nest parasites are kept to a minimum. In an environment free of nest parasites, the village weaver population soars the need for egg inspections disappears …. That is, until the cowbird is introduced. When the nest parasite known as the cowbird was released into a population of village weavers (that had lost their egg inspecting behavior), the village weavers did not notice the parasites and were unable to recognize them anyway. As the cowbird's parasitic eggs began to devastate the village weaver population, though, the village weavers began to inspect their eggs again, this time searching for cowbird eggs (Palumbi). The village weavers were forced to adapt rapidly or face extinction at the hands of a foreign predator. It is our ability to bring together many organisms, ill-adapted to compete with or prey on each other, that causes such organisms to evolve so rapidly -- not to doing so, would mean extinction. When nature has her way, animals do not go where they are not meant to. The evolutionary clash that humans create when we introduce new species to new ecosystems in wholly unique to, in fact, humans. In natures, the Asian boring beetle is never able to devastate the ill-equipped trees of North America, for it has absolutely no means of getting to North America. Had it the means, the flora of North America would have the defenses, because it would time for an entire population of beetles to evolve the means to get across the Pacific Ocean, and their onslaught would thus be gradual, giving the flora of North America the time to gradually evolve some manner of defense against the insects. Toss humans into the equation and millions of years of evolution go out the door. Flightless, blind, crippled animals can go from Africa to Antarctica in a day, as long as humans take them along. |