Perhaps the uniquely human trait with the most impact on the world is our propensity for changing our environment. We are experts at creating trash and we leave it behind everywhere in heaps and mounds. We also cannot travel far without our flocks of cattle, sheep, and goats that are numbering over 3 billion on the planet. We plough up fields, tear down forests, and light up the night sky. Wherever we go the native flora and fauna change. Some capitalize on our arrival, like the rats and birds that thrive on our garbage, but others shrink away and sometimes disappear for good.
Humans are so capable at manipulating the environment that we have even changed the global climate. Certainly global warming is a natural process caused by glacial cycles, but burning fossil fuels emits pollutants like carbon dioxide into the atmosphere where it gets trapped and causes "global warming." Scientists expect that within the next 100 years, temperatures may rise to 10 degrees Fahrenheit and sea levels could rise upwards of 20 inches. The world will look much different than it does today in just a century's time.
The polar ice caps are melting and threatening the livelihood of big mammals like polar bears whose hunting strategy depends on floating ice for catching prey like seals in the water beneath. Very slight changes in temperature affect smaller animals that are incapable of adapting or moving around with the climate. For example, tree frog species are dying off because those that live on mountain tops move steadily toward the peak until they can no longer find cooler temperatures.
Humans have a history of causing animal extinctions or at least being held responsible for them. For example, the disappearances of ground sloths in the West Indies and pygmy mammoths on Wrangel Island in the Arctic Ocean are blamed on human hunters. Extinctions of small and especially large animals (megafauna) occurred in the Americas between 12 and 10 Kya, in Madagascar between 6 and 1 Kya, and in Australia between 40 and 30 Kya and it is still debated whether they were induced by the arrival of humans to the regions or if they were spurred by climate change. In North America, the megafauna (including mammoths, mastodons, giant beavers, wild horses, camels, and saber-toothed cats) vanished from the fossil record just about the same time some of the earliest artifacts like Clovis points appear. Critics argue that the best evidence to show that overhunting by humans caused the extinctions would be an abundance of kill sites (butchered skeletons with spear points), but there are not an inordinate number of these. However, it is possible that climate change from regular glacial cycles combined with the threat of a cunning human predator could have been a deadly duo. Perhaps by overkilling grazing animals, humans indirectly caused environmental changes in the landscape, which affected the other animals. Today, ecologically friendly hunting patterns are managed by local, state, and federal government institutions in the United States.
Hunting and fishing regulations may not be enough to stop us from repeating our past mistakes, however. Because of overfishing and pollution, scientists have predicted that unless drastic changes are made, within the next fifty years nearly all marine species of seafood are going to collapse. Ironically, humans may be responsible for killing off one of the crucial food sources that contributed to making us "human," since incorporating marine animals into our Paleolithic diet could have influenced the evolution of our brain.
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