Natural selection. Only spiders that were more resistant to the pesticide lived through the first spraying of the pesticide, thus we're the only ones that could reproduce. This in turn made the offspring of the previous generation more resistant as well; thus making the pesticide less effective.
Answer:
Biology is the study of life and living organisms. Biology recognizes the cell as the basic unit of life, genes as the basic unit of heredity, and evolution as the engine that propels the creation and extinction of species.
If scientists played with buffalo genes a bit, they could make a new breed of beefalo that is tasty and tender, but resists cold and hot weather like the buffalo does. This is common and scientists do things like this all the time, it's how many of dog breeds were created. The cow can't stand weather that's too cold but the beefalo might which would mean more food in northern areas of the world where it's cold.
