The scientific definition of evolution refers to changes in a species or population over time.
Evolution is a long-term process. It may take millions of years and several generation for an evolution to occur. The cause of evolution can be genetic as well as environmental. The evolution is a result of mutation. Evolution generally gives rise to new species, that is different from its ancestral population.
Population is a group of similar type of organisms. These organisms live in the same habitat, require same resources and have same kind of habits. The most essential criteria that defines a population is that the organisms of a population can mate with each other and produce offspring.
Acid-laden ingesta flows out of the stomach, into the small intestine. Acid in the small intestine stimulates secretion of the hormone secretin<span> from endocrine cells in the intestinal epithelium.</span>
