What species is most fit for life? All have an equal chance, scientists say. There are more than 8 million species of living things on Earth, but none of them -- from 100-foot blue whales to microscopic bacteria -- has an advantage over the others in the universal struggle for existence.A trio of scientists report that regardless of vastly different body size, location and life history, most species are equally 'fit' in the struggle for existence. Source 7q.