There are millions of different types of living things on Earth. In order to keep track of them all, scientists put living things into groups based on characteristics that they have that are the same.

The question of what defines a species has vexed scientists across the ages, particularly in conservation, where decisions require a firm understanding of biodiversity. When you purchase through links ...

National Geographic estimates there are between 50 billion and 430 billion birds populating the planet, outnumbering humans by up to approximately 50 times. Spread across 9,700 species, according to ...