Living Organisms

The animal kingdom today probably contains more than 10 million different species, the vast majority of which are still unidentified by scientists. For more than 2,000 years, scientists have tried to explain and classify this great variety. The 19th-century theory of evolution by natural selection helped explain this, and the great insight of 20th century and early 21st century biology have allowed an ever deeper understanding of the biochemical activity that takes place in and between cells, and the relationship between the behavior patterns of a species and its need to survive in a competitive environment.