Evolution Charles Darwin is among one of the first scientists to predict the origin of mankind. His most famous book, On the Origin of Species by Means of Natural Selection (1859), is a landmark in human understanding of nature. According to the theory of evolution, life originated more than 3.4 billion years ago, when the earth's environment was much different than that of today. Especially important was the lack of significant amounts of free oxygen in the atmosphere. Experiments have shown that rather complicated organic molecules, including amino acids, can arise spontaneously under conditions that are believed to simulate the earth's primitive environment. Concentration of such molecules evidently led to the synthesis of active chemical groupings of molecules, such as proteins, and eventually to interactions among chemical compounds. A rudimentary genetic system eventually arose and was elaborated by natural selection into the complicated mechanisms of inheritance known today. The earliest organisms must have fed on nonliving organic compounds, but chemical and solar energy sources were soon tapped. Photosynthesis freed organisms from their dependence on organic compounds and also released oxygen so the atmosphere and oceans gradually became more hospitable to advanced life forms. The earliest organisms of which remains exist were already cells, resembling modern bacteria (see Cell). These simple unicellular forms (prokaryotes) were at first anaerobic (living without oxygen), but they diversified into an array of adaptive types from which cyanobacteria (formerly known as blue-green algae) descended, including aerobic photosynthesizers. Advanced cells (eukaryotes) may have evolved through the amalgamation of a number of distinct simple cell types. Single-celled eukaryotes then developed complex modes of living and advanced types of reproduction that led to the appearance of multicellular plants and animals.		Darwin, the founder of Evolution.

 

Relating Topics
- Natural Selection
- Artificial Selection
- Genetic Mutation