Theories of evolution

Darwin's theory of evolution explains how life on Earth has changed over geological time. Scientists believe this is the reason why all living things on Earth exist today. The theory is supported by evidence from fossils, and by the rapid changes that can be seen to occur in microorganisms such as antibiotic-resistant bacteria. Many species have become extinct in the past and the extinction of species continues to happen.

Evolution timeline

The basic idea behind the theory of evolution is that different species have developed over time from simple life forms. These simple life forms first developed more than three billion years ago (as the Earth is believed to be about 4.5 billion years old).

This timeline shows key events in the evolution of life forms on Earth, from the first bacteria to the human species.

Theories of evolution

Charles Darwin is famous for his theory of evolution, but he was not the only person to develop such a theory.

Darwin’s theory

Charles Darwin (1809 - 1882)

Charles Darwin was an English naturalist. He studied variation in plants and animals during a five-year voyage around the world in the 19th century. He explained his ideas about evolution in a book called On the Origin of Species, which was published in 1859.

Darwin's theory caused controversy among his contemporaries and his ideas were only gradually accepted, although some people still do not believe them today. The reasons for skepticism include:

• Darwin’s theory conflicted with religious views that God had made all the animals and plants on Earth
• Darwin did not have enough evidence at the time to convince many scientists
• it took 50 years after Darwin’s theory was published to discover how inheritance and variation worked.

Lamarck’s theory

Jean-Baptiste Lamarck was a French scientist who developed an alternative theory of evolution at the beginning of the 19th century. His theory involved two ideas:

1. A characteristic which is used more and more by an organism becomesbigger and stronger, and one that is not used eventually disappears
2. Any feature of an organism that is improved through use is passed to its offspring.

However, we now know that in most cases this type of inheritance cannot happen.

Lamarck's theory cannot account for all the observations made about life on Earth. For instance, his theory implies that…