HISTORY OF EVOLUTION
As described earlier, evolution is the theory of how living things (organisms) change over time. Many theories have been put forward to explain how evolution happens, beginning from 500BC up to the most recent and supported theory of evolution explained earlier (under “What is Evolution”). The most relevant theories in the history of evolution are explained below:
The concept of evolution is as ancient as Greek writings, where philosophers speculated that all living things are related to one another. This started around 500 BC, a whopping 2,517 years ago! Aristotle, one of these Greek philosophers, believed in the “ladder of life,” where simple organisms gradually change to more elaborate forms.
In 1801, French zoologist Jean-Baptiste Lamarck suggested a theory for evolution based on the development of new traits in response to a changing environment. His theory was that variation is acquired, and it involved two ideas:
1. A characteristic which is used more and more by an organism becomes bigger and stronger during its lifetime, and one that is not used eventually disappears
2. Any feature of an organism that is improved through use in that organism’ is passed to its offspring.
On the right is an example of Lamarck’s theory on giraffes. We now know that this evolutionary theory is wrong. Organisms cannot pass on skills or traits to their offspring. Only the traits that are linked to their DNA can be passed to their offspring.
In 1859, Charles Darwin, an English naturalist, published his theory of evolution in a book called “On the Origin of Species”.
His theory was shaped by his observations during his five-year voyage around the world aboard the ship H.M.S. Beagle. Darwin was particularly interested in the finches and tortoises of the Galapagos Islands, and pondered how different species of animals could have developed on this remote set of islands 200 miles west of Ecuador (south America).
In his book, Darwin defined evolution as "descent with modification," the idea that species change over time, give rise to new species, and share a common ancestor. Darwin also proposed a mechanism for evolution – natural selection – which he defined as the "principle by which each slight variation [of a trait], if useful, is preserved".
An example of Darwin’s theory on giraffes can be seen on the left.
Today’s theory of evolution is built upon that proposed by Charles Darwin, but with added information on genetics and the introduction of three additional mechanisms of evolution (mutation, gene flow and genetic drift). Darwin didn’t know that traits were inherited via genes.