In this week's episode, we take a look at how Charles Darwin postulated the Theory of Natural Selection. We also look at what that theory was and finally finish the episode with some interesting facts about Darwin.
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Two theories of evolution existed during Charles Darwin's time. Darwin, who read these two theories, was motivated to find out how evolution really happened [Citation1].
While Darwin was pondering over how evolution really happens, in 1838, he read an essay written by Thomas Malthus. In this essay, Malthus argues that, if left unchecked, all species have the ability to reproduce indefinitely and overpopulate the earth within a few hundred generations and outstrip food production. And yet, it doesn't happen. Every year, the populations of varied species remain stable.
While thinking about what Malthus had written, Darwin realized that there must be some combination of natural factors that keeps the populations of different species in check. Due to these factors, many of the organisms in varied species must have died even before they could have had the chance to reproduce. Darwin named this combination of natural factors 'Natural Selection,' because he felt that these factors select which organisms get to reproduce and have children, and which do not. According to Darwin, Natural Selection was the force behind evolution. Thus, the Theory of Natural Selection originated.
For example, in places where there was no grass, but only tall trees, giraffes with slightly elongated necks and front legs would have had a better chance of procuring food, while those that didn't possess these attributes would have died out, before reproducing. Thus, the next generation of giraffes would have longer front legs and necks. This process would have continued for hundreds of generations. As a result, the giraffes we see today have extremely long necks and front legs when compared to any other organism in this world.
Reluctance to publish his theory
But even though Darwin had come up with his own theory of evolution in the year 1838, he did not publish it then, because he was afraid that he might be ostracized by society for mentioning something like that. After all, he would be suggesting that human beings actually evolved from other organisms, and were not created by god. This would go against the beliefs of many major religions at that time. So, for the next two decades, he kept experimenting and gathering more evidence to prove his theory. (Darwin's drawing below is based on his belief that evolution would have begun with one organism (1 in the drawing) and then branched and rebranched, to produce the numerous varied species in this world).
On June 18th, 1858, Darwin read an essay [Citation 2] published by Alfred Russel Wallace, an English naturalist who had sailed to South East Asia and collected specimens there. Darwin was spellbound by the similarities Wallace's essay had, with his own theory of evolution. So, even though he had originally planned to write a big book on his thoughts about evolution, he hurriedly wrote an abstract, called 'On the Origin of Species.' Then, he had both his abstract and Wallace's essay read out in the Biological Society in London.
Then, he started working on the big book he had always dreamt to finish.
In his abstract (On the Origin of Species), Darwin explains that natural selection is not the only catalyst behind evolution. There was one more catalyst, called Sexual Selection. Sexual Selection is the process in which, in many organisms, the female (mostly) chooses which male to mate with. The males, on the other hand, compete with each other, to attract the attention of the female.
Sexual selection is another factor, which decides which members of a species get to reproduce and which do not. Able members of one sex (mostly males) can mate with many females and have lots of children, while less able males have the least chance of mating and reproducing. Thus, the next generation would have more individuals with the characteristics of the more able males, and fewer individuals with the characteristics of the less able males.
Darwin finally finished the first part of the big book, which he had always wanted to write, in 1868. He named it, 'The Variation of Animals and Plants Under Domestication.' But before finishing its second part, he died.
Darwin also published other books, like, 'The Descent of Man, and Selection in Relation to Sex' and 'The Expression of the Emotions in Man and Animals.' Both these books became hugely popular, exceeding his own expectations.
The Royal Society of London (Britain's national academy of sciences) honored Darwin for his lifelong contribution to science by awarding him the Copley medal (Britain's highest scientific honor) in 1864. (A picture of Charles Darwin in 1868 can be found below)
In 1882, Charles Darwin was diagnosed with 'Angina Pectoris.' It is an illness that causes chest pain due to the insufficient flow of blood to the heart. Darwin died on April 19th of the same year.
Finally, I end the episode by looking at some interesting facts about Darwin.
Picture of Charles Darwin - By Julia Margaret Cameron - Reprinted in Charles Darwin: His Life Told in an Autobiographical Chapter, and in a Selected Series of His Published Letters, edited by Francis Darwin. London: John Murray, Albemarle Street. 1892.Scanned by User:Davepape, Public Domain, Link