Charles Robert Darwin established that all species of life have descended over time from common ancestry, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection. He published his theory with compelling evidence for evolution in his book On the Origin of Species (in 1859) and changed the world forever.
He was born in Shrewsbury, Shropshire, England on 12 February 1809 at his family home, the Mount. His maternal grandfather was china manufacturer Josiah Wedgwood, while his paternal grandfather was Erasmus Darwin, one of the leading intellectuals of 18th century England.
Darwin himself initially planned to follow a medical career, and studied at Edinburgh University but later switched to divinity at Cambridge. In 1831, he joined a five year scientific expedition on the survey ship HMS Beagle.
The voyage of the Beagle
Beginning on 27 December 1831, the voyage lasted almost five years and, as FitzRoy had intended, Darwin spent most of that time on land investigating geology and making natural history collections, while the Beagle surveyed and charted coasts.
On the voyage, Darwin read Lyell’s ‘Principles of Geology’ which suggested that the fossils found in rocks were actually evidence of animals that had lived many thousands or millions of years ago. Lyell’s argument was reinforced in Darwin’s own mind by the rich variety of animal life and the geological features he saw during his voyage. The breakthrough in his ideas came in the Galapagos Islands, 500 miles west of South America. Darwin noticed that each island supported its own form of finch which were closely related but differed in important ways.
His five-year voyage on HMS Beagle established him as an eminent geologist whose observations and theories supported Charles Lyell’s uniformitarian ideas, and publication of his journal of the voyage made him famous as a popular author. As HMS Beagle surveyed the coasts of South America, Darwin theorised about geology and extinction of giant mammals.
In mid-July 1837 Darwin started his “B” notebook on Transmutation of Species, and on page 36 wrote “I think” above his first evolutionary tree. In London, from 1837, Darwin began to speculate about where species come from. This is a page from his Notebook B showing the first evolutionary tree diagram.
Puzzled by the geographical distribution of wildlife and fossils he collected on the voyage, Darwin began detailed investigations and in 1838 conceived his theory of natural selection.
Darwin’s scientific discovery is the unifying theory of the life sciences, explaining the diversity of life.
Darwin worked on his theory for 20 years. After learning that another naturalist, Alfred Russel Wallace, had developed similar ideas, the two made a joint announcement of their discovery in 1858. He published his theory with compelling evidence for evolution in his 1859 book On the Origin of Species.
Charles Darwin’s theory of evolution by natural selection is one of the most influential scientific ideas ever conceived. He wrote most of ‘On the Origin of Species’ at his Kent home, Down House, it was to be the book that changed science forever.
His theory is simply stated in the introduction:
“As many more individuals of each species are born than can possibly survive; and as, consequently, there is a frequently recurring struggle for existence, it follows that any being, if it vary however slightly in any manner profitable to itself, under the complex and sometimes varying conditions of life, will have a better chance of surviving, and thus be naturally selected. From the strong principle of inheritance, any selected variety will tend to propagate its new and modified form.”
Darwin invoked the idea of the ‘tree of life’, a way to describe the evolutionary relationships between all living things on Earth.
“The affinities of all the beings of the same class have sometimes been represented by a great tree.I believe this simile largely speaks the truth. The green and budding twigs may represent existing species; and those produced during former years may represent the long succession of extinct species. At each period of growth all the growing twigs have tried to branch out on all sides, and to overtop and kill the surrounding twigs and branches, in the same manner as species and groups of species have at all times overmastered other species in the great battle for life. The limbs divided into great branches, and these into lesser and lesser branches, were themselves once, when the tree was young, budding twigs; and this connection of the former and present buds by ramifying branches may well represent the classification of all extinct and living species in groups subordinate to groups. Of the many twigs which flourished when the tree was a mere bush, only two or three, now grown into great branches, yet survive and bear the other branches; so with the species which lived during long-past geological periods, very few have left living and modified descendants. From the first growth of the tree, many a limb and branch has decayed and dropped off; and these fallen branches of various sizes may represent those whole orders, families, and genera which have now no living representatives, and which are known to us only in a fossil state. As we here and there see a thin straggling branch springing from a fork low down in a tree, and which by some chance has been favoured and is still alive on its summit, so we occasionally see an animal like the Ornithorhynchus or Lepidosiren, which in some small degree connects by its affinities two large branches of life, and which has apparently been saved from fatal competition by having inhabited a protected station. As buds give rise by growth to fresh buds, and these, if vigorous, branch out and overtop on all sides many a feebler branch, so by generation I believe it has been with the great Tree of Life, which fills with its dead and broken branches the crust of the earth, and covers the surface with its ever-branching and beautiful ramifications.”
He put a strong case for common descent, but avoided the then controversial term “evolution”, and at the end of the book concluded that:
“Thus, from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows…There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whiles this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.”
In 1871, he examined human evolution and sexual selection in The Descent of Man, and Selection in Relation to Sex, followed by The Expression of the Emotions in Man and Animals. His research on plants was published in a series of books, and in his final book, he examined earthworms and their effect on soil.
The theory of evolution by natural selection, and with it the concept of the evolutionary Tree of Life, have since been thoroughly tested and verified by a wide range of evidence and especially by the discoveries of genetics. The universality of the genetic code – the DNA instructions that specify the make-up of the proteins from which organisms’ bodies are built – confirms a common ancestry for all life on Earth today.
Darwin died on 19 April 1882 and was buried in Westminster Abbey.