150 years ago, the world changed forever. On 24th November 1859 Charles Darwin’s book Origin of Species was published. For the first time a plausible explanation of how evolution worked was placed in the public domain.

Darwin comes face with the Gibraltar Neanderthal Skull. (Drawing by Alex Menez Junior)

We shall see in a while what this explanation is. But first a little history. Charles was not the first person to produce a theory of evolution and the ideas surrounding evolution go back over 2,500 years to Thales, Lucretius and others. Since that time many natural philosophers had a stab at explaining how evolution might work.

The 18th century was a dynamic time for evolution. There were strongly conflicting views on how species originated. Were all creatures created independently of one another and immutable, a view fervently supported by the Church, or could new species arise from existing ones? Charles’ grandfather, Erasmus, who Samuel Coleridge thought ‘possesses, perhaps, a greater range of knowledge than any other man in Europe’, wrote about evolution in his book Zoonomia (1794-1796), and Jean-Baptiste Lamarck thought that acquired characteristics could be inherited, describing his ideas in Philosophie Zoologique published in 1809.

But challenging the idea that the world was exactly as created by God was dangerous. The accepted order of the world, and specifically man’s place within it, was a reflection of Divine Will. This provides part of the explanation as to why Charles kept his ideas under wraps for over 20 years: he didn’t like controversy. In 1858 Charles was writing his ‘big species book’ when a 20 page letter arrived from the Moluccas. It was from the naturalist Alfred Russel Wallace who had independently arrived at Charles’ own theory of evolution. Charles’ friends Joseph Hooker and Charles Lyell arranged for a joint Darwin-Wallace paper to be read at the Linnean Society in June 1858, marking the first publication of Charles’ explanation of how evolution worked. After this, Charles condensed his book and published it as Origin of Species in 1859. The Linnean paper aroused little interest. But Origin was another story.

For the first time people had to grapple with their long-held beliefs about how species evolve in the light of a new explanation that was at once simple to understand and seductively plausible. So what was Charles’ explanation? In his own words: ‘In October 1838, that is, fifteen months after I had begun my systematic enquiry, I happened to read for amusement Malthus on Population, and being well prepared to appreciate the struggle for existence which everywhere goes on from long-continued observation of the habits of animals and plants, it at once struck me that under these circumstances favourable variations would tend to be preserved, and unfavourable ones to be destroyed. The result of this would be the formation of new species.’ He termed this Natural Selection and 150 years after Origin it still remains the fundamental explanation that drives evolution.

Origin created an immediate paradigm shift in the way the world would be understood from then on. The Victorian model of a benign creator bringing forth ready-made species was replaced by one of struggle, competition, death and survival. Instead of studying animals and plants to determine how they fitted into a creationist worldview, showing the wisdom of a creator at work, the naturalist now needed to understand behaviour, how organisms were related to one another and which properties were beneficial to ensure survival. The modus operandi of the naturalist changed forever.

Origin was based on many years of observational and experimental work. It is crammed with example after example supporting Charles’ two major theses: (1) that all organisms have descended with modification from common ancestors and, (2) that the chief agent of modification is the action of natural selection on individual variation. A major strength of Origin is that Charles anticipated and answered the possible objections of critics. He offered a test for what has become one of the popular criticisms of evolution: ‘If it could be demonstrated that any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down. But I can find no such case.’

This leads us to one of the most famous arguments against evolution, called the Argument from Design. In the 18th century the theologian William Paley stated that just as a watch is too complicated and too functional to have sprung into existence by accident so too must all living things, with their far greater complexity, be purposefully designed. The Watch Analogy was revived in the United States in the 1920s by Creationists who over time evolved to become creation scientists and ultimately intelligent designers. But evolutionary biologists including Richard Dawkins have demonstrated time and again that the analogy is false. Natural selection, the unconscious, automatic, blind yet essentially non-random process that Charles discovered, has no purpose in mind. It plays the role of watchmaker in nature; it is the blind watchmaker. We see intermediary steps in the evolution of organs, including the favourite example of the intelligent designers: the eye. There are eyes of varying complexity in living organisms, such as would have been found in intermediate steps during evolution: all the way from the rudimentary eye pits in worms to the very complex, and astonishingly similar, eyes of the octopus and human.

Some also assert that evolution is ‘just a theory’. The error here stems from using the word in the wrong context. In everyday speech a theory often means a hypothesis or even a mere speculation. In science, however, theory means a statement of what are held to be the general laws, principles, or causes of something known or observed. The theory of evolution is a body of interconnected statements about natural selection and other processes that cause evolution; just as the atomic theory of chemistry and the Newtonian theory of mechanics are bodies of statements that describe causes of chemical and physical phenomena. Like the heliocentric solar system, evolution began as a hypothesis, and achieved facthood as the evidence in its favour became so strong that no knowledgeable and unbiased person could deny its reality. Evolution affects almost all other fields of knowledge and is one of the most influential concepts in Western thought. It is the central unifying concept of biology, a fact elegantly portrayed by Theodosius Dobzhansky, a leading evolutionary geneticist who stated that ‘Nothing in biology makes sense, except in the light of evolution.’

It is remarkable therefore, that despite all the available evidence for evolution, there are still those who hold creationist views, for which absolutely no evidence at all exists. This, though, is a consequence of evolution itself. After all, we are only able to debate these issues and ponder on them as a result of one of the manifestations of our own evolution: a highly complex and conscious brain.

Charles wrote almost 20 books, dealing with geology, botany, animal behaviour and evolution. He initiated many new fields of research and studied closely the life histories and biology of groups as diverse as worms, barnacles and carnivorous plants. But Origin is his most famous work and he stated that ‘It is no doubt the chief work of my life.’ The first edition sold out on the day of publication, and the work ran to six editions which, as Charles said ‘Though considerably added to and corrected in the latter editions, it has remained substantially the same book.’

Charles Darwin corresponded with hundreds of naturalists around the world to gather facts for his research, and Gibraltar crops up in letters by and to Charles from age thirty-six in 1846, to age seventy-two in 1881, a year before his death. Some of these include letters from a botanical enthusiast who visited Gibraltar and collected plants that Charles then grew in Down House. But the best Gibraltar-Darwin connection is from 1864. That year Charles had a visit from two of his friends, Charles Lyell and Hugh Falconer, who took along the famous Neanderthal Gibraltar Skull for him to see. And so, at that moment, two very distantly related humans, both with extraordinary roles to play in evolutionary theory, came face to face.

Dr Menez is an authority on southern Iberian land molluscs and has been a student of evolution for thirty years.