160 years of (r)Evolution

Today, February 12th, is the birthday of a man known for having drastically changed our view of life and the world around us. He was born in 1809, in the midst of a wealthy family whose preceding line of men had already gained fame in the philosophical and scientific circles of Europe. Though pressured by his father to become an honourable doctor like himself, and later – when that failed - a respected Anglican parson, he neglected the paths set before him and succeeded, with the help of other family members, to follow his dream: to study and describe nature all around the world and travel across it by ship. Charles Darwin was a mere 22 years old when he embarked on the Beagle, not to return to the British Isles until 5 years later. During that time, he visited the East and Western coasts of South-America, New Zealand, Australia, South Africa, and the archipelago that was crucial for the development of his ideas: the Galapagos.

Yet, it took Darwin years to fully mature his ideas on what was then called the “transmutation of species” - that is to say, the ability of animal and plant species to change over time. The idea of a non-static, changing natural world was controversial and heavily debated at the time, yet it was impossible for scientists to oversee the overwhelming evidence that was being brought home by explorers – especially fossils of great creatures never seen before. Darwin carefully studied the hundreds of notes and specimens that he had brought back himself from his travels, discussed with other scientists and rethought, rewrote and refined his arguments innumerable times. 23 years after his journey on the Beagle, he finally published the synthesis of his ideas, his most famous and groundbreaking work: On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life (1859). Evolutionary Biology was born, exactly 160 years ago.

Left: the Darwin finches of the Galapagos are iconic for Darwins theory of Evolution, even if they in fact, didn't play a key role in the development of his ideas. Right: the sketch of the Tree of Life in Darwin's notes next to the words "I think" wonderfully summarize Darwin's pondering on the transmutation of species.

Certainly, Charles Darwin was the first one to describe evolution through means of natural selection in a complete, detailed and thoroughly written book, which rightfully granted him the title of “Father of Evolutionary Biology”. He was, however, not the first to ponder on the idea of a natural world that can change and modify itself through time. Many before him, such as his own grandfather Erasmus Darwin, had already questioned the mechanical and deterministic view of nature that was the norm in the eighteen-hundreds. In his poem The Temple of Nature, Erasmus traces the development of life forms from microscopic organisms into fully civilised societies, while mentioning the struggle for existence.

Around the time of Darwin’s birth, Alexander von Humboldt shocked the world with his new vision of nature, which described it as one global net of interactions between climate, weather, geography and vegetation which could vary over time and even be influenced by human kind. This way of perceiving nature – although seemingly obvious for us - had never been presented before and was absolutely crucial to kindle evolutionary thoughts. Humboldt’s pioneering work did not only fuel a new way of thinking in the scientific societies of his time; his books on his journeys of discovery in South-America were a direct inspiration for the young Charles Darwin without which he maybe wouldn’t have embarked on the HMS Beagle. Another crucial thinker for the development of Darwin’s ideas was Thomas Malthus, whose pondering upon the limited growth of populations published in 1798 were crucial for Darwin’s finding of natural selection.

Most famous of these pre-darwinian evolutionary thinkers was, however, Jean-Baptiste Lamarck, whose own theory of evolution from 1809 – the first one ever published - incorporated the idea of individuals passing on traits they had acquired, accentuated or disused in the course of their lifetime. Shortly after the publication of the Origin of Species, scientists – but interestingly not Darwin himself – started to see natural selection as the central and only force of evolution. They proclaimed Lamarck’s theory to be invalid and cast it into the shadows. Lamarck’s theory was nonetheless never truly forgotten and has even been reemerging as a plausible theory of late, with the discovery of new forms of inheritance.

Darwin's precessors. From left to right: Jean-Baptiste Lamarck, Thomas Malthus and Alexander von Humboldt

Also during his lifetime, others were asking the same questions as Darwin. Although often unjustly forgotten, the theory of evolution as described by Darwin was independently conceived by a second naturalist: Alfred Russel Wallace. Unlike Darwin, Wallace had set out to travel the world already convinced of the existence of evolution, and deliberately carried out field work to test his theories[1]. Darwin and he had long correspondences in which they discussed their evolutionary ideas and reviewed each other’s writing. Darwin, who was older and had more scientific authority, helped Wallace with the publication of his essays. Wallace in his turn, was a great encouragement for Darwin to finally publish the Origin of Species and became one of the book’s most avid defenders afterwards. Although they are sometimes depicted as competitors, it seems from their letters that they brought each other further than they could have managed alone. Therefore, it would be more correct to say that the field of Evolutionary Biology has at least two, if not many more founding fathers, but this is rarely heard of.

The list of scientists who thought and discussed evolution before and during Charles Darwin’s time is long and spans many countries and scientific disciplines. Evolution was a process not just discovered by one or two geniuses, but by many curious thinkers that belonged to several generations, spanning from the late 18th to the mid 19th century. However, his findings aren’t any less valid because of this – on the contrary: Wallace and he solved the long-lasting debate between sceptics and supporters of the transmutation of species by developing a sound theory, which was the ultimate link in a chain of ideas developed over decades by many different minds, all flowing together into one impressive piece of work. Darwin and Wallace were simultaneously the inheritors of and contributors to an intellectual legacy developed by countless thinkers which had started to see the world with newly awoken eyes – something made possible largely by travelling and witnessing strange new worlds. They questioned what they saw and how it could possibly have a place in the static, century-old world view imposed on them by previous generations, thus making a big leap forward in the understanding of our surrounding world.

What is most fascinating about the development of evolutionary thinking in the 19th century, was that it occurred despite a complete lack of knowledge on genetics whatsoever. Gregor Mendel, a friar who established the first rules of heredity through breeding experiments on the peas of his covent’s garden, was a contemporary of Darwin. Yet, they never met each other - never even heard of one another - and Darwin never came to learn of the existence of discrete, inherited units, now called genes, which determine our traits. In fact, no one really learned about Mendel’s findings until they were rediscovered by other scientists at the turn of the century, when both he and Darwin had since long passed away.

Gregor Mendel and the discrete variation in pea plant traits that led to his laws of heredity.

The rediscovery of Mendel’s work created a new challenge for evolutionary thinkers, since it had to be integrated with Darwin’s theory of evolution. This did not happen without difficulty: Mendelian genetics described a discrete way of inheriting traits, so that parents with different versions of a trait, such as blue and green eyes, cannot have children with a mixed form of this trait, such as a blue-greenish eye colour[2]. Instead, depending on which trait is dominant over the other, they will either have blue or green eyes. On the other hand, Darwin’s theory assumed a large and continuous variation of characteristics among individuals, of which some will offer greater chances of survival and be naturally selected. How could these two seemingly contradicting views be reconciled?

The scientific community was quickly torn, with some scientists being so convinced about mendelian genetics that they applied the concept of discrete inheritance on evolution and believed that new species arose by the mere occurrence of mutations. In 1918 however, almost twenty years after the comeback of Mendel’s work, a young statistician named Robert Fisher made a first breakthrough by mathematically showing that a trait can in fact vary continuously when based on a number of discrete genes. Moreover, the geneticist Thomas Hunt Morgan had shown in 1912 that mutations did not necessarily create new species in a single step, but provided an ever-growing pool of genetic variation whereupon natural selection could act. By 1930, Fisher and other scientists had found ways to reconcile natural selection and Mendelian genetics mathematically and to confirm this biologically through experiments. Natural selection had finally become a measurable and testable phenomenon, thanks to Mendel’s genetic framework. The merging of evolution and genetics into one became commonly known as the Modern Synthesis and signified the birth of population genetics, which is the study of genetic change within natural populations and is nowadays a central discipline in evolutionary biology.

By the 1930’s, however, evolutionary thinking had developed into a disputable set of ideas. As soon as Darwin’s theories were published, they nourished a certain form of thinking about human society which could in fact lead to gruesome things when placed in the wrong mind. Darwinism - that is to say, the belief that mainly natural selection has shaped all forms of life - was after all not just a scientific theory, but also a philosophical notion with great impact on society. For some, the theory of evolution could be applied not only on the natural world, but also on human society, describing it as a struggle between competing individuals. The 19th century sociologist Herbert Spencer, who coined the term “survival of the fittest”, is known as the founder of this school of thought named Social Darwinism. Under Social Darwinism, evolution became a means to justify colonialism, imperialism and racism by stating that the inferiority or supremacy of some races was entirely based on their genetics and had been shaped by natural selection. These ideas were particularly popular among the middle class at the end of the 19th century, and not even Darwin himself remained innocent and unspoiled by them.

Francis Galton, on the other hand, was inspired by Darwin’s ideas on artificial selection in domesticated plant and animal species, when developing his own scientific discipline: eugenics or the artificial selection of human beings. He believed that the human race could be greatly improved, if we only took as much care of our breeding as we did with our horses and cattle. This originally theoretical idea was widely supported by people from distinct countries and political views, and developed into compulsory sterilization and eugenics programs at the beginning of the 20th century in the USA, Scandinavia, Japan and other countries. Later on, fascist movements such as National Socialism incorporated these ideas into their own intellectual legacy. Social Darwinism justified their view of superiority of the German race and the application of eugenic methods to “further purify it”. After the Second World War however, the ugliness of these views was made clear and they became history for many. Nonetheless, some countries continued programs of forced sterilization up until very recently, and the dangers of Social Darwinism are far from evaded. Indeed, with the recent comeback of nationalistic and populistic movements, we must be cautious not to fall back into this mindset.

Left: Francis Galton, the founding father og the Eugenics movement. Right: Map of the USA showing the legislative status of eugenical sterilization in the 1930's, including the number of operations carried out in each state.

Despite evolutionary biology being put in a bad light after those stained years of history, scientists kept wondering about the evolution of life and the specific mechanisms and processes that drove it. In the 50’s, the world witnessed a major breakthrough when Martha Chase and Alfred Hershey showed that the DNA molecule was the bearer of genetic information. This was quickly followed by the discovery of DNA’s double helix by Watson, Crick and Franklin. In the same decade, Crick established what is now called the “dogma of molecular biology”: that DNA (and also RNA) contains genetic information which is translated into proteins, the executers of this information, and not the other way around. Finally, genetics and therefore evolution, had become a palpable concept with a physical, concrete form. Understandably, these discoveries opened the floodgates for a deeper level of knowledge on heredity and genetics. By the early 60’s, the genetic code of A, C, T and G was cracked, and molecular biologists understood much better how genetic information was translated into an organism.

In more recent years, the field of evolutionary biology profited from many of the fantastic technological advances made, and by doing so leaped forward with gigantic steps. One thing scientists from the 50’s and 60’s couldn’t do, was to read the genetic code of organisms. This already changed at the end of the 70’s, when Frederick Sanger developed the first sequencing (i.e. DNA reading) technology. Yet, it was extremely hard to obtain enough DNA from an organism’s cells to truly advance - until the early ’90’s, when a DNA amplification method was developed known as PCR, which could exponentially increase the quantity of DNA from a sample by copying the existing fragments. The combination of Sanger sequencing and PCR gave access to “the book of nature” – that is to say, the entirety of genes in every organism[3] - and was quickly applied not just for evolutionary research, but also in the pharmaceutical sector, in cancer research and many other disciplines. It took however, months if not years to read a mere word in this book, and it was very complicated, if not impossible, to have an overview of a paragraph, say not a chapter. But the DNA sciences truly hit the jackpot in the 2000’s, when automated ways of amplifying and sequencing DNA started hit the market. With these new technologies commenced what is commonly known as the genomics era: a time in which we can sequence not just little words, but several entire copies of this DNA book, which we in fact call the genome.

Rosalind Franklin's X-ray diffraction image of the DNA molecule (left) was crucial for James Watson and Francis Crick's discovery of the molecule's spatial structure in the form of a double helix (right).

Without realising it, modern scientists tumbled into a world of massive information, and had to grapple with the mere problem of how to process such impressive loads of data. More and more in recent years, the evolutionary biologist works at a distance from the lab bench and the field and can instead be found on their computer, often dealing with unrelated problems to their ultimate question, such as lack of memory or computational power. But in truth, scientists do have a grip on this flood of A, C, T and G’s that nowadays pour out of the sequencing machine, and they have learned how to use it. The genomics era brought us the most extensive knowledge of the genome and its evolution we have had in history. We discovered how many genes organisms have on average, and that an impressive part of the genome is composed not of functional genes, but of seemingly meaningless code that became known as “junk DNA”. Nonetheless, we are now beginning to understand that this black matter in the genome is probably no junk at all and plays all kinds of mysterious roles in evolution we still need to unravel. Scientists also learned how to use the genome as a whole to study processes such as species formation and hybridisation. Some technologies became so refined, that it became possible to sequence the genome of extinct species from fossilised material. That’s how we found out that Homo sapiens did not only, as was widely thought, massacre the Neanderthals, but also bred with them.

We are now standing very far from those first ideas published 160 years ago in the Origin of Species. Living in a world of information, we often find ourselves thinking that the more we discover, the more we realise how little we know of the world around us. Yet, we have disentangled a fair deal about this mystifying process since Darwin and Wallace’s times. We recognised other processes aside from natural selection which drive evolution, we found the molecule that bears our genetic information, we discovered astonishing truths about our history and that of the surrounding natural world, and, most importantly, we asked ourselves new question that lead to more knowledge. Sadly enough, we also wandered into trails of thought that would’ve best been left untouched, and that left a deep scar in our history. Therefore, whatever new technologies and knowledge lie ahead, we should always remember not to become obnubilated by their potential, and to solely use them for just means. But when it comes to the mere curiosity of the natural world, we are just like Darwin and his contemporaries taught us to be: we constantly rethink our arguments, reconsider discarded theories, and most of all, observe and question the world around us. Every day, something new is waiting to be discovered about the puzzling, marvelous process that is evolution.

Side notes:

[1] Interestingly, also Wallace came up with the idea of natural selection after reading Malthus’ work.

[2] Of course, nowadays we know that many, if not most traits aren’t inherited discretely. Forms of inheritance that do not follow Mendel’s laws are called non-Mendelian inheritance.

[3] Although in reality, scientists were often limited to the few “model organisms” such as the fruit fly or the zebra fish for which these technologies had been developed.

For further reading/listening:

Bowler, Peter J. (2003). Evolution: The History of an Idea. California: University of California Press

Costa, James T. (2014). Wallace, Darwin, and the Origin of Species. Cambridge, MA: Harvard University Press.

Wulf, A., 2015. The invention of nature. New York: Knopf.

Bowler, Peter J. (1989). The Mendelian Revolution: The Emergence of Hereditarian Concepts in Modern Science and Society. Johns Hopkins University Press.

BBC 4. (2014). In Our Time. Social Darwinism (Podcast). 20 February 2014. Available from: https://www.bbc.co.uk/programmes/b006qykl.

Kevles, Daniel J. (1985). In the Name of Eugenics: Genetics and the Uses of Human Heredity. University of California Press.

Judson HF (1979). The Eighth Day of Creation: Makers of the Revolution in Biology. Cold Spring Harbor Laboratory Press.

Mukherjee, S. (2016). The Gene: An Intimate History. Scribner.