When was evolution first considered to be proven fact by the majority of the scientific community?

Nowadays evolution is considered theory and fact. (If you wish to debate that, please start a new thread and debate that there.)

But at what timeframe or year could one first say that accurately? In other words, if one were to say “Evolution has been considered proven fact since XXXX” what would be a good value of XXXX?

That depends on what exactly you mean by “evolution.” It should also be understood that believing that life has evolved does not rule out the belief that it was divinely created.

If by “evolution” you mean the idea that modern species are descended from previous forms by modification over time, most scientists would have probably believed that by the later part of the nineteenth century, perhaps before. Some would still believe that the original forms were divinely created.

If you mean that the mechanism of evolution was natural selection, then there were significant controversies about that until the 1930s and even after. It wasn’t until the Neo-Darwinian synthesis that the paramount importance of selection was conceded by nearly all scientists.

The concept of evolution of species predated Charles Darwin’s work, and in fact was an aspect of the West Midlands Enlightenment movement in which Charles’ grandfather Erasmus Darwin was a key figure. Charles Darwin’s contribution was twofold: he suggested the theory of “descent with modification” e.g. gradual changes in the makeup of a lineage which made the organism more likely to survive and produce offspring resulted in individual differences and eventually resulted in the speciation he observed in his voyage on The Beagle, most famously evidenced in the closely related species of Galapagos finches; the other was developing an enormous body of observational evidence. Aside from his work on The Beagle (where he was not the ship’s botanist; he was invited on as the captain’s companion and financed his own way, but did as much to advance the knowledge of geology and anthropology as he did botany and zoology during the mission) at the Galapagos Islands and South America, both relatively uncharted in terms of scientific observation, Darwin devoted decades to the study of indigenous animals, and in particular barnacles, from which he developed clear notions of selective breeding and inheritance.

The one key Darwin was lacking was a mechanism for inheritance. We now know this to be the genome as distributed throughout chromosomes but the primitive state of cellular biology at the time had not identified the mechanism by which bodies are able to produce the vast array of proteins, enzymes, and sterols that comprise cells and allow them to function together to make up an organism. Unbeknownst to him, the Augustinian friar Gregor Mendel was doing the exact experiments and observations to lay out the science of genetics and the function of chromosomes in inheritance (hence why some features are selected over others and why there is not a smooth variation of characteristics). Mendel’s ground-breaking work wouldn’t be widely disseminated until the independent reproduction and rediscovery by Carl Correns and Hugo de Vries in the early 20th century, and as Colibri notes, it took the “modern synthesis” of what we now refer to as “natural selection” and genetics, and later the discovery of DNA as the physical mechanism for the encoding and transfer of information leading to the science of genomics. The development of statistically-based population genetics by Ronald Fisher, J.B.S. Haldane, and Sewall Wright in the 1920s placed modern synthesis on a qualitative basis.

Evolution is best thought of as a framework rather than a ‘fact’; in the modern evolutionary (“neo-Darwinist”) synthesis, lays out some basic principles of inheritance, expression, and ‘random’ variation (i.e. mutation), which along with more modern discoveries such as lateral gene transfer and endosymbiotic theory underpin our entire understanding of biological function at the intracellular level and above. There are certain aspects of biology that can be learned outside of the framework of evolution, such as anatomy and morphology, but that is basically mapping and button-sorting. Evolution, and the theory of natural selection as modified by endosymbiosis (in essence, the coevolution of species to interoperate and even merge into a unified organism) is necessary to understand biological systems in any depth.

To answer the question of the o.p., the essential principle of evolution was understood and accepted by Western civilization as a whole long before the current framework could ‘prove’ it to be true e.g. lay out a cohesive framework of mechanisms for inheritance and selection; it was essentially a quantitatively established framework circa 1930, and further developments such as genomics and endosymbiotic theory have only served to further advance and refine evolution as the essential framework for how life develops.

Stranger

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Fascinating, what specific advances did he make?

I find that hard to believe. Not because I doubt that he did great work in geology and anthropology, but because his contribution to biology was so great that it’s hard to imagine anything overshadowing it.

For one thing, he originated a theory for the formation of coral atolls through the slow subsidence of volcanic islands.

Oparin, Alexander; The Origins of Life; Moscow Workers Publishing; Moscow, Soviet Union; 1924

I don’t mean to suggest that his contributions revolutionized those fields as much as his work on natural selection influenced biology and evolutionary thought, but that he made some of the first systematic observations of the geological formations and indigenous populations of South America, and in fact his observations of the differences between native Tierra del Fuegons and people from those populations who were abducted on the previous voyage educated in European thought formed a lifelong belief in the mutability of human behavior and solidified his belief that humans had a shared origin and comparable cognitive and emotional capacities, contrary to both the conventional thinking that different human ‘races’ had differing levels of mental and moral capacities (justifying slave trade of Africans as subhuman) and the later school of ‘Social Darwinism’ (justifying inequality as a result of innate mental capability). This no doubt influenced his later and broader work (The Expression of the Emotions in Man and Animals, “A Biographical Sketch of an Infant”), setting aside the theological rationalization for behavior and mental processes for a more mechanistic explanation predicated both on genetics and the cultural environment.

Stranger

I would say it was the “modern synthesis” that did the trick. No one date, but first half of the 20th century, with many different contributors.

https://en.wikipedia.org/wiki/Modern_synthesis

This is a harder question than it looks because the notion of “the scientific community” did not exist in the same way in 1859.

Darwin himself was a gentleman naturalist. He did not teach at a university, held no formal positions, and conducted his experiments at his estate. His work was known and he was made a member of the Royal Society but there weren’t even 1,000 members in the 19th century. The modern profession of scientist doesn’t really form until towards the end of the 19th century, when universities - starting in Germany and fairly quickly after in the U.S. - themselves recognized they needed to professionalize, heavily revising their methods and curricula to make the Ph.D. a formal entry point.

The community that Darwin wrote for was the educated elite. They recognized the stupendous accomplishment, although they argued greatly over its meaning. The Origin of Species (1859) deliberately shaded its discussion of human evolution, not fully dealt with until The Descent of Man twelve years later, so that the general notion of species evolution could be more easily swallowed That left a hole leaving the larger notion of evolution open for longer. You might want to check The Book That Changed America: How Darwin’s Theory of Evolution Ignited a Nation by Randall Fuller. Despite the title, his real subject is how the small group of big-name Bostonians reacted to reading Origin. They devoured it, read it aloud to their wives, discussed it over weekly dinners, and wrote to Darwin in praise and for more information. That was in contrast to a few of the older university scientists who dismissed it out of hand.

The mechanisms of evolution took until the 20th century to, um, evolve. Many scientists would have held back from considering it proven until those issues were worked out. (Many scientists would have an issue with “proven” for that matter.)

If you’re asking when the majority of people who understood the subject well enough considered species evolution to be the logical answer to the underlying problem, that date is long before Charles Darwin. If you’re asking when the deniers were not merely in the minority but were mere ideologues, that was late 19th century. If you’re asking when genetics was accepted as the basis, that was early 20th century. The Scopes trial was 1925. It was a show trial specifically to overturn Tennessee’s law forbidding the teaching of evolution. By that time all modern science had thoroughly accepted evolution, so you can’t put the date any later.

Let me add something to Stranger’s excellent post.

To explain this, let us imagine that there was a selective advantage to a pea plant growing a foot taller than its ancestors. Suppose one plant carries a mutation that brings about a foot extra height. Darwin assumed that its offspring, the result of a mating with the ordinary ones would have an extra 6" of height, that the result would be a blend. The G3 offspring would have an extra 3" of height and G4 would be 1.5" taller. In the rare case of two G3’s mating, you would still only get an extra 3" of height. In other words, under blended evolution, the mutation would eventually basically disappear in the general population. Darwin was even aware of this problem. Once Mendel’s experiments came to light, this problem disappears. All peas will either be normal height or a foot taller and if the latter were advantageous, differential reproduction would result in the gene spreading out through the population.

In a way it is somewhat surprising that no one else had carried out similar experiments by then since the problem I am describing was known.

By 1973, it made sense to write:

Does that include the world outside America?

Yes, the worldwide “scientific community” included the whole world. It wasn’t the case that over in Germany the scientists still believed in creationism.

Sure, it’s something of a tautology. There were plenty of places in the world where nobody had heard of evolution, or if they had they didn’t believe in it. Those places didn’t have a scientific community though.

It really did take until the modern synthesis for evolution to be taken as an uncontested settled fact. It’s also hard to remember that it wasn’t until the 1950s that the physical basis for genetics was finally nailed down. Up until then they knew genes were carried on chromosomes, but figured it was probably the proteins that carried the information, not DNA.