The missing link, the failed story that tried to connect the evolution between primates and humans

For a long time, the search for a fossil that would prove the existence of this link was the obsession of a large part of the scientific community. The A. afarensis , the species of Lucy, whose skeleton was found in 1974, was one of many hominids with those believed to have found the missing link, the link between apes and humans.

The image is easily recognizable, a classic of popular science. In it, a series of characters walking in a single file is seen in the profile. The first in line is a monkey, usually a chimpanzee. The last one, a man. The four or five beings between them represent the transition between the primate and the human.

It is perhaps the most popular illustration to symbolize human evolution. And in the heat of that idea of ​​linear evolutionary progression, which seems to represent that image, another concept was consolidated, that of the missing link. This notion, which is still valid today in the popular imagination and in some media, alludes to the existence of some ancestor of current humanity, who was part ape and part human.

One of the many versions that represent human evolution, the missing link was the crucial piece that united humanity with the monkeys and, therefore, with the rest of nature. For a long time, the search for a fossil that would prove the existence of this link was an obsession of a good part of the scientific community, who saw the objective of their search as the Holy Grail of evolution.

But at this point, it is essential to clarify that there are two concepts that were expressed here that are not correct. It is that, for science, in the first place, the idea of ​​a progressive and linear evolution has no basis in natural history. And secondly, also from a scientific point of view, the missing link does not exist, or at least it is a completely wrong concept.

María Pía Tavella, anthropologist, and professor of human evolution at the National University of Córdoba (UNC) said, that's how it is. As attractive as it may be, it may be time to discard it. At the end of the 19th century, the missing link became a familiar expression that was used mainly in relation to human evolution and, specifically, with the hypothetical connection between primates and humans.

The missing link in the 19th century

Naturalists and popularizers of science used the term missing link in the 19th century, especially after the appearance of The Origin of Species, the book that Charles Darwin published in 1859. Then, many scientists began to search for this missing piece to connect humans with the rest of the animal kingdom, a crucial piece of evidence to demonstrate the theory of evolution by natural selection, explained Tavella, an anthropologist, and specialist. in genetic anthropology.

The German naturalist Ernst Haeckel argued, as this 1874 image illustrates, that from unicellular organisms to man, evolution consisted of 24 steps and that at step 23, there was the missing link.

This researcher was one of those who understood evolution as a progressive process from the simplest to the most complex forms. A few years after the publication of Darwin's book, this scientist stipulated that in nature there were 24 stages until the human being, and established the missing link in the second to last of them.

It was an entity that existed between the orangutan and Homo sapiens. Even without having the slightest evidence of the existence of that being, he gave it the scientific name of Pithecanthropus alalus or, in popular terms, the speechless ape-man.

The Dutch anatomist Eugene Dubois, for his part, also became obsessed with the idea of ​​finding the missing link and between 1891 and 1892 he discovered -in Java- the fossil remains of what would later be identified as Homo erectus. Then, his finding shook both the scientific universe and that of public opinion, and few doubted the fact that this Man from Java found was, strictly speaking, the famous link. But, despite the prevailing enthusiasm, it was not.

In 1898, the New York Journal announced the discovery of the remains of the man from Java and claimed that it was the living missing link and at the end of the 19th century, it became a familiar expression that was used mainly in relation to human evolution and, specifically, with the hypothetical connection between primates and humans.

Tavella said, it was used by both scientists and journalists. But also by entertainers and presenters of exhibitions of curiosities.

In relation to the latter, both in the United States and in Europe people of exotic ethnic groups began to be exhibited at fairs, to whom they were often presented as the living missing link.

An example of this was Kraos, a Laotian girl who suffered from hypertrichosis, a condition in which hair grows in areas of the body where it does not usually grow.

According to the Catalan biologist Alex Richter-Boix, on his biology and evolutionary ecology site Evoikos, Kraos was captured in his country in 1881 and years later toured all of Europe with the promoter of shows Canadian Antonio, the Great Farini.

The girl was presented as The Missing Link: Living Proof of Darwin's Theory of the Origin of Man. In this way, it is also verified how the idea of ​​a missing link served as an excuse to reaffirm Eurocentric prejudices with respect to other human groups and to confirm a racist perspective from a supposed evolutionary scientific theory.

Also, in the United States, many African Americans were exhibited as beings considered halfway between Homo sapiens and chimpanzees.

Tavella quoted the American anthropologist and writer Misia Landau, who pointed out that the standard narrative of human evolution necessarily began with a hero, and that was none other than the British naturalist, Charles Darwin, author of The Origin of Species and The Origin of Man, two key works for 19th-century science.

Given that the theory put forward by Darwin proposed a common origin between apes and humans, it was expected that their common ancestor would have the characteristic of both. Thus began the search for the missing link in the fossil record and the discipline that we know today as Paleoanthropology began, detailed the anthropologist.

Then it was also debated where on the planet it would be possible to find this nexus between apes and humans. Some scientists spoke of Asia, and others, of Africa. However, even before Darwinian theory, there was the concept of the Scala naturae of the Christian thought of the Enlightenment, or of the chain of living beings, which were ranked from the simplest to the most complex.

So, Tavella asserted, the idea of ​​missing links in the chain of beings, the notion of gaps in the fossil record, was well established prior to The Origin of Species in Victorian England.

By 1900, the missing link had gone from being a hypothetical scientific concept to becoming a materialized object illusory in excavation sites, museums, newspapers, cartoons, and markets. Many believed they found it, many were dismissed, but few doubted its existence. However, by then there were voices raised against what seemed to be a universal scientific concept.

This is the case of the British anthropologist Edward Clodd, who as early as 1895 wrote something that practically holds to this day: Man is neither a descendant nor brother of the apes, but a kind of cousin. And the answer to the question; Where is the missing link? There is no missing link, and there never was, said the scientist, who was also a banker and writer.

Clodd said, the similarities and differences between apes and humans are explained in the same way as the similarities and differences between apes and each other. The primates form the upper branches of the tree of life, the highest branch of which is the man.

Remains of Homo naledi, found near Johannesburg, South Africa

The quote is extensive, but it is worth understanding why the scientific refusal to talk about the missing link, although the concept insists on persisting until today and still appears in some headlines, almost every time that paleoanthropologists find the fossils of some hominid.

This was the case, for example, when Australopithecus africanus was discovered in 1924, with the appearance of Homo habilis in 1964, and with the discovery of Austalopithecus aferensis, the famous Lucy, in 1974.

Evolution as a branched tree

Tavella pointed out that there was no linear evolution. Instead, hominids branched out and diverged into separate genera and species from the beginning of their evolution. So, to represent the evolutionary process, the single file has nothing to do with, but rather the idea of ​​a highly branched bush where humans are just a twig, as noted by British anthropologist Robert Foley, author of the book Humans before humanity, 1997.

The anthropologist points out that linear representations convey the false idea that current primates are our ancestors when we rather share ancestors.

He said, the separation between the human lineage and that of chimpanzees and gorillas occurred between six and eight million years ago, so each evolutionary line followed its independent process all this time.

As proof that certain primitive specimens were not our ancestors, but rather our cousins so to speak - suffice it to say that there is genetic evidence that Homo Sapiens was crossed with hominid species with which it lived in the Pleistocene medium, such as Homo neanderthalensis or Denisovans.

Although homo sapiens, the current human being, inhabited the planet without other hominids for 30 thousand years, there is still evidence of the hybridizations that it carried out with archaic humans.

Tavella reported, we can observe 2-4% genetic ancestry of Neanderthal origin in current Eurasian populations and up to 6% ancestry from Denisovans in some oceanic populations.

Evolution is a fact, not a purpose

Another myth regarding evolution has to do with it being a progressive process towards better or higher organisms. On the contrary, as the famous American paleontologist Stephen Jay Gould argued, evolution is a fact, not a purpose. That is, evolutionary becoming is the result of a unique interaction between random and deterministic processes, it is not the result of a plan.

Tavella said, evolution is based on continuities and discontinuities. The biocultural nature of humans is the main discontinuity that emerges from our evolutionary history. Human beings define themselves by having become complex beings. The question is whether this complexity is exclusive of our species or if it has emerged in other species.

The truth is that human behavior and their mental capacity have been the real hallmark -more than the anatomical- to differentiate Homo sapiens from other animal species. These purely human traits are believed to have arisen in response to the frequent climatic changes that occurred in the Pleistocene period, thanks to which our ancestors developed skills for cooperation, social learning, and cultural accumulation.

In conclusion, contrary to what can still be believed, evolution is not a linear or progressive process, but rather a branching and random process. For this reason, since there is no stepped gradation between the species, it is not possible that there is a single link that makes the connection between one and the other. In other words, the missing link does not exist, or at least, it is a misconception.

At this point, it is hardly a myth, an old scientific utopia that has become extinct but that, in any case, continues to fight in the media and in the popular imagination.

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