Where does the term "the missing link" come from?
Like most great ideas that are actually wrong, "the missing link" comes from the ancient Greeks. Plato believed in a great chain of being: that there are absolute hierarchies of the universe wherein divinity is above humans, humans are above animals, animals are above plants, and plants are above non-living things. The earliest attempts to categorize animal life, which as far as we know are those of Aristotle, used this framework for thinking. There were higher and lower animals, and humans were, obviously, way way higher than even the highest of animals. Because we can sit around all day and make up ideas about how things work. Raptors never spent time doing that, so they're obviously less awesome.
This great chain of being got absorbed into early Christian theology/natural history as the scala naturae, and theology/natural history didn't really do much for ... about 2000 years, even though Leonardo da Vinci came up with an explanation for fossils. (Seriously. And it wasn't the wrong answer.) In the 18th and early 19th century CE, two very influential natural historians both used the scala naturae in their very different studies on the natural world. Linnaeus used it, complete with theological implications, in his organization of known species of plants and animals. Hierarchies are all over the place because Linnaeus believed that the Intelligent Designer (...which, back then, everyone just called God) had deliberately created categories of life and that the purpose of natural history was to discern these categories. If you learned anything about Kingdoms or Phyla or Orders in biology class, you have Linnaeus's belief in the scala naturae to blame for it, because he very literally could not make sense of the natural world without thinking that it was divinely ordered into very delineated organizations.
A very different early 19th century natural historian used the scala naturae to promote a very different idea, because he was French. Jean-Baptiste Lamarck was a pre-Darwinian evolutionist who gets made fun because he said that giraffes get longer necks because they try to hahaha what an idiot EXCEPT that he lived during a time where people thought bacteria spontaneously generated out of mud so honestly for the time he wasn't that dim.
Hey wait isn't that what evolution contrarians think evolution says is true? That life should be being formed out of non-life all the time?
Yeah, isn't that weird? Evolution contrarians think modern evolution says something from the 1680s.
Anyway. Lamarck accepted the scala naturae, but he made two giant departures from most previous natural historians. Firstly, he thought that these categories could be transcended: he thought that plants and animals could move up the great chain of being. Not all animals and plants were moving up the same chain... the best analogy is to imagine a row of ladders that every organism, alive now, has been moving up, and for which every step up the ladder represents a succession of species from least to most advanced. Secondly, since there are both very primitive and very advanced forms of life still present (literally no one knew this until the 1680s when microscopes were first used) that must mean that the most primitive forms of life are being created all the time from , and what separates (for example) man from (for example) monkeys is that monkeys haven't evolved for as long as man.
Hey wait isn't that what evolution contrarians think evolution says is true? That monkeys have been evolving for less time than man?
Yeah, isn't that weird? Evolution contrarians think modern evolution says something from the 1800s.
While not very good at convincing people that species could transmute into other species, Lamarck's writings were influential in many ways, particularly because popular accounts of his writing spread out. The 19th century was really the first in which popular science as we understand it existed, because a middle class capable of having leisure time to bother reading popular science existed. Fossil discoveries by amateur natural historians and professional proto-paleontologists showed that there used to be life on Earth that apparently was not around today. One of the people who used fossils to argue for an Earth older than any natural historian had ever before claimed was Charles Lyell. He helped found modern geology and for much of the 19th century he was very popular in both scientific and public scientific literature. And he's credited with the first English usage of the phrase "the missing link"-
Aha!
...in an image of a geological column, in an 1851 publication. In describing how two rock units of Ages X and Z must be missing a rock unit of Age Y from in-between, he referred to that missing rock as a missing link:
A break in the chain implying no doubt many missing links in the series of geological monuments which we may some day be able to supply.
To be extra confusing, in an 1863 publication, he proposed that human ancestry must be very far in the geological past, and that the linkage between humans and non-humans was, as of that time, missing.
So an evolutionist came up with the term "the missing link"!
If by "evolutionist" you mean "guy raised as a creationist who was struggling with evolution's implications", then, yeah. Darwin and his colleagues were, privately, pissed about Lyell's comment because they felt that it didn't help them out at all. Lyell, like many religious people 151 years later, had problems with accepting that humans had evolved from anything: he saw an enormous gulf between humans and non-humans. He, unlike religious people of today, had two great excuses for thinking this. Firstly, he was raised and taught that the scala naturae was a real thing, and secondly there were zero fossils at the time exhibiting the transition between humans and non-humans.
The only other scientist of the 19th century who really discussed "the missing link" in relation to evolution was Ernst Haeckel. In 1868, in a text which got translated into multiple other languages, Haeckel claimed that humans were the final or current stage in an evolutionary process of 22 steps, of which the 21st was...missing.
So an evolutionist used the term "the missing link"!
In Haeckel's case, yes, totally. But Haeckel's ideas weren't accurate. He still had been raised in the scala naturae mindset and he still was thinking in those terms as well. In addition, he had a concept of phylogeny through ontogeny that no one today thinks is accurate. In addition, when he first used the word... there were still zero fossils at the time exhibiting the transition between humans and non-humans. He embraced "the missing link" as a hypothesis that was in need of testing; that some form of animal would be found that would be not-quite-human but not-quite-non-human.
So "the missing link" is a pre-evolutionary concept only used in reference to evolution by two scientists, one of whom was a Christian struggling to understand evolution and the other of whom used it as a term indicating an as-of-yet undiscovered fossil record of human transitional fossils?
Yeah.
So when evolution contrarians ask for "the missing link" they are asking for something that was antiquated as soon as human transitional fossils were found?
Right, when they got found in 1891, that's when "the missing link" became something no evolutionary scientist was asking for. Once "the missing" link got found, congratulations, it's not missing anymore.
So why'd it become entrenched in popular culture?
The heck if I know, but part of the reason why is that the popular culture, including science fiction and fantasy, immediately jumped onto it, back in the 1860s. A lot of our "Stone Age" popular culture ideas started back then: Jules Verne's 1864 Voyage au centre de la Terre included a "man-ape" creature who was not civilized like man but wasn't as brutish as ape. A hundred years later The Flintstones were still showing this bizarre "missing link" between apes, which lack record players entirely, and ourselves, who have record players not powered by animals.
What, if anything, is scientifically accurate about "the missing link"?
Uck. Not much. It's one of those phrases that makes me die a little inside, like "homeopathic medicine".
1. Among life present today, there is no such thing as a more or less evolved species. Everything alive today has been evolving for at least 3 billion years. It's ...kinda... accurate to say that an animal living in the past is "less evolved" than a modern animal, but it still sounds weird, because...
2. Evolution isn't a progressive process.
Unlike what Lamarck might have told you, evolution is not a railway. It's a diverging and only-partially-predictable process in which there's no guarantee that a species present at Time 1 will have a "better" descendent species in Time 2. The only way in which a species at Time 2 will be "better" is that it will have survived for longer.
3. The kiwi bird is NOT a direct descendent of "the" Tyrannosaurus rex. What the heck, Sebastien Millon. You apparently are not the mayor of science town, because...
4. Evolution isn't a pit a ladder, evolution is a series of dichotomies.
Unlike what Lamarck might also have told you, a species does not evolve into a species into a species. Sometimes that process is what occurs (as the process of anagenesis), but other times a single parental species splits into two species (as the process of cladogenesis). This series of dichotomies is what gives rise to the hierarchy that Linnaeus, in his wisdom, saw: that some organisms are more closely related to one another than to other organisms. Life is... mostly... sorted like matroyshkas, in which categories are found within other categories.
5. Every fossil species is, until proven otherwise, a transitional fossil.
Transitional fossils are the closest thing in accurate scientific terminology to "missing links". They're fossils that show primitive traits and advanced traits. But every fossil species found is, unless it can be shown to be the last in a lineage, a transitional fossil. The only fossils that aren't transitional are those of the last species in a lineage.
Mammuthus primigenius? Not a transitional fossil: it doesn't show have any relationship to a later, more derived, animal. Smilodon fatalis? Not a transitional fossil, same reason. Australopithecus sebida? Probably a transitional fossil, since it shows a relationship to a later, more derived animal, namely, us.
How many fossils have to be ignored in order to claim that "the missing link" is still missing?
A couple thousand of them. There is literally more fossil evidence that humans evolved from non-humans than there is fossil evidence that Tyrannosaurus rex is a thing.
So if a person claims "the missing link" hasn't been found, they should be intellectually consistent and say that Tyrannosaurus hasn't been found?
Exactly. You can't be intellectually consistent unless you either deny, or accept, both hominin fossils and Tyrannosaurus.
