You may be familiar with the concept of organisms alive today that are relics of the ancient past, holdovers from times long ago. But this idea, misleading and poorly defined as it often is, is the source of much debate among scientists and science communicators, often revolving around the specific term we discuss in this episode: “Living Fossils.”
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What is a “Living Fossil?”
Depending on the source, “living fossil” can mean different things. Typically, the term is used to describe modern organisms, often rare or unique species, whose fossil relatives show little physical differences in shape and features. In other words, these are organisms that seem strangely similar to their ancient cousins. This usage of the term started with Charles Darwin in On the Origin of Species.
But there is no official definition of “living fossil,” and you’ll often see it used in varying ways, in the news, in books, in movies, and even in scientific discussions. There have been a few modern studies that have attempted to define the term in a more technical sense.
Lidgard and Love (2018) collected a list of criteria typically used to describe “living fossils,” which included prolonged persistence in the fossil record, slow evolutionary change, low diversity in modern groups, and retention of ancestral features, among other things.
Turner (2019) suggested a new phylogenetic concept of “living fossils” to describe organisms that: a) show little morphological change through deep time; b) contain few living species; and c) are unique in terms of their distant relation to other living species.
A Debated Term
“Living fossil” is a controversial term among scientists. Many criticize the term because of its lack of a clear definition, and because it can be downright misleading for the general public. Opponents of the term argue that it can give the impression that these organisms haven’t evolved since ancient times, which doesn’t fit with our understanding of evolution as a process that is always ongoing, even if it’s largely restricted to the kinds of things that don’t often fossilize, like soft tissues, genetic information, and behavior. Some have pointed out that it can even mislead scientists, that the perception of an organism as a “living fossil” can bias results of studies.
This kind of confusion can make it that much easier for misunderstandings to spread through schools or news media, and it’s not uncommon for anti-evolution groups to use the term (the idea of organisms that “don’t evolve”) to try to undermine evolutionary science.
Some have suggested we get rid of the term altogether, while others have recommended replacements like the term stabilomorph to refer to organisms whose stability over time has allowed them to persist through major extinctions and environmental change.
The list of organisms that have been called “living fossils” is very long, but as you might expect, there’s plenty of disagreement over which – if any – actually deserve the title.
If you’d like to read more about discussion of this term, take a look at these links:
– Evolution in the Slow Lane (non-technical)
– Rates of evolution and the notion of “living fossils” (technical)
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