Living Fossils
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[edit] Definition
The term "living fossil" is an informal term without a precise definition, but in general it refers to a lineage which is known from the fossil record to have gone a long time without meeting with either extinction or significant evolutionary changes. There is no precise definition of how little change over how much time qualifies a lineage as a living fossil.
The term is sometimes used to refer to newly discovered living taxa previously known only from the fossil record. Such taxa are more accurately known as "Lazarus taxa".
[edit] Origins of the phrase
The phrase "living fossil" was coined by Charles Darwin. So far as we can tell, it first appears in his published writings in the closing paragraphs of the Origin of Species, where he predicts their significance to the future development of evolutionary biology:
Species and groups of species which are called aberrant, and which may fancifully be called living fossils, will aid us in forming a picture of the ancient forms of life. [1]
[edit] Creationists and living fossils
Creationists sometimes claim that the existence of living fossils disproves the theory of evolution. They usually don't explain the reasoning by which they reach this conclusion, but it seems to be based on one or both of two possible errors.
The first error is to think that a handful of lineages which have stayed stable over a long period of time somehow means that all lineages do this. This is on a par with pointing to someone who's lived in the same house for fifty years as evidence that no-one ever relocates. The fact is that the same fossil record which shows us that some lineages have remained stable over long periods of time also shows that other lineages have undergone large evolutionary changes. If creationists were right, all species would have to be living fossils, but in fact they are the exception and not the rule: this is why there is a special name for them.
The second error is to think that the theory of evolution predicts constant change. It does not. Adaptive evolution by natural selection will happen only when there are new conditions to adapt to: when a lineage colonizes a new niche, or when its environment changes. When a lineage has adapted to its environment, and there are no nearby vacant niches for it to colonize, we should only see the sort of functionally insignificant changes brought about by genetic drift. (See also the article on Punctuated Equilibrium for further discussion of patterns of change and stasis in the fossil record.)
Creationists generally compound these errors in theory with errors in fact: they grossly overstate the stability of living fossils. Modern coelacanths, for example, are not the same species or even the same genus as the coelacanths found in the fossil record, but you will often hear creationists claim that they are identical and have "not evolved".
Another peculiar error is to characterize any creature new to science as a "living fossil". For example, one creationist[2] lists the gorilla as a living fossil. Now the fossil record does not, in fact, show gorillas remaining morphologically stable for hundreds of millions of years: his stated reason for listing it among "living fossils" is that it was only "discovered" (i.e. cataloged by Western scientists) in 1847. As usual with creationists, it is hard to tell whether the man is being disingenuous or just stupid.
[edit] Creationists and Lazarus taxa
The existence of Lazarus taxa is sometimes claimed as an objection to geologists' interpretation of the fossil record. If, as in the case of the Wollemi pine, it is absent from the fossil record for the past two million years[3], and yet there are living specimens, this might superficially seem to pose a problem for the view that the fossil record is, as claimed, a record of the Earth's history.
This overlooks two obvious points: fossilization is rare; and so is the Wollemi pine. It is known, indeed, from only a single stand of trees in Australia. If it has been in a similar state of rarity for the past two million years, then it is hardly surprising that no fossils of the Wollemi pine are known from that period. A species can only leave fossils in the places where its members live and die: if these happen to be small isolated areas, then the rarity of fossilization will be compounded by the unliklhood that some paleontologist should happen to dig in exactly the right spot.
