Friday, 14 March 2008
The Crab That Forgot To Evolve
Horseshoe crabs. Image from Wikipedia.
A recent study in the journal Paleontology includes a paper on the discovery of a horseshoe crab (Limulus polyphemus) fossil said to date from the Upper Ordovician period or some 445 million years ago. The study, conducted by David M. Rudkin of Royal Ontario Museum and colleagues reported on a recent find in Manitoba, Canada. The crab is “strikingly similar” to other horseshoe crabs, including those that are still found alive today.
The oldest horseshoe crab fossil is practically indistinguishable from its present-day descendants, showing no evolution at all. Some species seem to resist change at all costs. Darwinian evolution desperately needs evidence of change, especially transitional forms or fossils that would link different species, but the fossil record displays a very different kind of story.
The late Harvard zoology and geology professor Stephen Jay Gould wrote in Natural History in 1977, "The extreme rarity of transitional forms in the fossil record persists as the trade secret of paleontology. The evolutionary trees that adorn our textbooks have data only at the tips and nodes of their branches; the rest is inference, however reasonable, not the evidence of fossils." Gould and Niles Eldredge proposed the punctuated equilibrium view of evolution, i.e. that evolution consists of stasis or long periods of no change at all and then sudden changes happening too quickly to leave any fossil evidence. However, it is a stance that argues not from evidence but from silence.
The horseshoe crab is just one example of numerous living fossils or animals that have not changed for aeons of time. The most famous living fossil is the Coelacanth (Latimeria chalumnae) that was thought to be a link between fish and amphibians. Unlike “ordinary” fish, the Coelacanth gives birth to live offspring. Yet, the Coelacanth, dubbed the dino fish, is clearly a fish and not a half mammal. Evolutionists believed it used its fins to walk on the seabed but observations have shown this to be false. Scientists suspected that it became extinct some 65 million years ago, but in 1938 a living specimen was caught off the coast of Madagascar and since then several others have also been sighted living.
Other living fossils include the Wollemi Pine and the salamander. The blue-green algae or cyanobacteriae have resisted any change for 3.5 billion years on an evolutionary time scale. While dating methods involve many assumptions and potential sources of error, the absence of change in some of the most “primitive” life forms is a strong case against the Darwinian “just-so” story of molecules-to man-evolution.
The horseshoe crab also tells a story that differs entirely from the Darwinian version.
You can read about another living fossil, the tuatara, here.
Gould, Stephen Jay. 1977. Evolution's erratic pace. Natural History, 86:5, 12-16. (May 1977).
Rudkin, David M.& al. 2008. The Oldest Horseshoe Crab: A New Xiphosurid from Late Ordovician Konservat-Lagerstätten Deposits, Manitoba, Canada. Palaeontology 51:1 , 1–9 (January 2008).