Transitional form
A transitional form is a fossil or living organism that is intermediate between two other organism in an evolutionary sequence. A transitional form that has not yet been found is colloquially called a 'missing link'.
Creationists claim that transitional forms between different kinds of creatures are systematically absent. Other scientists typically reject this claim. One such attempted rebuttal is that by Kathleen Hunt who created a Transitional Vertebrate Fossil FAQ.[1]
Contents
Claims of transitional forms
In The Origin of Species Charles Darwin wrote that the fossil record (as it was known then) was lacking in transitional forms. He predicted, however, that transitional forms would be found. In accordance with that prediction, since the publication of The Origin of Species many transitional forms, both fossil and living, have been identified.
The following are some examples of known transitional forms[2].
Fishbians
The so-called “fishbian” sequence of fossils shows the steps by which fish crawled out of the water and onto the land during the Devonian period. Fossils exist that span the entire transitionfrom the distinctly fish-like Eusthenopteron to the four-legged amphibian Hynerpeton. The fossil record of the fish-to-amphibian transition is now among the best documented of all.
Rhinos
The fossil record of rhinoceroses is extensive. Starting with dog-sized creatures, such as the early Eocene Hyrachyus, that are barely distinguishable from early tapirs and horses, fossil rhinos gradually diversified into a wide variety of forms. Some of these forms became gigantic, culminating in the huge indricotheres, which were about 7 metres tall at the shoulder and weighed 20 tonnes. None of the early rhinos had horns. The living rhino family began in the middle Eocene with primitive creatures such as Teletaceras which looked much like the earlier “running rhino” type excepting for the development of a chisel-like upper tusk and pointed lower tusk.
Pinnipeds
The pinnipeds are seals, sea lions and walruses and are descended from primitive bears. A recently discovered fossil has provided a beautiful transitional form between the two groups[3]. Although superficially like a seal the fossil lacked most of the specialisations that modern pinnipeds require for their aquatic lifestyle. In addition, its “flippers” had long toes and claws, halfway between bear paw and pinniped flipper. There was subsequently a great “radiation” of seals and sea lions in the middle and late Miocene, all of which appear in the fossil record.
Other examples
There are many other examples of transitional forms including: velvet worms, lancelets, synapsids, ceratopsians, giraffes, ichthyosaurs and manatees.
Claims of a lack of transitional forms
Creationists claim that there is a lack of transitional forms. They use the following selective quotes in support of their claim:
The late paleontologist Stephen Jay Gould said in 1977:
The extreme rarity of transitional forms in the fossil record persists as the trade secret of paleontology.[4]
In 1979, the senior palaeontologist at the British Museum of Natural History, Colin Patterson, agreed with Gould, when asked why he didn't have any illustrations of transitional forms in his book:
I fully agree with your comments on the lack of direct illustration of evolutionary transitions in my book. If I knew of any, fossil or living, I would certainly have included them. ... Yet Gould and the American Museum people are hard to contradict when they say there are no transitional fossils. I will lay it on the line- there is not one such fossil for which one could make a watertight argument.[5]
In 1984 Gould wrote the following:
The absence of fossil evidence for intermediary stages between major transitions in organic design, indeed our inability, even in our imagination, to construct functional intermediates in many cases, has been a persistent and nagging problem for gradualistic accounts of evolution.[6]
However, in 1994, he wrote,
The supposed lack of intermediary forms in the fossil record remains the fundamental canard of current antievolutionism. Such transitional forms are sparse, to be sure, and for two sets of good reasons—geological (the gappiness of the fossil record) and biological (the episodic nature of evolutionary change, including patterns of punctuated equilibrium, and transition within small populations of limited geographic extent). But paleontologists have discovered several superb examples of intermediary forms and sequences, more than enough to convince any fair-minded skeptic about the reality of life's physical genealogy.[7]
See also
References
- ↑ Hunt, Kathleen, Transitional Vertebrate Fossils FAQ (Talk.Origins)
- ↑ The examples are taken from New Scientist magazine of 1 March 2008, What Missing Link? by Donald Prothero, professor of geology at Occidental College in Los Angeles and lecturer in geobiology at the California Institute of Technology in Pasadena.
- ↑ The early Miocene fossil Enaliarctos. See Science vol. 244, page 60.
- ↑ Gould, S.J., Evolution’s erratic pace, Natural History 86 (5):14, 1977 (quoted in Sarfati, Jonathan 15 ways to refute materialistic bigotry.)
- ↑ Sunderland, Lewis, Darwin's Enigma, 1988, pp. 88-90 (Quoted in Those fossils are a problem, Creation 14(4):44–45, September 1992).
- ↑ Quoted in Sarfati, Jonathan, Refuting Evolution, chapter 3.
- ↑ Gould, Steven Jay, Hooking Leviathan by Its Past Natural History 103 (May 1994): 8-15.
