Young Earth creationists, as always attempting to disprove any theory that disputes their belief that life on Earth has evolved rather than be divinely created, dispute evolution on the basis that there should be evidence of transitional species. In fact some sites (such as "Answers In Genesis") go as far as to insist there must be "billions of transitional fossils" if evolution was correct and not merely "a handful of questionable transitions".
In posing this supposed flaw in the fossil record creationists misunderstand one vital concept and that is that all non-current species (with the exception of the ultimate common ancestor) are transitional. Each and every species noted in the evolutionary tree are of a form that is transitional between its ancestor and its descendants.
The problem lies in the fact that once named; an animal (usually extinct) becomes regarded, as a species in itself so, where there were once two species with no transitional, there is, once the transitional is found and named, now three species with two transitional gaps. Any objective observer will realise that this process can continue ad infinitum and that no matter what explanation is offered, in the eyes of the lay critic, there will never be a satisfactory transitional filling the gap between any given species.
So, what is a transitional fossil? As it implies a transitional fossil is one that lies, in evolutionary terms, between two species and exhibits some features of one, some of the other and possibly some features that are at a stage of development some way between the two. In an ideal world the transitional would be unearthed in a location (in terms of the geologic column) at an appropriate position between the evidence for the species it is transitional too however there is no reason why a transitional fossil must only give rise to one descendent or that it must appear to die out as soon as it has done so.
By its very nature the fossil record is incomplete ... that is the nature of fossilisation and the rather unusual conditions required for it to occur so for creationists to ask where are the "billions of transitional fossils" in the way that they do borders upon complete stupidity.
That said there are a vast number of fossils that are regarded as being true transitionals.
De Ricqles (1983) and Horner et al. (1992) document possible cases of gradual evolution and some lineage's that show abrupt appearance or stasis. Examples are several species from the early Permian (reptiles such as Captorhinus, Protocaptorhinus, Eocaptorhinus, Romeria) and the "Montana" site (a coastal plain in the late Cretaceous) where many excellent transitional dinosaur were found including:
- Many transitional ceratopsids between Styracosaurus and Pachyrhinosaurus.
- Many transitional lambeosaurids (50 plus specimens) between Lambeosaurus and Hypacrosaurus.
- A transitional pachycephalosaurid between Stegoceras and Pachycephalosaurus.
- A transitional tyrannosaurid between Tyrannosaurus and Daspletosaurus.
These transitional animals, apparently lived over a 500,000-year period, but were known from a much larger site ("the Judith River Formation") where a 5 million-year evolutionary stasis occurred with the subsequent, and very abrupt, appearance of many new forms. Evidence indicates that climactic changes acted in such a way the sea level rose during the 500,000-year period temporarily burying the Judith River Formation under water and forcing the dinosaur populations into smaller areas such as the site in Montana. Evolution can proceed very rapidly within isolated populations and, when sea level fell again, the new forms spread out to the re-exposed Judith River landscape, thus appearing "suddenly" in the Judith River fossils, with the transitional fossils only existing in the Montana site.
The "missing link" ER1470 ("Lucy" or Australopithecus afarensis) was found by two independent anthropologists i.e. Donald Johanson (Hadar region, Ethiopia) and Mary Leakey (Laetolil, Tanzania). Lucy's obstetrics demonstrate that she would have been able to give birth to a baby no larger than a newborn male chimp or orang-utan and that that new baby's brain would have comprised around 10% of its total weight. Other facets of Lucy's structure (such as her hind limbs being adapted for walking whilst her toes were longer and more curved, her fingers longer and better adapted for grasping branches and trunks), arguably a direct or close ancestor of mankind indicate her transitional nature in comparison to modern man.
Archaeopteryx, the transitional fossil oft claimed by creationists to be a forgery, is another transitional between reptile and bird ... the German specimen, for example, has feathers and dinosaur like teeth. Independent investigators have verified the authenticity of several specimens of the fossil, in response to creationist allegations of forgery, and other investigators have found other specimens of the same fossil organism.
There are excellent skeletons of extinct animals showing transition from primitive fish to bony fish, from fish to amphibian (the first four-legged creatures walked on the ocean bottom, not on land), from amphibian to reptile, from reptile to mammal, from reptile to bird and even from land animal to whale (fossil whales have been found with four legs & whales today still have skeletal components that can be identified as parts of hind legs deep in their flesh whilst their front legs have evolved into flippers).
One, particularly well-defined fossil sequence of transitions documents the evolution of apelike creatures through 6 or more intermediate forms to modern-day humans.
The horse, perhaps the oldest known transitional sequence, starts some 55 million years ago with the terrier-sized Eohippus. Eohippus had four toes in front and three in back and, for technical reasons, has since been renamed Hyracotherium. From Eohippus a lineage descended through at least 14 steps, each step being represented by successfully competing animals, right through to the modern horse (the pony-sized creature designated as Equus) genus to which all modern horses belong.
Creationists believe that gaps in the fossil record "show fundamental biological discontinuities, while evolutionary biologists think they are the inevitable result of chance fossilisations, chance discoveries, and immigration events" (Hunt, 1997)
It must be admitted that there are gaps in the fossil record, enough to keep scientists in business for many decades (perhaps centuries) to come, and that most fossil types are extremely rare. Fossilisation, in relative terms, is a rare event as the animal to be fossilised must die in circumstances that bury it in sediment before scavengers or environment can destroy it and then that area must be subject to whatever processes are necessary to lift and expose the remains adequately enough for scientists to be made aware of its existence.
Even though there are gaps the fossil record does demonstrate to us the following:
- An obvious tendency for successively higher and more recent fossil finds to resemble modern species more closely i.e. a temporal - morphological correlation that is highly noticeable and appears to point toward an origin of all vertebrates from a common ancestor.
- Many chains or branches of genera that appear to connect primitive genera with modern radically different genera and by which major evolutionary change can be traced.
- Large numbers of species-to-species transitions that (often) cross genus & (sometimes) family lines and often result in significant adaptation.
- A lot of gaps. For stratigraphic reasons, there must always be gaps and no current evolutionary model predicts or requires a complete fossil record and no rational person expects that the fossil record will ever be close to complete.
It is also possible to argue that all species are transitional, that humans and other "end-branch" species are not transitional as they have not yet evolved into whatever species they one day will do.
So, to claim that there are no transitional fossils is not a valid interpretation of the available evidence it is, quite simply, wrong.
- "Transitional Vertebrate Fossils FAQ", Kathleen Hunt (1997)
- "Transitional Vertebrate Fossils FAQ (Part 2c)", Kathleen Hunt (1997)
- "5 Major Misconceptions About Evolution", Mark Isaak (1998)
- "It's a bird, it's a dinosaur - it's both", Paul Reger (1999)
- "How Science Responds When Creationists Criticize Evolution", Boyce Rensberger (1997)
- "The Natural History Book of Dinosaurs" Tim Gardom & Angela Milner (1993)