One of the common arguments brought up to cast doubt on the theory of evolution is the absence or paucity of transitional forms in the fossil record. After all, if there is a slow transition in the evolution of the diversity of animal life, intermediate forms should be, so the argument goes, abundant.
The following video gives one rather notorious example of the argument (start at 1:50 to see the relevant section of the clip).
Now I think that Kirk Cameron was playing to the camera here, building an audience for the debate later that night. He is a comedian and knows how to get a reaction. Nonetheless the point is serious, if evolution is true there should be transitional forms in the fossil record. A couple of months ago (here) I posted on the book by Karl Giberson and Francis Collins The Language of Science and Faith: Straight Answers to Genuine Questions and asked what arguments people found convincing or would like to see addressed in future posts. This issue of transitional forms, or related questions of fossils and evolutionary change, came up in a number of the comments.
What kind of evidence would you expect to find in the fossil record if evolution is true?
Does the argument from the absence of transitional forms seem reasonable? Why?
There are transitional forms found in the fossil record and more are being found. But the transitions are subtle with any one specimen showing small changes. Here I would like to bring as an example a report in Nature, published online yesterday, May 18, and in print today, that deals with transitional forms and evolution. This paper, Eocene lizard from Germany reveals amphisbaenian origins, describes a fossil that provides a transitional form between legged lizards and worm lizards. To see the whole article you will need a subscription, either institutional or individual, but the abstract is free. The paper was also highlighted in the New York Times, Fossil Sheds Light on the Lizard-Snake Divide (there is a very nice picture of the fossil here).
Amphisbaenia are a kind of lizard characterized by a snake-like body. They had been grouped with snakes based on morphology (the study of the form or structure of an organism or any of its parts), but molecular data grouped them with lacertids, a kind of legged lizard found Europe. Analysis of the fossil described in this paper “provides the first morphological evidence for lacertid–amphisbaenian monophyly on the basis of a reinforced, akinetic skull roof and braincase, supporting the view that body elongation and limblessness in amphisbaenians and snakes evolved independently.” (v. 473 p. 364) Basically the fossil shows characteristics of both legged lizards and worm lizards. Phylogeny is the connections between groups of organisms in ancestor/descendant relationships, monophyly means developed from a common form. This fossil isn’t a missing link as much as an indication of a common ancestor for both kinds of lizards. This also means that the worm lizards and snakes evolved to a similar form independently.
The report on this fossil demonstrates several points.
First, transitional forms are found in the fossil record, and more are being found all the time as research continues. They tend to be reported in the literature in rather specialized language. This one is particularly interesting and made at least an appearance in the more popular literature.
Second, identification of transitional forms requires a great deal of careful and painstaking work. This isn’t kitchen science. We’ve advanced a long way since the days of Darwin and the gentleman naturalists. The features of this fossil were studied by using x-rays to scan and produce a 3-dimensional image of the structure of the skull showing the outlines of the bones. The quality of the scan allows detailed analysis and comparison. This is state-of-the-art work on a nearly complete specimen.
Third, the body of data supporting the evolutionary theory comes from the cumulative weight of studies in genetics, molecular biology, anatomy, paleontology, combined with knowledge from chemistry, physics, and mathematics. As the puzzle is put together some hypotheses are proven wrong – others are confirmed and extended. But the evolutionary theory makes sense of all the data and is shaped and further refined by the data. Evolutionary theory isn’t Darwinism. It has advanced far beyond anything a 19th century naturalist could have imagined.
Studies like this one and more lead many of us to the conclusion that evolution is true – not random purposeless evolution but evolutionary creation as God’s method for producing the diversity of life found in the world today.
What do you make of studies like this?
What kind of evidence would you expect to see in the fossil record for or against evolution?
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