Leaps



Leaps: species suddenly appear - no transitional forms

Perhaps the most well-known problem are the missing transitional forms. Although it is often stated, few will be aware of the depth of this problem. A well-known evolutionary biologist Stephen J. Gould called this the "secrecy" of the paleontologists. Paleontologists are biologists who investigate fossils and Gould was himself a paleontologist. Darwin was aware of the lack of transitional forms in 1859: unless evolution is a pronounced gradual process, he sought an explanation for the manifest absence of innumerable transitional forms that according to his theory nevertheless have ever lived. For Darwin's theory to work,  it's fundamental that each step in the evolutionary process would be extremely small.

The conclusion of Darwin was this: the fossil record is very incomplete. He compared it with a book of which only a few pages are left, and on that few pages only just a few letters of a limited number of sentences are readable. In such an incomplete archive, Darwin thought, it's not really surprising that the transitional forms are missing. To give you an idea: in the figure below (taken from Nature 363), the solid lines represent the species that have been found (possibly fragmented) while the dotted lines show the species is assumed. See also "epistemological gap." What is the problem that Gould called a professional secrecy?


Missing LInks

                              Missing Links Gaps Transitional Forms

The secret where Gould is referring to, the profound contrast between the pattern of fossils archive on the one hand, and the assumed gradual process of natural selection on the other. In Darwin's time they had only thousands of fossils, but today there are millions. And guess what? They especially found more of the same. Not only there remains persistent lack of transitional forms, it appears from the fossils that species over millions of years remain immutable, and then again between relatively large jumps, i.e. the 'sudden' appearance of something similar but clearly different. The most egregious example perhaps is the Cambrian explosion about 540 million years ago in which massive new species suddenly appeared on the scene. This pretty jerky pattern of the fossils is at odds with the supposed extremely gradual process of random mutations and natural selection, even to the extent that many paleontologists have problems with the theory of neo-Darwinism.

To get a sense of the problem the paleontologists encounters, it pays to just go looking deeper into it. Take for example the evolution of the horse, whose fossils are best preserved in terms of gradual transitions. This relatively modest evolution ran over millions of generations. In comparison, the evolution from fish to amphibian or from reptile to bird, asks many more generations for the necessary changes to get so drastic. The question now is: how many links in this long evolution chain are missing now actually in the fossil record? The answer is: the great majority. In fact, almost all of them. In that regard, the term 'missing links' is very misleading: it gives the impression that in the long chain of evolution, only a minority of the missing links is lacking in the fossils. Nothing can be farther from the truth. The title of a recent book speaks volumes in this regard: the title is "Billions of Missing Links ..."

Paleontologists obviously know that the fossil records are very incomplete, but after millions of fossils increasingly confirmed the jerky pattern, Stephen J. Gould summed it up as follows: "why do we never see transitional forms? Evolution isn't always occuring somewhere else ... ?! "Or to use the analogy of Darwin about the book of the fossils in which are so many letters are missing, then there is obviously quite a lot of room for imagination for interpreting them. However, the secrecy that Gould exposes, is this: a few phrases that are still readable, show no evolution, on the contrary. This evolution is assumed to always were, 'secretly' to happen in those sentences of the book that are missing ...

Not only are transitional forms hard to find, they are sometimes difficult to imagine. I.e. sometimes turns fantasy inadequate. Known example is the bird lung: the lungs of their ancestors, the reptiles, end in small sacs where the air goes in and out (as in mammals), but in birds that is quite different, since the air is always in one direction through elongated tubes. It is not obvious how one gradually into the other can evolve. And this seems to be the general pattern: nature shows too many jumps, both in the fossil record as among the living. Too much to explain in the gradual process of neo-Darwinism.