Eric Rasmusen’s Weblog

This is a post about evolution— about two criticisms one might make of the theory : (a) the fossil record has big gaps where we ought to be finding fossils of intermediate forms, creatures halfway along an evolutionary path, and (b) we have observed no examples of actual new species arising. I think criticism (b) is wrong, but criticism (a) is correct (though by no means fatal to the theory, especially if we can invoke intelligent design).

One thing led to another and this post started to get too long for me to finish, so I will post it here in a form that gets increasingly ragged, but has some good links.

(a) Claim: The fossil record has big gaps where we ought to be finding fossils of intermediate forms, creatures halfway along an evolutionary path.

Using the Web to look at this is tricky, because the participants in the intelligent design debate are so partisan. The polar sites are The Discovery Institute (pro-ID) and The Panda’s Thumb (anti-ID).
What it looks like to me is that transitional forms can be found for
many species, but there are also major gaps. The DIS people don’t seem
to want to grant that there are transitional forms for many species,
and the PT people don’t like to admit that there are major gaps.

Here are some other links that someone sent me, which I haven’t checked:

http://pharyngula.org/

http://www.pandasthumb.org/

http://www.talkdesign.org/

http://www.talkorigins.org/

http://www.antievolution.org/

http://www.uncommondescent.com/

In response to my post,
Intelligent Design– Dennett Space Alien Example, Dr. Kenneth Pimple wrote

ThI also think you’re wrong about the missing link argument. There are many, many links in the fossil record between ancient life forms and current ones, and there are many, many links between ancient mammals and human beings. If the record as it stands is not good enough for you, could you specify what a knock-down convincing missing link would look like?

Convincing examples do exist– at least convincing at the level of my non-expert judgement. ere seems to be a good line of evolution for the horse, for example. What we want is a series of fossils that gradually move from one creature early in time to a quite different creature late in time. Also, we want the locations of the fossils to be consistent with the idea that one step evolves to another (so we don’t want Fossil A to be found only in Brazil and its successor, Fossil B, to be found only in Europe).

The unsatisfactory nature of the fossil record is an old and admitted problem for the theory of evolution, and has been the source for many subtheories (such as Gould’s “punctuated equilibrium” or the meteor theory of dinosaur extinction). It is a good example for why Popper’s metatheory of “testable implications” as a basis for a scientific theory is a bad metatheory. Evolutionary theory predicts we should find plenty of intermediate forms. We don’t, but that doesn’t mean we should or do reject the theory. Rather, in the absence of a satisfactory competing theory that does explain the lack of intermediate forms, we continue using evolutionary theory and trying to figure out how to explain the anomaly. Intelligent Design is one elaboration of the theory that tries to explain the anomaly.

(1) Darwin himself noted that his theory predicted a fossil record different from what we had found in his day. He said

The main cause, however, of innumerable intermediate links not now occurring everywhere throughout nature, depends on the very process of natural selection, through which new varieties continually take the places of and supplant their parent-forms. But just in proportion as this process of extermination has acted on an enormous scale, so must the number of intermediate varieties, which have formerly existed, be truly enormous. Why then is not every geological formation and every stratum full of such intermediate links? Geology assuredly does not reveal any such finely-graduated organic chain; and this, perhaps, is the most obvious and serious objection which can be urged against the theory. The explanation lies, as I believe, in the extreme imperfection of the geological record.

(2) Bats are a species for which we lack intermediate forms. The Panda’s Thumb, an anti-ID site, says,
citing the
New Scientist,:

Bats have been an evolutionary enigma. That’s because the oldest
fossil bats look remarkably like modern ones, each having wings formed
from membranes stretched between long fingers, and ear structures
designed for echolocation. No fossils of an animal intermediate
between bats and their non-flying mammal ancestors have been found….

Sears believes that bats began to evolve when this one gene became
activated. Although it is a small developmental change, if it allowed
the ancestors of bats to grow extended digits it could explain how
bats evolved flight so rapidly, Sears told the Society of Vertebrate
Paleontology meeting in Denver. Relatively few transitional forms
would have existed just briefly before being displaced by more
advanced forms.

The post is trying to explain why the intermediate forms of bats are missing— so note that its starting point is an admission that they are missing.

(3) There is a very good FAQ web report on Transitional Forms. Here is one section:

Transition from diapsid reptiles to birds

In the mid-1800′s, this was one of the most significant gaps in
vertebrate fossil evolution. No transitional fossils at all were
known, and the two groups seemed impossibly different. Then the
exciting discovery of Archeopteryx in 1861 showed clearly that the two
groups were in fact related. Since then, some other reptile-bird links
have been found. On the whole, though, this is still a gappy
transition, consisting of a very large-scale series of “cousin”
fossils….

I think the most noticeable aspects of the vertebrate fossil record,
those which must be explained by any good model of the development of
life on earth, are:

1. A remarkable temporal pattern of fossil morphology, with “an
obvious tendency for successively higher and more recent fossil
assemblages to resemble modern floras and faunas ever more closely”
(Gingerich, 1985) and with animal groups appearing in a certain
unmistakable order. For example, primitive fish appear first,
amphibians later, then reptiles, then primitive mammals, then (for
example) legged whales, then legless whales. This temporal-
morphological correlation is very striking, and appears to point
overwhelmingly toward an origin of all vertebrates from a common
ancestor.

2. Numerous “chains of genera” that appear to link early, primitive
genera with much more recent, radically different genera (e.g.
reptile- mammal transition, hyenids, horses, elephants), and through
which major morphological changes can be traced. Even for the
spottiest gaps, there are a few isolated intermediates that show how
two apparently very different groups could, in fact, be related to
each other (ex. Archeopteryx, linking reptiles to birds).

3. Many known species-to-species transitions (primarily known for
the relatively recent Cenozoic mammals), often crossing genus lines
and occasionally family lines, and often resulting in substantial
adaptive changes.

4. A large number of gaps. This is perhaps the aspect that is
easiest to explain, since for stratigraphic reasons alone there must
always be gaps. In fact, no current evolutionary model predicts or
requires a complete fossil record, and no one expects that the fossil
record will ever be even close to complete. As a rule of thumb,
however, creationists think the gaps show fundamental biological
discontinuities, while evolutionary biologists think they are the
inevitable result of chance fossilizations, chance discoveries, and
immigration events.

As Gould said (1994): “The supposed lack of intermediary forms in the
fossil record remains the fundamental canard of current
antievolutionists. Such transitional forms are scarce, to be sure, and
for two sets of 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 geological extenet). 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 geneology.”

Again, note the admission of the lack of intermediary forms. Gould admits it, but then switches the subject to the fact that for some creatures there do exist intermediary forms. Note, too his biological reasons for the absence of intermediary forms. These are not theories that were developed for other reasons and then happened to explain intermediary forms– these are theories designed specifically because basic evolutionary theory had trouble explaining speciation and lack of intermediary forms.

(4) The biggest example of hard-to-explain speciation seems to be the Cambrian Explosion alluded to at this Berkeley site:

The Cambrian Period marks an important point in the history of life on
earth; it is the time when most of the major groups of animals first
appear in the fossil record. This event is sometimes called the
“Cambrian Explosion”, because of the relatively short time over which
this diversity of forms appears.

(b) Claim: We have observed no examples of actual new species arising.

This faq-speciation.html on Speciation is very good at refuting the idea that we have not observed new species arise. It also has a good discussion of the troublesome term “species”.

For some reason I thought this Panda’s Thumb post on the The Last Universal Common Ancestor was relevant.

This entry was posted on Wednesday, September 21st, 2005 at 3:54 am and is filed under InDesign, Science, Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.