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A common objection posed to the account I have sketched of how natural selection gives rise to otherwise improbable features, is that some postulated transitions, for example from a leg to a wing, cannot be adaptive. The answer to this kind of objection is well known to evolutionists. For example, there are rodents, primates, and other living animals that exhibit modified legs used for both running and gliding. The fossil record famously includes the reptile Archaeopterix and many other intermediates showing limbs incipiently transformed into wings endowed with feathers.

One challenging transition involves the bones that make up the lower jaw of reptiles but have evolved into bones now found in the mammalian ear. What possible function could a bone have, either in the mandible or in the ear, during the intermediate stages? However, two transitional forms of therapsids (mammal-like reptiles) are known from the fossil record with a double jaw joint—one joint consisting of the bones that persist in the mammalian jaw, the other composed of the quadrate and articular bones, which eventually became the hammer and anvil of the mammalian ear.

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Go to Evolution Topic Index

Natural Selection as a Creative Process

Evolution: Topic Index
The Darwinian Revolution
Darwin's Discovery: Design without Designer
Natural Selection as a Directive Process
Natural Selection as an Opportunistic Process
Chance and Necessity
Teleology and Teleological Explanations
The Compatiblity of Teological and Causal Explanations
Coda: Science as a Way of Knowing

Source:

Dr. Francisco Ayala
Dr. Francisco Ayala

Bibliography

See also:

Genetics
Evolution
The Relation of Science & Religion
Purpose and Design
The Argument From Design
The Anthropic Principle
Opinions
Charles Darwin
Galileo
Copernicus
Sir Isaac Newton
DNA Double-Helix