His arguments were reminiscent of those made by William Paley (1743 - 1805), who used the analogy of finding a pocketwatch dropped in the heath.
"In crossing a heath, suppose I pitched my foot against a stone, and were asked how the stone came to be there;
I might possibly answer, that, for anything I knew to the contrary, it had lain there forever:
nor would it perhaps be very easy to show the absurdity of this answer.
But suppose I had found a watch upon the ground, and it should be inquired how the watch happened to be in that place;
I should hardly think of the answer I had before given, that for anything I knew, the watch might have always been there. (...)
There must have existed, at some time, and at some place or other, an artificer or artificers, who formed [the watch]
for the purpose which we find it actually to answer; who comprehended its construction, and designed its use. (...)
Every indication of contrivance, every manifestation of design, which existed in the watch, exists in the works of nature;
with the difference, on the side of nature, of being greater or more, and that in a degree which exceeds all computation.
-- William Paley, Natural Theology (1802)
Behe's arguments were similar: that the complexity of living structures could mean only that they had an Intelligent Designer.
Evolutionary biologists have met this contention with many examples of how neutral evolution and natural selection
could quite reasonably have "invented" such complex structures.
These genes were expressed in mucus-producing glands of the earliest venomous lizards.
Not necessarily fatal. Just enough to slow down the prey, or cause excessive bleeding (anticoagulant venom) and confer a selective advantage on the lizards with early venom.
For example, it's now known that the gene coding for a venom called crotamine (found in rattlesnakes, genus Crotalus) is very closely related to the genes coding for defensins, small proteins found widely in the animal kingdom (and even in plants) that provide anti-bacterial protection. In vertebrates, defensins are found in immune system cells where they help the cells kill bacteria.
These precursor defensin genes appear to have been readily mutable.
There are hundreds of different kinds in the many different species that have them.
By the time the earliest ancestor of snakes appeared (about 60 million years ago), it already had multiple genes coding for venom proteins.
Snake venoms are (molecularly) more similar in related species than in distant species: They have been inherited from common ancestors.
But they do show specialization, even within a lineage, that marks the effects of natural selection:
Green mambas and black mambas have chemically similar venoms. But green mambas hunt in trees, and black mambas hunt on the ground.
Natural selection is no miracle:
Today, however, we have the luxury of a vast trove of molecular and morphological data that make clear how such a progression could have been not only possible, but likely.
When light strikes this molecule, it dissociates into its two components (opsin and retinal), triggering a nervous system stimuls that is eventually perceived by the brain as a spot of light (corresponding to that photoreceptor in the visual field).
The opsin portion of the molecule is variable, and controlled by the genes in the particular species in which it occurs.
Eyes themselves may have evolved from simple patches of light-sensing cells on the skin to the complex structures we see today:
Perhaps the most amazing feature of the vertebrate eye is the light-focusing lens, composed of proteins called crystallins
When it comes to evolution, there seems to be no end to the amazing variety and...grandeur.
Recall the Central Dogma:
The above is synonymous with gene expression.
(We now know that there are exceptions to this general rule. For example, some genes are transcribed only into functional RNA, such as transfer RNA (tRNA) or ribosomal RNA (rRNA), and never translated into protein.)
As the genetic instructions guiding a vertebrate embryo's development change in each new cell, the cells themselves follow those instructions, and are modified...
All of this is governed by instructions on the DNA. Each cell has the same genome, but different genes are active and inactive in each type of cell.
Among these are the Hox Genes that determine the identity of the body segments in animals as diverse as fruit flies and mammals. How did these toolkits expand to make such different organisms? Duplication and Recruitment, as we have seen before. The Hox genes in fruit flies and mammals are homologous: inherited from a common ancestor.
In the two major lineages of animals, protostomes and deuterostomes, whom we have met before, major organ systems (circulatory, digestive, and nervous) are reversed in body position: