How some of our design evolved

In a recent post about Intelligent design, I discussed the notion that contrary to the claims of the intelligent design proponents, it isn't at all easy to distinguish between something that was "designed" and something that, as the intelligent design people say, is found "in nature." The feature of biological entities that the intelligent design proponents seem most convinced provides evidence of design is our sensory equipment.

In Edge's recent 2005 question, "What Do You Believe Is True Even Though You Cannot Prove It?'" Lynn Margulis answered:

that our ability to perceive signals in the environment evolved directly from our bacterial ancestors. … These abilities to sense our surroundings are a heritage that preceded the evolution of all primates, all vertebrate animals, indeed all animals. Such sensitivities to wafting plant scents, tasty salted mixtures, police cruiser sirens, loving touches and star light register because of our "sensory cells".

These avant guard cells of the nasal passages, the taste buds, the inner ear, the touch receptors in the skin and the retinal rods and cones all have in common the presence at their tips of projections ("cell processes") called cilia. …

I think that the common ancestor of the cilium, but not the rest of the cell, was a free-swimming entity, a skinny snake-like bacterium that, 1500 million years ago squiggled through muds in a frantic search for food. Attracted by some smells and repelled by others the bacteria, by themselves, already enjoyed a repertoire of sensory abilities that remain with their descendants to this day. In fact, this bacterial ancestor of the cilium never went extinct, rather some of its descendants are uncomfortably close to us today. …

[T]his bacterium who still has many live relatives, entered into symbiotic partnerships with other very different kinds of bacteria. Together this two component partnership swam and stuck together both persisted. What kind of bacterium became an attached symbiont that impelled its partner forward? None other than a squirming spirochete bacterium.

The spirochete group of bacteria includes many harmless mud-dwellers but it also contains a few scary freaks: the treponeme of syphilis and the borrelias of Lyme disease. We animals got our exquisite ability to sense our surroundings—to tell light from dark, noise from silence, motion from stillness and fresh water from brackish brine—from a kind of bacterium whose relatives we despise. Cilia were once free-agents but they became an integral part of all animal cells. Even though the concept that cilia evolved from spirochetes has not been proved I think it is true. Not only is it true but, given the powerful new techniques of molecular biology I think the hypothesis will be conclusively proved.