Margulis on Bacteria-Human collaboration:

Margulis herself on collaborative human-bacterial relations:

Our ability to perceive signals in the environment evolved directly from our bacterial ancestors.

That is, we, like all other mammals including our apish brothers detect odors, distinguish tastes, hear bird song and drum beats and we too feel the vibrations of the drums. With our eyes closed we detect the light of the rising sun. 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. Cilia have a recognizable fine structure. With a very high power ("electron") microscope a precise array of protein tubules, nine, exactly nine pairs of tubules are arranged in a circular array and two singlet tubules are in the center of this array. All sensory cells have this common feature whether in the light-sensitive retina of the eye or the balance-sensitive semicircular canals of the inner ear. Cross-section slices of the tails of human, mouse and even insect (fruit-fly) sperm all share this same instantly recognizable structure too. Why this peculiar pattern? No one knows for sure but it provides the evolutionist with a strong argument for common ancestry. The size (diameter) of the circle (0.25 micrometers) and of the constituent tubules (0.024 micrometers) aligned in the circle is identical in the touch receptors of the human finger and the taste buds of the elephant.

...

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. In the not-too-distant future people will wonder why so many scientists were so against my idea for so long!

*from (http://www.edge.org/q2005/q05_7.html#margulis)