Symbiogenesis: bug your elders

Mommy & Daddy (pic from Wikipedia)

So humans, fanatic wielders of Clorox wipes, are just one branch in long genetic lines of bacterial evolution. Our great-to-past infinity-grandparents were bugs and we are bugs, and we already know we can’t live without them, whether you’re pro-biotic or anti-biotic in nature. Just our digestive tract alone hosts a good ten times more organisms than we have cells in our body.

Bugs R Us. Not only do we contain them, the cells in our bodies quite probably evolved from them. Next time I see a toddler stuffing her face with dirt I’ll just call it a family reunion.

Our bodies are a vehicle of sorts, carting around 100 trillion microbes, according Carl Zimmer, who writes about the human biome, among other things (New York Times Magazine, 12/3/11). Amy Barth reported that we pack around 200 trillion microscopic organisms, including bacteria, viruses, and fungi and lists where they lurk in our guts, pits, scalp, elbows, skin, and so on (Discover, March 2011). What’s the diff among a few trillion microorganisms.

When I go out to feed my worms kitchen scraps and shredded junk mail, it is not the red wigglers I’m actually feeding, but all the bacteria in their guts, which they kindly process into yummy fertilizer I cast onto my broccoli plants. (Which just get eaten by the allegedly higher Orders, like isopods, crickets, and rabbits, anyway.) I call the composting shelves my Worm Condo but perhaps I should name it “Penthouse of Bacteria,” instead.

We like to think humans are more than just bacteria pods, but are we? And yet—some of us feel we have a certain intelligence in our guts, but that’s another story.

{An aside, or Station Break}

Speaking of bacteria pods, it’s not fair that our body’s high water content (70%) gets all the attention, such that creatures in one episode of Star Trek called the human species Ugly Bags of Water. Particle physicists used to say we’re just a lot of empty space, considering the corresponding distance between an electron and proton in just one atom of our trillions of cells is the equivalent of 11 miles, if you pinned the suckers down: The now-outdated Bohr solar system atom model is still useful for high school biology teachers, but now we understand, with quarks and their constituents buzzing around a nearly light speed inside a proton—or among whatever energy, magnetic, or gravitational field hangs out around there, that this “space” is much fuzzier and smearier, a whole dark matter of mystery inside and around an atom inside and around whatever n-dimensional space. (If anyone read this post I’d probably get canned for that new atomic cosmic analogy, but what can I say? It was a Thought Quark.)

{And now back to Bugs}

My Science Times podcast (in an interview with Carl Zimmer, sometime early 2011) reminded me that the DNA of microorganisms residing in our Gut Palace outnumbers the human genome a hundred fold. Who’s genes are we? What about that gut intelligence?

Microbial ecologists have also found that people have different types of biomes, or unique sets of microbial colonizations, not unlike the four different blood types (A,B,AB,O)–a sort of gut fingerprint is how I see it. (That from another Science Times podcast, which I listened to while walking the dogs so I don’t always note the date before the next synch casts it off.)

{Is it pejorative to call Bacteria ‘Bugs?’}

Evolutionist and academic rabble-rouser Lynn Margulis, now in her seventies, is still stirring up the worm castings. She’s a bio-logical provocateur, one of my favorite kinds of people.  Discover interviewed her in April 2011, from which I gleaned some of her concepts.

Margulis revolutionized our understanding of evolution in 1967 with her concept that eukaryotes (cells with a nuke) and other complex cells evolved as a series of mergers among bacteria living collectively and then symbiotically. She believes that symbiosis, or “symbiogenesis,” is what makes new species evolve, far more than random mutations and natural selection. The latter exists more to maintain and weed existing species, she says. (That’s some heavy culling, I’d say, going from Neanderthal to Sapien sapien or Erectus to Habilis–what were they eating back then? We’re headed for Homo plasticus, minus the sapience, I fear.)

Margulis has some interesting points. Symbiogenesis better supports Stephen Jay Gould’s “punctuated equilibrium,” which is what you see as time gaps in the fossil record, for one.

Protoctists (eukaryotes) appear in the fossil record around 452 million years ago, Hominidae (our apelike forebearers) maybe in the past 15-20 million years, and actual humans, gosh, just in the past 200,000 years, max.

Ancient bacteria and their ilk became pretty handy at finding specialized niches those hundreds of million years ago: Margulis posits that every visible life form is a combination or community of bacteria.

Our teeny cellular powerhouses, mitochondria, for example, came from oxygen-respiring bacteria. We can’t live without these mighty organelles. When you run out of energy, blame them. In plants and algae, the great photosynthesizer, chloroplast, came from cyanobacteria (formerly known as “blue-green algae”).

How? So a zillion years ago, an amoeba couldn’t digest a bacterium, but they worked pretty well together—the bacteria made oxygen or vitamins that were helpful and at some point transformed themselves into mitochondria, because “long-term symbiosis leads to new intracellular structures” and so on, and here we all are, the isopods, the crickets, the rabbits.

Evolution, according to Margulis, is a series of acquired genomes. Sounds bio-logical to me.

Take the cilia (in rods and cones in the eye; in the inner ear, for balance; in motility systems all over the body): Rather than evolving from random mutation they could have come from the acquired genome of a spirochetish symbiotic bacterium that could sense light or motion, oh so long ago. Margulis theorizes that our cytoskeletal system came from the incorporation (what a perfect word) of ancestral spirochetes.

And why not? It makes as much sense as anything else. She really pisses off a lot of evolutionary biologists, though, among other theorists. They say, “wormshit!”

Margulis posits that all living cells possess consciousness, if consciousness is a matter of responding to sensory stimuli, if I read her right. Says Margulis, bacteria have been around since the origin of life and are still running the soil and air and affecting water quality.

Humans have been around for just a relative teeny blip in time; let’s round and say 1 million years vs. bacteria’s 350 million years–and look at all the havoc we wreak on the planet (OK, we’ve kind of junked up the solar system, too). Like an invasive species, we consider ourselves special and intelligent as we nonetheless overgrow our habitats.

In Margulis’ line of thinking, we’re starting to act like “mammalian weeds.”

A buggy weed.