Shadows of Forgotten Ancestors

Other inhabitants of the soil kill off the young plants. Here is Darwin’s account of a little experiment he did to illustrate the hidden ferocity lurking just beneath the placid surface of a country garden:[On] a piece of ground 3 feet long and 2 feet wide, dug and cleared, and where there could be no choking from other plants, I marked all the seedlings of our native weeds as they came up, and out of 357 no less than 295 were destroyed, chiefly by slugs and insects If turf which has long been mown, and the case would be the same with turf closely browsed by quadrupeds, be let to grow, the more vigorous plants gradually kill the less vigorous though fully grown plants .  .¹³

Some plants provide food for specific animals, in turn, the animals act as agents for the sexual reproduction of the plants—in effect, couriers taking sperm from male plants and using it for artificial insemination of female plants. This is not quite artificial selection, because the animals are not much in charge. The currency these procurers are paid in is usually food. A bargain has been struck. Maybe the animal is a pollinating insect, or bird, or bat; or a mammal to whose furry coat the reproductive burrs adhere; or maybe the deal is food supplied by the plants in exchange for nitrogenous fertilizer supplied by the animals. Predators have symbionts that clean their coats or scales or pick their teeth in exchange for leavings. A bird eats a sweet fruit; the seeds pass through its digestive tract and are deposited on fertile ground some distance away: another business transaction consummated. Fruit trees and berry-bearing bushes often take care that their offerings to the animals are sweet only when the seeds are ready to be dispersed. Unripe fruit gives bellyaches, the plants’ way of training the animals.

The cooperation between plants and animals is uneasy. The animals cannot be trusted; given a chance, they’ll eat any plant in sight. So the plants protect themselves from unwelcome attention with thorns, or by producing irritants, or poisons, or chemicals that make the plant indigestible, or agents that interfere with the predator’s DNA. In this endless slow-motion war, the animals then produce substances that disable these adaptations by the plants. And so on.

The beasts and vegetables and microbes are the interlocking parts, the gear train, of a vast, intricate and very beautiful ecological machine of planetary proportions, a machine plugged into the Sun. Pretty nearly, all flesh is sunlight.

Where the ground is covered with plants perhaps 0.1% of the sunlight is converted into organic molecules. A plant-eating animal saunters by and eats one of these plants. Typically the herbivore extracts about a tenth of the energy in the plant, or about one ten-thousandth of the sunlight that could, with 100% efficiency, have been stored in the plant. If the herbivore is now attacked and eaten by a carnivore, about 10% of the available energy in the prey will wind up in the predator. Only one part in a hundred thousand of the original solar energy makes it to the carnivore. There are no perfectly efficient engines, of course, and we expect losses at each stage in the food chain. But the organisms at the top of the food chain seem inefficient to the point of irresponsibility.*

A vivid image of the interconnection and interdependence of life on Earth was provided by the biologist Clair Folsome, who asks you to imagine what you would see if all the cells of your body, flesh and bones, were magically removed:What would remain would be a ghostly image, the skin outlined by a shimmer of bacteria, fungi, round worms, pin worms and various other microbial inhabitants. The gut would appear as a densely packed tube of anaerobic and aerobic bacteria, yeasts, and other microorganisms. Could one look in more detail, viruses of hundreds of kinds would be apparent throughout all tissues.

And, Folsome stresses, any other plant or animal on Earth, under the same dispensation, would reveal a similar “seething zoo of microbes.” ¹⁴

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A biologist from some other solar system, in an unblinking examination of the teeming lifeforms of Earth, would surely note that they are all made of almost exactly the same organic stuff, the same molecules almost always performing the same functions, with the same genetic codebook in use by almost everybody. The organisms on this planet are not only kin; they live in intimate mutual contact, imbibing each other’s wastes, dependent on one another for life itself, and sharing the same fragile surface layer. This conclusion is not ideology, but reality. It depends not on authority, faith, or special pleading by its proponents, but on repeatable observation and experiment.