Coevolution and Artificial Selection

planting corn

The ancient relationship between bees and flowers is a classic example of coevolution. In a coevolutionary bargain like the one struck by the bee and the apple tree, the two parties acton each other to advance their individual interests but wind up trading favours: food for the bee, transportation for the apple genes. Consciousness needn’t enter into it on either side …

In The Botany of Desire: A Plant’s-Eye View of the World Michael Pollan tells the story of four domesticated species— the apple, the tulip, cannabis, and the potato—and the human desires that link their destinies to our own.

“Its broader subject,” he writes, “is the complex reciprocal relationship between the human and natural world.”

It’s a simple question really: Did I choose to plant these tulips or did they make me do it?

Pollan concludes that, in fact, both statements are true. Did the plant make him do it? Only in the sense that the flower “makes” the bee pay it a visit.

Evolution doesn’t depend on will or intention to work; it is almost by definition, and unconscious, unwilled process. All it requires are beings compelled, as all plants and animals are, to make more of themselves by whatever means trial and error present. Sometimes an adaptive trait is so clever it appears purposeful: the ant that “cultivates” its own gardens of edible fungus, for instance, or the pitcher plant that “convinces” a fly it’s a piece of rotting meat. But such traits are clever only in retrospect. Design in nature is but a concatenation of accidents, culled by natural selection until the result is so beautiful or effective as to seem a miracle of purpose.

The book is as much about the human desires that connect us to plants as it is about the plants themselves.

“Our grammar,” Pollan writes, “might teach us to divide the world into active subjects and passive objects, but in a coevolutionary relationship every subject is also an object, every object a subject.”

Charles Darwin didn’t start out The Origin of Species with an account of his new theory, rather, he began with a foundation he felt would be easier for people to get their heads around. The first chapter was a special case of natural selection called artificial selection.

Artificial wasn’t used in the sense of fake but as in things that reflect human will. He wrote about a wealth of variation of species from which humans selected the traits that will be passed down to future generations. In this sense, human desire plays the role of nature, determining what constitutes “fitness.” If people could understand that, they would understand nature’s evolution.

Pollan argues that the crisp conceptual lie “that divided artificial from natural selection has blurred.”

Whereas once humankind exerted its will in the relatively small arena of artificial selection (the arena I think of, metaphorically, as a garden) and nature held sway everywhere else, today the force of our presence is felt everywhere. It has become much harder, in the past century, to tell where the garden leaves off an pure nature begins.

We are shaping things in ways that Darwin could never have imagined.

For a great many species today, “fitness” means the ability to get along in a world in which humankind has become the most powerful evolutionary force.

Artificial selection, it appears, has become at least as powerful as natural selection.

Nature’s success stories from now on are probably going to look a lot more like the apple’s than the panda’s or white leopard’s. If those last two species have a future, it will be because of human desire; strangely enough, their survival now depends on what amounts to a form of artificial selection.

The main characters of the book—the apple, the tulip, cannabis, and the potato—are four of the world’s success stories. “The dogs, cats, and horses of the plant world, these domesticated species are familiar to everyone,” Pollan writes.

Apples

In the wild a plant and its pests are continually coevolving, in a dance of resistance and conquest that can have no ultimate victor. But coevolution ceases in an orchard of grafted trees, since they are genetically identical from generation to generation. The problem very simply is that the apple trees no longer reproduce sexually, as they do when they’re grown from seed, and sex is nature’s way of creating fresh genetic combinations. At the same time the viruses, bacteria, fungi, and insects keep very much at it, reproducing sexually and continuing to evolve until eventually they hit on the precise genetic combination that allows them to overcome whatever resistance the apples may have once possessed. Suddenly total victory is in the pests’ sight — unless, that is, people come to the tree’s rescue, wielding the tools of modern chemistry.

Put another way, the domestication of the apple has gone too far, to the point where the species’ fitness for life in nature (where it still has to live, after all) has been dangerously compromised. Reduced to the handful of genetically identical clones that suit our taste and agricultural practice, the apple has lost the crucial variability — the wildness — that sexual reproduction confers.

The Tulip

The tulip’s genetic variability has in fact given nature–or, more precisely, natural selection–a great deal to play with. From among the chance mutations thrown out by a flower, nature preserves the rare ones that confer some advantage–brighter color, more perfect symmetry, whatever. For millions of years such features were selected, in effect, by the tulip’s pollinators–that is, insects–until the Turks came along and began to cast their own votes. (The Turks did not learn to make deliberate crosses till the 1600s; the novel tulips they prized were said simply to have “occurred.”) Darwin called such a process artificial, as opposed to natural, selection, but from the flower’s point of view, this is a distinction without a difference: individual plants in which a trait desired by either bees or Turks occurred wound up with more offspring. Though we self-importantly regard domestication as something people have done to plants, it is at the same time a strategy by which the plants have exploited us and our desires–even our most idiosyncratic notions of beauty–to advance their own interests. Depending on the environment in which a species finds itself, different adaptations will avail. Mutations that nature would have rejected out of hand in the wild sometimes prove to be brilliant adaptations in an environment that’s been shaped by human desire.

In the environment of the Ottoman Empire the best way for a tulip to get ahead was to have absurdly long petals drawn to a point fine as a needle. In drawings, paintings, and ceramics (the only place the Turks’ ideal of tulip beauty survives; the human environment is an unstable one), these elongated blooms look as though they’d been stretched to the limit by a glassblower. The metaphor of choice for this form of tulip petal was the dagger. … Though these … traits are not uncommon in species tulips, attenuated petals are virtually unknown in the wild, which suggests that the Ottoman ideal of tulip beauty—elegant, sharp, and masculine—was freakish and hard-won and conferred no advantage in nature.

All in all The Botany of Desire is one of the best books I’ve read on how our Apollonian desire for control and order increasingly butts up against the natural Dionysian wildness.

(Image via flickr commons)


Comments

  1. carvel says

    Any other good books on coevolution? Something I’d like to read more about.

  2. Steven says

    Carvel, this is a long article rather than a book and isn’t about coevolution of speces so much as coevolution of man with the Mississippi river, but it may interest you.

    http://www.newyorker.com/archive/1987/02/23/1987_02_23_039_TNY_CARDS_000347146?currentPage=all

    I recently moved to Louisiana, and was aware of some of the ways in which humans have unintentionally encouraged erosion that has harmed the interests of subsequent humans, but hadn’t realized the degree to which humans have had to fight natural changes in order to preserve the infrastructure that has been built (e.g., if the river changed course the way it would “like” to, the largest port in the western hemisphere would be nearly useless).

  3. Greg says

    Are you familiar with the adaptive markets hypothesis that Andrew Lo (MIT) proposed as an alternative to EMH?

    He built off the initial work of Victor Neiderhoffer who looked at evolution and natural selection as a metaphor to understand the behavior of and interactions between various market participants.

    http://en.wikipedia.org/wiki/Adaptive_market_hypothesis
    http://opim.wharton.upenn.edu/~sok/papers/l/JPM2004.pdf
    http://papers.ssrn.com/sol3/papers.cfm?abstract_id=1977721