In Sue Burke’s Semiosis, humans reach an alien world with intelligent plants.

The settlers find themselves afflicted by inexplicable infertility.  Most women are able to bear children, but many men are sterile.  The settlement develops a culture in which women continue to marry based on the vagaries of affection, but from time to time, a woman will kiss her spouse goodnight before venturing off for an evening’s energetic tussle with a fertile man.

The human settlement has established itself at the base of a single plant.  This plant has ocular patches and can recognize individual humans.  The plant provides fruit that seems exquisitely tailored to each person’s nutritional needs.  In return, the humans carefully tend the plant – irrigating its groves, clearing away competitors, and fertilizing new growth.

The plant manipulates its human caretakers.  By tweaking the composition of their food, it controls the humans’ health.  Selectively instilling infertility or fecundity allows the plant to direct human evolution.  Among the fourth generation of human settlers, more than half of all children were sired by a placid man who was so contemplative and empathetic that he learned to communicate with the host plant.

The plant domesticated its human caretakers.

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Here on Earth, flowering plants also co-evolved with animals. 

Plants could very well consider themselves the dominant species in these relationships – after all, plants use animals to do their bidding.  Plants offer tiny drips of nectar to conscript insects to fertilize their flowers.  Plants offer small fruits to conscript mammals to spread their seeds.  And plants far outlive their servants – thousands of generations of animals might flit by during the lifetime of a single tree.

Some plants directed the evolution of their helpers so well that the species are inextricably linked – some insects feed on only a single species of plant, and the plant might rely on this single species of insect to fertilize its flowers.  If either the plant or insect disappeared, the other would go extinct.

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In Semiosis, the alien plant changes its attitude toward humans over the generations.  At first it was concerned only with control and utility.  The motile beasts were a tool that it could manipulate with pleasing colors and psychoactive fruits. 

Eventually, though, the plant develops an affection for its human wards.  Of course, these humans are markedly different from the people who first arrived on this planet.

The plant’s affections changed in the same way that our own attitude toward wolves softened as we manipulated the species.  Many humans are still reflexively afraid of wolves.  We tell children stories about Little Red Riding Hood; when I’m walking in the woods, sometimes I find myself humming the refrain from “Peter and the Wolf.”  The ecosystem of Yellowstone Park was devastated when we murdered all the wolves during the 1920s; willow and beaver populations have rebounded since wolves were reintroduced in the 1990s (most likely because wolves mitigate the damage done by uncontrolled elk populations); now that Yellowstone’s wolf population isn’t critically endangered, states surrounding the park are letting human hunters shoot wolves again.

And yet, we giggle at the antics of domesticated dogs.

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Among wild animals, the most aggressive individuals are often the most fecund.  Wolves who can fight for and hold the alpha rank get to breed; the others don’t.

During domestication, breeding patterns are altered.  To create dogs, we selected for the most docile individuals.  If you could expand your temporal horizons wide enough, all populations might seem as mutable as clay.  A species flows through time, ever changing, evolving such that the traits that best lead to viable children become more common.  In the wild, a speedy rabbit might have the most children, because it might survive for more breeding seasons than others.  On a farm, the most docile rabbit might have the most children, because its human handlers might give a docile male more time among the females.

Domestication seems to change animals in stereotyped ways.  Zoologist Dmitry Belyayev designed an experiment with wild foxes.  Only the foxes that were least fearful of humans were allowed to breed; over the course of some dozen generations, this single criterion resulted in a large number of behavioral and morphological changes.  The domesticated foxes produce less adrenaline; they have narrower faces; they have floppier ears.  This suite of traits seems to be present in almost all domesticated species.

Cats still have pointy ears.  As it happens, cats are barely domesticated.

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Humans seem to be self-domesticated. A few hundred thousand years ago, our ancestors lived in very small groups, maybe one or two dozen individuals.  After humans diverged from the last common ancestor that we shared with bonobos and chimpanzees, most human species still lived in groups of about this size.  Neanderthals may have lived in groups as small as six.

Eventually, Homo sapiens drove all other human species to extinction.  A major competitive advantage was that Homo sapiens lived and worked in groups as large as a hundred.  With so many people cooperating, they could hunt much more efficiently.  A violent conflict between six Neanderthals and a clan of a hundred Homo sapiens would not go well for the Neanderthals.

In the modern world, the population densities of urban areas force humans to be even more docile than our recent ancestors.  But even with our whole evolutionary history promoting cooperation, many people struggle to be calm and kind within the crowded confines of a city.  Some can do it; others feel too aggressive.

When a person’s disposition is ill-suited to the strange environment we’ve made, we punish.  We shunt people to high school detention, or jail.

In Semiosis, the plant overlord reacts by limiting fertility.

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As in Richard Powers’s Overstory, the perspective of a long-lived, immobile plant would be markedly different from ours.  Human generations flit by as a plant continues to grow.

Domestication takes generations – in Belyayev’s fox experiment, twenty generations passed before a third of the population was tame – but an intelligent plant could wait.  By selecting which individuals get to pass on their genes, huge changes can be made.  From wolves, we created Great Danes and Chihuahuas.  From a scruffy grass we evoked buxom ears of corn, as though by glacial magic.

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In particularly dark eras of our past, humans have tried to direct our own evolution.  Social Darwinists in the United States forcibly sterilized people whom they disliked.  Politicians in Nazi Germany copied the legal language of the United States when they sought philosophical justification for the murder of entire religious and ethnic groups.

By putting the motivation inside the mind of a plant, Burke is able to explore the ramifications of directed human evolution without alluding to these evil regimes.

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In jail, somebody said to me, “I heard that humans were evolving to have really long fingers, so we could type real fast, and big-headed hairless bodies.”

“Yeah, yeah,” somebody added, “I saw this thing on the Discovery channel, it was like, you know the way they show all those aliens on the X-Files?  That humans were gonna be like that, like the aliens were just us coming back to visit from the future.”

I murmured in disagreement. 

“Humans are definitely still evolving.  But evolution doesn’t have a goal.  It just selects for whichever properties of a creature are best for making copies of itself.”

“With modern medical care, we don’t die so easily.  So the main driver of evolution is the number of kids you have.  If you have more kids than I do, then you’re more fit than I am.  Future humans will look more like you than me.”

“There’s not much data yet, because evolution happens over such a long time, but the one study I’ve seen recently showed that humans in the United States are evolving to be shorter.”

“But it’s not like we’re getting shorter so that we’ll fit better inside spaceships.  It’s just that shorter people have been having more kids.”

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Plants have directed the evolution of bees.  Of bats – there’s a bat species that fertilizes agave, another that fertilizes mangoes, and so on. 

Plants directed our evolution, too.  We owe our color vision to our history as fruit eaters – we needed to see the difference between ripe reds and green buds.

And, like all populations, we are changing.  Evolution isn’t done.

What might a clever plant want us to become?