Scientists have a hard time deciding what Homo Futurus might look like. Will our evolutionary descendants resemble us, only with uniformly brownish skin, no pinky toes, and better resistance to disease? Will they be cyborgs, with robot limbs and A.I. brains, as futurists predict? Or, as many biologists stubbornly argue, will they be disappointingly similar to us?

It’s hard to say: Part of the reason we’ve struggled to predict how, and whether Homo sapiens will evolve, is because our definitions of evolution and speciation have become maddeningly vague. Are we talking about Darwinian evolution and its patient engine, natural selection? Are we simply using “evolution” as a stand-in term for genetic or phenotypic flux? What does it mean to be a member of a species, anyway? Fruitful discussions can only start if we are all on the same page. Here’s a guide to talking about what’s next for our species.

Darwinian Evolution

Darwin’s OG brand of evolution is an explanation for how different species came to be. It’s driven by the process of natural selection, a method of accumulating genes that takes place over many generations. Evolution and natural selection are, somewhat confusingly, not the same thing.

Most of the time, when articles claim humans are “evolving,” in the Darwinian sense, what they really mean is that the process of natural selection is still at work. There’s plenty of evidence that this is happening — for example, a recent study in Science reports that genes for fair skin and blue eyes have become more prevalent among British people in the past 2,000 years — but to say such changes are leading to a new species is a stretch. As far as we can tell, the blue-eyed, light-skinned Brits of the world are still human beings.

Darwin’s ideas about evolution don’t lend themselves well to futurist discussions about the cyborgian future of our species because he strictly defines traits as heritable, meaning a parent can pass them onto their kids through their genes. Cyborg humans will probably be able to procreate, but there’s no way their robot qualities — whether they be artificial intelligence, bionic limbs, or “smart” cells — can be inherited, unless CRISPR gets involved.

According to Darwin, the theory of evolution explains how species come to be, and natural selection is the process that drives it.
According to Darwin, the theory of evolution explains how species come to be, and natural selection is the process that drives it.

Natural Selection

At any given point in human history, some individuals, carrying naturally occurring mutations — essentially genetic mistakes — in their DNA, have better chances of surviving and making babies than others. That’s not to say there are any “good” or “bad” genes — that all depends on what the environment requires. Take, for example, the finding that genes for lactose tolerance has become more prevalent in Northern European populations over the past 8,000 years. This suggests that this trait somehow made those people more likely to survive — and therefore, able to pass on those dairy-permissive genes to the next generation.

Still, lactose intolerance is a common human trait. Selection doesn’t inevitably lead to the emergence of uniform traits. This is important to remember as technologies and the availability of food and shelter make pressures less effective at eliminating or privileging genetic variance.

Unnatural Selection

Darwin was compelled by the emergence of genetic patterns based on environmental pressures. This is how natural selection leads to evolution in the wild. But we now live in an age when we can actively choose to alter the genetics of our offspring, or even ourselves, using cutting edge technologies or data. (For instance, Ashkenazi Jews use a database to avoid passing along the DNA associated with the genetic neurological disease Tay-Sachs.) Humans can interrupt with genetic change or predetermine what traits will be passed on. As such, humans now exert a pressure on the evolutionary process that is independent — at least in part — from natural pressures.

Wetware, technologies that can be incorporated into the human body, won’t evolve through this process, but it might play a role in shaping how Homo sapiens adapt to their environment. Just as the genes that made early humans smart enough to avoid lions and bears, survived, pre-engineered and installed instincts could help humans thrive in a cyborg age.

Macroevolution and Microevolution

Hairier discussions about human evolution often lead to some nitpicking about macroevolution and microevolution. In a nutshell: The former refers to the rise and fall of individual species, while the latter refers to the minor genetic changes that take place within a species, without any major effects on their ability to have offspring.

It's not exactly accurate to call cyborgs the next step in human evolution.
It's not exactly accurate to call cyborgs the next step in human evolution.

Speciation

There is only one surefire way to tell if you are face-to-face with a different species: Have sex with it, and if you manage to make a baby, wait and see whether your babies can make babies. The biological definition of a species is, broadly, a population of individuals that can mate and make fertile offspring (although in some circles, even this is up for debate. Let’s make one thing clear now: Robot-human hybrids aren’t going to constitute a new species of human under this definition.

Though natural selection still seems to be happening, the changes that are taking place in the human gene pool are mostly minor ones — increases in cigarette smoke tolerance and later menstrual periods, to name a few — and are unlikely to result in a subset of humans that’s genetically so drastically different from us that we can no longer procreate with them.

And if you want to talk about genetic differences leading to different “races” of humans, science would politely suggest that you don’t: Biologists largely agree that race is a social construct, and suggesting interracial mating is anything akin to cross-species reproduction just makes you kind of a jerk.

Yasmin is a writer and former biologist living in New York. A Toronto girl at heart, her writing also appears in The Last Magazine and SciArt in America. You might recognize her as a past host of Scientific American's YouTube series.