What’s in a newborn brain? It’s a question we’re obsessed with, because its answers seem to promise us basic truths about what we humans are as a species before our culture muddies the waters. A paper in Nature Neuroscience this week shows that monkeys raised without exposure to faces don’t develop specialized face-recognition domains in their brains. The results help to explain our own brains a little better, and the research also sketches an idea of how environmental input might lead to specialized brain circuitry over time.

Face recognition is something that seems to be profoundly central to us as a social species. Adult human brains have circuitry dedicated to processing faces, and even very young babies seem to look at faces more than at other objects in their environment (although these results are debated by researchers in the field). Other primates also preferentially look at faces and have dedicated brain circuitry to handle it.

As an incredibly social species, are we born with the concept of “face” somewhere in our brains, enabling us to latch on to this all-important part of our environment as soon as we’re out in the world? Some researchers think that this is the best explanation of infants’ preference for looking at faces. Others think it’s more likely that we develop the concept of what a face is over time, based on our experience of the world.

Face-free macaques

To understand how development affects facial recognition in the brain, Michael J. Arcaro, a neurobiologist at Harvard Medical School, led a team of researchers who raised three baby monkeys with no exposure to faces. Obviously, this is a wildly abnormal environment for macaques, which are normally social, so the researchers tried to ensure that their lives were as normal as possible otherwise. They played with them every day to help with socialization (wearing welding masks to hide their faces) and made sure the monkeys had interactive toys, soft things to cuddle, and the smell and sound of other monkeys nearby.

Starting when the monkeys were three months old, the researchers started comparing their development to four control monkeys who had been raised normally. In fMRI scans, the control monkeys showed developmentally normal patterns: they had more brain activation when looking at images of faces than at other objects. The deprived monkeys, on the other hand, showed no differences when they were looking at faces and other objects.

To see whether their visual development in general was affected, the researchers also explored whether the deprived monkeys were developing other specialized visual recognition domains. Reasoning that these monkeys saw their own hands and the researchers’ hands a lot of the time, they looked at whether the face-deprived monkeys showed greater activation when looking at hands compared to other objects. They did, suggesting that they were developing a hand recognition domain. The deficit, the researchers write, was “face-specific.”

Finally, Arcaro and his colleagues used gaze-tracking equipment to explore what the monkeys were looking at most in a series of pictures. For everyday objects like hammers or clothespins, there was no difference. But when the images included faces, the control monkeys focused on them intently, while the deprived monkeys’ gaze was more scattered around the image. Conversely, the face-deprived monkeys looked much more at hands.

So we’re not born with face recognition?

The results suggest that experience with faces is essential for normal face recognition to develop—it’s not already in place by the time the monkeys are born. Past research has shown that monkeys develop similar specializations for anything that they have intensive, early experience with. Arcaro and his colleagues suggest that the results could help to explain how it is that specialized visual domains develop: if something appears a lot in the environment, babies look at it; the neurons that interpret those stimuli get a workout; and eventually a domain is formed.

The results, write Arcaro and his colleagues, suggest that “face looking by infants is not innate.” A simpler explanation, they suggest, is that newborns have something much more basic in their brains: a perceptual bias for a particular set of shapes and a bias to look at moving things. Put those biases in an environment with a lot of faces, and face recognition emerges.

This is not the last word on the topic, and plenty of researchers will disagree on how to interpret the findings. For instance, it’s possible that the infant monkeys were born with some kind of robust preference for looking at faces, but depriving them of faces caused these structures to wither. More research with very young human and primate infants could help with this question.

There’s a risk, when talking about innateness, of using it as a sharp dividing line between “nature” and “nurture.” If something is there when we’re born, we seem to think it’s immutable, part of our essential nature. If it happens afterward, we chalk it up to nurture and therefore think of it as malleable or less central to us as a species.

Reality is so much more complicated than these sorts of binary shortcuts. We’re born not able to walk, or talk, or eat solid food, but walking, language and eating are still clearly part of natural human development (barring disability). And we’re born with the beginnings of awareness of our native language, having heard it from the womb; but Spanish, or Igbo, are not remotely universal parts of human nature.

So face recognition might still be a normal, core part of humans and other primates. But this evidence suggests that the template for what a "face" is and the preference for looking at faces require exposure to a normal environment before they develop properly. And, intriguingly, it suggests a mechanism for how that might work.

Nature Neuroscience, 2017. DOI: 10.1038/nn.4635 (About DOIs).