In last month's blog, I provided a simple story of (man)spreading on the subway. If two individuals—Taylor and Ari—have differently sized ‘bubbles’ of personal space, they may well end up taking vastly different amounts of personal space while sitting next to each other on a crowded subway train. Ari, whose personal space bubble is bigger, requires more of a buffer zone between their body and others’ bodies. Taylor might have a smaller bubble, and thus might subtly shift towards others’ bodies without even noticing what they are doing. In this way, Taylor might ‘spread’ into a more expansive, relaxed position, even as Ari shifts further and further into a compressed, squeezed position.

This doesn’t mean that Ari—who compresses their body to take up less space—is being more ‘demanding’ in their personal space requirements, and Taylor is being less ‘demanding.’ There is a bigger story to tell about the nature of personal space. It is a fundamentally protective zone around the body. Its representation in the brain helps modulate defensive, instinctive behaviors like cringes and startles. And this personal space ‘bubble’ in humans is sensitive to anxiety and perceived power differentials between people. All of this can help us understand what happens on the subway when people start to spread.

Let’s get into some details. We will start with a little bit of monkey neuroscience.

In the brain of a macaque, researchers like Michael Graziano have found clusters of neurons responsible for monitoring a volume of space that extends beyond the monkey's skin (and fur), and into the airspace around the monkey. These neurons respond to things touching the monkey, but also to things that the monkey sees or hears in the airspace around its body. Giacomo Rizzolatti, working in the 1980s, called these neurons “peripersonal” neurons—hence the modern term “peripersonal space” for the bubble of space that they monitor and represent.

In Graziano's engaging and illuminating retelling of his (and others’) discoveries about personal space, something surprising comes up. Graziano and company realized that the monkey’s peripersonal neurons wouldn’t respond to just anything in the personal space bubble around the monkey. Instead, they would respond to threats more than attractive objects—e.g. plastic snakes, rather than plastic apples. This discovery made sense of another fact about this same area of the macaque brain: it helps to produce involuntarily movements that protect the body, like the famous startle reflex. This evolutionarily ancient defensive motion involves squeezing the eyes shut and contracting your body into a smaller target. (See, e.g., these slo-mo scare reactions.)

Peripersonal neurons have been studied less directly in the human brain, partly for ethical reasons involving invasive brain surgery. But the human brain and the macaque brain are similar, and studies of peripersonal space in humans confirm its defensive function. This protective personal space is well known to shrink when you’re relaxed and grow when you’re anxious (in ways that interact with crowding). You want more room around you when people of authority or greater status are around you. Several studies find that women’s personal space bubbles are particularly large around men in ways that interact with other social features like status.

The most important point here for our purposes is that peripersonal space is specifically a zone of protection. There are other networks in the brain that represent space in other ways. In Chapter 9 of her recent book Mind the Body, the philosopher Frédérique de Vignemont convincingly argues that each of us has two kinds of bodily space representations: not only the “protective body map” that Graziano and company have studied, but also a “working body map” that helps you plan movements like reaching for things and using tools. (It’s your protective body map, she adds, that grounds your sense of body ownership—what you experience as yours—but we don’t need to agree with that for the purposes of our story here.)

Let’s return to Ari and Taylor. Now that we understand that peripersonal space is a protective space that monitors threats and modulates often involuntary defensive behavior, we can see that it wouldn’t reflect badly on Ari to say that Ari has a bigger personal space bubble. Instead, what it would suggest is that Ari is more anxious, or Ari’s brain represents more things as threatening, or Ari’s awareness of social inequities extends their bubble to make this protective zone bigger. Put another way: Taylor may enjoy the lack of anxiety, the lack of a feeling of threat, or the comfort of knowing that they are in a position of relative social power.

These are the kinds of factors that the neuroscience suggests may contribute to the shrinking and expanding of peripersonal space as a protective zone. And these factors are ripe for intersectional and systemic analysis. My simple but speculative story doesn’t crowd out crucial contributions of sociologists, ethicists, and feminists—both in and outside of the academy. On the contrary, it opens up space to show exactly why intersectional and systemic approaches are necessary here.

For instance, we might ask: why might women in particular see men’s presence and gestures as threatening in public spaces? Perhaps it has to do with sexual assault and harassment on the subway and in other crowded spaces. Perhaps it has to do with systematic discounting of women’s testimony about being harassed or assaulted. Perhaps it has to do with the stigma and shame that women unfairly face when we are touched in ways that we do not ask for or allow. And all of these factors are modulated, and often exacerbated, by intersectional factors like race.

So there’s a simple story of spreading for you. It starts with simple resources: just two people on a train with different ‘preferences’ for personal space. But it leads us to a new understanding of the ways that even everyday gestures can trigger structural and systematic inequities.

One last word before you go: none of this excuses egregious spreaders—whether manspreaders or not. If you aren’t personally uncomfortable on crowded subways, it’s still on you to make sure you’re not making others uncomfortable. Pay attention to the body language of those around you. Spread the space around. I know that your fellow subway riders will appreciate it.