两个身材相似的陌生人，阿里和泰勒，上了一辆拥挤的地铁。他们坐在最后两个相邻的空位上。一开始，它们占据了相同的空间。然而，30分钟后，情况就大不一样了。阿里很紧，很克制，他们交叉着腿，耸起肩膀，肘部紧贴着。另一方面，泰勒性格开朗、放松，将手肘、肩膀和膝盖伸开。

This is a story about spreading out on the subway, and what we need to understand to explain it.

The phenomenon of taking up too much room on the subway as aman在过去几年里以"大爷式占座"的名号引起了很多关注The OEDchronicled a huge rise在2014年11月至12月期间使用了“男子蔓延”一词。New York City’s MTA started postingnoticesof subway etiquette reading “Dude… stop the spread. It’s a space issue.” Particularly egregious spreaders areshamed on social media. Academic analysts like Emma Jane use the public discussion of manspreading totake the pulse of contemporary feminism online.

But why does this spreading happen? And what does it have to do with men in particular?

Easily Googleable answers oftenstartwith the fact that the spreaders are often men to explain the spread: men feelentitled; men areless comfortable in narrow positions; or men seemproportionately more attractivethan women do when spreading out in expansive poses.

这可能都是事实。但我们实际上不需要假设任何花哨的东西来解释基本的扩张和挤压现象。

I’m going to offer a different kind of explanatory story, one which starts with minimal explanatory resources. It’s a story that doesn’tbeginwith the fact that it’s mostly men who spread, but ultimately offers a way to explain为什么men spread more. The speculative story I offer will open space for more systematic, intersectional analyses of the (man)spreading phenomenon.

Start with something simple: preferences for personal space.

How will two people divide a squeezed space between them? If they’re the same size, and they havethe same preferences for personal space, they may split the space evenly.

Roughly speaking, we can specify a person’s preferences for personal space in terms of a 3D buffer zone around their body that they prefer to keep empty. If this zone is evenly spread out around the body, we can imagine it as an invisible bubble of space with a human-like shape. (To a very unscientific approximation: this invisible space is shaped more likethisthan likethis.)

Now here’s the simple move that explains Taylor’s spread and Ari’s contraction: assume that Ari and Taylor havedifferentlysized个人空间泡沫。If Ari has abigger当他们共享一个有限的空间时，他们会以完全不同的方式分配空间。Because Ari wants more space between them and other things, Ari will end up taking upless space而不是泰勒所做的，以最大化它们与其他事物之间的距离——尤其是泰勒。

Here’s how we can use this to explain spreading and squeezing behavior. When Ari and Taylor first sit down on a crowded train, Taylor is more likely to be in Ari’s personal space bubble than vice versa. Ari might thus shift slightlyaway从泰勒那里恢复他们的私人空间泡沫。Then, either in the natural shift of subway motionorin virtue of intentional readjustment, Taylor might shift their body too. Taylor is likely to move closer to Ari than Ari would prefer, because Taylor’s personal space bubble is smaller—that is, Taylor is cool with being closer to things (including Ari) than Ari is.

But each time Taylor drifts towards Ari, Taylor might intrude again into Ari’s personal space bubble, before Ari ever intrudes into Taylor’s. Each timethat我们认为阿里会再次撤回。如果这种情况持续足够长时间，阿里和泰勒可能会达到一个自然极限，在那里阿里不能再挤了，而泰勒舒服地被拉伸到阿里的自我收缩打开的额外空间。

这是一个关于传播的简单故事。But it might seemtoosimple—too simple, that is, to explain the microaggression that is themanspread. Saying that Ari and Taylor have different preferences in this hypothetical case can seem reductive of all the systemic forces that contribute to the manspread as it happens in the complicated real world.

One particular worry goes like this: if men who spread into women’s personal space do so just because they have ‘less demanding’ preferences, doesn’t that put the burden on women to be ‘less demanding’ in their own preferences for personal space?

I don’t think it does. To understand why not, we need to understand more about the nature of personal space involved. We need to understand that it is fundamentally aprotectivespace, encoded in primitive pathways of the brain. And we also need to see that this protective space primarily functions to link intrusions into this bubble withinvoluntary defensive movementslike cringes and startles. Getting into this story will let us link this simple analysis with a broader understanding of the systemic forces that contribute to microaggressions like the (man)spread.

Tune in forPart II为了听一听小猴子的大脑如何解释你在拥挤的地铁上的情况。