For close to three minutes, this huge herd of deer can be seen lining up in orderly fashion to bound calmly and gracefully over a fence, one by one. Then, out of nowhere, the deer turn tail and jump back over the fence, en masse. What the hell, deer? WHAT DO YOU KNOW THAT WE DON'T?

The video provides a good example of a phenomenon sometimes referred to as "escape panic." In a 1971 article titled "Geometry for the Selfish Herd," evolutionary biologist and theorist W.D. Hamilton hypothesized that the herd behavior like that seen in the video up top is, in fact, an emergent feature of each individual acting selfishly to preserve its own livelihood, as opposed to "an unselfish concern for the welfare of the whole group." The tendency to copy one's neighbor or congregate around a single exit point, for example, are behavioral patterns seen throughout the animal kingdom. Deer do it, fish do it, bats do it. Even humans do it. From a 2000 study on the nature of escape panic in humans, published in Nature:

One of the most disastrous forms of collective human behaviour is the kind of crowd stampede induced by panic, often leading to fatalities as people are crushed or trampled. Sometimes this behaviour is triggered in life-threatening situations such as fires in crowded buildings; at other times, stampedes can arise from the rush for seats or seemingly without causes.

That study was led by Hungarian physicist Tamás Vicsek, a pioneer in the scientific investigation of swarms. And here's what's interesting: the more Vicsek and others learn about the science of animals (or plants, or cells) in groups, the more evidence they find that these behaviors are governed by simple sets of rules – but as Ed Yong explains in a recent feature over at Wired, different animals often follow very different rules. Swarm dynamics in locusts, for example, are thought to be dictated by cannibalism, whereas starling swarms (called "murmurations") emerge when the birds mimic the speed and direction of their immediate neighbors.