I imagine that very few species would consider not having to worry about leopard attacks a bad thing. The enthusiasm for any story claiming that human beings continue to being driven upwards and onwards by natural selection suggests that we pine for those halcyon days of yore when being eaten alive by jungle cats was a major source of morbidity[1]. We worry about a lack of selection for things like good eye-sight and gobble up cheap, pop evolutionary psychology[2] stories of adaptive behavior.

We really want to know are human beings still evolving and how can reclaim the benefits of natural selection without feeding our offspring to leopards?

Unless a species is extinct (e.g., T. rex) or does not reproduce (e.g., Europeans), it is evolving. Natural selection – the process that drives populations toward becoming better adapted to their surroundings – is not necessarily the driving force for all species. Evolution is the change in frequency of alleles (different versions of the same gene) over time (zero change is still a rate of change).

Two key factors that determine the importance of natural selection in shaping the evolutionary fate of a species are effective population size and the intensity of selection (note about this being the same as large effect sizes). In small groups, chance effects can dominate directional effects like natural selection, in the same way that 10 coin tosses is more likely to significantly deviate from the 50% heads:50% tails expectation than 1000 tosses.

The effective population size is inversely proportional to the intensity of selection required for natural selection to dominate the evolutionary dynamics. Small populations require more intense selection for natural selection to take charge than do small populations.

Unfortunately, the effective population size of humanity does not appear to be particularly large (~10000), especially relative to the actual population size (~7000000000). At the same time, culture reduces selective pressures from the external environment[3] (e.g., the odds of me being ambushed by a leopard while writing this are almost zero). So, how do the advanced human societies of science fiction get to be societies of advanced humans?

You could try to increase the effective population size by bringing cultural practices in line with the assumptions of Hardy-Weinberg Equilibrium, which boils down to random mating[4]. While some will argue that we humans are not emotionally set up for terminal monogamy, it is pretty clear that we are also not equipped for truly random mate selection.

Alternatively, you might try using your culture to create more intense selection pressure. How do you create an environment that amplifies the fitness impact of genetic variation without denying yourself the benefits of an advanced society, like videophones, the end of disease, and jet packs?

The set designers of science fiction films seem to have embraced this second option and come up with an elegant solution: Get rid of railings.

Many science fiction sets are already designed like a Prince of Persia level. Really, is there any point to having super-strong, super-agile folks with Jedi powers running around your set if your environment is not set-up for jumping ridiculously from one platform to another?

Sure, removing railings makes things look cool and cleans up sight lines for the cameras, but how it amplify the fitness impact of genetic variation?

What happens when you stumble on a balcony?

Assuming, for the moment, that you are not wandering around Delroy Lindo‘s balcony at the end of Get Shorty, you bang into a railing, look really embarrassed, thank your favorite deity for stainless steel screws, and maybe get a bruise or two.

Without railings, you plunge to your DOOM! Or, at least, your painful maiming.

Railings minimize the fitness impact of genetic variation that makes someone slightly more likely to stumble. Without railings, those little missteps zero out one’s fitness at 9.8m/s2. Such an environment would intensify selection for individuals with exceptional balance, core body strength, and situational awareness – essentially gymnasts without the stunted growth.

But, do highly advanced groups really litter their architecture with inadequate safety measures? Let’s take a look:

Just look at one of greatest engineering feat of popular science fiction, the Death Star. Apparently, one of the numerous advantages of running a fascist, tyrannical Empire is undoubtedly being able to bypass building safety codes at will. The Death Star is lousy with bottomless pits, but almost no railings.

As the execrable prequels suggest, stormtroopers are all clones of Boba Fett[5]. This means that the variability between stormtroopers will be very small (due only to environmental variation or spontaneous mutation). Distinguishing between the most fit and least fit clone will require incredibly intense selection.

The Death Star’s architecture may be a strategy for identifying the Empire’s “best” soldiers.

Personally, I have small children. I am a big fan of railings. We maybe able to reclaim the benefits of efficient natural selection without feeding our offspring to leopards, but at the cost of having them tumble off precipices left and right. Maybe humanity is cool enough as it is. Yeah, probably not worth it, unless there are jet packs.

Oh, who am I kidding? As any fan of good science fiction knows, the future is going to be a dystopian hell hole anyway. Have at it.

The title is a play off defenestration. In Latin, de- means “out of” and fenestra means “window”. Thus, defenestration is to throw something out of a window. The Latin for “railings” is cancelli.

  1. In the business, we refer to this dilemma as the “leopard problem”.
  2. I refer to the unsophisticated use by self-help writers or those with an ideological axe to grind, rather than the rigorous investigation of an interesting academic field, which while worthy of criticism is not worthy of mockery.
  3. It may, however, increase other selective pressures, such as disease risk.
  4. Which is not exactly the same as advocating Roman orgies or Stranger in a Strange Land free love. Maintenance of selective pressure for altruism by males may be best supported by avoiding situations of uncertain paternity.
  5. Technically, they are clones of Boba’s “dad”, but, since Boba is a clone of his “dad”, the transitive rule of clones can be applied.

Author: Josh Witten

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