"Illusionary" Benefits

The size-weight illusion refers to our tendency to incorrectly perceive the weight of two objects of equal mass but different sizes. Even if we are aware of the equal weight of both objects, we tend to judge the larger object as lighter. An article (abstract) published in the journal Evolution and Human Behavior suggests that the illusion is functional:

Here we show that perception of heaviness (including the illusion) and perception of optimal objects for throwing are equivalent. Thus, the illusion is functional, not a misperception: optimal objects for throwing are picked as having a particular heaviness. The best heaviness is learned while acquiring throwing skill.

This immediately reminded me of another functional illusion: Robin Hanson's Homo Hypocritus hypothesis. Robin proposes that our big brains evolved in response to social pressures, specifically to bend rules in our favor. Self-deception is central to being perceived as honest, even when breaking or bending the rules:

In a messy real world, social norms expressed in language typically have many iffy boundary cases and ambiguities. How much of what sort of food of what quality offered how conveniently counts as food sharing? How big a frown is a grimace? Sex with how close a relative counts as incest? And so on. This wouldn’t matter if boundary cases were decided randomly, but that seems unlikely. Instead big brain gains come five ways:

Unnormed – coalition politics on acts uncovered by norms.
Skirt – keep actions near but not over edge of violating norms.
Cover – politics of observers on if to report an act to others.
Frame – lawyer-like arguing on if acts violate social norms.
Conspire – form coalitions on how to publicly interpet iffy acts.

Most norms have meta-norms against consciously trying to evade them. Self-deception should help here; foragers might sincerely believe they usually just do their job and “tell it like it is”, and then unconsciously try to act, selectively report and frame acts, and support interpretation coalitions, to their advantage. Instead of “man the tool user”, we might be better understood as “man the sly rule bender.”

The authors of the size-weight illusion article speculate that the advantage granted by the illusion may have helped us out-compete the Neanderthal:

The human ancestor with the larger brain was always the one to succeed and survive with the sole exception of Neanderthal, whose brain was actually larger than that of homo sapiens. Why did homo sapiens win out despite the smaller brain size? Evidence now reveals structural differences, namely, homo sapiens had relatively enlarged cerebellum and posterior parietal cortex as compared to Neanderthal. Perhaps our throwing abilities were the key.

I wonder, what other illusions have benefited us in our rise to biological dominance? And I wonder at the ultimate cost we may pay for allowing some of our illusions to run amok.