Is recognizing faces all that special?

I've seen some headlines recently saying that fish can be taught to recognize human faces.  It's not clear why these would be circulating now, since the original paper appeared in 2016, but it's supposed to be newsworthy because fish weren't thought to have the neural structures needed to recognize faces.  In particular, they lack a neocortex (particularly the fusiform gyrus), or anything clearly analogous to it, which is what humans and primates use in recognizing faces.  Neither do the fish in question normally interact with humans, unlike, say, dogs, which might be expected to have developed an innate ability to recognize people.

The main thesis of the paper appears to be that there's nothing particularly special about recognizing faces.  As a compugeek, I'd say that the human brain is optimized for recognizing faces, but that doesn't mean that a more general approach can't work.  It makes sense that we'd have special machinery for faces.  Recognizing human faces is important to humans, though it's worth pointing out that there are plenty of people who don't seem to have this optimization (the technical term is prosopagnosia).

The authors of the paper also point out that recognizing faces is tricky:

[F]aces share the same basic components and individuals must be discriminated based on subtle differences in features or spatial relationships.

To be sure that the fish are performing the same recognition task we do, though presumably through different means, the experimental setup uses the same skin tone in all the images and crops them to a uniform oval.  Frankly, I found it hard to pick out the differences in what was left, but my facial recognition seems to be weaker than average in real life as well.

This is interesting work and the methodology seems solid, but should we really be surprised?  Yes, recognizing faces is tricky, but so is picking out a potential predator or prey, particularly if it's trying not to be found.

The archerfish used in the experiments normally provide for themselves by spitting jets of water at flies and small animals, then collecting them when they fall.  This means seeing the prey through the distortion of the air/water boundary, contracting various muscles at just the right rate and time, and finding the fallen prey.  For bonus points, don't waste energy shooting down dead leaves and such.

Doing all that requires the type of neural computation that seems easy until you actually try to duplicate it.  Did I mention that archerfish have a range on the order of meters, a dozen or so times their body length? It's not clear why recognizing faces should be particularly hard by comparison.

Computer neural networks can recognize faces using far fewer neurons than a fish has (Wikipedia says an adult zebrafish has around 10 million).  Granted, the fish has other things it needs to do with those neurons, and you can't necessarily compare virtual neurons directly to real ones, but virtual neurons are pretty simple -- they basically add a bunch of numbers, each multiplied by a "weight", and fiddle the result slightly.  Real neurons do much the same thing with electrical signals, hence the name "neural network".

It doesn't seem like recognizing shapes as complex as human faces should require a huge number of neurons.  The question, rather, is what kinds of brains are flexible enough to repurpose their shape recognition to an arbitrary task like figuring out which image of a face to spit at in order to get a tasty treat.

Again, is it surprising that a variety of different brains should have that kind of flexibility?  Being able to recognize new types of shape in the wild has pretty clear adaptive value, as does having flexible brain wiring in general.  Arguably the surprise would be finding an animal that relies strongly on its visual system that couldn't learn to recognize subtle differences in arbitrary shapes.

And yet, this kind of result does seem counterintuitive to many, and I'd include myself if I hadn't already seen similar results.  Intuitively we believe that some things take a more powerful kind of intelligence than others.  Playing chess or computing the derivative of a function is hard.  Walking is easy.

We also have a natural understanding of what kinds of intelligence are particularly human.  We naturally want to draw a clear line between our sort of intelligence and everyone else's.  Clearly those uniquely human abilities must require some higher form of intelligence.  Language with features like pronouns, tenses and subordinate clauses seems unique to us (though there's a lot we don't know about communication in other species), so it must be very high level.  Likewise for whatever we want to call the kind of planning and coordination needed to, say, build a house.

Recognizing each other's faces is a very human thing to do -- notwithstanding that several other kinds of animal seem perfectly capable of it -- so it must require some higher level of intelligence as well.

Now, to be clear, I'm quite sure that there is a constellation of features that, taken together, is unique and mostly universal to humanity, even if we share a number of particular features in that constellation with other species.  No one else we're aware of produces the kind of artifacts we do ... jelly donuts, jet skis, jackhammers, jugs, jujubes, jazz ...  or forms quite the same kind of social structures, or any of a number of other things.

However, that doesn't mean that these things are particularly complex or special.  We're also much less hairy than other primates, but near-hairlessness isn't a complex trait.  Our feet (and much of the rest of our bodies) are specialized for standing up, but that doesn't seem particularly different from specializing to swing through trees, or gallop, or hop like a kangaroo, or whatever else.

Our intuitions about what kind of intelligence is complex, or "of a higher order" are just not very reliable.  Playing chess is not particularly complicated.  It just requires bashing out lots and lots of different possible moves.  Calculating derivatives from a general formula is easy.  Walking, on the other hand, is fiendishly hard.  Language is ... interesting ... but many of the features of language, particularly stringing together combinations of distinct elements in sequence, are quite simple.

What do I mean by "simple" here?  I mean one of two more or less equivalent things: How hard is it to describe accurately, and how hard is it to build something to perform the task.  In other words, how hard is it to objectively model something, in the sense that you'll get the same result no matter who or what is following the instructions.

This is not necessarily the same question as how complex a brain do you need in order to perform the task, but this is partly because brains have developed in response to particular features of their environment.  Playing chess or taking the derivative of a polynomial shouldn't take a lot of neurons in principle, but it's hard for us because we don't have any neurons hardwired for those tasks.  Instead we have to use the less-hardwired parts of our brain pull together pieces that originally arose for different purposes.

Recognizing faces seems like something that requires a modest amount of machinery of the type that most visually-oriented animals should have available, and probably available in a form that can be adapted to the task, even if recognizing human faces isn't something the animal would normally have to do.  Cataloging what sorts of animals do it well seems interesting and ultimately useful in helping us understand our own brains, but we shouldn't be surprised if that catalog turns out to be fairly large.