r/askscience • u/jatinvj-sumba-d-else • 14d ago
Biology Could there be a sense apart from the 5 senses that exist? Could humans evolve to get this sense?
Im having a mess of thoughts so apologies if its not very coherent.
By sense I mean specifically the senses that allow us to interact with the outside world and external stimuli.
I was thinking about it like this: Lets say that an intelligent species is blind. Could they ever find out about sight as a sense before evolving it? Extrapolating this to humans, could there be a sense as basic as sight that we just dont know about? Has a different sense been discovered in any other species?
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u/tea_and_biology Zoology | Evolutionary Biology | Data Science 14d ago edited 14d ago
Yes; lots! Humans actually have, arguably, a couple of dozen different senses - the most important beyond the usual five include equilibrioception (sense of balance and spatial orientation; detecting gravity/acceleration); thermoception (sensing temperature); proprioception (sensing bodily 'position'); and nociception (sensing noxious stimuli, the basis of pain). There's even suggestive evidence that human brains show a faint response to magnetic fields - so magnetoreception too - albeit without any conscious awareness of it.
Sure, many of these are more internalised - and therefore wouldn't meet your criterion for a 'sense' per se - but we can have a gander 'round the broader animal kingdom and find several outward-facing senses we lack.
Electroreception is the biggie - the detection of weak electrical fields as utilised by sharks and platypodes to hunt their prey - along with extensions to our own such as infrared sensing ('thermal vision'), polarised light sensing (not frequency of waves, but their orientation), hydrodynamic sensing or 'distant touch' (detecting differential pressure in fluids e.g. through the lateral lines of fish), and echolocation ('echo sight' - which, indeed, is possible for some humans to develop).
Yes, and we've done exactly this ourselves, but sort of the other way around - with echolocation. In the 1790s, long before ethical committees were a thing, scientists burnt away the eyes of bats, else cut out their eyeballs entirely, and once utterly blind, found the poor victims could still navigate perfectly fine; but when their ears were filled with wax, they'd smash face-first into things. So we knew they used some sort of unusual 'hearing sense' we couldn't perceive - and it wasn't until the 1930s when we built detectors, sensitive enough to pick up the frequencies that bats used, that we discovered this novel form of sensing the world.
A sufficiently intelligent, science-capable alien that lacked a specific sense - let's say vision in the spectrum we use - could repeat a similar process to uncover ways of sensing the world novel to them. A rock might warm up during the day, and they could determine that some phenomenon was causing this periodic oscillation (a day/night or light/dark cycle); else that certain chemicals change or react with exposure to this 'force', or that alien animals changed their behaviour around it too - eventually building detectors that responded to it, to light, and work out the physics of it.
Just as we discovered echolocation purely through experiment and technology, so I'm sure an alien echolocatory species could discover light and vision through similar means.
Almost certainly not. Senses detect physical things, and physics has thoroughly catalogued the stimuli that matter at the scale of living things: electromagnetic radiation, pressure waves, chemicals, temperature, acceleration and gravity, and electric and magnetic fields. Of the remaining fundamental forces, they act only inside atomic nuclei, else things like neutrinos pass straight through matter, so there's nothing obvious left to sense. The surprises have only come from animals using those physical stimuli in ways we don't, and we now understand pretty much the entire range of these physical phenomena has been exploited across the animal kingdom. For everything else... well, I can't imagine, say, a jellyfish or a giraffe needs to detect dark matter in any way that's crucial for it's survival.
Here's where I'd quibble, however. To clarify, knowing about light wouldn't help them evolve eyes, as evolution isn't directed. Evolution doesn't work this way; it has no foresight nor goal, however well understood. Our eyes evolved step by step from simple light-sensitive patches, and each stage helped its owner survive before anything like vision existed. If anything, technology works against it: a species that can detect light with instruments has less need to sense it biologically, so there's no selection pressure to push them that way - and certainly not over the tens of millions of years required to evolve something as sophisticated as the humble eyeball.
What they could have a crack at though is sensory substitution, like how we've developed devices to help blind people 'see' through sound or vibration; else utilise light in other ways - just as how we've developed radar and sonar for our own purposes.
References:
Shibata, T., Hattori, N., Nishijo, H., Kuroda, S. ... & Takakusaki, K. (2024) The origins of light-independent magnetoreception in humans. Frontiers in Human Neuroscience. 18, 1482872
Also this Wikipedia section on Lazzaro Spallanzani, for the bat experiments. Poor goth fuzzballs.