The common consensus is that bacteria are not conscious. But some bacteria are attracted to, or repulsed by light. What, then, is being attracted or repulsed?
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Let’s start with an easier example – photosensitivity in plants, I don’t think anyone would argue that a plant is sentient, yet how do they “know” where light is and how to grow towards it?
What basically happens is plants produce new cells for growth and the mechanism that controls the rate of growth is deactivated by light. So ironically the side of a plant that is exposed to the most like grows *the least*, meaning the dark parts grow more causing a bending motion *towards the light*. No self-awareness or consciousness is required, it’s just a chemical reaction.
Bacteria operate in a similar way. They have various “sensors” in their bodies that can sense things like light, heat, acidity, etc. Those “sensors” are essentially spring loaded, tightly packed molecules. Should light “spring the trap” the molecule unravels, changing it’s physical size causing a “push” or “bulge” of the cell either towards, or away from, the stimulus. The actual process is much more complicated but that’s the general gist while also showing how it’s a “dumb” reaction and not a something that involves “thought” or “planning”.
They’re more like machines.
I can make a little robotic car with a light sensor that stops and reverses when it detects light, or tries to turn to face a bright source of light. That is behavior, but does not require consciousness.
In this case, the bacteria have cell structures that change size or shape when exposed to light. Those changes in size or shape cause the bacteria to change how it’s moving. But the bacteria isn’t “thinking” or “making decisions”. It’s just a pile of biological machinery that’s designed to react the same way every time to stimulus.
There’s not an easy definition for what makes a creature “conscious”, but in this case we can say a conscious creature might realize sometimes there is a reason to stay in bright light even if the bacteria would normally avoid it. These bacteria will never behave that way, thus we do not think they’re conscious.
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