Question: is it possible for humans to evolve to be able to photosynthesize?

Kevin Arbuckle answered on 18 Mar 2014:

For some reason or another, animals seem to find it really difficult (maybe even impossible) to evolve photosynthesis. This is because even in plants the bits that do the photosynthesising (called chloroplasts) were not originally plants! They were little photosynthetic single-celled organisms, similar to bacteria, that ancestral plants took into their cells and made use of their metabolism to work together. The plants got a ready supply of food, and the ancestral chloroplasts got a nice, stable home. This is called ‘symbiosis’, and the same actually happened in animals. Our cells have energy ‘factories’ called mitochondria which were also taken from a (different) single-celled organism in a similar way.

So photosynthesis is pretty difficult and only seems to happen in bacteria-like organisms (and plants which have ‘stolen’ these organisms). Interestingly, some animals also manage to provide a home for photosynthetic single-cell organisms, though not as ‘intimate’ as in plants. This means that you do get some animals that are kind of photosynthetic, including corals and even a salamander, but these are very rare and it seems unlikely that the same will happen with humans.