system
Given the following post, respond as if you're commenting on Reddit:
human
Have most fruits that we eat today always been sweet?

It's been a while since I've taken a biology course, so sorry if I don't explain this very well.

Have the fruits that we eat today always been sweet, or was there once a mutation that was favored by natural selection since fruits that are eaten more by animals have a higher chance of reproducing due to seed dispersal through fecal matter?
gpt
Most wild fruits are adapted to be palatable for the animal (or set of animals) that acts as the primary seed disperser. Whether that is sweet or not very much depends on the palate of the animal.

Sweet berries often have birds as their primary disperser. And tropical sweet fruits will often attract a large number of different herbivorious and omnivorous mammals.

Plenty of non-sweet fruits exist though;

Wild chilli peppers are principally disperesed by birds who can not feel/taste the heat. These aren't especially sweet and the heat wards off mammals. The avocado is thought to have been dispersed by now extinct South American mega-fauna such as the giant ground sloth, it is not especially sweet.

With regards to the fruits that humans eat today many of these are very sweet because we've selectively bred them to be that way. Citrus fruit are probably the best example of this. As far as we can tell the Pomelo is likely the orginal cultivated citrus, and possibly cultivated from a less sweet ancestor. Pomelo are moderately sweet and very sharp (though not quite as tart as grapefruit). We've subsequentially bred these into very sweet fruits such as tangerines , mandarins and oranges.

Grapes are a interesting example, the grapes we eat as fruit have been bred to be quite a lot less sweet than the grapes we cultivate for wine production.