Potato in itself is poisonous, no need to go looking for any relatives (and there's plenty more poisonous plants in the nightshade family). Yet we still eat it.
> The majority (30-80%) of the solanine in potatoes is found in the outer layer of the potato.[26] Therefore, peeling potatoes before cooking them reduces the glycoalkaloid intake from potato consumption. Fried potato peels have been shown to have 1.4–1.5 mg solanine/g, which is seven times the recommended upper safety limit of 0.2 mg/g.[18] Chewing a small piece of the raw potato peel before cooking can help determine the level of solanine contained in the potato; bitterness indicates high glycoalkaloid content.[18] If the potato has more than 0.2 mg/g of solanine, an immediate burning sensation will develop in the mouth.[18]
Potatoes are inherently poisonous, especially if they are sprouting. But in the potato tuber itself, the doage is low enough not to worry... as long as you're older than 3 or 4. Beneath that, and you can subject children to poisoning accidentally.
https://www.huffingtonpost.co.uk/2014/08/14/girl-8-orphaned-...
There's a couple of orders of magnitude of errors in your comment: it's hundreds of millions, for centuries, or tens of millions, for millennia.
But potato has nothing on cassava, which has also been a staple for tens of millions for millennia. Looks like you're a Yank, like half the people on this godforsaken website, so you might only know it as "tapioca". In both cases, being poisonous discourages insects and other wildlife from expropriating your crops, and James C. Scott famously argues that being underground makes it more difficult for a certain kind of human pest to expropriate them as well.
So the humans deliberately eat roots because they are full of cyanide. Truly they are space orcs.
Green potatoes are very poisonous because they have a defensive substance called solanin. But crops were selected to remove the solanin.