We can't have come from any non-ape because we currently are a variety of ape. This has been very well known for a very long time. When Carl Linnaeus founded the field of taxonomy (a nested hierarchical structure for the classification of living things) he couldn't put the human species anywhere else, and he tried. This was pre-Darwin, and he likely believed in special creation (though his studies did some work eroding that assumption), he wasn't happy about it, but he saw, clearly, that every part of our anatomy is ape anatomy. We have all the same structures. We now know that we have all the same genes, in fact some of the genes that have the physical effects that set us apart are not special human genes, but rather broken versions of monkey genes. That's why, for example, we have such tiny and weak jaws: the genetics required for strong, robust jaws like other primates have are all fucked up, but that opens the way for a larger cranium.
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It does not please [you] that I've placed Man among the Anthropomorpha, perhaps because of the term 'with human form', but man learns to know himself. Let's not quibble over words. It will be the same to me whatever name we apply. But I seek from you and from the whole world a generic difference between man and simian that [follows] from the principles of Natural History. I absolutely know of none. If only someone might tell me a single one! If I would have called man a simian or vice versa, I would have brought together all the theologians against me. Perhaps I ought to have by virtue of the law of the discipline.
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We are apes for the same reason that ducks are birds. "Ape" is not a different kind of animal, it is a group, a subset of old-world monkeys, which are a subset of primates, which are a subset of mammals. And the
Homo genus is a subset of great ape. We can construct from comparative genetics very detailed family trees. We know that from the combined lineage of the great apes, the common ancestor of all four genera of great ape, it was the orang-utan lineage that broke away first. Then the gorilla lineage broke away in at the next fork. Then the human and chimpanzee lineages split apart. Of the various species they each gave rise to, only one human and two chimpanzee species remain. The very same evidence that proves that we evolved also proves our shared ancestry with modern non-human apes.