[tdba]

Orcs are elves who were corrupted and mutilated by Morgoth, so hypothetically elves and orcs might have more shared biology. Hobbits are probably an offshoot or variant of men. Elves, dwarves and men all had separate "awakenings" so they don't have any shared ancestry at all. However, earlier races of men (and especially Numenoreans) were more similar to elves, being larger, wiser and having longer lifespans.

[labster]

The thing about orcs being corrupted elves isn’t canon, as Tolkien himself never settled on a theory for the origins of orcs. I’m personally against this theory because an elf put under extreme duress will likely just pop back to the Halls of Mandos; when orcs were first bred the way from the West was still open.

[tdba]

Fair, I was just stating the commonly accepted origin. Personally, I think the origin of orcs remaining shadowy and mysterious with numerous contradictory accounts is the best canon. After all, Morgoth works secretly to sow confusion and dissent.

[rossdavidh]

Arguably, Tolkien did say (in the Silmarillion) that orcs were corrupted elves, and then also said (in Unfinished Tales) that orcs were corrupted Wose. Then he also said that Saruman made orcs from corrupted Men.

Most plausibly, since there are numerous cases of different groups of orcs looking at least as different from one another as, say, Hobbits and Men and Wose and Dwarves, "orc" is just a term for any humanoid whose form has been corrupted by a Dark Lord.