Made from the human body!
In alchemy, human beings are considered to be composed of three things: body, soul, and spirit. Tool: no ads, full text, moreover, in other words, as long as these three things can be refined, in theory, humans can be born without relying on the mother's womb. But because this is an act that violates the laws of nature and social ethics, it is considered a taboo.
However, in order to see their dead mother's smile again, the two brothers Edward and Alphonse stepped into this taboo field and tried to refine the human body. The end result was that Edward lost a leg, Al lost his entire body, and in order to keep his brother alive, Edward sacrificed his right hand as a sacrifice to 'truth' and brought back the soul of his brother Alphonse.