What condition must exist for the production possibilities curve to be concave to the origin?

A production possibilities curve (PPC) is concave to the origin when the opportunity cost of producing one good increases as more of that good is produced. This typically occurs due to the law of increasing opportunity costs, which suggests that resources are not perfectly adaptable for the production of different goods. As production shifts from one good to another, increasingly less efficient resources must be utilized, leading to a bowed-out shape of the curve. This reflects the trade-offs and the diminishing returns associated with reallocating resources.