Is the very origin of the “natural law” religious or philosophical?

Question

Is the very origin of the “natural law” religious or philosophical?

Definition (Wikipedia):

Natural law[1] (Latin: ius naturale, lex naturalis) is a system of law based on a close observation of human nature, and based on values intrinsic to human nature that can be deduced and applied independently of positive law (the express enacted laws of a state or society).

I can read that the natural law dates back to classical philosophy (Socrate, Plato, Aristotle, the Stoics).

But I can also read that it has origins in the Old Testament: “Because of its origins in the Old Testament, early Church Fathers, especially those in the West, saw natural law as part of the natural foundation of Christianity.” (Wikipedia).

And also crossed upon sentences like: “Natural law, both in its first (religious) sense and in its subsequent secular extensions (…)”.

Answer 1

The source of the notion of natural law is the same as the source of any notion of law, namely the nature of the human brain as a cognitive system. A law is just a perceived regularity in the data. Whatever the source of the data, the perception of regularities allows the brain to apply good logic to produce reliable predictions about the real world and relevant to the survival of the subject.

Natural law is presumably based on the perceived regularities in the data issued from social interactions and human relations.

It likely evolved from what humans believed about themselves in more primitive societies.