It is often stated that science does not admit the term ‘why’ in its vocabulary, the reason being that it implies purpose (that is, teleology, a metaphysical notion originated by Aristotle). For example, a kidney (liver, etc.) is an organ that has a function, does some work, but it cannot be said that it – or anything else in nature – has a purpose. There is no divine plan!
Natural selection is a substitute for purpose: that which favours survival of a species. However, as soon as you consider that intelligence does exist in the world or the universe*, then there is but one more step to concluding that the universe is intelligent, and then teleology is back at the centre of things. Empirical scientists abhor the notion of ‘intelligent design’.
Teleological descriptions are unavoidable in biology, and even ‘function’ cannot escape such connotation. J.B.S. Haldane said, “Teleology is like a mistress to a biologist: he cannot live without her but he’s unwilling to be seen with her in public.”
* Is it not plausible to say that if there is a single being in the univers which is intelligent that means that the universe is intelligent? Of course, scientists will say that intelligence is an emergent property… of matter (that the greater comes from the lesser).