When can 要 replace 需要? In an answer to the post 要 to indicate &quot;will [verb]&quot; vs &quot;need&quot;, it is argued that

要；yào；want to, need to, going to

is actually the short form of either

需要；xūyào；to need, to want

or

将要；jiāngyào；going to.

However, in another answer it is said:

We cannot use 要 in place of 需要 here:

为什么人类需要氧气才能生存?
Why does mankind need oxygen to be able to survive?

Question: When can we use 要 to replace 需要? Is there a difference between 需要 and 要 in the sense of need to / want to?
要；yào；want, want to (想要), need to (須要), going to (將要).


需要；xūyào；need

We can use 要 instead of 須要 when we want to express need to + verb. However, we might not always want to replace 需要 with 要, because the meaning of 需要 is clearer: it always means 'need', while the meaning of 要 might cause confusion, as it can mean 'want to, need to or going to'.
On the other side, we shouldn't use 要 in place of 需要 when we want to express need + noun, such as in:

为什么人类需要氧气才能生存?
Why does mankind need oxygen to be able to survive?

氧气 is a noun; '需要氧气' (need oxygen) cannot be changed to 須要氧气 (need to oxygen), 想要氧气 (want to oxygen) or 將要氧气 (going to oxygen).
If the sentence was '須要有氧气' (need to have oxygen), then it can be changed to 要有氧气 because 有 is a verb.