Brain stem - oldest part of brain?

Test Preparation AP History & Social Sciences
1

I get that the brain stem is the “oldest part of the brain.” I see two ways of interpreting that: (1) it is the first part of the brain developed in fetal development, or (2) evolutionarily speaking, it was the first to exist. I cannot find any source that verifies the exact meaning. </p>

Anybody have any sources that confirm the meaning?</p>

2

It is the the first to develop during fetal development, for sure.</p>

3

It’s the most primitive. It controls the automatic functions of the brain, and as such is the oldest. Humans are unique in that the cerebrum is huge relative to other animals.</p>