ancient parts is mentioned more than once in the book (twice to be exact). The first one is in
WHY THIS EMOTION NOW chapter and the other one is in
HOW THE BRAIN GREW which includes the paragraph you mentioned.
Let's talk about the 1st paragraph.
[...] This flood of neurobiological data lets us understand more clearly
than ever how the brain's centers for emotion move us to rage or to
tears, and how more ancient parts of the brain, which stir us to make
war as well as love, are channeled for better or worse.
In this scope, the phrase
ancient parts is used to define the emotion base that directs us to impulse decisions which are managed by our brain's earlier developed parts. As mentioned in the paragraph these are
ancient parts and these parts evolved in the early periods of our lives. The growth of the brain in the human embryo roughly retraces this evolutionary course as well.
Let's check the 2nd paragraph.
[...] Over millions of years of evolution, the brain has grown from the
bottom-up, with its higher centers developing as elaborations of
lower, more ancient parts.
The following paragraph after this one, mentions the most primitive part of the brain which is a supportive approach to the 1st and the 2nd paragraphs.
ancient parts is a direct reference to the actual early step of neurologic evolution. And this is supported in
HOW THE BRAIN GREW chapter with the following paragraphs:
[...] From the most primitive root, the brainstem, emerged the emotional
centers. Millions of years later in evolution, from these emotional
areas evolved the thinking brain or "neocortex," the great bulb of
convoluted tissues that make up the top layers. The fact that the
thinking brain grew from the emotional reveals much about the
relationship of thought to feeling; there was an emotional brain long
before there was a rational one.
The most ancient root of our emotional life is in the sense of smell,
or, more precisely, in the olfactory lobe, the cells that take in and
analyze smell. Every living entity, be it nutritious, poisonous,
sexual partner, predator or prey, has a distinctive molecular
signature that can be carried in the wind. In those primitive times
smell commended itself as a paramount sense for survival.
From the olfactory lobe the ancient centers for emotion began to
evolve, eventually growing large enough to encircle the top of the
Finally, the phrase
ancient parts is a direct reference to the human brain's earlier developed parts in evolutionary steps.