"Hedonic eating, obesity, and addiction result from increased neuropeptide Y in the nucleus accumbens during human brain evolution"
Mary Ann Raghanti cs 2023 PNAS 10.1073/pnas.2311118120

Significance:
Studies of human brain evolution have traditionally concentrated on the cerebral cortex (significantly larger >other primates),
but the more central & ancient portion of our brain is not enlarged, and houses the nucleus accumbens NAc = cardinal in the brain’s reward pathway.
NPY (the neuro-transmitter neuropeptide-Y) promotes fat+sugar-seeking behavior when injected into the NAc,
it is elevated in our species >other primates.
Vigorous fat+sugar-seeking behavior probably permitted our cerebral cortex to expand early in our evolution,
but it now appears to encourage syndromes ass.x excessive fat+sugar intake & drug+alcohol addiction.
We are thus essentially wired for hedonic eating & addictive behaviors.

Abstract:
The NAc is central to motivation & action, exhibiting one of the highest densities of NPY in the brain.
Within the NAc, NPY plays a role in reward, it is involved in emotional behavior & increasing alcohol+drug addiction & fat intake.
Here we examined NPY innervation & neurons of the NAc in Hs & other anthropoids:
are there differences among these various spp, that would correspond to behavioral or life history variables?
We quantified NPY-immuno-reactive axons & neurons in the NAc of 13 primate spp incl. Hs, gr.apes & monkeys.
Our data show:
the human brain is unique among primates in having denser NPY-innervation within the NAc (axon length density to neuron density), even after accounting for brain size.
Combined with our previous finding of increased dopaminergic innervation in the same region, our results suggest:
the neuro-chemical profile of the human NAc appears to have rendered our species uniquely susceptible to neuro-physiological conditions, such as addiction.
The increase in NPY specific to the NAc may represent an adaptation that favors fat intake,
it contributes to an increased vulnerability to eating-disorders, obesity & alcohol+drug dependence.
Along with our findings for dopamine, these deeply rooted structural attributes of the human brain are likely to have emerged early in the human clade, laying the groundwork for later brain expansion & the development of cognitive & behavioral specializations.

Interesting article,
but the just-so "explanations" in Medical Xpress are ridiculous:

"Overeating and addiction may have roots in early human brain evolution and prosocial behaviors"
Justin Jackson 2023 Medical Xpress
.... The adoption of cooking is often considered pivotal for supporting brain expansion,
but the preference for fat-rich foods may have preceded it by mill.of yrs.
The authors speculate:
did a preference for fat-rich foods (driven by elevated NPY in the Hs NAc) play a role in the expansion of the human brain during the Plio-Pleistocene 5 Ma?
They point out:
Plio-Pleistocene BP hominins possessed reduced, non-dimorphic male canines = a major shift in social behavior from aggressive to more affiliative.
Did increased NAc NPY influence prosocial behaviors in early humans, incl. monogamous pair-bonding?
Was this dietary shift, driven by the preferences & requirements in the brain, accompanied by changes in socio-behavioral strategies?
did it contribute to the success of early human ancestors?
The study concludes:
did the shift in NAc function (driven by increased fat intake?) have deep evol.origins?
did it contribute to the unique responsiveness of the human reward pathway to various stimuli.?
This same pathway makes current modern Hs more susceptible to reward pathway addictions than other primates.

- cooking 2 Ma??
- erectus' brain-expansion = seafood DHA ...
- "from aggressive to affiliative"??
- early hominids originally had short canines! not "reduced"!
- " increased NAc NPY influenced prosocial behaviors"??
- "dietary shift, driven by the preferences & requirements in the brain"??

Apparently, brain changes *followed* the "dietary shift":
Indonesian H.erectus regularly dived for shellfish:
• atypical tooth-wear caused by "sand & oral processing of marine mollusks" (Towle cs 2022) https://onlinelibrary.wiley.com/doi/10.1002/ajpa.24500
• H.erectus s.s. fossilized in coastal sediments: Mojokerto amid barnacles & corals, Trinil amid edible Pseudodon & Elongaria, Sangiran-17 "brackish marsh near the coast".
• Stephen Munro discovered sea-shell engravings made by H.erectus (Joordens cs 2015 Nature 518:228) https://pubmed.ncbi.nlm.nih.gov/25470048/
• ear exostoses (H.erectus & H.neand.) develop after years of cold(er) water irrigation https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5696936/
• pachyosteosclerosis = slow+shallow-diving tetrapods (de Buffrénil cs 2010 J.Mamm.Evol.17:101), e.g. erectus’ parietal bone is 2x as thick as in gorillas.
• brain size in erectus (2x apes-australopiths) is facilitated by sea-food, e.g. DHA docosahexaenoic acid in shellfish, cf. Odontocetes, Pinnipedia.
• late-Pleist.descendants or relatives colonized islands far oversea (fossils Flores 100–50 ka, Luzon 67 ka) https://www.academia.edu/36193382
• stone tool use & dexterity is typical for molluscivorous sea-otters.