Brain size in human vs chimp

Grok

MY QUESTION

Assume body mass of 50 kg in both human and chimp. What are the comparative brain masses?

ANSWER FROM GROK

Human brain mass is roughly 1.3–1.4 kg; chimpanzee brain mass is roughly 0.38–0.42 kg (about 1/3 as large), for a body mass of ~50 kg in both.⁠Chimpanzeebrain

Typical adult values (species averages, with chimps naturally near 40–60 kg body mass and humans scaled or noted near that range):

Chimpanzee (Pan troglodytes): Average adult brain mass ≈ 384 g (commonly cited as ~0.38–0.42 kg). Body mass is typically 40–60 kg for males and 32–47 kg for females, so 50 kg is a realistic adult value. One comparative dataset explicitly lists chimpanzee body mass 50 kg with brain mass ≈ 0.42 kg.⁠Chimpanzeebrain

Human (Homo sapiens): Average adult brain mass ≈ 1.3–1.4 kg (often ~1,350 g). Average body mass is higher (~70 kg), but brain size varies only modestly with body size within adults; a 50 kg human (smaller adult) still has a brain mass in essentially the same range (typically well above 1 kg). Absolute human brain size remains ~3–3.5× that of a chimpanzee of similar body mass.⁠Chimpanzeebrain

Relative to body mass this yields a much higher brain-to-body ratio (and encephalization) in humans. Humans are a clear outlier among primates/mammals in absolute and relative brain size; chimpanzees fall closer to the general primate scaling trend. Note that brain mass itself is only one factor—neuronal packing, connectivity, and energy costs also differ—but the mass comparison at matched 50 kg body mass is straightforwardly human ≈ 3–3.5× chimpanzee.