Table 3.

Comparison modern human and chimpanzee absolute and relative brain size

	Average neonatal brain size (g)*	Average adult brain size(g)†	% adult brain size at birth	Age 90% of adult brain size attained	Age at sexual maturity (years)	Years from adult brain size to maturity (years)	% subadult pd left after reaching adult brain size
Modern human‡	364	1352	27%	5	19.5	14.5	74%
Chimpanzee§	137	384	36%	4	13.3	9.3	70%

^*Neonate defined as individuals from birth to 10 days old.

^†Average adult brain size was calculated as the mean of all individuals between 20–40 years old for modern humans and the mean of all individuals between 7 and 30 years old in chimpanzees because this range safely precedes a known trend toward declining brain weight with age (Dekaban & Sadowsky (1978); Herndon et al. (1999).

^‡Modern human brain data from Marchand (1902).

^§Chimpanzee brain weight data from Herndon et al. (1999).