AGE CHANGES IN DIMENSIONAL DIFFERENCES BETWEEN THE SKULLS OF MALE AND FEMALE APES

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Summary.

  • 1Comparison has been made between the mean values of corresponding cranial dimensions of samples of male and female chimpanzees, and of male and female gorillas of various ages.
  • 2The skull of the adult male chimpanzee is, on the average, 5 per cent bigger than that of the female. No consistent sexual differences in skull size appear to exist in immature specimens of this ape.
  • 3The skull of the adult male gorilla is about 18 per cent bigger than that of the female, sexual differences first appearing when the permanent incisors, second molars and premolars are erupting.
  • 4It is suggested that the greater degree of sexual differentiation in the gorilla arises because its adolescent growth-spurt begins earlier, and possibly lasts longer, than in the chimpanzee.

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