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Humans on average can hear up to 20 KHz whereas an average chimpanzee can hear close to 30 KHz. Using sophisticated algorithms to predict acoustic frequencies and the transmission probabilities depending upon the morphology of hearing organs (ear pinna, bones, auditory canal, etc), it is well documented that a logarithmic plot of bodyweight versus acoustic frequency shows an inverse relationship for primates. However, humans are mild outliers using a comparatively lower acoustic frequency for communication. Given the body mass and close evolutionary relationships of humans and chimps, the highest audible acoustic frequencies should be comparable. The evolution of the human acoustic frequency range can give insights about the ecological (geographical, interspecific, and intraspecific interactions) constraints acting upon them.
Acoustic signals are used for various purposes by animals, the most notable being communication, hunting, courtship, and environment sensing. The primate ear is sensitive to only a particular frequency range. If the receptivity of the ear for a particular frequency range shifts, it can lead to poor vocalization skills, disadvantages in courtship, and environment sensing.
Humans’ highest frequency (20 KHz) is ~10 KHz lower than the Chimpanzee high-end frequency, although the deviation is comparatively low. It is possible that the frequency difference is due to non-functional ear pinna. Addition information about the ear structure of other hominins is needed for conclusive evidence.
It is universal throughout human populations, although certain studies suggest that infants have a higher frequency reception than adults. This might suggest a developmental trajectory of retained ancestral sensitivity. However, it should be noted that most mammalian infants have a higher frequency range as compared to adults.
One possibility was the availability of acoustic frequency bands in ancestral ecological niches. This would imply that high frequency acoustic signals were already in use by other species in the vicinity, and as such shifting to a lower frequency avoided acoustic signal overlap. Another possibility could include sexual selection as cohabitating hominids used higher frequencies.
This may provide insights into the acoustic environment in which humans evolved.
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