Hideko Takeshita

Preference for consonant music over dissonant music by an infant chimpanzee

It has been shown that humans prefer consonant sounds from the early stages of development. From a comparative psychological perspective, although previous studies have shown that birds and monkeys can discriminate between consonant and dissonant sounds, it remains unclear whether nonhumans have a spontaneous preference for consonant music over dissonant music as humans do. We report here that a five-month-old human-raised chimpanzee (Pan troglodytes) preferred consonant music. The infant chimpanzee consistently preferred to produce, with the aid of our computerized setup, consonant versions of music for a longer duration than dissonant versions. This result suggests that the preference for consonance is not unique to humans. Further, it supports the hypothesis that one major basis of musical appreciation has some evolutionary origins.

Fetal brain development in chimpanzees versus humans

Summary It is argued that the extraordinary brain enlargement observed in humans is due to not only the human-specific pattern of postnatal brain development, but also to that of prenatal brain development [1,2]. However, the prenatal trajectory of brain development has not been explored in chimpanzees ( Pan troglodytes ), even though they are our closest living relatives. To address this lack of information, we tracked fetal development of the chimpanzee brain from approximately 14 to 34 weeks of gestation (just before birth) in utero using three-dimensional ultrasound imaging. The results were compared with those obtained for the human brain during approximately the same period. We found that the brain volume of chimpanzee fetuses was only half that of human fetuses at 16 weeks of gestation. Moreover, although the growth velocity of brain volume increased until approximately 22 weeks of gestation in both chimpanzees and humans, chimpanzee fetuses did not show the same accelerated increase in brain volume as human fetuses after that time. This suggests that maintenance of fast development of the human brain during intrauterine life has contributed to the remarkable brain enlargement observed in humans.

Development of combinatory manipulation in chimpanzee infants (Pan troglodytes)

I made systematic observations of three infant chimpanzees aged 2–4 years, who participated in a series of diagnostic tests of combinatory manipulation. The tasks were stacking blocks, seriating nesting cups, and inserting an object into the corresponding hole in a plate or a box. These tasks were originally devised for developmental diagnosis of human infants. The chimpanzee infants displayed combinatory manipulation comparable to that of 1-year-old human infants. Common motor characteristics were observed across the tasks, namely “repetition” of actions, “adjustment” of actions, “reversal” of actions, and “shifts” of attention. Humans and chimpanzees share these actions when manipulating multiple objects to complete a task. Repetition, adjustment, and reversal of actions and shifts of attention underlie higher levels of cognition common to both species.

Mechanism of birth in chimpanzees: humans are not unique among primates

Researchers have argued that the process of human birth is unique among primates and mammals in that the infant emerges with its face oriented in the opposite direction from its mother (occiput anterior) and head rotation occurs in the birth canal. However, this notion of human uniqueness has not been substantiated, because there are few comparative studies of birth in non-human primates. This paper reports the mechanism of birth in chimpanzees (Pan troglodytes) based on the first clear, close-up video recordings of three chimpanzee births in captivity. In all three cases, the foetus emerged with an occiput anterior orientation, and the head and body rotated after the head had emerged. Therefore, these characteristics are not uniquely human. Furthermore, in two of the three cases, the chimpanzee newborns landed on the ground without being guided from the birth canal by the mother. The fact that the human newborn emerges with an occiput anterior orientation has thus far been taken as evidence for the necessity of midwifery in modern humans, but this view also needs revision. Our observations raise the need to reconsider the evolutionary scenario of human birth.

A New Comparative Perspective on Prenatal Motor Behaviors: Preliminary Research with Four-Dimensional Ultrasonography

Organisms adopt various postures and actions while adjusting their bodies to the environment. Orientation to gravity, the surfaces, and media of the environment is the most fundamental prerequisite for organisms to perform any functional activities such as foraging and reproduction (Reed 1996). It is noteworthy that in primates such a basic orientation system develops through mother–infant interactions immediately after birth. For a primate neonate, the mother’s body functions as an environmental substrate. The neonates sense the speed and direction of actions through the movements of their mothers, to whom they cling and by whom they are carried. The mothers support their neonates to maintain physical contact with them, and the neonates explore and learn how to coordinate their own postures and actions with those of their mothers while sensing any other maternal stimuli, such as warmth, taste, and softness of the skin. The dynamic organization of actions and perceptions that emerges from the mother–infant interactions underlies the early development of motor behaviors in primates.

Fetal Behavioral Development and Brain Growth in Chimpanzees Versus Humans: A View from Studies with 4D Ultrasonography

This chapter initially describes how to perceive the relationship between individual development and evolution, then examines the essential nature of heterochronic evolution in humans and chimpanzees, the closest relative of humans, by comparing their fetal behavioral and brain development. We discuss the results of our recent studies on human and chimpanzee fetuses by using four-dimensional ultrasonography. Results showed that the growth velocity of the brain volumes of chimpanzee fetuses does not accelerate during late pregnancy, whereas that of human fetuses does accelerate through late pregnancy. Additional analysis and findings show that the timing of cessation or deceleration in the increase of growth velocity of brain volume among species crucial to clarify how much earlier human infants are born and how retarded is the development of their postural reactions is. Accumulated data suggest that further verification of temporally modified growth and development among species will help us to understand the effect of individual development on the evolution of human behavior.