Marc Verha
Sat, Jun-30-07, 06:16
Ontogenetic development of upright bipedal behaviours in the
gorilla and in human children V Zacher, BA Stein, C Biemann, N
Clauß & C Niemitz 2005 XXIX ethol.confer.Budapest
A comparison of the ontogenies of bipedal behaviours in apes
and human children contributes further to the understanding of
the upright gait in human evolution. We combined the findings
of several studies of quantitative analyses of bipedalism in
children (Homo sapiens) and western lowland gorillas (Gorilla
g. gorilla). For this purpose, 152 children between 4 and 48
months and eight gorillas between 3 and 47 years of age
were observed. We defined a behaviour as bipedal, if the
hind limbs supported all or most of the body weight.
Already at the age of 13 months shortly after learning
how to walk (12.2 months average) bipedal behaviour was
the most frequent behaviour children up to the age of 48
months showed - 50.4 % of time points recorded. At this
point 44.2 % was upright bipedal behaviour, that is 88 % of
all bipedal behaviour. The maximum of bipedal behaviour was
reached half a year later -
72.6 %, when 91.3 % of bipedal behaviour is marked as upright.
From this time onwards, bipedal behaviour decreases, but
never reaching a value below 50 %. Upright bipedal
behaviour constitutes 90 % constantly. One three-year-old
gorilla showed 33.1 % bipedal behaviour; being his most
frequent behaviour at this age. Concerning the
four-year-old gorilla, bipedal behaviour was only second
frequent behaviour (25.3 %). However, his upright bipedal
behaviour contributed 2.1 %; 8.3 % of all bipedal
behaviour, whereas in the younger juvenile the
corresponding value was 16.9 % (equivalent to 5.6 % of all
behaviour). The eight-year-old gorilla showed only 9.0 %
bipedal behaviour, 21.1% of it was upright bipedalism. From
this age onwards, bipedality constitutes the fourth
frequent behaviour. This decrease proceeded with age, the
adult gorillas showing only 6.1 % of bipedal behaviour, 13
% of it was upright (0.5 %). There was an opposite
ontogenetic development of bipedalism of human children and
in the juvenile gorillas observed. In the gorillas, the
time budget used for upright bipedalism showed a low but
constant value, whereas in human infants, it is of
outstanding significance at varying values. Our results
elucidate a number of comparative quantitative aspects of
the ontogeny of bipedalism for the two primate species
concerned.
gorilla and in human children V Zacher, BA Stein, C Biemann, N
Clauß & C Niemitz 2005 XXIX ethol.confer.Budapest
A comparison of the ontogenies of bipedal behaviours in apes
and human children contributes further to the understanding of
the upright gait in human evolution. We combined the findings
of several studies of quantitative analyses of bipedalism in
children (Homo sapiens) and western lowland gorillas (Gorilla
g. gorilla). For this purpose, 152 children between 4 and 48
months and eight gorillas between 3 and 47 years of age
were observed. We defined a behaviour as bipedal, if the
hind limbs supported all or most of the body weight.
Already at the age of 13 months shortly after learning
how to walk (12.2 months average) bipedal behaviour was
the most frequent behaviour children up to the age of 48
months showed - 50.4 % of time points recorded. At this
point 44.2 % was upright bipedal behaviour, that is 88 % of
all bipedal behaviour. The maximum of bipedal behaviour was
reached half a year later -
72.6 %, when 91.3 % of bipedal behaviour is marked as upright.
From this time onwards, bipedal behaviour decreases, but
never reaching a value below 50 %. Upright bipedal
behaviour constitutes 90 % constantly. One three-year-old
gorilla showed 33.1 % bipedal behaviour; being his most
frequent behaviour at this age. Concerning the
four-year-old gorilla, bipedal behaviour was only second
frequent behaviour (25.3 %). However, his upright bipedal
behaviour contributed 2.1 %; 8.3 % of all bipedal
behaviour, whereas in the younger juvenile the
corresponding value was 16.9 % (equivalent to 5.6 % of all
behaviour). The eight-year-old gorilla showed only 9.0 %
bipedal behaviour, 21.1% of it was upright bipedalism. From
this age onwards, bipedality constitutes the fourth
frequent behaviour. This decrease proceeded with age, the
adult gorillas showing only 6.1 % of bipedal behaviour, 13
% of it was upright (0.5 %). There was an opposite
ontogenetic development of bipedalism of human children and
in the juvenile gorillas observed. In the gorillas, the
time budget used for upright bipedalism showed a low but
constant value, whereas in human infants, it is of
outstanding significance at varying values. Our results
elucidate a number of comparative quantitative aspects of
the ontogeny of bipedalism for the two primate species
concerned.