Young chimpanzee at Kalinzu (Uganda). Credit: K. Koops
Young male chimpanzees play more with objects, but do not become better tool users. http://bit.ly/1P0FTwx #biology
Young male chimpanzees play more with objects, but do not become better tool users
07 October 2015
Cambridge, University of
New research shows a difference between the sexes in
immature chimpanzees when it comes to preparing for adulthood by
practising object manipulation – considered ‘preparation’ for tool use
in later life.
Researchers studying the difference in tool use between our closest
living relatives, chimpanzees and bonobos, found that immature bonobos
have low rates of object manipulation, in keeping with previous work
showing bonobos use few tools and none in foraging.
Chimpanzees, however, are the most diverse tool-users among non-human
primates, and the researchers found high rates of a wide range of
object manipulation among the young chimpanzees they studied.
While in adult wild chimpanzees it is females that are more avid and
competent tool users, in juvenile chimpanzees the researchers conversely
found it was the young males that spent more time manipulating objects,
seemingly in preparation for adult tool use.
“In numerous mammalian species, sex differences in immatures
foreshadow sex differences in the behaviour of adults, a phenomenon
known as ‘preparation’,” said Dr Kathelijne Koops, who conducted the
work at the University of Cambridge’s Division of Biological
Anthropology, as well as at the Anthropological Institute and Museum at
Zurich University.
Much of the time young male chimpanzees spent manipulating objects
was dominated by ‘play’: with no apparent immediate goal, and often
associated with a ‘play face’ – a relaxed expression of laughing or
covering of upper teeth.
The sex bias for object manipulation the researchers found in
juvenile chimpanzees is also found in human children. “The finding that
in immature chimpanzees, like humans, object-oriented play is biased
towards males may reflect a shared evolutionary history for this trait
dating back to our last common ancestor,” write the researchers from
Cambridge, Zurich and Kyoto, who studied communities of wild chimpanzees
and bonobos in Uganda and Congo for several months, cataloguing not
just all tool use, but all object manipulation.
Immature females, on the other hand, showed lower rates of object
manipulation, especially in play, but displayed a much greater diversity
of manipulation types than males – such as biting, breaking or carrying
objects – rather than the play-based repetition seen in the object
manipulation of immature males.
This seems to prepare the females better for future tool use. In an
earlier study at Gombe (Tanzania), immature female chimpanzees were also
observed to pay closer attention to their mothers using tools and
became proficient tool users at an earlier age than males.
“Immature females seem to focus their attention on relevant tool use
related tasks and thus learn quicker, whereas males seem to do more
undirected exploration in play,” write the researchers.
They say they believe the findings show that not all object
manipulation in juvenile chimpanzees is preparation for tool use, and
the different types of object manipulation need to be considered.
The researchers say that the apparent similarity between human
children and young chimpanzees in the observed male bias in object
manipulation, and manipulation during play in particular, may suggest
that object play functions as motor skill practice for male-specific
behaviours such as dominance displays, which sometimes involve the aimed
throwing of objects, rather than purely to develop tool use skills.
However, the researchers also point out that further work is needed
to disentangle possible functions of object manipulation during
development.
“We found that young chimpanzees showed higher rates and,
importantly, more diverse types of object manipulation than bonobos.
Despite being so closely related on the evolutionary tree, as well as to
us, these species differ hugely in the way they use tools, and clues
about the origins of human tool mastery could lie in the gulf between
chimpanzees and bonobos,” Koops said.
“We found that male chimpanzees showed higher object manipulation
rates than females, but their object manipulation was dominated by play.
Young female chimpanzees showed much more diverse object manipulation
types,” she said.
“We suggest that the observed male bias in young chimpanzees may
reflect motor skill practice for male-specific behaviours, such as
dominance displays, rather than for tool use skills. It seems that not
all object manipulation in immatures prepares for subsistence tool use.
It is important to take the types of manipulation into consideration.”
The researchers also found that in chimpanzees, but not bonobos, the
types of objects manipulated became more tool-like as the apes age. “As
young chimpanzees get older they switch to manipulating predominantly
sticks, which in this community is the tool type used by adults to
harvest army ants,” Koops explained.
This practice of ant ‘dipping’, when chimpanzees lure streams of
insects onto a stick, then scoop them up by running a hand along the
stick and into the mouth, provides a quick source of protein.
Koops added: “Given the close evolutionary relationship between
chimpanzees, bonobos and humans, insights into species and sex
differences in ‘preparation’ for tool use between chimpanzees and
bonobos can help us shed light on the functions of the highly debated
gender differences among children.”
The research is published today in the journal PLOS ONE.
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