快猫短视频

IF YOU think kids grow up quickly these days, think again. The uniquely human
habit of taking 18 years or so to mature is a recent development in our
evolutionary history. Growth patterns of fossil teeth have shown that a
prolonged growing-up period evolved long after our ancestors started walking
upright and making tools.

Our great ape relatives, the chimpanzees and gorillas, take about 11 years to
reach adulthood. 快猫短视频s speculate that delaying this process allows children
to absorb our complex languages, culture and family relationships. What鈥檚 more,
we need extra time for our large brains to grow鈥攖hey are half as big again
as those of the earliest humans, Homo erectus, who appeared some 2
million years ago.

Christopher Dean of University College London and his team studied teeth from
H. erectus, our Australopithecus human-like ancestors such as
the famous 鈥淟ucy鈥�, and Proconsul nyanzae, an ape ancestor. The rate of
tooth development is tightly linked to how long it takes to become fully
grown.

Teeth grow by adding on enamel in small increments, leaving striations rather
like shell ridges or tree rings. By studying these rings, the team could work
out how fast the teeth grew. They found that H. erectus鈥檚 teeth grew at
almost the same rate as those of both modern and fossil apes and
Australopithecus鈥攕uggesting a shorter growing-up period. This was
surprising, as H. erectus walked upright, was about the same size as us
and made simple tools鈥攁ll traits associated with being human, says Dean.
But it fits with the fact that H. erectus鈥檚 brain was much smaller.

By comparing the growth rate of the back and front teeth, the team estimated
that H. erectus children produced their first permanent molars at around 4陆
years, and their second at 7陆 years. This compares with 6 and 12 years in
modern humans and 3 and 5 years for modern apes, indicating that H. erectus was
starting down the road of modern dental development.