Humans’ lightweight skeletons are pretty recent

Our lightweight skeletons are recent development

New research shows that modern human skeletons evolved into their lightly built form only about 12,000 years ago and even more recently in some human populations. The work, based on high-resolution imaging of bone joints from modern humans and chimpanzees as well as from fossils of extinct human species, shows that for millions of years now-extinct humans had high bone density until a dramatic decrease in recent modern humans.

The findings, published in the Proceedings of the National Academy of Sciences, reveal a higher decrease in the density of lower limbs than in upper limbs, suggesting that the transformation may be linked to humans’ shift from a foraging lifestyle to a sedentary agricultural one.

“This is the first study to show that human skeletons have substantially lower density in joints throughout the skeleton, even in ancient farmers who actively worked the land,” said Brian Richmond, an author of the study and curator in the American Museum of Natural History’s Division of Anthropology.

Gliding lizards use falling leaf colors as disguise

By mimicking the red and green colors of falling leaves, lizards in Borneo avoid falling prey to birds as they glide between trees in the rainforest.

The research, published in the journal Biology Letters, suggests that populations of the Southeast Asian gliding lizard, Draco cornutus, have evolved extendable gliding membranes, like wings, that closely match the colors of falling leaves to disguise themselves. Draco is the only living lizard with extendable membranes that allow them to glide.

A team of Australian and Malaysian biologists observed two populations of gliding lizards in Borneo. One population has red gliding membranes, which match the color of the red falling leaves of their coastal mangrove forest habitat. The other has dark brown and green gliding membranes, which match the colors of falling leaves in their lowland rainforest habitat.

They determined how the colors would be perceived by a predatory bird and found that the gliding membrane color would be indistinguishable from a falling leaf in the same forest.

U.S. cities are literally brighter than Germany’s

German cities emit several times less light per capita than American cities of comparable size, according to a study publication in the journal Remote Sensing. The size of the gap grew with city size: Light per capita increased with city size in the U.S. but decreased with city size in Germany. The study also examined regional differences, and surprisingly found that light emission per capita was higher in cities in the former East Germany than from those in the former West.

A main point of the study by the German Research Center for Geosciences is to emphasize the great improvement in the quality of nighttime imagery of Earth since 2012. The European Space Agency’s NightPod instrument has allowed astronauts to take high-resolution images of individual cities.

The study also demonstrated a practical use of the new data: Since maps of nighttime light emission highlight the areas where light pollution is especially prevalent, they spot which areas can best be targeted for energy savings.