SCIENCE

Compared with other primates and our early human ancestors, we modern humans have skeletons that are relatively lightweight—and scientists say that basically may be because we got lazy. (NPR)

Watch our video on the Hadza, the last hunter-gatherer communities on Earth.

Discussion Ideas

• The NPR article says that scientists were studying the bones of different primates, including humans. Besides humans, can you name some other primates?
  • Primates are mammals that include monkeys (such as baboons and howler monkeys), apes (such as gorillas and chimpanzees), and prosimians (such as lemurs and marmosets). Learn more about primates here.
  • The scientists in the article studied fossils of humans, human ancestors (such as Australopithecus africanus, Paranthropus robustus, and Homo neanderthalensis), and chimpanzees.

• The scientists discovered that modern human bones were less dense than the bones of other primates. What does this mean? What are characteristics of dense bones?
  • Bone density measures the amount of minerals per square centimeter of bone.
  • Dense bones are usually stronger and heavier than less-dense bones. Denser bones can withstand more pressure and are harder to break.

• Before the recent discovery, when did scientists think humans developed less-dense bones than other primates?
  • According to the NPR blog, many scientists thought that humans developed less-dense bones “a couple of million years ago, about when Homo erectus, a kind of proto-human, left Africa.” Learn more about Homo erectus here.

• Why did scientists think less-dense bone structure developed millions of years ago?
  • “Having lighter bones would have made it a lot easier to travel long distances.”

• Today, some scientists think “The change [in bone density] occurred much later in our history.” Why do these scientists think the change happened about 12,000 years ago?
  • “That’s right when humans were becoming less physically active because they were leaving their nomadic hunter-gatherer life behind and settling down to pursue agriculture.” Learn more about the development of agriculture here.

• The Hadza, a community in Tanzania, is one of the last societies that live a primarily hunter-gatherer lifestyle. Watch the video on our site or above, showing the diet of a Hadza family. What foods do you see them hunting? What foods to you see them gathering?
  • Hunting
    • birds
    • meerkats and other small mammals
  • Gathering
    • honey (they’re using smoke to get rid of the bees!)
    • tubers or other plant roots
    • fruit

• Why would the NPR writer say agriculture-based diets create “wimpy” or “lazy” people?
  • She’s joking by saying that less-dense bone structure makes someone “wimpy.”
  • She’s making a half-serious point by saying that hunter-gatherer lifestyles such as the Hadza require much, much more physical activity than “lazy” lifestyles whose diets rely on agriculture.

TEACHERS’ TOOLKIT

NPR: When Humans Quit Hunting And Gathering, Their Bones Got Wimpy

Nat Geo: Evolution of Diet – The Hadza of Tanzania

Nat Geo: What is agriculture?

(extra credit!) Proceedings of the National Academy of Sciences of the United States of America: Recent origin of low trabecular bone density in modern humans