June 30, 2015

Add handedness (having one dominant hand) to the rather short list of physical characteristics that humans share with kangaroos, according to a study in Current Biology published by the zoologist Yegor Malashichev of Saint Petersburg State University in Russia and his colleagues. And it seems that, unlike humans, kangaroos are nearly all lefties.

A recent study showed that kangaroos are usually left-handed. (© Shutterstock)

The scientists spent months observing different species of marsupials in Australia. Marsupials are animals that give birth to underdeveloped young, which the mother then carries in a pouch. They include kangaroos, koalas, and many other animals native to Australia. The species studied by Malashichev included Goodfellow’s tree kangaroo, the eastern grey kangaroo, the red kangaroo, and the closely related red-necked wallaby. Other marsupials observed were the Bush-tailed bettong, sugar gliders, and grey short-tailed opossums. The scientists recorded information on hand preference as the animals groomed themselves, grabbed and held food, and leaned on their forearms while eating. What stood out among the data was that nearly all kangaroos used their left hand exclusively for the tasks.

No one knows for certain why some people are right-handed and others are left-handed. Malashichev and his colleagues propose that bipedal locomotion (two-legged walking) helps foster a hand preference. Humans are unique among living primates in that we make extensive use of walking on two legs. Among mammals, only kangaroos are known to move about primarily on their hind legs. The scientists noted that marsupial species that spent time in trees, including sugar gliders and opossums, showed little hand preference.

Many human cultures have traditionally discouraged left-handedness. In English, the word left comes from the Anglo-Saxon word lyft, which means weak or broken. The word sinister comes from the Latin word for left. Many phrases in English demonstrate a traditionally unfavorable view of left-handedness. For instance, the phrase left-handed compliment actually implies an insult. The scientists presume kangaroos do not share this bias against southpaws.

red-necked wallabies,

Nov. 23, 2011

A comparison of the whiskers on a small South American marsupial with those of modern mice and rats have led researchers in the United Kingdom to an interesting theory about the evolution of mammals. Whiskers, say scientists from the University of Sheffield, may have represented an important milestone in the development of the first mammals. The marsupial, called the grey short-tailed opossum, is similar in many ways to an early mammal that lived about 125 million years ago. Scientists believe that the ancestors of modern rodents and marsupials split from a common ancestor several million years before that.

Most mammals other than humans have long, stiff hairs, commonly known as whiskers, growing around mouth or other parts of the head. These highly sensitive touch organs are also called vibrissae or tactile hairs. Around the tactile hairs lie many nerves, which transmit signals to the brain when the whiskers brush against objects. “Whisking” help animals to feel their way through narrow or dark places. It also helps animals, particularly mice and rats, build maps of their surroundings.

A mother opossum carries its young on its back. Baby opossums stay in their mother's pouch for about two months after birth. They remain near her for several more weeks. E. R. Degginger

The University of Sheffield researchers found that both modern mice and rats and the grey short-tailed opossum whisk rapidly from side to side if the animals are traveling in a straight line. As they turn, however, their whiskers follow the turn. If the whiskers contact an object or a surface, the whiskers on the opposite side sweep around to collect more information.

The researchers proposed that the first mammals developed whiskers to help them survive in a challenging environment. At that time, mammals were small, tree-dwelling creatures that hunted at night in the shadow of the dinosaurs that dominated the land areas of Earth. In addition to learning about whisking, the scientists are using their findings to help to develop robots with artificial whiskers that could be used in search-and-rescue operations at disaster sites.

Additional World Book articles:

• Animal (Adaptations for sensing the environment)
• Perception
• Senses