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Chimps Choosey About Wood Type for Their Beds

The Beatles sang about Norwegian wood, but for chimps, only one kind of wood will do when constructing beds. Continue reading →

What's the best wood for constructing beds? According to chimpanzees, one wood is superior to all others for beds: Ugandan ironwood.

And chimps should know. They make their own beds and sleep in them too, as the old saying goes. Each chimp is a bed builder.

They seem to be picky as well.

Say Cheese! Similarities of Human, Primate Expressions

"Chimpanzees, like humans, are highly selective when it comes to where they sleep," David Samson of the University of Nevada said in a press release. "This suggests that, for apes, there is something inherently attractive about a comfortable bed - down to what kind of wood you use to make it."

Samson and colleague Kevin Hunt of Indiana University studied chimps at the Toro-Semliki Wildlife Reserve in Uganda, which has seven tree species commonly used by chimpanzees.

Although the chimps had plenty of trees to choose from, a vast majority of the primates selected Ugandan ironwood to construct the 1844 chimp beds/nests documented by the researchers. "Ironwood" is a common name for a large number of woods that have a reputation for hardness.

Ugandan ironwood represented just 9.6 percent of all trees in the study area, showing that the chimps really took time and effort to seek it out. What's then so special about it?

For the study, published in PLOS ONE, Samson and Hunt measured the stiffness and bending strength of 326 branches from the seven common tree species.

Chimps Trust Some People More Than Other Chimps

Ugandan ironwood was the stiffest and had the greatest bending strength of all the trees tested. It also had the smallest distance between leaves on the branches, and had the smallest leaf surface area.

In short, it produced a firm and stable "mattress" upon which the chimps could slumber. The authors further note that chimp beds constructed out of Ugandan ironwood may provide protection from predators and pathogens, as well as provide temperature regulation and comfort.

Worldwide, there are more than 100 species of trees and shrubs with the common name of ironwood, so it's possible that this type of wood, in general, is favored by all chimps that can get their hands on it.

Image: "Charles" (an adult male chimp) shown sitting in a C. alexandri tree; Credit: David Samson

A study in the latest issue of Biology Letters shows that human facial expressions are very similar to those of other primates, and are produced in similar ways. "Some of the basic human expressions have clear counterparts in other species, such as the human smile -- equivalent to the bared-teeth display in other primates -- and laughter—equivalent to the primate play face, used during play," lead author Bridget Waller of the University of Portsmouth's Center for Comparative and Evolutionary Psychology, told Discovery News.

While smiles show teeth that could potentially bite onlookers, the relaxed nature of the rest of the face reveals that the tooth showing is not tied to aggression.

"Based on our facial muscle analyses so far, chimpanzees seem to show the most similarity to humans," Waller said. Here, a wide-eyed chimp looks relaxed, yet alert, as he surveys his territory.

When having one's picture taken, the subject usually prepares to look alert, instead of having eyes downcast or otherwise looking away. This was especially true for older photography sessions, which required more time for the sitter that, in this case, was David Davis, a former Supreme Court Justice.

There is little doubt that these chimps are curious about what the middle one is holding. Waller thinks that many expressions are produced subconsciously. The observers' responses may also happen at a subconscious level.

An important difference between human and other primate facial expressions is seen in the human look of determination. These women appear to be both curious and determined to investigate something online. In children, a look of determination incorporates components of anger, Waller said. "Primates have a similar expression used during bluff displays, but this doesn't seem to be produced when they are engaging with a difficult task." She and her colleagues believe humans could use the look to solicit help from others.

The wide-open eyes and mouth -- with teeth flashing -- of this marmoset suggest that he is feeling dominant. When an individual is submissive, he or she will be greater inclined to protect the face by closing the eyes and mouth more.

Actor Jim Carrey, shown in wax at Madame Tussauds museum, often exaggerates his facial expressions for comedic effect. He is definitely not conveying shyness, but rather dominance.

Sometimes facial expressions are paired with entire body displays. This siamang appears to be informing others who is king of the jungle. While our interpretations of non-primate expressions are inherently human-centric, it is clear that the photographed siamang -- at least in this moment -- is not afraid to make his presence known.

Wrestler Bobby Fish flaunts his rippling muscles in this victorious pose. Other research has found that such spontaneous expressions of triumph and pride, commonly seen at the Olympics and other sporting events, have their roots in non-human primate displays. "We believe that the triumph expression signals victory and achievement, which in turn signals dominance and aids in establishing status in a hierarchy," David Matsumoto, who conducted the research, told Discovery News. "This enables social coordination and enhances reproductive success."