Orangutans are lefties, chimps and gorillas right-handed

Photo showing an orangutan engaged in the TUBE task. Photo used with permission of the researcher  William Hopkins. 

Mmm, love that peanut butter
Apes are right-handed or left-handed, just like us. Not a big surprise, since they're our closest evolutionary relatives. A research team led by William Hopkins of Agnes Scott College recently tested 777 captive apes  - orangutans, gorillas, chimpanzees, and bonobos. Each ape was given a PVC tube 15 cm in length and 2.5 cm in diameter, with peanut butter smeared in both ends. The peanut butter was too far inside to reach with their mouths. The apes had to hold the tube with one hand and reach inside with a finger of the other hand. The researchers recorded which hand the apes used to reach inside for the peanut butter.  Each ape was tested on 2 to 4 occasions, in solitude if possible.

Only the orangs were left-handed
Orangutans turned out to be the only southpaws. The majority of gorillas and chimps are right-handed, as are 90% of humans. Bonobos showed no significant handedness at the population level. Hopkins believes that handedness at the population level in apes may be a result of ecological adaptations associated with posture and locomotion (personal communication with Hopkins).  He plans further research to try to understand why orangutans are left-handed, while other apes and humans are right-handed in general. It may be somehow related to the fact that orangutans are the most arboreal of the apes.

Hopkins' research will soon be published: Journal of Human Evolution 60 (2011) 605-611.

 

 Orangutans at a sanctuary on Borneo, drinking milk. Note that they're holding hands!  Photo: Sally Kneidel

Handedness in crows too
Apes are not the only nonhumans to display handedness.  In 2007 I wrote this post about research by Gavin Hunt of the University of Auckland, who documented handedness and tool-making in New Caledonia crows.

Post by Sally Kneidel, PhD

For further reading on primate conservation and behavior, and my observations of wild orangutans on Borneo and Sumatra, check out some of my earlier primate posts:

Some of my earlier primate posts:
Trade a major threat to primate survival. March 21, 2011
We are family: new evidence of our close link to chimps Feb 16, 2011
Is males' attraction to trucks and balls genetically based? Jan 14, 2011
Hunting may threaten orangutans even more than habitat loss Dec 6, 2010
Wildlife trade rivals drug trade in profits September 20, 2010
Laws flaunted: flourishing pet trade threatens orangutans' survival August 23, 2010
My search for a wild orangutan in Borneo and Sumatra August 16, 2010
Orangutans dwindle as Borneo, Sumatra converted to palm-oil plantations August 3, 2010
The great apes are losing ground March, 2010
The U.S. imports 20,000 primates per year. February, 2010
Baboons are Africa's most widespread primate. Females rule! December 30, 2009
Mama monkeys give in to tantrums....when others are watching. April 23, 2009
Angry chimp reveals a "uniquely human" ability. March 21, 2009
Monkeys and parrots pouring from the jungle. September, 2008
Chimps' short-term memory is better than humans'  April 2, 2008
Chimps share human trait of altruism August 3, 2007

Keywords: orangutans chimps gorillas apes handedness William Hopkins

Exposure to a widely used chemical in utero leads to less masculine play in male children

Boys exposed in the womb to chemicals called phthalates are less likely to engage in masculine play during childhood.  So says a study soon to be published in the International Journal of Andrology.  Masculine play was defined as playing with guns, cars, trucks and other toys typically favored by boys.  The greater the exposure during pregnancy, the more dramatic was the behavioral effect later. Girls' play was not affected.

Hormones program the fetal brain
According to Heather Patisaul, a neuroendocrinologist at NC State, male sex hormones program fetal brain development, and this programming explains why boys like trucks and girls tend to prefer dolls. Anything that interferes with this hormonal influence can subtly reduce masculinization of a male's brain.

Phthalates have previously been reported to affect male hormones, but it was not known how this affected behavior.  The current study began several years ago when researchers measured phthalates during mid-pregnancy in a group of women across four states.  Three to six years later, the researchers asked the mothers to rate their children's play using the Pre-school Activities Inventory.  Each mother recorded how often in the past month her child had engaged in activities such as playing house, playing with dolls, dressing up in girls' clothes, playing with toy cars and trucks or guns, or play-fighting.  The study included 71 girls and 74 boys.

Less masculine play; more gender neutral play
The behavioral assessment revealed that boys with the highest exposure to phthalates in the womb had the lowest incidence of typically male play and a higher incidence of gender-neutral play. The phthalate-exposed boys did not have higher scores for typically female play. The lead researcher, Shanna Swan of the University of Rochester School of Medicine & Dentistry, said "We'd describe their play as less masculine," but not more feminine.

These findings are thought to be particularly significant because exposure to phthalates is so widespread and includes virtually everyone in the U.S.  Phthalates are industrial chemicals widely used as solvents, including use in cosmetics such as nail polish and hair spray. They are also widely used in plastic tubing involved in food processing.

The summary I read of the study, in Science News, did not offer any suggestions about how to avoid ingesting phthalates.  If I do find any information about that, I'll post it on http://veggierevolution.blogspot.com and on http://sallykneidel.com.  I'll keep an eye out for the report of the study that will soon be published in the academic journal mentioned above.

by Sally Kneidel, PhD

Source: 
Janet Raloff. "Chemicals from plastics show effects in boys: Fetal exposure to phthalates linked to less masculine play." Science News. December 19, 2009.

My previous post on behavioral effects of chemical exposure in womb:  

BPA exposure in womb linked to childhood behavioral changes  Dec 26, 2009.