LOS ANGELES, June 7 (UPI) -- U.S. psychologists say they've found remarkable similarities in comparing gestures by ape and human infants at comparable stages of communicative development.

Analysis of video footage of a female chimpanzee, a female bonobo and a female human infant found all three species made gestures including reaching, pointing with fingers or the head and raising the arms to ask to be picked up.

Chimps and bonobos are the two species most closely related to humans in the evolutionary tree.

"The similarity in the form and function of the gestures in a human infant, a baby chimpanzee and a baby bonobo was remarkable," UCLA psychology Professor Patricia Greenfield said.

Writing in the journal Frontiers in Psychology, the researchers said the gestures of all three species were "predominantly communicative," a finding they called "striking."

To be classified as communicative, they said, a gesture had to include eye contact with the conversational partner, be accompanied by vocalization (non-speech sounds) or include a visible behavioral effort to elicit a response.

Overall, the researchers said, the findings support the "gestures first" theory of the evolution of language.

"Gesture appeared to help all three species develop symbolic skills when they were raised in environments rich in language and communication," study lead author Kristen Gillespie-Lynch said.

The pattern, she said, suggests gesture plays a role in the evolution, as well as the development, of language.