humans speak, monkey speech

Why Humans Are the Only Animals That Speak

August 22, 2009 07:00 AM
by Shannon Firth
A new study says the expansion of a specific region of the brain designated as a speech and language area may hold the answer to why humans are the only species that talks.

Scientists Compare Chimps’ Brains With Our Own

For years, scientists have associated humanity’s capacity for language with an area of the brain known as Broca’s area, named for Pierre Paul Broca, a French doctor who discovered that patients with damage to this area were nearly incapable of speech.

In 2008, scientists at Yerkes National Primate Research Center found that when three chimpanzees “gestured and called out” for food, brain activity increased in chimps’ brains in an area corresponding to Broca’s area in humans, disputing the idea that Broca’s area served a unique function for humans.

The study’s co-author, Jared Tagliatela, told Wired that his results challenged the established belief that vocalizations from chimps and other nonhuman primates were simply “visceral” and “emotive.”
Tagliatela argued, “This involvement of a pre-motor planning area suggests that there’s more intentional communication going on.”

More recent studies have set this theory back. Researchers at George Washington University analyzing the differences between Broca’s area in humans and a comparable region in primates, believe that although both chimpanzees and humans make use of this brain region, it “ballooned after humans split from chimpanzees,” reported New Scientist.

Ewen Callaway, who authored the article, explained one scientific theory that hinges on the imbalance in the size of Broca’s area, which is larger on the left side than the right in most humans. “[T]his seems to correlate with the finding that 94% of right-handers do most of their speech and language processing on the left sides of their brains,” reports Science magazine.

It may also be the critical difference that enables humans to process language, reported Callaway.

Chet Sherwood, a neuroscientist at George Washington University, and his colleagues, studied the brains of 12 chimpanzees after their deaths. They found that the area correlating with Broca’s area in humans, though it varied widely between individual chimps, did not show the same “population-wide differences.” He also did not find a correlation between chimps’ “-handedness” and differences in symmetry.

According to Science magazine’s blog, Origins, the team’s study reported, “[T]his evidence supports the conclusion that enlargement of Broca’s area on the left side is an evolutionary specialization.”

Opinion & Analysis: Locating Broca's area

Origins writer, Michael Balter points out that one of the biggest problems in any study of Broca’s area is that scientists have not reached a consensus on where in the frontal lobe it lies. “Thus, many brain experts define Broca’s area as two adjacent regions called Brodmann’s areas 44 and 45 … But others have included a somewhat larger area in their studies.”

Video: Elaine Morgan discusses the aquatic ape theory

According to Elaine Morgan, the reason other primates can’t speak while humans can is because we’re able to consciously control our breathing. “The only creatures that have got conscious control of their breath are the diving animals and the diving birds. It was absolutely a precondition for being able to speak.”

In her TED talk, Morgan details the aquatic ape theory, the belief that our primate ancestors didn’t go directly from the trees to the plains, but stopped in the oceans first. This theory explains how humans gained control over their breathing, and explains other physical qualities, such as our furless, streamlined bodies and the fatty layer under our skin.

Background: How different are apes and humans?

In 2006, Time writer, Michael D. Lemonick recounted the similarities between apes and humans. Both are able to fashion tools, both live in social hierarchies and both commit murder. He added, “[Apes] can’t form words, but they can learn to communicate via sign language and symbols and to perform complex cognitive tasks.” Humans and apes share 98 to 99 percent of the same genes. From a genetic standpoint, they are more similar than mice and rats.

Still, C. Owen Lovejoy, an anthropologist for Kent State University, argues, it’s much more complex than that.  “It’s like having the blueprints for two different brick houses. The bricks are the same, but the results are very different,” he told Time.

Reference: The Science of the Brain

findingDulcinea: Science of the Brain

It may seem like the Internet has an overwhelming number of sites but it’s really quite simple compared to the human brain, which has roughly 1,000 trillion connections—about the same as the number of leaves on all the trees in a rainforest.

NEXT: Baby Apes Shed Light on the Evolution of Laughter

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