Primatologist Frans de Waal says chimpanzees can do almost everything that was once considered a distinctively human trait.

The idea that only humans make tools is today "an unsustainable position," de Waal writes by email. "Then we also got the apes-have-no-theory-of-mind claims, which now have been seriously weakened, the culture claims, the idea that only humans are great at cooperation, and so on, none of which really holds up."

The only unique trait of humans, he says, might be that we have symbolic language.

De Waal’s latest book—"Are We Smart Enough to Know How Smart Animals Are?"—describes a monumental shift in our understanding of animal intelligence in recent decades. In one fascinating part, he takes on a theory about tools by pointing to new observations of chimps, a species that shares 99% of the same DNA as humans.

Anthropologist Kenneth Oakley laid out the old viewpoint in his 1957 book, "Man the Toolmaker," which argued that mankind was the only animal that systematically made tools.

That stance was challenged by anthropologist Jane Goodall’s observations of chimps in the wild. When, in 1960, she described chimps stripping leaves from a stem to make a tool to dig for termites, her colleague Louis Leakey telegrammed: "Now we must redefine tool, redefine Man, or accept chimpanzees as humans."

Still, Oakley wasn’t convinced. In subsequent writings, he dismissed Goodall’s observations as "a far cry from the systematic making of stone tools, the earliest known examples of which … evidently require much premeditation, a high order of skill and an established tradition implying some means of communication."

Thus, whether man is the only true tool-making animal remained an open question. Yet today, per de Waal, we can answer with a definitive no.

De Waal, the director of the Living Links Center at the Yerkes National Primate Research Center in Atlanta, Georgia and a professor at Emory University, lays out overwhelming examples of complex tool use by chimps. For instance:

—Chimps in the Congo have been repeatedly observed traveling with a combination of two sticks—a meter-long sapling and a flexible slender stem—which they use for digging into an ant nest and grabbing ants.

—Chimps in Gabon have been repeatedly observed hunting for honey with a five piece toolkit, including a stick for breaking open a hive, a stick for perforating the honey chamber, a stick for widening the opening, a stick with a frayed end for dipping into honey, and strips of bark to scoop honey up—all tools that are prepared and carried to the hive before the work begins.

—Chimps in one community are known to use pointed sticks to hunt, jabbing them into a tree cavity to kill a sleeping bush baby.

All told, per de Waal, chimpanzees communities tend to use between 15 and 25 tools, many of them prepared ahead of time with techniques that are passed from generation to generation.

Young chimpanzees play at a Congo sanctuary. http://en.wikipedia.org/wiki/Chimpanzee#mediaviewer/File:2006-12-09_Chipanzees_D_Bruyere.JPG Although chimps make and use tools to a greater degree than other non-human species, plenty of species—from gorillas to elephants to otters to crows—have shown they can use tools too. All of that weakens the idea of homo faber ("man the maker"), which claims that we have a unique ability to control the environment through tools.

As for other supposedly special traits of humans, de Waal says they have fallen one by one: chimps and other species have been observed showing empathy, regret, and friendship; recognizing faces; recognizing themselves in a mirror; understanding when other creature know or don’t know something; remembering distant events; exercising self-restraint; and more.

It may, again, be only in language that humans are unique: "We honestly have no evidence for symbolic communication, equally rich and multifunctional as ours, outside our species." de Waal writes in the book.

Whatever the differences between humans and the rest, there are clearly fewer than we once thought. Charles Darwin may have said in best in a quote featured by de Waal: "The difference in mind between man the higher animals, great as it is, certainly is one of degree and not of kind."