All living primates have the ability to hold objects tightly with their hands, whether tree limbs or tools. Try again.

Correct! Chimpanzees and other apes can walk on two legs for short distances, but there is a difference between being able to do something occasionally and doing it all the time. Select another correct answer. You selected all the correct answers.

Correct! Our large brains, relative to our body size, are a trait that sets humans apart from other primates. Select another correct answer. You selected all the correct answers.

Correct! There is a reason that the Leakeys knew they were in the right place to find fossils of our human ancestors when they found sharpened pieces of stone in Olduvai Gorge: humans rely on tools for their everyday survival. Select another correct answer. You selected all the correct answers.

Both skulls were found in the same rock layer and were roughly the same age, around 1.8 million years old. Try again.

Correct! Characteristics of the second skull, in particular its relatively larger brain and flat face, suggest that it came from a closer relative to Homo sapiens than the first skull. Select another correct answer. You selected all the correct answers.

Both skulls belonged to hominid species that likely walked upright. One was more likely in the lineage that eventually gave rise to humans; the other one, as Dr. White said, was on a "side branch" of human evolution. Try again.

The characteristics of the first skull, in particular its large teeth and relatively small brain size, suggest that it was not the toolmaker. Try again.

Correct! By comparing the protein and DNA sequences of two closely related species, scientists can estimate approximately when their last common ancestor lived. Select another correct answer. You selected all the correct answers.

The oldest stone tools date back to about 2.6 million years ago and do not provide evidence about when the common ancestor of modern humans and chimps lived. Try again.

Modern humans did not evolve from modern chimpanzees. The two species share a common ancestor that was neither a human nor a chimpanzee. Try again.

The rates of evolutionary changes for specific characteristics vary depending on the selective pressure, population size, generation time, and other factors. It is not possible to predict how many years a given evolutionary change would take without knowing these other variables. Try again.

Larger brains and bipedality, or the ability to walk exclusively on two legs, did not appear at the same time in our evolutionary history. Try again.

Stone tools have never been found in rock layers older than about 2.6 million years ago. Try again.

Correct! Lucy's hip structure suggests that Lucy (an Australopithecus afarensis) was bipedal. Bipedality preceded the other two traits because Lucy had a relatively small brain compared to that of modern humans and stone tools have not been found in rock layers older than about 2.6 million years. Select another correct answer. You selected all the correct answers.

Lucy had a relatively small brain, about 500 cc, or one-third the volume of a modern human’s brain. There is, however, evidence that it had one of the other two traits mentioned here. Try again.

While DNA sequences can be remarkably durable, to date they have not been obtained from material in a fossil as old as Ardi. Try again.

Scientists can make predictions about when a species evolved based on its features, but the predictions are imprecise because evolution does not occur in an orderly step-by-step manner. Other types of evidence offer more precise measures of age. Try again.

No stone tools are associated with Ardi. Try again.

Correct! Layers of volcanic deposits can be given precise ages by radiometric dating. Volcanic activity has been common along the East African Rift Valley for millions of years, making it possible to obtain dates for many significant finds. Select another correct answer. You selected all the correct answers.

Ardi represents a much older species than Lucy. The Lucy fossil is about 3.2 million years old and Ardi is 4.4 million years old. Try again.

Correct! By analyzing tens of thousands of plant and animal fossils, paleontologists concluded that Ardi lived in woodland setting. This was surprising because previously scientists predicted that bipedality evolved in a grassland setting. Select another correct answer. You selected all the correct answers.

Fossils of plants and animals found with Ardi were not those of grassland organisms, which surprised scientists who predicted that bipedality evolved in a grassland setting. Try again.

Evidence of animal and plant domestication does not appear until millions of years after Ardi. Try again.

Correct! Charles Darwin made this prediction before any hominid fossils had been found. Modern discoveries of fossils like Ardi, among the oldest known fossils in the human lineage, in Africa support this hypothesis, as do genetic data. Select another correct answer. You selected all the correct answers.

Humans, like all other species, are still evolving. For example, the increased prevalence of lactose tolerance among humans and differences in skin color among human populations are evidence of recent human evolution. Try again.

Correct! Ardi is one example of a hominid with a mix of traits today associated with modern humans and modern chimpanzees. Select another correct answer. You selected all the correct answers.

Correct! Remember that Dr. White described Homo as "technological primates," meaning that they adapt through culture as well as biology. Select another correct answer. You selected all the correct answers.