As hominins diverged from other primates, which of the following appeared first?

(A) reduced jawbones

(B) an enlarged brain

(C) the making of stone tools

(D) bipedal locomotion

Hominins include the present-day human beings along with all the extinct primate species that resembled Homo sapiens. The traits found in today's hominins were developed slowly due to evolution, and the acquisition of new traits occurred one after the other; rather than simultaneous development of all traits.

The reduction of jawbones and the development of smaller teeth were firstly discovered in the fossils of Homo ergaster, which existed approximately 1.9 million years ago. This trait was not the first acquired character that led to divergence from other primates.

Thus, reduced jawbones developed at a much later stage in hominin evolution.

Therefore, the given option is false.

The enlargement of the brain size was the last character to be developed during hominin evolution. It was observed around 1.5 million years ago and accounted for better socializing skills in human ancestors.

Thus, an enlarged brain was developed in the last stages of evolution.

Therefore, the given option is false.

Making and using tools from stone or sticks is an old hominin trait but not the first acquired character in the hominin lineage. Fossil studies in the Ethiopia region suggest that the use of stone stools dates back to around 2.5 million years ago.

Thus, this trait evolved around 2.5 million years ago but was not the earliest trait to mark divergence.

Therefore, the given option is false.

The hominins exhibited character similar to the humans, and the first trait that diverged hominin members from other primate organisms was the acquisition of an upright structure of the skeleton and bipedal locomotion. This trait evolved approximately 4.2 million years ago.

Thus, bipedal locomotion was the first trait to appear in hominin divergence from other primates.

Therefore, the given option is true.