Final answer:
The timeline of human evolution shows the earliest emergence of bipedalism, followed by the reduction in teeth size due to dietary changes, culminating with a significant increase in brain size.
Step-by-step explanation:
The human lineage shows a particular sequence of evolutionary traits: bipedalism, the development of smaller teeth, and the increase in brain size. Bipedalism is one of the earliest traits that emerged among hominins and is evident in species like Australopithecus, which appeared around 4 million years ago. Hominins with features such as bipedal and a humanlike gait, including a broader pelvis and arched feet, indicate an adaptation to walking on two limbs. As dietary changes occurred due to the availability and cooking of meat, our ancestors experienced a reduction in the size of jaws and teeth. This reduction is particularly notable in Homo erectus, which had smaller teeth and smaller faces in comparison with their predecessors. Finally, there was a progressive increase in brain size, which was quite substantial by the time Homo sapiens evolved. This progression is highlighted by earlier species like Homo habilis, which exhibited larger brain sizes than their australopithecine ancestors, and Homo erectus which further developed larger brain capacities up to 1,250 cc.