Bipedalism, walking on two legs, first separated the homonids from the four-legged apes. Scientists used to believe that the size of the brain was what made homonids and four-legged apes different. Scientists soon began to understand that bipedalism was linked to the skull, mainly the foramen magnum. The foramen magnum is a hole in the skull where the spinal cord enters. The first homonid foramen magnum is very similar to us humans, which indicates a stooped posture and walking on two feet. Below is a photo of the basic evolution of the homonid into what us humans are today. This timeline also shows what objects were invented during the time, perfectly coordinating with Taylor's theory about objects' roles in human evolution.
Photo Credit: Vice, Is Homo Naledi, the New Species of Human, a New Species at All?
https://www.vice.com/read/heres-homo-nadeli-a-possible-new-human-species-542
https://www.vice.com/read/heres-homo-nadeli-a-possible-new-human-species-542
One huge misconception of evolution is that humans did not evolve one after another in a singular line. The human family tree is deep, with many branches. There was a time where three or four species of human were living at the same time! We can tell this by human fossils. Fossils played a huge role in the book since Taylor is an archaeologist.
Photo Credit: Tech Times, Where Homo Naledi Fits.
Click the link to play an interactive game where one can click on a human fossil skull and be given information on its ancestry and age. You can also see the family tree picture above and can click on any of these groups and be given more information about them. This is on the Smithsonian Website.
http://humanorigins.si.edu/evidence/human-family-tree
http://humanorigins.si.edu/evidence/human-family-tree