Fossil footprints indicate that hominins were already as large as modern humans by 1.52 million years ago.
Undamaged fossil skeletons from that time are rare, and so determining characteristics such as the size and walking speed of human ancestors has been challenging. Brian Richmond and Heather Dingwall at George Washington University in Washington DC and their colleagues measured foot size and stride length from fossil footprints of seven individuals — which were probably Homo erectus or Paranthropus boisei — discovered in northern Kenya. To translate these measurements into physical attributes such as stature, body mass and walking speed, the researchers studied the relationship between body dimension and gait in habitually barefoot modern adults from Kenya. The authors were then able to infer that the size of these hominins was comparable to that of modern humans.