Research reveals that modern-day people are about 10 per cent smaller and shorter than their hunter-gatherer forebears.
The human species may have passed its physical peak, reports The Australian.
Scientists say most of the decline has happened in the past 10,000 years, and has been accompanied by a 10 per cent decline in brain size.
The research reverses the popular belief that humans have grown taller and larger.
The finding has emerged from systematic studies of fossilised human remains, including skulls, found across Africa, Europe and Asia. The earliest of these date back about 200,000 years, the daily says.
"The fossil evidence for the next 190,000 years is patchy, but shows that humans remained tall and robust until about 10,000 years ago when many populations show reduced stature and brain size. It is a striking change," Marta Lahr, co-director of Cambridge University's Leverhulme Centre for Human Evolutionary Studies was quoted by the daily.
The decline in stature may be linked to agriculture, which began about 9000 years ago. However, if agriculture is the explanation for the change in stature, it would not clarify why human brain size has also decreased.
The Homo sapiens with the biggest brains lived 20,000 to 30,000 years ago, in Europe. Known as Cro- Magnons, they were tall with barrel chests and large jaws and teeth. Most impressive, however, were their brains, with males averaging a volume of 1500 cubic centimetres.