The big toe was one of the last parts of the foot to evolve, a new study has revealed.
A rigid toe allows us to walk and run upright, however, scientists say this bone structure evolved well after the rest of the toes in the human foot.
The latest findings suggest that while early humans were able to walk upright for more than 4.4 million years, they did not start walking like we do until much later.
Until now, debate has raged over whether our earliest ancestors strode like modern humans or used a more awkward crouching stance like that of gorillas.
Scientists believe the toe was one of the last parts of the foot to change because humans still needed it to grip when climbing trees.
A rigid toe allows us to walk and run properly but scientists say it did not look as it does today until well after the rest of the foot (stock image)
‘Our ability to efficiently walk and run on two feet, or be “bipedal”, is a crucial feature that enabled humans to become what they are today,’ lead author of the study Dr Peter Fernandez, from Marquette University in Milwaukee told BBC.
‘For everything to work together, the foot bones first had to evolve to accommodate the unique biomechanical demands of bipedalism.
‘The big toe could still be used for grasping, as our ancestors spent a fair amount of their time in the trees, before becoming fully committed to walking on the ground,’ said Dr Fernandez.
MailOnline has contacted the researchers to find out exactly when they now believe the big toe evolved in early humans.
The latest findings suggest the change in bone structure that created the rigid big toe started around the same time as the evolution of the genus Homo, which is widely believed to have happened some two million years ago.
Researchers analysed the changes in ancient toes by creating three-dimensional scans of the toe bone joints from living and fossilised human species, as well as a number of primates.
These were then mapped onto an evolutionary tree.
‘The primate foot functions as a grasping organ,’ researchers wrote in the paper published in the journal Proceedings of the National Academy of Sciences.
‘As such, its bones, soft tissues, and joints evolved to maximise power and stability in a variety of grasping configurations.’

Scientists believe that it might have been last to change because we still needed it for climbing trees (stock image)
It is still not known exactly why our ancestors started walking on two feet, but some experts believe it’s likely because it allowed us to carry things with our hands.
Others have credited the change with a global deforestation at the time.
Marquette University researchers say they would now like to conduct similar analyses on the remaining bones in the forefoot.
Debate has raged over whether our earliest ancestors strode like modern humans or used a more awkward crouching posture like that of chimpanzees and gorillas.
Analysis of new footprints in Africa suggest humans walked fully upright 3.6 million years ago, according to previous research published in April.
It means Lucy, the famous ‘mother of man’ discovered as a 3.2 million year old skeleton, may have paced around just like us.

Lucy, the famous ‘mother of man’ discovered as a 3.2 million year old skeleton (pictured in a model in Houston), may have paced around just like us