Fighting Led to Upright Posture in Humans

Studies have shown that animals that walk on four limbs stand on their hind legs when fighting. The standing position is thought to facilitate better use of the forelimbs to hit the opponent with a greater force. This study attempted to see if this posture could generate more striking power in humans than when a person stands like a four-legged animal. Results showed that when a person stood on his legs, he generated around 44 percent more force downwards and 47 percent more force upwards, than when he was on all fours. “These results indicate that bipedal posture does provide a performance advantage for striking with the forelimbs.” The author concludes that this has promoted the adoption of  an upright posture in humans.

Many mammals that walk on all four limbs stand up on their hind limbs while fighting an opponent. This impulse is seen in a wide range of mammals such as the cat family (cats, lions, tigers, etc.), the dog family (dogs, wolves, foxes, bears etc.), horses, anteaters and apes. It is speculated that the bipedal posture lends more power to the strike and is hence adopted by these animals. Striking downwards with the forelimbs is also speculated to generate a greater striking power than striking upwards. This study involved human volunteers who were tested in both bipedal and four-legged postures, to see if their striking power was greater upwards or downwards.

* For the study, a total of 15 healthy men who had had prior training in boxing and other martial arts were chosen.
* The men were asked to strike a punching bag connected to a device to measure the force of the strike.
* The strikes were orchestrated in both standing on two feet and the four-legged posture. The latter posture involved supporting oneself on the knees and a hand and using the other arm to strike. Both forward, side ways, downward and upward strikes were also recorded.

Key findings
* The results revealed that bipedal posture allowed for a 44 percent more impact downward and 47 percent more impact upward, when compared to the four legged posture.
* A forward hit registered the highest force – 49 percent greater in the bipedal posture compared to the four legged posture.
* A sideways hit showed a 43 percent higher force in the two legged posture compared to the four legged posture.
* While assessing the total amount of work energy expended, it was noted that downwards strikes needed 2.3 times more energy than did upward strikes in both two- and four-legged positions.

Next steps/Shortcomings
The author admits that since human beings are bipedal by habit, this study may not be completely relevant for them. A similar study could be conducted in animals that walk on four limbs and adopt a bipedal posture to fight, especially the great apes. However, it is difficult to train the animal to fight for such an experiment.

This study shows that when humans strike with their hands while standing on their lower limbs, they tend to exert 40 to 50 percent more force in their strikes than when they are on their knees and supporting their body with one of the arms, like a four-legged animal. It is also seen that a bipedal posture can generate around 200 percent more energy when striking downwards than when striking upwards. Observing that the males of the great apes compete and fight from a bipedal position to win the right to mate with a female, the author concludes that a similar incentive drove human beings into adopting a bipedal posture.

For More Information:
The Advantage of Standing Up to Fight and the Evolution of Habitual Bipedalism in Hominins
Publication Journal: Plos One, May 2011
By David R Carrier; University of Utah, Salt Lake City, Utah

*FYI Living Lab Reports Are Summaries of the Original Research

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