Carry On Walking!

[Guest guest]

Carry On Walking!

http://www.sciencedaily.com/releases/2007/04/070402103004.htm

The next time you are struggling to carry your bags home from the

supermarket just remember that this could, in fact, be the reason

you are able to walk upright on two legs at all! How we have evolved

to walk on two legs remains a fundamental but, as yet, unresolved

question for scientists. A popular explanation is that it is our

ability to carry objects, particularly children, which forced early

hominins onto two legs.

Researchers looked at the energy expended when walking whilst

carrying a 10kg load. Importantly, the distribution of the weight

varied in each instance. Female participants, of child bearing age

(20-30 years old) were assessed walking at a constant speed carrying

either a symmetric load, in the form of a weighted vest or a 5kg

dumbbell in each hand, or carrying an asymmetric load, which was a

single 10kg weight carried in one hand, or a mannequin infant on one

hip.

Results indicated that when carrying an evenly spread load humans

are actually more efficient at carrying than most mammals but

carrying awkward loads, such as an infant on one side of the body,

uses much more energy. However this sort of carrying would have been

inevitable once early hominins lost the ability to cling on with

their feet. " The high energetic cost of carrying an asymmetric load,

suggests that infant carrying would need to generate significant

benefits elsewhere in order to be selected for, " says Dr Johanna

of the University of Manchester.

This work is part of a larger project, run by Dr Bill Sellers at the

University of Manchester, which also uses computer simulations to

try to understand evolutionary processes, particularly the way in

which we and other animals move.

Future plans are to extend this study to assess the energy cost of

carrying in great apes which will be very tricky indeed. Computer

models of early hominins carrying will also be built to try and

evaluate whether their body shape and posture - long arms and short

legs - would have made them noticeably better or worse at carrying

than ourselves. This will help to build up a picture of how we

evolved to walk to two legs.

Dr Johanna presented work supporting this theory on Saturday

31st March 2007 at the Society for Experimental Biology's Annual

Meeting in Glasgow.