The body weight of AL 288-1 (‘Lucy’): A new approach using estimates of skeletal length and the body mass index

A method of estimating the body mass of hominids by use of the skeletal length and physique index is described. The body mass indices (BMI) of female humans and female chimpanzees are known and this permits an estimate of the probable BMI for the female common ancestor and thus for female morphs intermediate between the common ancestor and modern humans. AL288-1 (‘Lucy’) probably had a BMI of about 22.3 kg m⁻² and for a height of 105cm this yields a body weight estimate of about 25 kg. Body weight estimates of 28–29 kg would imply a body mass index similar to female chimps and are improbable. These conclusions will be compromised if the chimp–gorilla–homo phylogenetic relationship proves to be a trichotomy rather than a chimp–homo dichotomy.