Height And Weight Evolved At Different Speeds In The Bodies Of Our Ancestors

Hominin Bodies Developed in `Pulse & Stasis’ Variation

 
An extensive latest research of fossils covering over four million years suggests that physique and body mass advanced at different speeds at the time of evolution of hominins, the ancestral heredity of which Homo sapiens alone still prevails.

As published in the journal Royal Society: Open Science, the research portrayed that instead of progressively growing in size, hominin bodies developed in `pulse and stasis’ variation with some linages that seemed to be shrinking. Discoveries have come from the largest research of hominin body sizes comprising of 311 specimens that date back from earliest upright species of 4.4m years from the modern humans and followed the last ice age.

Though the researchers have defined the physical evolution of assorted hominin species as `long and winding road having several branches and dead ends,’ they have informed that broad patterns in the data recommends bursts of growth at crucial stages together with plateaus with little alteration for several millennia.

The scientist had been amazed to discover `decoupling’ of bulk and stature of about one and a half million years back when hominin grew about 10cm taller though could not consistently gain any weight for a further million years having an average increase of 10-15kgs taking place at about 500,000 years back.
 

Increase in Stature – Increase Slimmer Structure

 
The height and weight in hominin species, before the event seemed to evolve `in concert’ according to the authors of the first study to jointly analyse the aspects equally of body size over millions of years.

Lead author Dr Manuel Will from Cambridge’s Department of Archaeology and Research Colleague at Gonville & Caius College had mentioned that an increase exclusively in stature could have increased a slimmer structure with long legs and narrow hips and shoulder. This could have been a variation to new environments and endurance hunting as early Homo species who had left the forests and progressed to more arid African savannahs.

He further added that the higher surface-to-volume ratio of tall, slender body would be beneficial when stalking animals for hours in dry heat since larger skin area tends to increase the capacity for evaporation of sweat. Besides this he also added that the later addition of body mass tends to coincide with the increasing migrations to higher latitudes wherein a bulkier body would be suited better for thermoregulation in colder Eurasian climates.
 

Body Size Highly Variable

 
But Dr Will points out that though these seem valid theories, vast openings in the fossil record endure to cover the complete truth. Dr Will together with his colleagues in fact had to evaluate body sizes often from highly fragmented remains and in some instances, from only a single toe bone.

From the study it was observed that the body size was highly variable at the time of the earlier hominin history having a range of various shaped species, from broad, gorilla-like Paranthropus to the more gracile Australopithecus afarensis.

 The hominin from four million years back had weighed around an average of 25kg and stood at 125-139cm. Dr Will and his colleagues state that evolutionary pressures which could have made their contribution, comprise of `cladogenesis’ the splitting of a lineage with one line, in this instance, the smaller-bodied one seemed to be extinct, probably as a consequence of inter-species competition.