variability that occurred during the same period may have favored an
increase in brain size, since larger brains allow for behavioral plasticity
and cognitive mechanisms that produce novel behaviors,which are important
for survival in a wide range of environmental conditions (the
“variability selection” hypothesis; Potts, 1998; Ash and Gallup, 2007).
Finally, the extreme wet-dry climate short-term cycles in East Africa –
and the concomitant changes in general environmental conditions –
has been proposed as the factor that could explain the noticeably
change in brain size that occurred with the appearance of H. erectus
(sensu lato) at 1.8 mya (the “pulsed climate variability” hypothesis;
Shultz and Maslin, 2013).