Aboriginal population's ice age plunge AUSTRALIA'S prehistoric population suffered an "astounding" decline at the peak of the last ice age, with food and water shortages more than halving the number of inhabitants, a new study suggests. Alan Williams, an archaeological consultant and PhD candidate at the Australian National University, said cool and incredibly dry conditions between about 21,000 and 18,000 BC had cut a swathe through the population, which at that time numbered around 20,000.