1. Climate change: The charging cycles of climate and weather have greatly affected the human evolution to a very large extent. The last,6 to 8 million years has generally seen cooling trends marked by recurring ice ages. The onset of ice age around 2.5 million years ago covered most parts of earth with snow and there were major changes in climate and vegetation. The cooling and drying conditions led to the contraction of forests which expanded the plains or grasslands and deserts. This increased the competition among plants and animals for food.
The species which could better adapt to the climate change and procure food survived and the others became extinct.
2. Growth in Brain Size: The human species evolved larger and complex brains due to the environmental challenges they faced. They had to survive against physically powerful animals. The size of the brain in the habilis was 600 cubic centimetres. The erectus species had a brain size of 800-1100 cc, the Neanderthal man 1200-1900 cc and the **** sapiens of today has the brain of about 1400 cc.
It is more than twice the size of the brains of Chimpanzees or Gorillas. The growth in the brain size induced many activities like improved vision, upright posture, bipedal ism, tool making, use of ****, language etc.,
