We are all related and we are all Africans under the skin.  Based on his research, Dr. Spenser Wells stated:

Everybody in the world is very closely related to each other.  We are all part of a big family.  

In fact, we all related to be people who lived in Africa recently as 50,000 years ago (or about 2000 generations away).

Our ancestors were very tough people.  They survived drought, famine, and ice age, which allows us to reach this far: migrating out of Africa to all over the world.

Summary

If Africa is the cradle of the mankind, then central Asia is its nursery.  Here are the human journey summarized from [1]:

• Why our ancestors left Africa?

  • They suffered from the drought caused by Ice Age (from 70,000 to 50,000 years ago)

  • Note that what they suffered was not cold (just a few degrees cooler in Africa), but draught

• The early groups of people were Saan Bushmen in Southern Africa and they still live there.

• The first big migration took the coastal route and started around 50,000 years ago, which is accounted for 10% of the human population:

  • Africa ➜ India ➜ Australia (Aboriginals) 

    • The animals and plants in Australia are unlike the other parts of the world.

    • Artifacts left by those migrants may be dated back from 40 to 45 thousand years ago

    • The skin color of coastal migrants can afford to be darker because they eat fishes which are full of vitamin D.

• The second big migration took the inline route and accounted for 90% of the human population:

  • Africa ➜  Middle East ➜ Central Asia➜ Europeans / Asians / Native Americans

    • African hunters followed grassland (i.e., food) into Kazakhstan (in Central Asia) at around 35,000 to 40,000 years ago

    • 1st wave headed for Northern India  

    • 2nd wave headed for China / Russia / America

      • Chukchi people still live in northern East Siberia who arrived there around 15,000 years ago; eventually they cross the land bridge and reached North America at around 13,000 years ago.

      • The Navajo are native American people who still live in the Southwestern United States.

    • 3rd wave headed for Europe

      • They left about 10,000 years ago from Middle East and from Central Asia about 35,000 years ago.

      • They have to adapt to the colder and darker life by the protection of clothing and housing.

      • Their skin became paler to absorb more lights for vitamin D (important for bone health).

References

1. The Journey of Man - A Genetic Odyssey