What are the underlying reasons for encephalization , and how did humans further develop as a result of it ?

The two major costs to encephalization appear to be developmental and metabolic (Bennett and Harvey, 1985b). All other factors being equal, bigger brains require a longer time to develop and are energetically more expensive to maintain.

abraham lincoln  (february 12, 1809  – april 15, 1865) was an american statesman, politician, and lawyer who served as the 16th  president of the united states  from 1861 until  his assassination  in april 1865. lincoln led the nation through the  american civil war, its bloodiest war and its greatest moral, constitutional, and political crisis.[2][3]  he preserved the  union,  abolished slavery, strengthened the  federal government, and modernized  the u.s. economy.

darwinism is survival of the fittest there for social darwinism is the survival of the wealthiest