Assisting developing countries should be the responsibility of developed countries. To what extent is this statement true?

Backing to the beginning of prehistoric period when early humans inhabited the Earth, the style of humane society differed substantially to the modern one. Commonly, they presented a “nomadic hunter-gatherer” behavior which “tended to be very small and egalitarian”, according to Wikipedia (2014, ‘Prehistoric’). This means that mankind was not very numerous, and the daily routine was based on survival which just basic needs were supplied by themselves with considerable effort, involving activities, such as, hunting for food, farming, manufacturing their own clothes, and seeking for a safe shelter, usually a cave. Thus, possibly, situations of “pronounced deprivation in well-being” with “the inability to acquire the basic goods and services necessary for survival with dignity” were fairly common in that time, which is a definition of poverty according to The World Bank quoted in a Wikipedia’s publication about the subject (Wikipedia, 2014, ‘Poverty’).
However, as human society grew, from the core named family, and then becoming clans, after that villages, and finally, cities and countries, more complex structures of communities were established, since survival was no longer a major challenge. In this way, other necessities were created, as well as, different specialized roles, shared resources and development of new technologies, always focusing in the enhancement of both, productivity and resources usage. Consequently, the impact that population growth has presented has been positive for the humanity, according to Rittenberg & Tregarthen (2009). They allege that “the growth rate of per capita income roughly equals the difference between the growth rate of income and the growth rate of population” (Rittenberg & Tregarthen, 2009).