Answer to Question 1
In general acquiring human capital is a costly endeavor so the supply of workers with a lot of human capital is less than the supply of workers with little human capital. The difference in supply means that the more human capital an individual attains, the more income that individual will likely earn, other things remaining the same. Greater variation in human capital across the population of households increases the degree of income inequality among households. While the level of human capital attained varies across households, this factor alone does not completely explain the observed variation in income across households in the United States
Answer to Question 2
Income within nations generally has become distributed less equally. However because the average income within the poorest nations has been rising more rapidly than average income within richer nations, the world distribution of income has become more equally distributed.
A vertebrate digestive system, as shown in the human.
Although Neandertal brain sizes fall well within the modern human range, their EQ is lower than mode
Barbara Kruger, Untitled (We won't play nature to your culture).
Structure and function of human teeth.
Loci of Some Human Genes
Human Progeroid Conditions