Blacks are underrepresented at higher levels of socioeconomic achievement because the average IQ for a black American is 85. A large percentage of them, something like 1/4 or more, are at 70 or below, which is the legal threshold for being considered "retarded." Sociologists estimate that a person's odds of being a functioning, successful, independent member of society are about 50/50 at IQ 75. Africa, as a whole, has an average IQ of 70.
The average IQ of any population is normalized at 100. The average white IQ is a little over this, and east asians are even higher, by about 4-6 points or so over whites.
Blacks additionally account for more than 50% of the homicides, assaults, and rapes in the United States, about 54%, and have for the last 30 years. Criminological data is available at the DOJ website for anyone interested. Bear in mind that the DOJ may classify hispanics as white for the purposes of their statistical breakdowns. For example, on
http://www.ojp.usdoj.gov/bjs/homicide/race.htm, hispanics are not referenced. Other pages, such as the quote that follows, discriminate between hispanics and whites. The race/homicide table does not. On that page, you have blacks vs. whites&hispanics vs. others (asians). As you can see, blacks have committed a majority of homicides in the last 30 years. Other data is available from BJS as well as from other sources showing their grossly disproportionate contribution to ALL other violent crimes.
Blacks outcommit whites in crimes of violence by about the same ratio as men outcommit women, that is approximately 10:1. Hispanics in the United States tend to be around 3.5-4:1 with respect to whites. Asians' criminality averages lower than whites. Roughly 1/3 of black males will do State or Federal time for a major crime at some point in their lives. The percentages are far lower for other groups, lowest among east asians. Among various demographics, the homicide rate of young black males is the highest, astoundingly higher than the average rate in the USA, by a factor of 20. Homicide is the leading cause of death for young black males in the USA.
It is difficult to imagine a group so prone to criminality and low IQ to be able to achieve socioeconomically in proportion to their share of the population. IQ may or may not "really" measure "intelligence," whatever that is, but it VERY strongly correlates to socioeconomic success, just as the SAT correlates strongly to same as well as to academic performance. Unfortunately, standardized tests ARE predictive of aggregate outcomes. There are multiple, independent sources for this data, including "IQ and the Wealth of Nations," "Bell Curve," "Taboo" and others, which can demonstrate the strong correlation that average IQ has to both technical and economic achievement.
As an ethnic group, jews possess the highest average IQ. Who is surprised when they dominate Nobel Prize totals? IQ really does matter, much as many would like to believe it doesn't, and it is predominantly hereditary.
The black illegtimacy rate is far higher than the white one. In excess of 70% of black births are out-of-wedlock. They suffer from far higher incidence of drug use as well. In DC, a predominantly black city, fully 40% of the population functions at a 4th grade or lower academic competency.
It is categorically impossible for a population with these negative factors to expect to succeed in competition with other populations which have far higher testable aptitudes in the relevant attributes. Heredity is responsible for this.
If you want the DOJ crime stats, they are at:
http://www.ojp.usdoj.gov/bjs/welcome.html
This is the Bureau of Justice Statistics and, again, they may include hispanics with whites except where explicitly separated. There are other sources which demonstrate that non-hispanic white crime rates are far lower than represented by the DOJ in some cases where they reference "whites."
Here's a brief stat:
"Lifetime likelihood of going to State or Federal prison
Based on current rates of first incarceration, an estimated 32% of black males will enter State or Federal prison during their lifetime, compared to 17% of Hispanic males and 5.9% of white males.
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During the early 90s, the 18-24 black homicide rate was in excess of 350/100000. That is roughly equivalent to NINE TIMES the current rate of Washington DC (murder capital), or 5 times the rate of S. Africa, the most homicide-prone nation that keeps official statistics.
If you look at white+hispanic violent crime rate curves and attribute 80% of those values to hispanics (which is a correct attribution based upon other data), you can see how really much more violent blacks are than whites.
Also, as IQ is predominantly hereditary, rampant miscegenation among slave populations is credited for the difference between American black IQ and African black IQ. In fact, a substantial percentage of US blacks (80%) have a white male ancestor within the last few generations. This fact was borne out by DNA analysis of Y chromosomes. Whites' contributions to US black DNA have caused a significant elevation in average IQ.