Inbreeding is certainly a problem, particularly where Blacks lived in small rural communities. Few Blacks relocated from outside, and so the gene pool became stale.

Take a look at photographs of Black murderers. The IQ is evident from the look in their eyes.

Genetics.

I've got a surprise for some people on this Thread.

Photographic evidence.

Google the following to wipe your eyes clear of the lies. Black soldiers fought gallantly for the Confederacy, to defend the South.

Google:

"Images for Black soldiers in the Civil War Confederacy"

Then, consider these facts:

"Union soldiers robbed, raped and murdered Free Black and slave Southerners they had come to "emancipate." Union "recruiters" hunted, kidnapped and tortured Black Southerners to compel them to serve in the Union Army. At the Battle of the Crater white Union soldiers bayoneted retreating Black Union soldiers and the 54th Massachusetts was intentionally fired upon by Union Maine troops while assaulting Battery Wagner. The Federal Official Records and memoirs of the USCT document all of these war crimes."

Then, there is this regarding Union treatment of the Black soldiers they conscripted:

" ...As usual with the enemy, they posted their negro regiments on their left and in front, where they were slain by hundreds, and upon retiring left their dead and wounded negroes uncared for, carrying off only the whites, which accounts for the fact that upon the first part of the battle-field nearly all the dead found were negroes." - Federal Official Records, Vol. XXV, Chapter XLVII, pg. 341 - report of the Confederate Commander, Savannah, April 27, 1864 - Battle of Ocean Pond."

[link to rense.com]