Just A Video Debunking Racists

[Angrboda]

I don't see how anyone could prove that poverty causes low IQ.

Prove may be too strong a word, but it's a well known correlate of poverty that poor mothers receive less pre-natal care and lower quality pre-natal care than more affluent mothers, including generally poorer pre-natal nutrition. It seems perfectly plausible that this would have a negative impact upon the intelligence of the developing fetus.