RL: Do we know how mixed with Whites Blacks were 100 years ago in the US? Because the Black IQ in the US was 77.5 a century ago. They have gained 7.5 points since then. I suspect White IQ is worth 1 IQ point for every 3-4% White.
jm8: I don’t know about the early US black scores. But i suspect that 3-4% would be worth less since, as I calculated:
Assuming a black iq of 85 and a white iq of 100, a 1/8 white, 7/8 black population would average 86.8.
I’m not sure what the US score was a century ago. Ive heard it was about the same as now for most of the 20th century (starting in the 1920’s-30’s) I remember one very early 1920’s study being late 80’s or 90 (from the old “Occidentalist” blog again), but I’m not sure how representative it was. I will see If I can look for some data on the early US scores.
A 7.5 point reduction in the B-W IQ gap from 1920-present by averaging all test scores has been documented by Charles Murry of all people.
The average IQ scores of around 70 for Black Americans in certain areas of the Deep South of the United States where the degree of White admixture is significantly below the general average (Chakraborty et al., 1992; Parra et al., 1998) are also consistent with the hereditarian interpretation of the effects of hybridization. An average IQ of 71 was found for all of the Black children in an entire school district from a rural county in Georgia; the average White IQ in the same county was 101 (Jensen, 1977).
There is excellent evidence from as late as 1990’s that Black genotypical IQ is as low as 70 as I always suspected. Rushton could not believe that African IQ’s were as low as 70, so he undertook a trip to South Africa and tested Black students there and obtained a 70 score on Raven’s Progressive Matrices. He then tested Black university students and got a score of 85, which is about right as university students tend to average 25 IQ points higher than the general population.
This makes the case for Black environmental IQ gains much stronger.
If Black IQ is really genotypically 70, then each 3% of White admixture in Blacks ought to result in a 1 point IQ gain, which is the figure I have been using for my own work for a long time.
Putting genotypical IQ at 70 and adding 1 IQ point for each 3% White admixture gives us:
US Black IQ of 78 with 25% White admixture. This leaves a 7 point environmental IQ gain to an IQ of 85*.
Bermudian Black IQ of 85 with 50% White admixture. This leaves a 15 point environmental IQ gain to an IQ of 100**.
Bahamian Black IQ of 75 with with 15% White admixture. This leaves an 18 point environmental IQ gain to 93 IQ**.
UK Black IQ of 74 with 13% White admixture. This leaves a 26 point environmental IQ gain to 100 IQ**.
*By actual IQ test.
**By achievement tests that are considered to be proxies for IQ tests.