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One of the most extreme cases from the annals of IQ research is Isabelle:

  • Isabelle was discovered living in a darkened room with her deaf-mute mother as her only contact.
  • When Isabelle was discovered she was almost seven years old and had no sense of language.
  • She had been deprived of learning how to speak because of her mother being both deaf and mute.
  • As a result, when authorities found her they believed that she was also deaf and mute like her mother, because she could only make noises.
  • This was proven wrong when she started to speak after receiving intense training.
  • When Isabelle was initially tested, at almost seven years old, her mental age concluded to be at about 19 months old.
  • Within two months of being trained, Isabelle was putting together logical sentences.
  • Within a year she was already learning how to read.
  • While her IQ score was extremely low when she was found; at almost nine years old she was completely caught up with her peers and had a normal IQ.

The case is fascinating because when Isabelle was tested in 1938, being almost seven, she likely had a far bigger brain than the average 19 month old, yet scored the same as the average 19 month old.

Commenter Race Realist argues that IQ tests measure exposure to the culture, and he’s partly right because Isabelle’s lack of culture caused her development to be extremely delayed.

But what’s interesting is that it takes the average baby 19 months of culture to acquire the same level of skill that Isabelle acquired almost instantly.  This shows that IQ tests are not merely measuring cultural exposure, but the brain’s physical development, and being almost seven, Isabelle likely had a much bigger and more complex brain than the average baby.  Having the physical brain of a seven-year-old, Isabelle was able to learn in a few months what the smalled brained average baby learns in 19 months, and in just 2 years she had acquired 7.5 years of childhood intellectual development.

Once she had caught up to her chronological peers at age 9, her progress became completely average because her neurological development no longer exceeded her intellectual development.

She graduated from high school an average student.

The question is was Isaebelle ever less intelligent than her chronological peers, or was the test simply culturally biased against a girl who had no language or culture for the first 6.5 years of life?  One wonders if on a more culture fair test, like the one the crow below is taking, she would have had an average IQ from the moment she was discovered.

Of course it’s worth noting that Isabelle was discovered young.  Not all cases of extreme deprivation end so well: