I don’t have any good evidence that humans raised without language per se are less intelligent (if we understand “intelligence” to refer to a general ability to solve new problems). For example, Genie was raised in isolation for the first 13 years of her life, and never developed a first language. Some researchers have, for various reasons, guessed that she was born with average intelligence, but that she, as a 14-year old, had a mental age “between a 5- and 8-year-old”. However, here we have the confounding factor that she also was severely abused, and that she got very little mental stimulus in general for the first 13 years of her life, which would presumably obstruct mental development independently of a lack of language. This makes it hard to draw any strong conclusions (and we would regardless have a very small number of data points).
However, just to clarify, the argument I’m making doesn’t crucially rely on the assumption that a human with language is significantly more intelligent than a human without language, but rather on the (presumably much less controversial) assumption that language is a significant advantage regardless of whether or not it is also paired with an increase in intelligence. For example, it would not surprise me if orangutans with language (but orangutan-level intelligence) over time would outcompete humans without language (but otherwise human-level intelligence). This, in turn, makes it difficult to infer how intelligent humans are compared to animals, based on what we have achieved compared to animals.
For example, one might say
“Humans have gone to space, but no other species is anywhere close to being able to do that. This proves that humans are vastly more intelligent than all other species.”
However, without access to language, humans can’t go to space either. Moreover, we don’t know if orangutans would eventually be able to go to space if they did have access to language. This makes it quite non-trivial to make a direct comparison.
I don’t have any good evidence that humans raised without language per se are less intelligent (if we understand “intelligence” to refer to a general ability to solve new problems). For example, Genie was raised in isolation for the first 13 years of her life, and never developed a first language. Some researchers have, for various reasons, guessed that she was born with average intelligence, but that she, as a 14-year old, had a mental age “between a 5- and 8-year-old”. However, here we have the confounding factor that she also was severely abused, and that she got very little mental stimulus in general for the first 13 years of her life, which would presumably obstruct mental development independently of a lack of language. This makes it hard to draw any strong conclusions (and we would regardless have a very small number of data points).
However, just to clarify, the argument I’m making doesn’t crucially rely on the assumption that a human with language is significantly more intelligent than a human without language, but rather on the (presumably much less controversial) assumption that language is a significant advantage regardless of whether or not it is also paired with an increase in intelligence. For example, it would not surprise me if orangutans with language (but orangutan-level intelligence) over time would outcompete humans without language (but otherwise human-level intelligence). This, in turn, makes it difficult to infer how intelligent humans are compared to animals, based on what we have achieved compared to animals.
For example, one might say
“Humans have gone to space, but no other species is anywhere close to being able to do that. This proves that humans are vastly more intelligent than all other species.”
However, without access to language, humans can’t go to space either. Moreover, we don’t know if orangutans would eventually be able to go to space if they did have access to language. This makes it quite non-trivial to make a direct comparison.