No, mental retardation is defined by poor functioning in everyday life due to widespread mental deficiencies, or due to profound focal deficiencies. A focal deficiency in IQ alone has to be quite severe before it substantially impairs life skills. Living well mostly requires talents like working well with other people, procedural memory of how to gather and cook food, manual dexterity, learning and ignoring extraneous stimuli, episodic memory, and so forth. These talents do not depend strongly on the symbolic reasoning skills measured by IQ tests.
Your confusion arises from treating correlation as causation. Mental retardation is commonly caused by genetic or developmental problems that cause global brain changes, producing deficits in many or all talents. This usually includes the specialized brain circuits involved in symbolic reasoning, lowering the IQ. So in a population with shared genes and environment, low IQ is strongly correlated with mental retardation, but neither is caused by the other.
"Either our ancestors were dullards, or the IQ test measures something other than innate intelligence."
The Flynn effect proves what we already knew, that human development is partially driven by the environment. Few serious scientists thought that each human is born with a exact fixed amount of smarts, like every atom of iron-56 has 55.93 AMUs of mass.
Your confusion arises from treating correlation as causation. Mental retardation is commonly caused by genetic or developmental problems that cause global brain changes, producing deficits in many or all talents. This usually includes the specialized brain circuits involved in symbolic reasoning, lowering the IQ. So in a population with shared genes and environment, low IQ is strongly correlated with mental retardation, but neither is caused by the other.
"Either our ancestors were dullards, or the IQ test measures something other than innate intelligence."
The Flynn effect proves what we already knew, that human development is partially driven by the environment. Few serious scientists thought that each human is born with a exact fixed amount of smarts, like every atom of iron-56 has 55.93 AMUs of mass.