Historical note on Darwin's consideration of early-onset dementia in older persons, thirty-six years before Alzheimer's initial case report.

In February 1871, the great naturalist Charles Darwin received a letter from Dr. James-Crichton Browne, who was serving as Director of the largest lunatic asylum in England. Darwin had been introduced to Crichton-Browne 2 years earlier by Henry Maudsley, who believed that the young psychiatrist could provide Darwin with clinical examples of extreme emotional expression, to aid him in preparing to write Expression of the Emotions in Man and Animals (1872). This particular letter from Crichton-Browne contained the first and only reference to "premature dotage" or "senile decay" found anywhere in Darwin's entire corpus of correspondence, which amounted to more than 80,000 pages of handwritten letters to nearly 2,000 individuals throughout his lifetime. Moreover, this letter from Crichton-Browne, received by Darwin 36 years before the first case report of senile dementia by Professor Alois Alzheimer, explicitly noted that such premature dotage is the result of "brain wasting." Crichton-Browne believed that senile dementia was the result of a central nervous system disease, with the emotional lability observed in his patients linked inextricably to the disease process. This early hypothesis, of interest to Darwin in 1871, anticipated the groundbreaking neurohistopathologic research and case description by Alzheimer 36 years later, and has been confirmed by all clinical research in this field since 1907. This concordance between psychological symptoms and Alzheimer's disease continues to be an important area of study, leading to recent advances in our understanding of the genetics, neurobiology, and neurochemistry of psychiatric illness in older adults.