As the longest lived primate species, humans present a remarkable divergence from brain aging processes of their lineage. One way to investigate genetic infl uences on aging is to make informative comparisons among closely related species. Even though they are nearly identical to chimpanzees and bonobos in nucleotide sequence, humans appear unique in the primate lineages in their vulnerability to neurodegeneration at later ages, although this level of neurodegeneration was not common until the 20th century. The great apes typically have minor neurodegenerative changes of aging relative to the longer lived humans after the age of 70 years or even compared to shorter lived monkeys by the age of 20 years. Surprisingly, an even shorter lived monkey (marmoset) and a prosimian (grey mouse lemur) have extensive earlier deposits of brain amyloid before 10 years, which offer experimental opportunity for interventions into brain aging.