She knew of his condition, didn't she? I remember her telling him at the end that the plant he needed for a possible cure was extinct. (A classic "sorry about your luck, David" ending for the series!)

"Logical! If they were logical, they wouldn't be human!
They are driven by strange impulses"
General Urko (Mark Lenard), Planet of the Apes TV series, "The Surgeon". (1974).