A planet where apes evolved from men? That strange, sci-fi concept of Ted Post’s Beneath the Planet of the Apes is mere child’s play compared to bizarreness of the director’s outré exercise in suburban horror that is The Baby. Dudes, this one’s colored in all shades of fucked-up.

Newly widowed social worker Ann Gentry (Anjanette Comer, The Loved One) is assigned to investigate the Wadsworth family, headed by a frowny, chain-smoking matriarch (Ruth Roman, Strangers on a Train). Mrs. Wadsworth lives with her two daughters and one son, which isn’t all that odd until you realize that the boy, her “Baby,” isn’t a baby at all, but a fully grown adult (David Manzy) who never matured beyond infancy. He wears diapers and all.

Initially repulsed, Ann starts to ignore most of her other clients to visit this special case. She recommends Baby be put in a clinic — a suggestion that, to Mrs. Wadsworth, goes over about as well as that 10th vodka tonic. Weirdness grows as Baby cajoles his naive teen babysitter (“What kind of question is that? Of course I’m wearing panties. Don’t I always?”) into breast-feeding him on the job.

It all leads to an expected tragic ending, but what is not expected is how disturbing The Baby feels as a whole. It’s not just Baby’s chalkboard-nails crying fits that bother, but an overall pervading sense of unease, and yet somehow, this thing earned a PG rating. Unlike most horror films of the 1970s, it’s not fun — just remarkably confounding and unsettling. I recommend giving it a watch, if only so I’m not the only one so agitated afterward. —Rod Lott

Buy it at Amazon.