I’m trying to find a sci-fi novel or short story my dad told me about. It involves discovery of a peaceful alien race and humans study them, admire them and many start to body modify themselves to live among these aliens. But since said aliens are mating with humans and not each other, eventually all the aliens go extinct with no original alien left among them. Further these misguided and tragic humans body modified so much in mimicry to a dead alien race and so changed themselves they are doomed.
From the Baen description of the book
In a clearing in a continental forest on the planet BoskVeld, a hominoid species of alien, the Asadi, daily act out their enigmatic rituals. These lithe, mane-bearing simian creatures trudge about obsessively, their rainbow eyes spinning like pinwheels. Egan Chaney in his anthropological study, “Death and Designation among the Asadi,” has persuasively suggested that their lifestyle has devolved from a level of high technological sophistication to one of brute simplicity.
Six years after his disappearance into the Wild, Chaney’s daughter, Elegy Cather, arrives on BoskVeld to find him. With her she brings an intelligent ape, Kretzoi, genetically adapted to resemble the Asadi. Together with Thomas Benedict, once Chaney’s assistant and later the compiler of his controversial “Death and Designation” monograph, Elegy strives to unravel the secret history of the Asadi.
As Kretzoi infiltrates their rituals, we, too, begin to grasp the full incomprehensibility of a truly alien species and the complex horror of its devolution. Working in the modes of Stanislaw Lem’s Solaris and the anthropology-inspired fictions of Ursula K. Le Guin, Michael Bishop dramatizes in Transfigurations both the innate difficulty and the scientific rapture of unriddling the unforthcoming Other.
I haven't found any description of the end of the book to determine if the human interaction with the Asadi ruins them, so I can't confirm that part (yet)