The Adults (from 1967) by Larry Niven is the short version of his later novel Protector. It introduces the species known as the Pak, which has three stages of life: child, adult and Protector, with the Protector stage only achieved by exposure to a virus carried by an edible tuber on their planet. Unfortunately, the virus will not reproduce without thallium in the soil - and the Earth doesn't have enough, so humans evolved into their current form, instead of being the "adult" form of Pak (who are subhuman in intelligence, while the Protectors are supersmart and superstrong). The plot involves a human space traveller, who encounters a Pak protector who is coming to Earth to "rescue" the lost colony of Pak adults, not realizing that they have become humans.
This is a review of the short version of story, written as if by someone in 1967:
From the center of the galaxy comes Phthsspok, a super-intelligent,
highly determined alien looking for a long lost colony. He has reason
to believe it is Earth…or was, hundreds of thousands of years ago.
Phthsspok is a Protector, with armored hide and hyper-reflexes.
Utterly beyond human capabilities.
Except, when Phthsspok runs across and kidnaps Jack Brennan, a Belter
in his middle-40s, the connection between Protectors and humanity
turns out to be closer than anyone expected.
Set in the same time and setting as World of Ptavvs, and featuring
Lucas Garner and Lit Schaeffer from that book, The Adults is a
fascinating read. And it offers the compelling question: would you
trade your sex and your outward humanity at age 45 for the privilege
of immortality and extreme intellect?
Forty-four year olds in the audience, are you reading?
As you recall, Brennan, the space traveller feels a compulsion to eat tree-of-life when he encounters it.
I'd normally report this as a duplicate, but this is specifically looking for the short version, not the novel, so it may not be considered a duplicate of this
