My father and I are trying unsuccessfully to locate a science fiction short story we both remember reading but can’t identify.

The detail we remember is that some human crew members meet who they believe is an alien. The alien informs them that they are the same species, but that the human form metamorphoses into the alien form after consuming some particular substance. The alien then says something to the effect of “we seeded you on earth but forgot to give you the substance, so you’re all stuck in the first stage of the metamorphosis.”

If I remember correctly, one of the crew members came across the substance and felt compelled by instinct to consume it, transforming into an alien himself.

I suspect (but may be wrong) that this is a Ray Bradbury short story. It would have had to have been written in at latest the 50s because my father read it as a young child.

Can you help us figure out what this story is?

  • 16
    Sounds like Larry Niven’s “Protector”
    – andrewsi
    Commented May 10 at 21:04
  • @andrewsi agreed - details wrong, but big picture matches Commented May 10 at 21:10
  • 6
    Do the terms "Pak" and "Tree of life root" sound familiar? (And it wasn't that the Protectors forgot to bring the root to Earth, it just didn't grow properly.)
    – DavidW
    Commented May 10 at 21:13
  • Substance was perhaps thallium, more common in the galactic core where the pak breeder evolved? Sounds very much like Niven's short stories about the Pak, the makers of the Ringworld.
    – chiggsy
    Commented May 12 at 1:39

1 Answer 1


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

  • 2
    That’s it! Funny how the details of the story got distorted by the lens of memory. And my father read it in college, not as a boy, so the chronology makes sense. Commented May 11 at 1:26
  • 1
    Glad to help out. You can click the checkmark too if I'm right.
    – Andrew
    Commented May 11 at 1:50
  • 2
    "fruit of a common tree" -- is that something that was changed between The Adults and Protector? I haven't read the short story, but in Protector and everything after it, it's a root/tuber (kinda like sweet potato) of a small shrub or a bush. The tree-of-life name being coined by Brennan-monster in reference to Garden of Eden...
    – Dan Mašek
    Commented May 11 at 9:36
  • 1
    My mistake - I'll fix
    – Andrew
    Commented May 11 at 10:39
  • 1
    We all might as well read it again, hmm? :D
    – chiggsy
    Commented May 12 at 1:40

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.