Already Here: Inside the Cryptoterrestrial Theory That UFOs Come From Earth

In early June 2024, a paper with an eyebrow-raising title started racing around the internet.

Its authors were Tim Lomas and Brendan Case, both of the Human Flourishing Program at Harvard University, and Michael P. Masters, a professor of biological anthropology at Montana Technological University. The headlines said Harvard researchers thought aliens might be living among us.

That's not quite what the paper said. What it actually argued is more careful, and in some ways more unsettling: that the intelligence behind some UFOs might not be alien at all, but native to Earth, and hidden.

The name for that idea is the cryptoterrestrial hypothesis.

What the paper actually says

The paper, published in the journal Philosophy and Cosmology (volume 33), opens by dividing UFO explanations into two familiar camps: conventional human technology, or visitors from elsewhere in the cosmos.

Then it adds a third. The authors call it the "ultraterrestrial" hypothesis, which includes as a subset the "cryptoterrestrial" idea: that UFOs "may reflect activities of intelligent beings concealed in stealth here on Earth (e.g., underground), and/or its near environs (e.g., the moon), and/or even 'walking among us' (e.g., passing as humans)."

They're upfront about the reception they expect. The idea "is likely to be regarded sceptically by most scientists," they write, but some UFO reports are strange enough that it "should not be summarily dismissed."

"We are not arguing that UAP do have a cryptoterrestrial explanation, but simply that they could, and the judicious approach is to consider all valid theories until the evidence decisively demonstrates they should be rejected."

According to Fox News, the version that went viral carried a note calling it a "speculative thought piece" not affiliated with the Human Flourishing Program, and it had not yet been peer-reviewed. The authors also wrote that they believe the hypothesis to be "in all likelihood false, but nevertheless believe it still merits scientific investigation."

Four ways to hide on Earth

The most useful part of the paper is its taxonomy. The authors lay out four distinct cryptoterrestrial hypotheses:

• CTH1, human cryptoterrestrials: a technologically advanced ancient human civilization, largely destroyed long ago, that survived in remnant form.
• CTH2, hominid or theropod cryptoterrestrials: a nonhuman species that evolved to live in stealth, perhaps another hominin, or descendants of unknown intelligent dinosaurs.
• CTH3, former extraterrestrials or time travelers: aliens, or our own descendants from the future, who arrived and then concealed themselves here.
• CTH4, magical cryptoterrestrials: beings closer to what European folklore called fairies, elves or nymphs.

That range matters. CTH1 and CTH2 are, at least in principle, biology and archaeology questions. CTH4 isn't. Lumping them together under one label is part of why the headlines got so muddled.

The roots: from Lemuria to Keel

The idea is far older than 2024, and the paper says so.

It traces one early strand to writer Richard Shaver, whose underground-civilization story "I Remember Lemuria!" ran in the March 1945 issue of Amazing Stories, revised by editor Ray Palmer. Many condemned it as a hoax; the authors cite it as a pop-culture starting point, not as evidence.

The more serious ancestor is John Keel. In a 1968 Saga magazine article titled "Secret UFO bases across the U.S.," quoted in the paper, Keel argued that because UFOs had "been consistently active in the same areas for many years," they were more likely "a part of the Earth's environment than extraterrestrial craft flying in from some distant point."

Then there's Mac Tonnies, an American author and blogger who died in 2009 at 34. His book The Cryptoterrestrials: A Meditation on Indigenous Humanoids and the Aliens Among Us was published posthumously by Anomalist Books in 2010, with a foreword by Nick Redfern. Tonnies argued that the beings tied to UFO and abduction reports might be secretive races of earthly origin who present themselves as extraterrestrials or occult beings.

The strongest case for it

Steelman it, and the cryptoterrestrial idea solves some real problems.

It avoids interstellar travel. The paper notes that CTH1 and CTH2 don't have to explain how anyone crosses light-years, "an extraordinary technological feat for any species."

It explains the focus on Earth. If the intelligence lives here, Keel's point about UFOs returning to the same areas makes sense. So would an apparent interest in nuclear weapons, which the paper notes would endanger the cryptoterrestrials themselves.

It explains the human-like bodies. Many reported entities look surprisingly like us. A species related to Homo sapiens would account for that, though the authors concede convergent evolution could make even true aliens look somewhat human.

The deep past is mostly blank. The paper leans on the "Silurian hypothesis" of Gavin Schmidt and Adam Frank, published in the International Journal of Astrobiology. Schmidt and Frank asked whether an industrial civilization millions of years ago would have left detectable traces in the geological record. It's a serious question, but note that their paper proposes ways to look for such traces; it doesn't claim one existed.

Some UAP are reported in water. The authors point to "Unidentified Submersible Objects," or USOs, and to rising official attention to objects reported moving between air and sea.

The strongest case against it

Here's where it gets hard, and the paper deserves credit for saying much of this itself.

Where is everything? An advanced civilization sharing our planet would presumably leave cities, waste, mining, heat, something. The authors acknowledge the problem of explaining "why the remnants of an advanced past civilization haven't yet been discovered despite our broad temporal and geographic archaeological and paleoanthropological knowledge."

Why hide? On the ETH, you can imagine a few recent scouts with orders not to interfere. But a civilization that has been our neighbor for millennia, and our technological superior, staying silent is "more puzzling still," the authors write.

The physics doesn't get easier. Even homegrown craft would still have to perform maneuvers that look like they'd kill anything living, a problem the paper notes CTH1 through CTH3 share with the ETH.

The evidence is thin and secondhand. Parts of the paper's case rest on testimony relayed through news write-ups and interviews: claims about recovered beings, underground bases and anomalous encounters that have never been independently documented. Interesting as folklore, but not the same thing as data.

It's hard to test. CTH4, the "magical" version, is close to unfalsifiable. The authors concede its "principal weakness" is "its utter strangeness" for anyone working within standard physics.

Former British government UFO investigator Nick Pope, asked by Fox News Digital, described the paper as a thought experiment rather than research claiming evidence, aimed at sparking debate in a skeptical academy.

What would settle it

Unlike some UFO theories, parts of this one could be checked.

A genuine anomaly in the geological record of the kind Schmidt and Frank describe would be a start. So would biological samples with an unexplained relationship to the human lineage, documented and published. So would sensor data tracking an object into, or out of, the ground or deep ocean, with the raw data released for others to analyze.

What wouldn't settle it: more anonymous testimony, more lore about secret bases, more articles quoting other articles.

What we know, and what we don't

What we know

• Lomas, Case and Masters published "The cryptoterrestrial hypothesis" in Philosophy and Cosmology in 2024 and called it likely false but worth investigating.
• The idea has roots in Keel's 1968 writing and Mac Tonnies' 2010 book.
• The paper itself lists the key objections: no remnants, no motive for hiding, and physics problems shared with the ETH.

What we don't

• Whether any deep-time civilization ever existed on Earth before us.
• What, if anything, lies behind reports of objects moving between sky and sea.
• Whether the cryptoterrestrial idea can be framed in a way that's truly testable.

Our neighbors, or our reflection?

The cryptoterrestrial hypothesis has a strange kind of logic. It takes the "nonhuman intelligence" language now heard in Washington and asks why that intelligence has to come from somewhere else.

But a theory isn't evidence, and three academics saying "don't rule it out" isn't the same as three academics saying it's true. They were clear about that. The headlines weren't.

So what do you think: is a hidden Earth civilization more plausible than visitors from another star, or is it just a new hiding place for an old mystery?

Sources

• The cryptoterrestrial hypothesis: A case for scientific openness to a concealed earthly explanation for Unidentified Anomalous Phenomena — Tim Lomas, Brendan Case and Michael P. Masters, Philosophy and Cosmology, 2024
• Philosophy and Cosmology, October 2024 (journal listing) — Directory of Open Access Journals, 2024
• Aliens may be living among us disguised as humans, Harvard researchers claim — Fox News via FOX 10 Phoenix, 2024
• Aliens Could Be 'Walking Among Us', Harvard Researchers Say — Decrypt, 2024
• The Silurian Hypothesis: Would it be possible to detect an industrial civilization in the geological record? — Gavin A. Schmidt and Adam Frank, International Journal of Astrobiology (doi:10.1017/S1473550418000095), 2018
• Mac Tonnies — Wikipedia
• The Cryptoterrestrials (publisher listing) — Anomalist Books, 2010