- 2025年10月19日
What Is Humanity?
Underwater Archaeology Will Change Human History
What Is Humanity?
Underwater Archaeology Will Change Human History
The human history we read today may be an excerpt that omits the main stage now lying under the sea. During the Last Glacial Period (roughly 115,000–11,700 years ago), sea level fell by up to about 120 meters, exposing vast coastal plains such as Doggerland in the North Sea and Sundaland in Southeast Asia.
Within the glacial period, stadials (colder phases) and interstadials (warmer phases) alternated in short cycles, so the zones suitable for human habitation repeatedly flipped south↔north and coast↔interior.
—If so, relying only on the surviving land sites makes it easy to miss the mainstream of human history. As underwater archaeology advances, cases that have looked like “peripheral anomalies,” such as Jōmon sites in Japan or Göbekli Tepe in Turkey, will likely be repositioned as edges of a lost mainstream.
Everything Important Lies Under the Sea
In short, when thinking about human civilization, the most crucial traces from the Last Glacial Period are mostly under water (or, where preserved, beneath today’s deserts).
To “overstate” the point on purpose: during the Ice Age, expansive land spread across habitable low– and mid–latitudes; areas now desert—like the Sahara—were green and are known as Green Sahara. In other words, it was a time quite favorable for human life.
By contrast, in our present interglacial, land is relatively limited; deserts dominate around the Tropics of Cancer and Capricorn; and the high latitudes’ permafrost make for an awkward, less hospitable world with a narrower human habitat—to put it bluntly.
Therefore, we cannot understand (the crucial parts of) human history merely by studying the sites that remain on today’s land. As underwater archaeology develops, a fundamentally different view of human history will spread—perhaps a paradigm shift even larger than the one from “dinosaurs as oversized reptiles” to “dinosaurs were feathered.”
For example, underwater archaeology is progressing in the English Channel (the Dover Strait)—no doubt aided by proximity to both Paris and London. As this work advances, exceptionally early-looking sites such as Japan’s Jōmon or Turkey’s Göbekli Tepe—sometimes treated like “OOPArts”—will instead look like special cases preserved because they sat on narrow ridges or hills that escaped submergence when sea level rose and deserts expanded, while the main Ice Age record was hidden or erased.
To Know Ice Age Human History, We Need Seafloor Maps
Today’s landforms are only today’s landforms. We often see maps forecasting coastlines under continued global warming. Likewise, to understand the Ice Age we need maps of the seafloor.
At the coldest stage of the glacial, sea level stood more than 120 m lower than now; the seafloor down to that depth would have been dry land.
Even in an Ice Age, the equatorial belt and low—indeed, even much of the mid—latitudes were not glacier-covered or utterly uninhabitable. Some regions now too hot or desertified may have been pleasantly mild then.
When we look carefully and concretely—grounding our imagination in physical reality—our mental images can flip. Historiography often experiences such reversals (think of the Annales School in Europe; in Japan, the work of Amino Yoshihiko and Abe Kinya famously reframed common views).
Human Civilization Is Compressed into the 10,000 Years Since the Last Glacial
What we call “civilization” begins after the Last Glacial ended, as sea level rose with warming about 10,000 years ago.
The continental shelves and shallow seafloors—prime Ice Age living space and corridors—are now beneath the sea. From that perspective, the sites we can study today lie in the periphery of the Ice Age human habitat.
During the glacial, sea level fell and habitable low– and mid–latitude lands expanded; even deserts like the Sahara were green. We now live in an interglacial.
“What is essential is invisible to the eye” (Saint-Exupéry). “We dwell within unseen structures” (Lévi-Strauss). Their original meanings may differ, but across anthropology, archaeology, and indeed all inquiry, humility about the unknown is crucial.
To Understand Human History, the Ice Age Matters
Modern science’s strength—evidence-based empiricism—is also its weakness when over-applied. In recent decades some have dismissed what lacks evidence as if it were disproven. Yet absence of evidence is not evidence of absence: in statistics, “no significant difference” means we cannot say, not that something is false.
Fields like medicine have ethical barriers that long limited experimentation; the push for EBM sometimes caused confusion on the ground. Wittgenstein said, “Whereof one cannot speak, thereof one must be silent,” but likewise: when we don’t know, we should resist easy denial and avoid clinging to an illusion of knowledge.
Time Scales: Even 10,000 Years Isn’t Enough
Older generations learned history starting from the “four great civilizations,” a text-based horizon. But to really grasp human history we must think on logarithmic scales: 100, 1,000, 10,000, 100,000 years.
The last 10,000 years saw agriculture and writing after the Ice Age ended. Anatomically modern humans emerged in Africa about 300,000 years ago and began dispersing out of Africa around 50,000 years ago.
From a Japanese vantage point—asking “What is humanity?”—we should look on 100,000-year horizons. As the 2022 Nobel Prize underscored, modern humans admixed with Neanderthals and Denisovans. Neanderthals lived roughly 400,000–40,000 years ago. Homo erectus in Java (“Java Man”) spans roughly 1.8 million to 200,000 years ago; whether they interbred with later humans is unknown, but at minimum their presence shows the human line had already spread globally in the earlier stages.
Viewing Humans as a Biological Species
If we view humans not as exceptional, but as organisms among organisms, ranges shift with time.
The romantic “Great Journey” can make us forget that, before civilization, humans—though equipped with culture, language, and tools—were still biological populations responding to changing habitats. Seeing late Pleistocene humans in this biological frame reveals a different picture.
Climate Change and Humanity
For us modern humans, the Last Glacial Period is key—roughly 70,000 to 10,000 years ago in common parlance (more strictly, ~115,000–11,700 BP). Temperatures oscillated; within these 60,000+ years came the coldest stage, the Last Glacial Maximum (LGM) around 26,500–19,000 years ago.
At the coldest times, vast ice sheets spread across much of the Northern Hemisphere; sea level dropped ~120 m, exposing land bridges and enabling intercontinental movement. In Japan, mean annual temperature was about 7°C lower, pushing evergreen broadleaf forests southward. Mammals like Naumann’s elephant, giant deer, moose (and mammoths in Hokkaidō when it was connected to the continent) roamed. The Sea of Japan became more enclosed, almost lake-like.
About 10,000 years ago, the glacial ended; rapid warming melted the ice, sea level rose, and today’s coastlines formed. In the Middle Jōmon (the mid-Holocene warm period), seas pushed far inland into lowlands like the Osaka and Kantō plains.
Southern Corridors
From a northern, Euro-American historical gaze, the Ice Age looks grim. But the south wasn’t necessarily so. The Sahara was green. Even at the LGM, low– to mid–latitude cooling averaged ~5.8°C, and Japan’s mean fell by ~7°C—serious, but not uniformly catastrophic.
With sea level lower and continental shelves exposed down to ~120 m, land area was vastly larger than today. With water, coasts, and rich biota abundant, there was little need to push into extreme northern cold. If another glacial came, migrating south could even make Earth more livable for many.
A Geophysical Perspective
From 70,000 to 10,000 years ago, temperatures oscillated repeatedly. Though “out-of-Africa” is commonly dated to ~50,000 years ago, seafloor evidence might yet show earlier excursions beyond today’s Africa-as-land. The cutting edge in anthropology and archaeology is moving toward submerged traces.
With each warm/cold swing, sea level and coastlines shifted again and again, expanding and shrinking land. Those lands are now beneath the sea—precisely the places that may have been most habitable.
This helps re-think why Homo erectus remains turn up in places like Indonesia: through multiple glacials and interglacials, they simply lived and moved where life was good, and at times that included Java. Much of Southeast Asia, the Pacific archipelagos, Eurasian shelves, and the Australian shelf have had epochs as broad subaerial plains. The tropics were not ice-covered; regions prone to desert today—beneath the tropical belts—could be verdant in glacials (e.g., Green Sahara).
The Waves of Ice-Age Temperature
As noted, the Earth cycles between glacials and interglacials; within glacials, stadials (colder) and interstadials (warmer) alternate. That means habitable zones shifted many times.
People—then as now—favor coasts, rivers, and lakes. Repeated cold/warm swings likely drove range shifts, with humans moving northward in warmer phases and southward in colder ones. Movement wasn’t one-way out of Africa; it could be pendular, to and fro, not only north–south but also east–west. Think of chemical equilibrium or steady states in physics: momentum carries populations back and forth.
We often see neat arrows on maps (“reached region X by N thousand years ago”), but a thousand or ten thousand years is an awfully long time. To think clearly about ~50,000 years since the main out-of-Africa wave, we need a logarithmic sense of scale, not everyday yardsticks.
Human generation times were short; people were active and mobile. It’s natural to expect rapid, expansive spread across easily traversed low– to mid–latitude belts.
Surviving Ice-Age Sites Are Not the Main Body
Empiricism demands archaeological and genetic evidence—but over-reliance blinds us to what’s hard to evidence. One could even call it Lao-Zhuang-like (Daoist) or structuralist: we are shaped by unseen structures.
If the Ice Age’s principal living zones lie under water, then the sites that remain on land are those that met special conditions. Japan, for instance, preserves an extraordinary number of sites (notably Jōmon), a culture oddly between Paleolithic and Neolithic—polished stone tools without agriculture—that flourished.
Why so many sites in Japan? Because places high enough yet near the sea can both access Ice Age coastal cultures and avoid submergence during later sea-level rise. Ridges and steep relief tend to survive as long, narrow islands—think the Japanese Archipelago, Java, the Andamans. Some high-latitude or high-altitude locales, seemingly harsh, might have had niche advantages. Environmental change always creates winners and losers; for some, staying put would have carried strong incentives.
Civilization: Even If Submerged, Traces Remain
From the Nile and Tigris–Euphrates to the Indus, Yangtze, and Yellow River, each delta opens onto broad shelves and shallow seas—lands in glacials, shifting repeatedly between land and sea.
Humans favor coasts and river basins. We don’t fully know Ice-Age seafaring, but by the Jōmon it clearly existed. People must have lived closely tied to waters; even in the current interglacial, early civilizations used coasting and river travel.
High-latitude interiors are generally harder living; while people certainly lived there at times, they likely weren’t the mainstream of Ice-Age cultures. Many great northern rivers in Russia reach the Arctic, yet no early urban “cradle” formed there. Meanwhile, multiple river-basin civilizations (beyond the old “four”) are now recognized; Yangtze civilizations are close to home for Japan. It’s more natural to see later navigation as inheriting Ice-Age techniques than as a fresh invention out of nowhere.
In everyday speech, “logical” needn’t mean formal logic; and even formal logic comes in many systems. Over-insisting on one narrow “logical” lens can be as unbalanced as over-insisting on evidence alone. In any case, it’s not hard to see that low-latitude life in the Ice Age may well have been favorable.
High Latitudes Weren’t Necessarily Bad
While I have emphasized lower latitudes, high latitudes could also offer advantages—unique goods, hunting, fishing, gathering. Cold-weather adaptations are possible. If wide-ranging trade already existed, comparative advantage would support rich lifeways: furs, northern fauna, minerals, and other resources. Some species thrive only in the north; humans may likewise have specialized, and with tools, reshaped environments to fit them.
Still, this essay’s purpose is to highlight the submerged mainstream, rather than visible northern land stories we already know. Of course there were many streams of human movement, and low latitudes also carried hazards (strong nature, pathogens, water quality). Jungle survival over long periods is notoriously hard (as veterans of WWII’s southern fronts testified).
Humanity Moved Back and Forth
Given stadials and interstadials, habitable zones drifted over long spans; humans likely shuttled north–south accordingly. Some groups surely stayed and endured colder swings. The popular image of a one-way westward spread is suspect.
Follow the rivers linking coast and interior: when sea level rises, river mouths move inland; when it falls, they shift outward over land that is now sea. In glacials, these estuaries were population hubs and trade nodes, likely frontiers of culture and technology—just as ports form today.
From such hubs at various river mouths, people and goods likely moved along coasts and inland waterways, and between estuaries—overland or by sea. This is a natural pattern that matches ordinary reasoning. The catch is simply that many of those hubs are now underwater. Whether for resources or for archaeology, the sea remains a vast frontier.
The Value of Multiple Lenses
Using multiple modes of thought is itself deconstruction. History is often seen through single ideologies. Over-reliance on empiricism, or on written sources alone; prewar emperor-centered narratives vs. postwar Marxist materialism in education; media that once praised the Cultural Revolution or the Great Leap Forward—all remind us how perspectives shift.
In the end, there is no single, final “correct” history. (And to note: Foucault—often labeled post-structuralist—famously resisted fixed labels himself.) History changes; like a person, it lacks a static identity. Even within one mind, viewpoints shift with methods and moments.
From messy social facts to technical limits and cognitive biases (our Ice-Age imagery, shifting coastlines, the texture of climate change, the non-uniformity of “Ice Age” or “Stone Age”), narratives are malleable. Going forward, the grand task is how we will investigate underwater archaeological and anthropological heritage.