The historical demography of Japan to 1700Population during the Yayoi and Tomb periods
Beginning with the Yayoi period, about 900 bce, Japan’s population must have entered a long
phase of growth. The primary causes for the demographic boom were the importation through
southern Korea of agriculture, especially wet- rice farming, and the introduction of new and
better tool technology using iron. The older forager livelihoods did not die out, but fared best in
eastern and northern Japan, where remnants of the older Jōmon population, genetically dissimi-
lar to the new Yayoi people, retreated to hunt, fish, and gather. No one knows for sure the extent
of population gain, but there are at least two estimates. Kitō has given a figure of 594,900 for
200 ce, but the basis for his claim is unclear. One of the world’s leading archaeologists for the
Yayoi period, the late Sahara Makoto, stated that by the end of the Yayoi period, around 250 ce,
Japan may have contained 1.5–4.5 million people.^9 If accurate, Sahara’s estimate would equal at
least a ten- fold increase over Jōmon numbers. This guesstimate—its basis is never made clear—
reflects Sahara’s belief that the Yayoi age marked the inception of widespread wet- rice cultiva-
tion, especially in formerly under- populated western and central Japan.
Demographers have devised another fascinating set of figures for the Yayoi and Tomb periods.
Using Koyama’s figures for the Jōmon and Sawada’s number of around six million for the 700s,
anthropologist Hanihara Kazurō has estimated that substantial migration from southern Korea
to Japan took place over the Yayoi and Tomb periods.^10 According to Hanihara, the gains
between the end of the Jōmon epoch and around 700 would have meant a natural growth rate of
0.427 percent per year—extraordinarily high in comparison with other places in the world
during the first millennium. He presumes that the natural growth rate would have been closer to
0.1 percent per year, although he does not explain his reasons. For Hanihara, the difference must
have been made up from overwhelming in- migration to the Japanese archipelago from Korea.
While he gives no figures for the Tomb era, Hanihara estimates that during the Yayoi period
3,000 persons per year immigrated to Japan. Because Hanihara assumes (wrongly, according to
most archaeologists) that the Yayoi period was 600 years long, the total number of immigrants
for the Yayoi period alone would have amounted to 1,800,000 persons.
Reactions to Hanihara’s “Dual Structure Hypothesis” have been mixed. On the one hand,
Mark Hudson has endorsed Hanihara’s basic idea of large- scale immigration from southern Korea
to western Japan, arguing that the genetic makeup of the modern Japanese was substantially
altered by the influx of people during the Yayoi period and later.^11 (Hudson, however, declines
to provide figures for this in- migration.)
Keiji Imamura, on the other hand, argues that the rate of increase advocated by Hanihara
(0.1 percent/year) is much too low and believes that much of the increase must have been due to
rising fertility based on occupational and technological improvements.^12 In any case, most
demographers have concluded that whatever the amount of in- migration to Japan, it must have
been large to help account for the dramatic growth of population between the end of the Jōmon
and the 700s.
The remarkable eighth century
Japan’s eighth century, often called the Nara age (710–794), is unique in world history because of
the wealth of information available to us about many aspects of life. Law codes and other regula-
tions portray institutional structures in some detail. Archaeological excavations are varied and
plentiful. Literary sources such as the classic poetry collection Man’yōshū combine compositions
from all levels of society. Most importantly for demography, about 10,000 documentary frag-
ments have been preserved in the ancient storehouse in Nara known as the Shōsōin. These