For Japanese people, every single day has astrological associations with good luck, misfortune, or something in between. (See also Rokuyo)
As with most other people in the world, such superstitions are largely ignored in everyday living, but one in particular is so ingrained into the very fabric of Japanese life, that it could partly explain the significant drop in the Japanese birth rate.
The culprit: Hinoe Uma.
Hinoe-Uma is a calendar event that occurs every 60 years. The last was in 1966 and the next will be in 2026.
As with the astrological birth signs of the West, the Japanese use a modification of Chinese astrology; a twelve year cycle of astrological beasts. 1966 was the Year of the Horse, but it was a special kind of rather nasty horse; a Fire Horse, or hinoe-uma in Japanese.
Girls born in that year became known as 'Fire Horse Women' and are reputed to be dangerous, headstrong and generally bad luck for any husband. In 1966, a baby's sex could not be reliably detected before birth; hence there was a large increase of induced abortions and a sharp decrease in the birth rate in 1966.
Why did the population growth not continue its post-war upward trend in the following years? The fertility rate did have a massive surge in 1967 but since few women had babies in 1966, fewer women left work that year for maternity. This significantly increased the proportion of working women in 1966 and may have triggered a general trend of more working women, leading to a reduction in the fertility rate and fewer babies.
There are alternative theories as to why the birth rate declined, but the superstition explanation is more fun! Stay tuned for the next Fire Horse year in 2026!
According to the OECD (http://stats.oecd.org/), the annual percentage growth rate in Japan twixt 1960 and 1970 was:
1960 0.84%
1961 0.93%
1962 0.95%
1963 1.02%
1964 1.06%
1965 1.12%
1966 0.77%
1967 1.16%
1968 1.12%
1969 1.17%
1970 1.13%