A twofold blow of planetary cooling and a resulting food shortage caused a sharp decline in the population at the end of the Jomon period, according to a University of Tokyo research team.

The period is considered to have started about 14,500 B.C. and ending about 1,000 B.C.

The team, led by Jun Ohashi, an associate professor of population genomics at the university, based its findings on an analysis of 122 present-day Japanese males believed to possess the Y chromosome that originated in the indigenous Jomons.

It is the first time that genetic evidence has been presented to show that climate and population change occurred simultaneously.

The study was published in the British science journal Scientific Reports on June 17.

Based on previous studies and archeological findings, it is believed that the population of the hunter-gatherer Jomon people declined by between one-half and one-third about 3,000 years ago.

With the introduction of rice farming by Yayoi immigrants from continental East Asia, the mainland population eventually increased by about 10-fold.

"The latest Y-chromosome analysis supports a population shift indicated by the number and size of ancient sites from different eras," said Ohashi.