Japan’s population fell at the beginning of this year at the fastest pace since 1968, when the earliest comparable figures started getting collected. As of January 1, the number of Japanese people (excluding resident foreigners) fell by a record 308,084 from a year earlier to 125,583,658, marking the eighth consecutive year of declines, government data showed Wednesday. These changes highlight a mounting demographic challenge to Japan’s economic growth that has been roughly two decades in the making. Some economists even