And most of those slaves were African born, because the brutal living and working conditions prevented natural population growth.

这些奴隶中的大多数都是非洲出生的，因为残酷的生活和工作条件阻碍了人口的自然增长。

" That's a pretty big thing; most of the world is transitioning into natural population decline, " researcher Prof Christopher Murray told the BBC.

“这是一件相当大的事情；世界上大部分地区正在过渡到自然人口下降，”研究员克里斯托弗默里教授告诉 BBC。

From a national perspective, the natural population growth rate in 2021 was 0.34 per thousand, which was declined by 1.11 per thousand than 2020, NBS data shows.

国家统计局数据显示，从全国来看，2021 年人口自然增长率为 0.34%.，比 2020 年下降 1.11%.。

And in every single year after 1974, the average has been less than two children meaning that Japan's births have been below the country's natural population replacement level for nearly half a century.

1974 年之后的每一年，日本的平均生育率都低于两个孩子，这意味着日本的出生率在近半个世纪里一直低于该国的自然人口更替水平。