There is nothing odd in countries having different population patterns: you would expect that. But it is odd that countries should clump together into two broad clusters. That needs explaining.

• 不同国家有不同的人口模式并不奇怪：你会预料到这一点。然而这些国家扎堆形成两个明显的集群就奇怪了。那就需要解释。