So we're left with a situation where we know that our earliest ancestors were moving around on four legs in the trees, before the savanna ecosystem even came into existence.
这留给我们我们如此一个局面 我们知道，我们最早的祖先 在树上生活时已经开始用两条腿开始到处活动了 那时草原生态系统还没有形成呢