我们是进化的产物，并且不仅仅是发生在数十亿年前的进化。
We are the products of evolution, and not just evolution that occurred billions of years ago.
数十亿年前，宇宙太热，不适合生命存在。
Billions of years ago the universe was too hot for life to exist.
据测在数十亿年前，一些自由生活的细菌进入到活细胞内部，变为负责提供能量的线粒体。
Billions of years ago, free-living bacteria are thought to have become incorporated into living cells as energy-providing mitochondria.
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