The [?] of life has been driven in part by [?] in the physical environment. No single kind of living thing can perform well in all environments. The differences among living things that enable them to live in different kinds of environments and adopt different lifestyles are called [?].
For a long period of time, there was no life on Earth. Then there was an extended period of only uni-cellular life, followed by a [?] of multi-cellular life. In other words, the nature and diversity of life has changed over time. [?] of the processes that result in biological [?] was one of the great scientific advances of the nineteenth century.