A lot of chance events had to happen for it to be as it is.

它之所以是这样，是有很多偶然事件发生。

Evolution on Earth is a coming together of the adaptations of genetics and the environment, an environment which is itself the result of a long succession of chance events.

地球上的进化是基因和环境的适应结合在一起的产物，而环境本身就是一连串偶然事件的结果。

This kind of movement is called a " sweepstakes dispersal" - a rare or chance event where an animal is able to cross a pretty extreme barrier.

这种运动被称为“抽奖活动”——一种动物能够跨越相当极端的障碍的罕见或偶然事件。

This is where chance events, like a small group becoming stranded on an island, change the frequency of gene variants in the gene pool, with some variation being lost entirely.

这就是偶然事件， 比如一小群人被困在一个岛上，改变基因库中基因变异的频率，一些变异会完全丢失。

The evolution of bone wasn't a grand aha! moment in the story of evolution, it is just one of many such chance events, influenced by the environment, that sent one arm of life on earth on a completely new course.

骨骼的进化不是进化故事中的一个伟大的啊哈！时刻，它只是受环境影响的许多偶然事件之一，将地球上的一个生命分支送上一条全新的道路。