would have been是表示与过去发生的情况相反么?下面这段话中的would have been我感觉应该是假设的意思啊
Now let's look at another theory,uh,an alternative to the hunting theory,the climate change theory.At around 11,500 B.C.E.,the world was coming out of an Ice Age .And with that came increased seasonality,that is,the summers became warmer,and the winters actually became colder.These extreme shifts would have put a lot of stress on the bodies of animals that were used to a more moderate range of temperatures.