I think that the idea of first life moving into second life doesn’t necessary means that human have to completely migrate into the virtual world. It can be that some sort of digital technology is being integrates into our body to change us from completely human form to some sort of like “humanic-robotic” form, and we can call this the second life of human being.
After World War 3, earth is almost being destroyed and the environmental condition is not anymore suitable for human habitation. However those who survived have to find a way to adapt themselves to the current condition. This is when the second life started. History proved that living things will evolve themselves to adapt the environment to become better in surviving and reproducing, but it takes decades for evolution to occurs. In order to increase the speed of evolution, scientists will invent a technology that can be used to integrates into human being to enable modification of our genetic code to evolve into a form that are able to adapt to the current environmental condition in a short period of time, or even instant adaptation. With this technology, human can survive in almost any condition (under water, up the mountain, extreme hot or cold condition etc).
Research on evolution: