We grew big brains and bipedal travel which explains how we could think of how to handle new environments and get there but it doesn't explain those changes in our phenotype happened:-https://www.newscientist.com/article/mg22730394-100-key-moments-in-human-evolution-were-shaped-by-changing-climate/-"A climate that shifts from wet to dry every 10 or 20,000 years would have selected for humans that had a capacity to adjust to change, whatever it may be. For example, big brains would have allowed us to solve problems caused by changes in rainfall, such as by making different stone tools to exploit changing food resources."-Comment: Back to hoping passive natural selection drives everything.-"Matthew Grove from the University of Liverpool in the UK agrees with Potts that variability is responsible for human evolution, but with a caveat. He thinks that early humans would have gained their adaptable skills where they were, and only spread to new environments during calmer periods, once wild climate events had died down.-“'It would have been easy for these populations to tolerate conditions in surrounding areas, because they would have already experienced those conditions in situ in the past,” says Grove.-Comment: At least some folks are thinking clearly.