Very enjoyable description of the various -- currently 27 -- different "human" species discovered so far. How they are similar, how they differ, how they are reflected in modern humans. I did notice occasionally a lack of supporting evidence for his descriptions of various traits in other species, but I'm not sure I would have noticed if it hadn't been previously mentioned by others. But it didn't bother me. I think a work like this must be speculative to a certain extent, because there is so little definitive evidence. On the other hand, one of the things I most enjoyed was learning how much can be stated with certainty on the basis of very little evidence.
Walter's writing style is very easygoing. He brings all the various species to life, partly though his "speculations", making what could be dry reportage more like telling a story. A story that I found very interesting.