It's an interesting piece of speculative fiction and definitely not what I expected.
It's a novel that reads like a collection of short stories, each placed in different point in past and, eventually, a possible future, with the story of Joan Useb's attempt to save the dying world via science as framing device. The main focus is on the primates.
The strongest part are the stories of the past, particularly those before we enter the history we are more familiar with. Now, Baxter admits in the afterword that not everything is based on hard facts, and it shows; still, most of his speculations are based on mostly solid foundations. Furthermore, he has to make allowances for narrative techniques, giving "protagonists" names even when they would not be familiar with the concept, or showing the example of how speech and grammar rules were formed via English even when it would not have been developed for centuries.
I'm not that fond of the latter part; it is by no means a work of a rabid "we are ruining everything" eco-activist, but it leans close to it near the end, starting with murder of one of earliest paleontologists and destruction of fossil and then going on into the world breaking down with combination of geological activity and terrorism sparked by globalization, which in their turn caused war. How did the war come to be, however, is not explained well, and the timely eruption feels like a bit of deus ex machina. (Actually, it stars with hunting via forest fire, but it doesn't become that obvious until later on.) The idea that in the end human race will regress and machines that evolved from what we sent into space will be what inherits the universe, while SF-y, is not explained and consequently seems silly when placed next to the fact-based speculations about the past. Likewise, chromosomes are nowhere near purified of junk; junk still makes up more than 70% of it, and even if there has been less and less of it with every step, it seems unlikely it would come to the point of lessening variation because there is less material that will be variable anytime before an organism so far apart from humsn as human is from an earthworm. Mutation can happen as long as there is a gene to mutate. As a matter of fact, mutation in junk does not effect anything until the junk gene becomes active. Don't get me wrong, overpopulation and depletion of resources is a problem; and yes, there were animals have dies out via ruining of the ecosystems. But there is a reason why evolution moved from strength to intelligence; and I'd like to think that when the inevitable death of Earth comes, life from Earth has found the means of living outside it. After all, after conquering the entirety of home planet, moving on to the universe seems like the next step to take.
But the bulk of the story is still in the history, and even the shift from science-backed tales of the past into fantastic visions of the future at the end wasn't enough to spoil it.