"The past belongs to everyone"
It takes Ancestors a while to warm up, but when it does, it is really fabulous. Roberts takes us through the detailed archaeology/anthropology of burials in Britain, exploring what we know and what we guess about what this means.
The first few chapters stick closely to explaining the science of the specifics, with various detours into similar burials, and a little history of archaeology. It is when Roberts gets the Beaker culture era - the Amesbury Archer chapter in particular - that she starts to let this tight focus, and the formality of the writing, morph into a broader conversation about the relationship between genetics as a discipline and archaeology, and the very nature of scientific enquiry. 
In this fabulous passage she sums up the developments:
"Archaeologists have been asking the question about ancient migrations and culture for so long, with no real means of answering it, that the question seemed to have elevated itself to some metaphysical level – where the only means of approaching it was through theory. As one suggestion fell out of favour, another would emerge to take its place, and all of them were ultimately untestable. The debate becomes quasi-theological. How many angels could possibly dance on the head of a pin?
"Then a new branch of science comes along, with some seriously disruptive technology, and says: we may be able to provide an Answer to this Question. The priests of Archaeology stroke their beards (some of them really do have beards, even quite long ones – while many don’t) and express doubts as to whether a geneticist could even begin to understand the Question. But the geneticists go ahead and drill the bones, extract the ancient DNA, retreat to their labs, do some fancy statistics, and – like some kind of alchemist cooking up a dull lump of lead into gold – they come up with an Answer. They present it to the priests: ‘We think this is what you’ve been looking for.’ But the priests narrow their eyes, sigh and fold their hands in their laps. It's just Fools Gold', they say, "Iron pyrites. You can make fire with it. But it is not the Answer. It isn't the Answer because it doesn't agree with the sacred texts of Post-Processualism"."
But Roberts' frustration here is not one-sided. The implications of migrations being associated with the spread of the Beaker culture she puts into perspective, including the deep-seated fear of a return to processualism, which was part of a view of human development used to justify colonialism and genocide. Roberts is not afraid to talk about the politics behind scientific debate, nor to call on scientists to move through, not away, these discussions.
"Genetic identity and social or cultural identity are two separate things: sometimes they happen to coincide; sometimes they don’t. The picture is complex and complicated – and nowhere can we point to a circumscribed Beaker ‘race’. (Well, of course not – because the fundamental idea of ‘race’ is flawed. It makes no sense biologically or historically. In fact, it doesn’t make any sense to anyone apart from people who are determined to ignore complex reality in order to persist in being racist.) The spread of the Bell Beaker culture was mediated by migration, but the culture has a life of its own as well – as a network of ideas." She injects caution in reading evidence, and caution in assuming meaning.
We need to be as objective as possible in our approach to history and archaeology while recognising that our interpretations will always be coloured by our own political and cultural perspectives. "
I need to stop before this review contains half the book, but be certain: I am a fan of this, and I think it charts a way forward in a discipline that is becoming increasingly contested around unstated political assumptions. Roberts focuses on the evidence, and how we understand it - but also calls in her readers around their assumptions, excitements ("have a cup of tea" she advises, dealing with a collision of circumstances that could lead to unearned "gotcha" moments) and assumptions. This is one of the few such books I've read which discusses how most of our ancestors have left no trace in our DNA, due to the way DNA replication works. She does not ask if we are more than our DNA, she reminds us that we are. That what a Briton looks like is someone who lives in Britain, right now, and that, as always, our past belongs to all of us.