What agenda did you think he was pushing?

I think you may be confusing "agenda" with "perspective". He was pushing one perspective: his own, as all authors do. But it's our job as readers to understand the author's perspective and recognize it as such.

Neither history nor anthropology permits storytelling without a perspective. There's always a perspective. Reading for learning means understanding that perspective and determining which aspects (if any) we'll choose to adopt ourselves.

>I think you may be confusing "agenda" with "perspective". He was pushing one perspective: his own, as all authors do.

If you're used to science, it can come as a surprise that a person can willfully ignore (not just focus away from, ignore), all but one option for an entire book, and it still be considered an intellectual effort as opposed to a sales pitch or campaign tool.

To be honest most of the times he lists the multiple concurrent theories and simply points out why he believes one of them to be closest to reality.

Of course, sometimes none of the theories can be proven or disproved. So unless you want to leave a black hole you simply choose the theory that fits best, with the risk of it being overturned in the future.

He is a historian, not a scientist. I don't think there is a good way to analyze the past scientifically, because you can't run experiments.

A huge number of scientists analyze the past scientifically. Between dinosaurs dying, creatures evolving, continents shifting, planets forming, climates changing, and the universe beginning, we analyze a ton of the past scientifically.

Any dig for old stuff or old bones is an experiment, which will strengthen or weaken, at a minimum, the hypothesis that stuff is at or near that spot.