The book is broken into two half's defined by the coming of Jesus. Chesterton starts off with the cave man and states that we know nothing about the pre-historical man simply because he is pre-historical. The caricature of the cave man clubbing a cave woman on the head to have his way with her is in fact false, or at least speculation as what we find in the caves is not female skulls that are broken, but art work on the walls.We know they painting on caves, but we do not know why. For all we know the caves could have been a nursery for the babies to draw on the walls. What we do know is that no other animal started to finger paint and over time it was the humans who perfected it.
And then after the cave man there is evidences of civilisations, not small civilisations, but ones that have left their mark on the earth for thousands of years later with their structures and craft work still standing. Chesterton also speculates on some other primitive cultures and how they perhaps were ruled not by the strongest man, but maybe more like a democracy, but points out that either way there is no evidence for one or the other.
On religions he points out that polytheism was the dominate religion. Chesterton states that over time polytheism got more complex over time, and so wonders if it was possible to go back to the beginning what it would look like. The Hebrews seem to be the only anomaly here. They came out of Egypt, went into Canaan, were captured by Babylon and then dominated by the Greeks and yet they remained monotheistic. But perhaps that was not as strange as we might think. Chesterton talks of Aborigines (later changed to be the American Indians in the second appendix) when told of the one head God by missionaries, they responded "they are talking about Atahocan". It seems that in polytheism there was a God of the gods. Chesterton also wonders if people were really monotheists as they would really only worship their own local god and only worship others if they felt the need arise. Chesterton also wonders if they really took their gods as seriously as we think they did. Chesterton points out that in polytheism science never met with religion. What the Egyptians knew about astrology was never connected with Khepera, the dung beetle who rolled the sun across the sky every day. What Aristotle taught on the sciences and philosophy was never joined with his knowledge of Zeus. Chesterton points out that there was always a chasm between religion and philosophy until Christianity.
Christianity came on the scene in the same way the book started, in a cave or sorts. The story itself was quite a strange one of a man claiming to be God who died and rose again. The teachings of Jesus were not things you found in Aristotle or the like the moral standards were not from that age or any other, they were from another world all together. Christianity did not come in force but became quite powerful, but it was completely different from the culture. In fact it is quite a anomaly that it arose and stood tall after the Roman Empire declined. Christianity could not be called a movement but maybe rather a revolution and it had this nasty habit of outliving every other social/political structure ever since.
Like this review, the book was quite wordy and I found I had to read some bits quite slowly. There were a few nice paradoxes presented but not in the neat way Orthodoxy was written. The first half of the book to me did feel a bit long, and I know Chesterton must have skipped entire cultures and religious examples (you would have to in order to do a brief history of the world) he went into some (maybe too much) into others. He did show he understood a lot more religions and gods than I think your average 21st century person had heard of. The best bits I think came in the second half of the book. It was much smaller and tied some loose ideas together.
This book will maybe make you think and questions your Western assumptions about past cultures. It presents some ideas that seem a little off the cuff mixed in with some others that probably are well researched. His appendixes give the impression Chesterton was not one hundred percent happy with his book. If nothing else, I think Chesterton debunked our modern idea of all religions being the same and he does raise some challenging questions as to why Christianity ever rose in the first place and how form a humanist perspective it has continued on for so long.
You can read it all online
Other books by Chesterton that I have read: