The book takes a look at an enigma which stumped Darwin - the start of the Cambrian was marked by the sudden appearance of advanced animal forms with no precursors, something which Darwin put down to the insufficiency of the fossil record. Ever since Darwin we have accumulated more and more evidence of what was occurring before the Cambrian diversification, yet it still remains largely shrouded in mystery. The fossils we have found are all problematic and difficult to fit neatly into the grand scheme of things. Brasier tackles this mystery superbly and his contribution deserves to be on my list of recommended palaeontology books. If I were to recommend only three pop. palaeontology books they would be Gould's Wonderful Life, Fortey's Trilobite and this one. Interestingly enough these books all overlap in their subject and both of these authors get a good mention in Darwin's Lost World. I don't want to compare Brasier to Gould and Fortey, as it is unfair to compare any science writer to Gould (he really was in a league of his own) and Fortey is my personal favourite. Further to that though, Brasier's writing is spot on and stands on its own. He writes with clarity and his book should be highly accessible to non-palaeontologists. He writes very personally as well, recounting his own involvement in the deciphering of the fossil record of the events in question. He also writes with humour, throwing in some very playful analogies throughout.
The title might suggest that this is a book about Darwin, but it is so much more than that. Darwin is quoted often, however, the book is more a look into the enigma itself. Brasier does a good job of showing where palaeontologists in the past have been asking the wrong questions or making unwarranted assumptions. Politics also play a part and not in a boring way. Tensions ride high when countries are competing for the same goal, something which palaeontology is not devoid of. As with any good book written by an accomplished palaeontologist, Darwin's Lost World gives insight into palaeontology, from the competition, to the extreme field work sometimes required. It also gives a good sense of science's ability to cross international boundaries, with much of the important work coming from countries thousands of miles apart.
An important question, though, is whether or not I learnt anything. As this book covers my favourite subject there was a risk that I might already know the majority of things mentioned. I am pleased to say that I still have a lot to learn and Darwin's Lost World has taught me rather a lot, putting much of it into perspective too. I've never looked at the early Cambrian trilobite Fallotaspis before, which is now high on my 'to do' list, nor have I looked at the earliest brachiopods such as Aldanotreta.
|Fallotaspis - an early Cambrian trilobite, with holochroal eyes.|
One of the stand out parts of the book is when Brasier looks at three different approaches to explaining the Cambrian explosion and whether it was a real phenomenon. He names these Lyell's Hunch, Daly's Ploy and Sollas's Gambit. Lyell's Hunch is the view that the Cambrian explosion is not real, but due to the paucity of the fossil record; this view exists today in a more modified form, where the ancestors of modern phyla are believed to be quite deep into the Precambrian, yet avoided fossilisation due to something such as having small-sized soft bodies. Daly's Ploy instead looks to environmental factors, suggesting that something such as ocean chemistry may have prevented the secretion of hard parts, so when this changed organisms were able to explode in diversity; this view is rather common today, with many scientists looking for environmental triggers. Sollas's Gambit is the view that the change was due to the organisms themselves, perhaps the ability to secrete shells had evolved; again, this view is found today and has many different variants. Brasier does an excellent job of exploring these possibilities and throughout the book he keeps a good level of scepticism towards the interpretations of others.
Predation, causing predator-prey relationships, is held to be one of the most important factors. The evolution of the mollusc shell is linked in with the evolution of predatory worms, perhaps chaetognaths, which Protohertzina might possibly be. Brasier uses the analogy of a landslide to show how small changes within the system may cause large amounts of change, and although I agree with him on that point, I do think it gives an idea which is incorrect. It gives the idea that the origin of phyla were big changes, rather than pointing out that they are only phyla in hindsight, after millions of years of evolution, but at the time two groups diverged they were likely as similar as two closely related species. New body plans become difficult to evolve at later stages as they become rather fixed, so something we would label as a phylum is not to be expected as we look at more recent organisms. I get the feeling that Brasier did not intend for the interpretation of "large jumps in the past", but it is a plausible reading.
|A modern chaetognath worm.|
Darwin's Lost World explores many of the big ideas surrounding the Cambrian explosion. It is an excellent book to read for an introduction to how fossilisation has evolved and to how the substrate in the ocean changed significantly in the early Cambrian through bioturbation. It also takes a good look at the snowball Earth hypothesis and how it has been caught up in the conflation of cause and effect in the study of early animal life. Brasier raises the interesting possibility that the end of snowball Earth did not trigger multicellular evolution, but that the evolution of mutlicellularity caused the snowball Earth glaciations.
If you read the book and like me are interested in Ediacarans then this book will be highly informative, though if you desire resolution you will be disappointed (I personally loved that I came out with more questions than answers, which is a good sign with Ediacarans). Brasier beautifully shows just how enigmatic this fossil group is, keeping them shrouded in mystery even though he teaches us a lot about them. All connections to modern organisms are shown to be rather unreasonable and he even does so for Kimberella, which many believe to be a mollusc. He does this merely by suggesting that the least exciting explanation is more likely, offering the possibilities of partial moulds by either microbial filaments, protozoa or the decay of something like Dickinsonia, possibilities which have not been properly examined (I am sceptical, but the latter possibility intrigues me).
Brasier does not just successfully show how little we know about Ediacaran phylogeny, but also how little we know about such ancient ecosystems. We have a bad habit of trying to work out how things lived based on how their relatives live now. Sponges, for example, are considered to be very primitive, yet their modern ecological habits are intertwined and dependent on more advanced organisms. Trying to picture a world of simple sponges is simply wrong if we see them as functioning like their modern representatives.
Overall Darwin's Lost World is an excellent contribution from a world expert on such a fascinating subject, covering a breadth of evidence. It is easily accessible yet highly informative and even-handedly assesses the evidence, rather than forcing a particular conclusion. If you like science then this book should be a thrilling read. If you are interested in palaeontology this should be on your bookshelf. And if like me you are interested in the Cambrian diversification events, then this book is an absolute must read!