How are you related to a duck-billed platypus? Do you know?
At a quick glance, you might suspect that mammalian evolution is like a flight of stairs. At the bottom, there's reptiles. Take a step up, and you find the weirder egg-laying mammals, including our friend, the platypus. Another step up, and you've reached the marsupials, which are much less reptilian, but still don't quite have the same reproductive system as we do. Finally, at the top, you find the majority of the mammal kingdom—creatures like us, neither egg-laying nor pouch-wearing.
This progression seems so obvious. It's neat and tidy, and orderly. It's also wrong.
The process of evolution is actually much, much messier. In its wake, it leaves multiple dead ends, whole orders or classes gone extinct, or whittled down to a sole surviving species—the last bastion of a once-proud lineage. And evolution does not work towards making humans. That's entirely the wrong way to think about it. The creatures alive today are not our ancestors. Instead of a stair-step, with humans at the top, we stand alongside the kangaroo and the platypus, each of us at the end of its own narrow road. If we look back, into the past, we can see those paths turn and branch and cul-de-sac. Go far enough, and our paths meet at a crossroads. But in between that common ancestor and ourselves, the road is littered with cousins that didn't quite make it.
It's not an easy road map to follow. Not for us laypeople, certainly. That's clear anytime you read a news story about a new fossil discovery, or watch yet another school board debate whether evolution should be taught at all. But the path of evolution wasn't obvious to the people who first traced it, either. In fact, many of the mistakes and misconceptions common with the general public today were first made by natural historians and paleontologists, themselves. Evolution is messy, and the evolution of evolution was doubly so.
It's that story—how the theory of evolution arose and how the details shifted to fit new evidence—that science blogger Brian Switek tells in his book Written in Stone: Evolution, the Fossil Record, and Our Place in Nature, a handy primer for anyone who wants to better understand evolutionary theory, or the way that science, in general, works.
In the past year, I've become convinced that it is much easier to understand complicated scientific concepts if you can "re-discover" them for yourself by following the history of how scientists came up with those concepts in the first place.
When I reviewed Marcus Chown's The Matchbox that Ate a 40-Ton Truck, I told you that Chown explained nuclear fusion by telling the centuries-long story that led scientists from the question, "Why is the sun hot?" to our modern understanding of the processes at work in the sun's heart.
That story was not a triumphantly straight line. Along the way, scientists got things wrong, they made predictions that turned out to be incorrect. But, as they were able to collect new information, they corrected the mistakes. We might not understand the sun's inner workings perfectly today. But we're much closer to the truth, precisely because many individual scientists built on and corrected one another's ideas.
Written in Stone is like that, but for evolution.
Beginning in the 1600s with Nicolaus Steno, a young Dutchman who published evidence that the triangular stones found throughout Europe were actually fossilized shark's teeth, the book winds its way through four centuries of scientific thought. Along the way, disconnected observations like Steno's coalesce into a cohesive theory of how species might change—and new data from fossil records and biology help to revise and expand that basic evolutionary theory to explain the mechanisms of change, and trace more-precise histories for living species.
At the end, you'll come away with a much better understanding of how evolution works, because you'll understand where the theory came from. It's like baking. A cake is kind of an intimidating thing to make if you've only ever seen the finished product. But once you've followed along with an experienced baker, the whole thing becomes much more clear.
The downside: As you might imagine, this book is pretty dense in places. Switek breaks the story down into easy-to-follow chunks—the first few chapters trace the basic idea of evolution from Steno to Darwin; after that, the individual chapters focus on specific evolutionary questions, like the relationship between dinosaurs and birds, or where mammals came from. The structure of the book makes it relatively simple to keep track of what you've learned in a big-picture sense. But, on a more detail-oriented level, there's a lot of information coming at you fast.
Each chapter introduces lots of proper names—both of scientists, and of fossils—and re-introduces key figures from previous chapters. Unless you have a particularly good memory (or you're taking notes), it's likely that you'll have to flip back and re-orient yourself from time to time. If reading a book is like a journey, most people who read Written in Stone will remember the train ride, but not all the little towns they stopped at along the way.
That's unfortunate, but it shouldn't discourage you from reading the book. Even if you get your Ichthyostega mixed up with your Eusthenopteron, this book is still going to help you better understand their place in the history of life.
I talk a lot about the importance of understanding the context behind what you read in the newspaper. Written in Stone is all context. You, as a layperson, don't necessarily need to be able to name every extinct species of limbed proto-amphibians (of which Ichthyostega and Eusthenopteron are two), but it would be valuable to you to have a general understanding of how amphibians first came to exist, and why scientists believe it happened in the way they think it did. Written in Stone will get you there. Even if, in your head, you read "Ichthyostega" as "Ickthawhatever".
The book:Written in Stone: Evolution, the Fossil Record, and Our Place in Nature
by Brian Switek
Disclaimer: I received a free review copy of this book from the author. That said, I receive a lot of free review copies of books. I only tell you about the ones I think you really need to read.
