Sunday, April 10, 2016

Review: The Most Perfect Thing

If you watch enough bird documentaries you're bound to run across video of a Common Murre egg rolling around and around a central point (check the gif here for an example). Common Murres (aka Common Guillemot in Great Britain) don't build nests, but instead lay their eggs on bare rock, often on narrow cliff ledges, where a disturbance could easily displace the egg into the sea -- a loss of both effort and opportunity for the parents. The prevailing wisdom of why Murre eggs evolved their pyriform shape is that instead of rolling out into oblivion, they remain right where they should. It's an intuitive explanation, and we can see the evidence with our own eyes.

Open Tim Birkhead's newest book "The Most Perfect Thing: Inside (and Outside) a Bird's Egg" and the first thing you'll read is that the prevailing wisdom is bunk (for one thing, the eggs you see in documentaries are empty shells; eggs full of yolk and albumen don't move the same way). Easy explanations are boring anyway, and Birkhead - whose specialty is Common Murres at their breeding grounds - guides us through the ornithological literature and his own field studies to reveal how the truth about eggs is far more complex and interesting than we might suppose at first blush.

Like his earlier writing ("Bird Sense" is an excellent example), Birkhead goes deep into the history of early speculations, practices, and research and uncovers how these changed over time until we arrive at our current scientific understanding. Surprisingly - until you stop and think about it - is how much of what's known is due in large part to the poultry industry. Even so, the ingenuity of both nature and the ornithologists struggling to uncover nature's secrets are fascinating. You'll read about how Egyptian Plovers, to protect their eggs from intense desert heat, bury their eggs in sand and keep them cool with water dripped from their soaking bellies. And how Goldcrests, fighting near-freezing temperatures stir their eggs with their feet, which they keep warm by pumping blood to their extremities.

Although the book doesn't dwell extensively on the eggs of non-birds, we do see some commonalities, like how egg-laying mammals are hatched with an egg-tooth. And we see some differences: for example that birds' eggs have a hard shell, unlike reptile eggs, which poses a unique set of challenges, like how to store enough water to support an embryo from the time the egg is laid to the time the chick emerges.

But the solutions that evolution has generated aren't foolproof, by any means, and hatching success is highly variable. Birkhead was, of course, aware of this when he chose his title "The Most Perfect Thing." The number of things that can possibly go wrong for an egg are legion, and attempts to combat one problem often create trade-offs that make the egg more vulnerable in some other respect. As Birkhead explores these trade-offs it becomes clear that eggs really are the perfect compromise between myriad different selection pressures.

We think of eggs as having a small number of very uniform elements: shell, albumen, and yolk. But each layer is more complex and finely tuned to solve specific problems than we might realize. We tend to think of eggs as examples of extreme fragility, but after reading this book I came away with a much greater appreciation for their resilience. With "The Most Perfect Thing" Tim Birkhead proves he's one of ornithology's greatest popularizers. Through the passion he has for his subject and the clarity of his writing, he'll have you wondering how you ever managed to take eggs for granted.

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