Science is occasionally a life-threatening career choice, particularly for those scientists who risk shipwreck, starvation, disease, and large, arctic carnivores to unlock the mysteries of the life's past.

Sean Carroll, in Remarkable Creatures, looks at how the drive to explore, the itch for discovery that pushed Columbus and Magellan on their great voyages, has worked its magic on those great scientists who have pursued scientific adventures to the most extreme corners of the earth.

What makes a scientific adventurer tick? Carroll answers this question by taking us through a series of mini-biographies of great scientific adventurers. He starts with scientific adventurer par excellence, Alexander von Humboldt, who, after spending 5 years exploring South America (getting zapped by electric eels and attacked by jaguars), was almost shipwrecked on his way to America, where he stopped to talk fossils with President Thomas Jefferson before returning home and writing thousands of pages about his scientific discoveries.

We read about Charles Darwin's constant seasickness, Alfred Wallace's long bouts with tropical diseases as he puzzled over the odd split between the animals of Southeast Asia and Oceania (known today as the Wallace Line), and paleontological explorer Roy Chapman Andrews' Indiana Jones'-like fear of the snakes he encountered when discovering the first fossil dinosaur eggs at pit viper-infested sites in a remote corner of Central Asia.

These adventures are a pleasure to read about, since, unlike too many popular science books, Carroll tells these stories without dumbing it down or becoming excessively campy. Science is exciting, but it's also serious business.

What all of Carroll's epic adventurers have in common is a gnawing itch to understand the deep history of life on earth, which is ultimately a desire to understand where we came from. Not all of these discoverers were trained professional scientists; Louis Leakey, equipped with a shovel, plenty of drive, and a bit of luck, showed that you don't need a Ph.D. to make great discoveries about life's past. Yet such a strong drive to discover has its dangers, apart from the physical ones: self-deception has sunk many would-be scientific heroes. All of Carroll's explorers, with or without formal training, kept their heads about them. They set the bar high for themselves, and their desire to know was tempered by an honesty about evidence. And that is the essence of what makes a great scientist: an obsessive desire to know the answer, coupled with an intuitive understanding of what it takes to not deceive yourself into thinking you've succeeded when in fact you haven't.

In addition to taking us back to science's roots in adventure, Carroll shows how in recent years, the quest to understand the history of life has been transformed by the modern tools of physics and genetics.

For centuries, in the spirit of Humboldt, paleontologists and evolutionary biologists have made great progress by setting out for distant corners of the world with their notebooks and shovels, tracking down clues found in fossils and in the great biogeographical patterns of life around the world. But, if you're willing to be a little more technically savvy, the earth has more subtle clues to offer up. Carroll relates the story of the K-T boundary, that odd geological anomaly which coincided with the demise of the dinosaurs in the fossil record. The father-son team of Luis and Walter Alvarez (along with several other scientists) used nuclear physics and geochemistry to persuasively argue that the K-T boundary was the result of a massive asteroid impact 65 million years ago, which clearly had a negative effect on the survival of the dinosaurs. The lesson is that there are clues to life's past that must be discovered with mass spectrometers instead of shovels.

Scientists who piece together the evolutionary history of life from fossils are frequently forced to draw inferences from a few fragmentary samples. These fossil fragments can be powerful, but they can difficult to interpret without introducing some subjectivity - it's challenging to decide which characteristics are informative. This is clearly illustrated in one of the most hotly debated question in human evolution: did modern humans evolve in Africa, and then spread to the rest of the world, replacing earlier Homo species in the process? Or did modern humans evolve from arhcaic species, in place, all over the world (with modern Europeans, for example, descending, at least in part, from Neanderthals)?

Carroll describes how DNA sequencing came in and turned this field upside down. While fossils are undeniably important, our DNA is filled with information about our past.

Instead of drawing conclusions about human evolution from a few dozen traits found in a few hundred fossils, DNA is packed with thousands of informative traits, ones that can be interpreted much more unambiguously (in large part because, unlike continuously varying fossil traits, DNA is digital). There is a wealth of data in DNA, which gives anthropological geneticists a level of statistical power beyond the reach of any fossil study. DNA evidence, together with fossil evidence, has largely settled the debate about the evolution of modern humans. They evolved in Africa, and spread out from there - for the most part. The most extreme version of the multi-regional evolution model has been ruled out, but it is still possible that we'll find some evidence of modern humans intermixing with archaic ones.

The most definitive evidence for this intermixing might come from a source that Darwin and Humboldt never dreamed of - DNA extracted from ancient bones. Soon the world will be presented with a Neanderthal genome, a fitting culmination of centuries of adventure in search of life's origins.

Carroll has written one of the most impressive books of this year of Darwin celebrations, reminding us that science, for all of our (justified) talk about economic benefits and medical cures, is ultimately rooted in an epic spirit of adventure.

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Remarkable Creatures, by Sean B. Carroll
Houghton Mifflin Harcourt, 2009