Consider the Platypus

PREFACE: THE LOADED WORD

When your passion is communicating with the public about science, you’ll talk about your work to anyone who will listen, and listen to anyone who will talk. You start to notice patterns in people’s reactions to certain topics. Evolution, it turns out, is a word that gets a reaction, which can range from name-checking terms like “survival of the fittest” to jokes about being a monkey’s uncle, to starting debate about theology.

Evolution is a weighty topic, with as many data points as the number of cells that are alive on Earth. Only biologists who really specialize in the subject are willing to lean in to conversation about it, as it is so fraught with core beliefs.

Take, for instance, this anecdote by the evolutionary biologist Jonathan B. Losos, from his book Improbable Destinies. He describes a conversation he had on an airplane, en route to conduct a field study on the evolution of color in desert mice, for which he invented a special fencing technique. When the gentleman in the seat next to him asked about his work, he happily described the experiment. His fellow traveler had grown up on a farm, so he was familiar with animal proliferation—that’s what breeding livestock is all about, after all. But as soon as Losos let the name Darwin fall from his lips, the mood of the conversation nosedived. When they were talking mice and mating and coat color and fencing, the two men were speaking the same language. But when animal husbandry became evolution, it became a loaded word.

Sometimes the best way to make a concept less weighty is through a story, such as Red Riding Hood’s cute cautionary tale as a stand-in for the harsh risks of talking to strangers. The stories here belong to the animals. Or rather, they belong to entire families of animals, lineages, their arcs told in geological time.

In selecting stories for this book, I attempted to be democratic in my sampling, to include animals from far-flung corners of the animal kingdom, animals beloved and reviled and rarely heard of. Animals that have been scantly researched appear alongside heavily researched animals—those “greatest hits” animals that show up in every evolution textbook.

I grilled evolutionary biologists for their favorite critters and plowed through texts for standouts. I stood on the shoulders of those who went before to see what they’d seen and hadn’t seen, then went to Google Scholar to see if anyone had seen anything lately and how many people had cited them for it. I thought I’d settled on about 140 animals at one point, then painstakingly whittled the list down to the menagerie you see here.

Together, I hope they help illuminate some of the vast, deep, weighty, loaded story of evolution. If nothing else, the experts I talked to seemed to be glad I was taking on this effort instead of them, so heyyyy! Happy to help! Even though this project sometimes made me feel like Red Riding Hood herself, venturing one step at a time into a big dark woods with way too many paths and a basket not nearly big enough for everything I needed to carry. It was worth it though to meet the creatures that teemed in the branches and streams and under the dirt.

WHO YOU CALLIN’ AN ANIMAL?

This is a book about animals, by animals, for animals. I’m an animal. And so are you.

If you have an adverse reaction to being called an animal, remember this: it’s just a word, a word made up by animals to describe other animals, only to later realize that we’re among them.

For the purpose of this book, though, I use the definition of animal that is currently universally accepted by the scientific community: an organism (living thing) that:

In short: something that is alive but is not a plant, fungus, virus, bacteria, or other single-celled thing. If you’re disappointed to find your favorite animal missing from this book, let me tell you: me too. (The scarcity of birds profiled is downright criminal.)

Overall, though, the choice of featured animals herein represents a microcosm of the study of animal evolution.

WHAT IS THE STUDY OF EVOLUTION CALLED?

Not even that has a single name. Evolutionary biology is the most common, but the researchers can be paleontologists, ecologists, zoologists, taxonomists, physiologists, behavioral neuroscientists, embryologists, oncologists, and now geneticists. Researchers can even be laypeople committed to counting the ticks on their dogs or crows in their yards each season.

Like the process of evolution itself, the process of understanding it is messy. It started blind, crawled along from one fossilized tooth to another, one dissection, one fuzzy DNA gel, one scattershot genome to the next, until slowly those patterns started to emerge.

DARWIN, DARWIN, DARWIN…!

You’ll be seeing a lot of Charles Darwin in this book. He’s credited with the theory of evolution, and although he wasn’t the only one onto it, he really kicked things off. His isn’t the only voice that has contributed to our understanding of evolution, but his was the primary, foundational voice. Think of his presence here as a case study in evolutionary biology, much in the same way each animal here is a case study.

By the end of his life and long after, Darwin is a key figure in the study of evolution, but he wasn’t always a formidable genius.

His evolutionary story, if you will, began at age 16, when young Charlie escaped the relative drudgery of his medical apprenticeship to learn from one John Edmonstone, a freed slave who taught taxidermy at the University of Edinburgh.

At age 22, much to the dismay of his wealthy doctor father, Charles snuck off to board the HMS Beagle, having accepted relatively meager wages to be resident naturalist on what was to be a two-year voyage charting the coastline of South America. By the time he returned to London, Darwin had been away four years, circumnavigated the globe, and observed a lifetime’s worth of biodiversity. This journey sowed the mental seeds that would become his theory of evolution.

It took Darwin 20 years after his return on the Beagle to take his ideas public. He might never have gotten up the gumption had it not been for Alfred Russel Wallace, a young naturalist and admirer of Darwin’s who wrote him a series of letters about a nascent theory of his own. Fueled by passion and friendly competition, the two joined forces and published as soon as they could. Though Darwin claimed the legacy, Wallace remained a key collaborator and eventually became his friend.

Darwin’s theory laid the foundation upon which all modern evolutionary scientists have continued to build. It holds up even today under the ever increasing informational mass of fields like genetics and genomics, despite the fact that the gene itself—the key mechanism for heritability—was so elusive to Darwin that he nearly suffered a mental breakdown in its pursuit.

Beyond this, you won’t see too many names of other scientists in this book, as I don’t want you to get sidetracked by them. Or by dates. Or by a lot of jargon, which is necessary for science, but it’s a double-edged sword. If you understand the jargon, you’ve got an automatic “in”; if you don’t, it might drive you away.

THE TREE RIVER OF LIFE

The notion of a family tree is a comfortable one, a useful tool for one to trace one’s proud parentage back through the ages. It’s a logical leap to extend the tool to connect all life on Earth, an image that has emerged repeatedly in the minds of naturalists even pre-dating Darwin. But Darwin made it famous. For 32 years, as he worked through the ideas that would become his theory, he sketched “trees of life” over and over, most especially in a private, back-burner notebook he’d simply labeled “B.”

One particular tree from this notebook has become iconic and is sometimes hailed as his eureka moment. It depicts a single ancestor (1) begetting many others who beget others and eventually we end up with living species (A on one branch; B, C, and D on another). You’ll see it posted on laboratory walls and classrooms—even tattooed on the bodies of true evolution nerds.

But while this is one of the cleaner and more complete versions of Darwin’s tree, it was one of his first. It dissatisfied him. (Note the “I think” scrawled above it, as if to ward off the ill luck of hubris, even in his own private journals.) It was incomplete. For starters, the tree itself is alive, which is sort of like using a word to define itself. On another page he considers instead another option, ruminating:

“The tree of life should perhaps be called the coral of life, base of branches dead; so that passages cannot be seen.”

But later he decides:

“No only makes it excessively complicated… contradiction to constant succession of germs in progress.” (By “germs” he meant genes, or what would eventually come to be called genes. Another term he hunted for all his life.)

Naturalists before Darwin and many more after him have all tried to reimagine the tree of life, up to and including a massive cross-institutional effort published in a 2016 article in the scientific journal Nature, that allowed the tree to spiral in on itself so as to accommodate all the information springing from it. In the two years since, the explosion of genomic science has begun to work with the image of a web of life, acknowledging connections shared by species that haven’t shared an ancestor for millennia or more.

For the purposes of this book, consider a river.

Like a tree, a river branches, but its path is determined only by its environment and the laws of physics (such as gravity, friction, and motion). It does not have a predetermined shape; it doesn’t have a driving “life” force. It simply runs toward the ocean, diverted by rocks, hills, valleys, and weather. Over time and space, some rivulets dry into gas and reenter the water cycle (like animals dying off, ending lineages and returning organic molecules to the environment), while other rivulets might split, shrink, or grow.

The river has volume, too, three dimensions rather than single points linked by lines. When we talk about “an animal” here we’re not (usually) talking about a single animal from which all others spring. We’re not even talking about two animals and their lineage, like the “begats” on a human family tree. We’re talking about groups of animals, populations over time, that bred and changed en masse, branched and met back up, grew and shrank, left a few fossils behind and brought traces of all of those changes with them.

It’s much easier to picture the complexity and sheer amount of information in the mix this way, a flooded gene pool in motion. The weight of the information we’ve learned (and have yet to learn) from the study of genomes has become too great for a tree branch to hold. A river can always grow wider and deeper.

In the larger context, the headwaters become the place where life begins. Imagine organic molecules coming together for the first time, like how water exists in the water table and soil and as water vapor in the atmosphere, but it doesn’t become a river (life) until it burbles forth or rains down into the riverbed. It only becomes a river (life) when it gains momentum and runs. It is life as long as it is moving forward.