Planet of the Bugs: Evolution and the Rise of Insects (33 page)

Let’s consider what might have been happening simultaneously on other planets around other stars like our own sun while life was evolving on earth. Astronomers have determined that the critical components of living planets—carbon, oxygen, water vapor, iron, amino acids—are visibly abundant across the universe. Since there are billions of stars just like our own within the Milky Way and also trillions of other galaxies, each with billions of stars, many of which must be similar to our sun, we must assume that similar aggregations of matter would condense into habitable planetary systems in many places where other yellow stars exist.

Moreover, based on the observation that life on earth first evolved very quickly after our atmosphere developed, the planet cooled sufficiently, the liquid-water oceans formed, and the late bombardment of meteors declined, it is plausible, even probable, that life would evolve elsewhere under similar conditions and in terms of the simplest bacterial forms emerging. This idea has been widely embraced and pervades our scientific culture in several ways. It forms the rational basis for the science of astrobiology. We employ and provide grants to scientists who are engaged in the search for extraterrestrial life, even though no such life has ever been discovered, because we
do
consider it to be plausible, even likely. It’s the reason why we are currently searching for evidence of fossil microbes on Mars and why we probed for evidence of living processes on Titan, the moon of Saturn with atmospheric conditions similar to ancient earth. The plausibility of bacterial life elsewhere is also the reason why most modern introductory astronomy books include a chapter on the chemical origins of life.

Although astronomy books will tell you how likely it seems for single-celled life to get started, they will tell you virtually nothing about the directions life may take beyond this point. For that perspective you need to review biology textbooks—but they will discuss the history of life on earth and often don’t mention possibilities elsewhere. Nevertheless, by looking at this history, we may be able to surmise much about potential extraterrestrial patterns of life. One obvious conclusion is that single-celled organisms probably do not develop rapidly into multicellular organisms, anywhere. The biggest reason for assuming that life does not progress swiftly to complexity is the observation that bacterial life on earth remained single-cellular for billions of years, and it took more than three billion years for multicellular life and animals with rapid metabolisms to emerge. This slow pace of events certainly doesn’t make the progression to complexity look inevitable, yet perhaps we can liken it to the slow pace of events in stellar evolution. A star like our own sun may appear to be constant or unchanging for billions of years, but eventually it will rapidly transform into a red giant because of conditions that were predictable at the outset. So assuming similar, earthlike chemical conditions on similar planets around stars of similar intensity, we have to assume that extraterrestrial life forms would evolve the capacity to split water molecules with starlight (the most abundant and predictable source of
energy across the universe), form organic molecules with the released energy, and produce free oxygen. Photosynthetic life would, by its very nature, transform the atmospheric conditions on any planet. Oxygen reacts with iron in the oceans and rocks until stable compounds are formed, and once production of this gas exceeds the amount used in reactions with iron, any atmosphere would change and become more oxygen-rich. If the evolution of respiring multicellular animals is indeed a natural adaptation to avoiding oxygen toxicity, then an explosion of multicellular forms is an inevitable outcome of physically predictable processes.

It is one thing to suggest that oxygen might stimulate the evolution of multicellular complexity and a diversity of animal forms. It’s another thing entirely to suggest that it might stimulate a progression to a particular form of animal: namely arthropods, but that’s precisely what I am arguing. Aerobic respiration leads to more rapid metabolism, which promotes the evolution of fast-moving predators and more complex ecological food webs. Rapid metabolisms require that locomotion systems with articulating, muscle-manipulated, skeletal parts evolve. Skeletal systems can either be on the exterior or in the interior, and we have seen that external skeletons are easy to produce metabolically from excretion byproducts. It wasn’t just luck that the Cambrian explosion produced a predominance of external skeletal forms—they are more effective for defense and therefore better for survival—and if we can learn any lesson from earth insects it is simply this: small is good. Small creatures require fewer resources to survive, they can occupy tinier and increasingly specialized niches, and they evolve more quickly than large organisms because of short generation times. So I’m arguing that the arthropods were not only a predictable product of the oxygen-generated Cambrian explosion but also the predictable colonizers and survivors over subsequent periods. Arthropods colonized earth’s soils, forests, and air because they were the most diversified and best-adapted organisms to make those transitions. The very simple traits of small size, wings, and metamorphic growth ensured that insects were better colonists and survivors than any other organisms, and they proved themselves resilient to even the most catastrophic events, whether it was continental collisions, global climate change, massive volcanism, or asteroid impacts. For all of these reasons, I believe that small arthropod- and insectlike
creatures would also be likely to evolve and survive on other planets, wherever the right conditions for life exist.

Perhaps you are skeptical about my idea. That’s fine; skepticism is healthy for scientific thought. Some people might think that it isn’t scientific at all—just a bunch of armchair speculation. Alright then, let’s express my idea as a scientific hypothesis. I’ll call it the buggy universe hypothesis, which, simply stated, goes like this: the living universe is full of bugs. I’m not predicting that other worlds are full of insects just as we have them on earth: butterflies, ants, beetles, flies, and such. Life elsewhere might have any number of possible variations. It might be based on DNA that spirals differently than our own or on other self-replicating molecules entirely, and it might have evolved multitudinous body forms, but on any planet where life develops beyond bacteria into multicellular animals, and where plantlike photosynthetic organisms colonize the land, the most abundant and diversified forms of life should be small exoskeletal creatures approximating arthropods. They might have different kinds of body regions, types of segmentation, and numbers of legs, but they will resemble arthropods nevertheless.

The buggy universe hypothesis is verifiable and has already passed one test: this planet is observed to be astronomically full of bugs. We can easily imagine other pathways by which life on earth might have evolved without any humans, or even without any mammals or dinosaurs, but given the unfolding of the earth’s history as we understand it, it’s difficult to imagine how terrestrial ecosystems could have evolved without insects or insectlike creatures. I can also conceive of three possible future tests. We might actually make contact with intelligent extraterrestrial beings. Once we learn to communicate with them, assuming they are friendly and conversational, we could ask them about conditions on their planets and so learn about extraterrestrial biology. We might also develop the optical technology to view conditions on distant planets. At present we can’t even see those planets, so it’s a stretch to believe that someday we might be able to resolve distant surfaces well enough to see plants and insects. Then again, when I was a kid nobody imagined that we would have satellites with optics capable of resolving license plates from outer space. The most likely possibility, in my opinion, is that we might discover and travel to other habitable planets. I’m skeptical about doing it the Star Trek or Star
Wars way. That is to say, I’m not so sure we will ever develop warp drives or hyperdrives or a way to exceed or even approach the speed of light. But with existing technologies we could devise ways of getting to other stars at slower speeds. Interstellar travel might take a long time, but humans could possibly traverse such distances using cryogenic hibernation systems or simply send robotic probes capable of conducting studies and returning data.

There’s an old saying that goes, “You only hit a target if you aim for it.” We have already proven that we can detect life-sustaining planets from a remote distance using the simple methods of spectral analysis and infrared photography, and it seems to me that these methods will continually enable us to search for planets with the traces of life known to us.
¹
If astronomers (and botanists) find it plausible that plants might exist elsewhere—enough that we build spaceships with remote sensors to detect the presence of chlorophyll—then why shouldn’t we consider it plausible that other planets might be highly diversified with arthropod- and insectlike creatures? The presence of chlorophyll across whole continents suggests not only the mere presence but a broad diversity of plants, and, as a biologist, I find it impossible to imagine how such wide-ranging plant systems could have evolved without the ecological interactions of insects, or similar arthropods. After all, arthropods affect soil quality and nutrient cycling, and, as we have seen, they also promote plant diversity through pollination, seed dispersal, and herbivory. The colonization of a planet by plants is not a solitary process—it is a complex symbiosis involving coevolution with soil microbes, fungi, and multitudes of small animals, especially insects.

My buggy universe hypothesis is contrary to much of what I was taught, but lately, I’ve been finding it compelling. At night, when I stargaze, I start to see insects and wonder if they do in fact live on other planets. When I look at constellations, I join those ancient people who saw arthropods and imagined Scorpio, the scorpion, and Cancer, the crab. The Big Dipper looks more like a long-tailed wasp, Draco the Dragon more like a millipede. Taurus the bull resembles a long-horned beetle, and the Gemini twins might be the eyespots of a saturniid moth. During these moments, I sometimes reflect on the biologist J. B. S. Haldane, who, when asked “what one could conclude as to the nature of the Creator from a study of his creation” reportedly responded “An in
ordinate fondness for beetles.”
²
For decades, evolutionary biologists have treated his remark as a humorous anecdote, but I think we should take it seriously and contemplate why there are so many insects. And, if you are among the large number of people who believe in one creation story or another, you still need to reconcile your thinking with Haldane’s compelling observation that this planet is full of insects. If God crowded the earth with bugs, then he must have done so for a reason. I’d have to conclude that, in his infinite wisdom, he would have made other planets buggy as well.

Maybe we never will discover life anywhere else. Or maybe, just maybe, someday we will detect another planetary system that shows all the signs of potential life. Perhaps we will devise a spaceship and travel to that distant land. I’m not sure when or if this will happen, but if it does, I hope my message will reach through time to the people who build that ship. I’m not asking them to believe me. I’m only asking them to consider whether my thoughts are plausible, because in the end, my request is simple: whoever you are, please don’t forget to pack a net, some jars, some vials, and some plastic bags. These items won’t take up much space, and they won’t cost much, compared to the trip’s expense. I just have the feeling that you might need them. I’ve found these simple things to be very useful on our Planet of the Bugs.

Acknowledgments

      
So, as fast as I could,

      
I went after my net.

      
And I said, “With my net

      
I can get them I bet.

      
I bet, with my net,

      
I can get those Things yet!”

DR. SEUSS,
The Cat in the Hat

When I was 4 years old, my brother Ted gave me a homemade butterfly net, and I’ve been fascinated with insects ever since. Some of my earliest memories are of chasing them in Detroit’s Fargo Park, armed with my net, an empty glass jelly jar, and inspiration from Dr. Seuss to “get those things yet!” That’s one of the great things about the science of entomology: you don’t need much equipment to get started. Fifty years later, I’m a professor of entomology and curator of an insect museum. I’ve discovered and named 162 new insect species from 29 different countries all around the world. I’ve been fortunate to pursue a professional career centered on a lifelong interest, but I realize that it was possible only because many kind people supported and nurtured me along the way.

Writing this book took a lot longer than I expected when I started it. At several points I experienced writer’s block and spent time pondering various parts. I’d like to express my sincere gratitude to Harold Greeney, founder of the Yanayacu Biological Research Station and Center for Creative Studies, and also I thank professors Lee Dyer of the University of Nevada at Reno and Tom Walla of Mesa State College for starting the research project that introduced me to Yanayacu, Ecuador. Yanayacu provided me with the biological inspiration and fresh air needed to finish this book.

Profound thanks to Professor Duncan Harris, director of the UW Honors Program, for encouraging me to teach three honors courses: Cosmology of Insects, Cosmology of Life, and Cloud Forest Ecology in Ecuador. Teaching these classes allowed me to sketch out the ideas presented in this book and gave me the opportunity to formulate them more clearly. I especially owe Professor Harris a debt of gratitude for allowing me to teach Cosmology of Insects, and not simply reminding me that such a discipline doesn’t exist yet.