Your Inner Fish - Weebly

1 2 CONTENTST itle PageDedicationPreface ONE Finding your Inner FishTWO Getting a GripTHREE Handy GenesFOUR Teeth EverywhereFIVE Getting AheadSIX The Best-Laid (Body) PlansSEVEN Adventures in BodybuildingEIGHT Making ScentsNINE VisionTEN EarsELEVEN The Meaning of It All EpilogueNotes, References, and Further ReadingAcknowledgmentsCopyright3 TO MICHELE4 PREFACEThis book grew out of an extraordinary circumstance in mylife. On account of faculty departures, I ended up directingthe human anatomy course at the medical school of theUniversity of Chicago. Anatomy is the course during whichnervous first-year medical students dissect humancadavers while learning the names and organization ofmost of the organs, holes, nerves, and vessels in the is their grand entrance to the world of medicine, aformative experience on their path to becoming first glance, you couldn t have imagined a worsecandidate for the job of training the next generation ofdoctors: I m a paleontologist who has spent most of hiscareer working on turns out that being a paleontologist is a hugeadvantage in teaching human anatomy.

2 Why? The best roadmaps to human bodies lie in the bodies of other simplest way to teach students the nerves in thehuman head is to show them the state of affairs in easiest road map to their limbs lies in fish . Reptiles area real help with the structure of the brain. The reason is that5the bodies of these creatures are often simpler versions the summer of my second year leading the course,working in the Arctic, my colleagues and I discovered fossilfish that gave us powerful new insights into the invasion ofland by fish over 375 million years ago. That discovery andmy foray into teaching human anatomy led me to explore aprofound connection. That exploration became this CHAPTER ONEFINDING your Inner FISHT ypical summers of my adult life are spent in snow andsleet, cracking rocks on cliffs well north of the Arctic of the time I freeze, get blisters, and find absolutelynothing.

3 But if I have any luck, I find ancient fish bones. Thatmay not sound like buried treasure to most people, but tome it is more valuable than fish bones can be a path to knowledge about whowe are and how we got that way. We learn about our ownbodies in seemingly bizarre places, ranging from the fossilsof worms and fish recovered from rocks from around theworld to the DNA in virtually every animal alive on earthtoday. But that does not explain my confidence about whyskeletal remains from the past and the remains of fish , noless offer clues about the fundamental structure of can we visualize events that happened millions and,in many cases, billions of years ago? Unfortunately, therewere no eyewitnesses; none of us was around. In fact,nothing that talks or has a mouth or even a head was7around for most of this time. Even worse, the animals thatexisted back then have been dead and buried for so longtheir bodies are only rarely preserved.

4 If you consider thatover 99 percent of all species that ever lived are nowextinct, that only a very small fraction are preserved asfossils, and that an even smaller fraction still are ever found,then any attempt to see our past seems doomed from FOSSILS SEEING OURSELVES I first saw one of our Inner fish on a snowy July afternoonwhile studying 375-million-year-old rocks on EllesmereIsland, at a latitude about 80 degrees north. My colleaguesand I had traveled up to this desolate part of the world totry to discover one of the key stages in the shift from fish toland-living animals. Sticking out of the rocks was the snoutof a fish . And not just any fish : a fish with a flat head. Oncewe saw the flat head we knew we were on to something. Ifmore of this skeleton were found inside the cliff, it wouldreveal the early stages in the history of our skull, our neck,even our did a flat head tell me about the shift from sea toland?

5 More relevant to my personal safety and comfort, whywas I in the Arctic and not in Hawaii? The answers to thesequestions lie in the story of how we find fossils and how weuse them to decipher our own are one of the major lines of evidence that we useto understand ourselves. (Genes and embryos are others,which I will discuss later.) Most people do not know thatfinding fossils is something we can often do with surprisingprecision and predictability. We work at home to maximizeour chances of success in the field. Then we let luck paradoxical relationship between planning andchance is best described by Dwight D. Eisenhower s famousremark about warfare: In preparing for battle, I have foundthat planning is essential, but plans are useless. Thiscaptures field paleontology in a nutshell. We make all kindsof plans to get us to promising fossil sites. Once we re there,the entire field plan may be thrown out the window.

6 Factson the ground can change our best-laid we can design expeditions to answer specificscientific questions. Using a few simple ideas, which I ll talkabout below, we can predict where important fossils mightbe found. Of course, we are not successful 100 percent ofthe time, but we strike it rich often enough to make thingsinteresting. I have made a career out of doing just that:finding early mammals to answer questions of mammalorigins, the earliest frogs to answer questions of frogorigins, and some of the earliest limbed animals tounderstand the origins of land-living many ways, field paleontologists have a significantlyeasier time finding new sites today than we ever did know more about the geology of local areas, thanks to9the geological exploration undertaken by localgovernments and oil and gas companies. The Internet givesus rapid access to maps, survey information, and aerialphotos.

7 I can even scan your backyard for promising fossilsites right from my laptop. To top it off, imaging andradiographic devices can see through some kinds of rockand allow us to visualize the bones these advances, the hunt for the importantfossils is much what it was a hundred years still need to look at rock literally to crawlover it and the fossils within must often be removed byhand. So many decisions need to be made whenprospecting for and removing fossil bone that theseprocesses are difficult to automate. Besides, looking at amonitor screen to find fossils would never be nearly asmuch fun as actually digging for makes this tricky is that fossil sites are rare. Tomaximize our odds of success, we look for the convergenceof three things. We look for places that have rocks of theright age, rocks of the right type to preserve fossils, androcks that are exposed at the surface.

8 There is anotherfactor: serendipity. That I will show by example will show us one of the great transitions inthe history of life: the invasion of land by fish . For billions ofyears, all life lived only in water. Then, as of about 365million years ago, creatures also inhabited land. Life inthese two environments is radically different. Breathing inwater requires very different organs than breathing in same is true for excretion, feeding, and moving about. Awhole new kind of body had to arise. At first glance, thedivide between the two environments appears almostunbridgeable. But everything changes when we look at theevidence; what looks impossible actually seeking rocks of the right age, we have a remarkablefact on our side. The fossils in the rocks of the world are notarranged at random. Where they sit, and what lies insidethem, is most definitely ordered, and we can use this orderto design our expeditions.

9 Billions of years of change haveleft layer upon layer of different kinds of rock in the working assumption, which is easy to test, is that rockson the top are younger than rocks on the bottom; this isusually true in areas that have a straightforward, layer-cakearrangement (think the Grand Canyon). But movements ofthe earth s crust can cause faults that shift the position ofthe layers, putting older rocks on top of younger , once the positions of these faults arerecognized, we can often piece the original sequence oflayers back fossils inside these rock layers also follow aprogression, with lower layers containing species entirelydifferent from those in the layers above. If we could quarrya single column of rock that contained the entire history oflife, we would find an extraordinary range of fossils. Thelowest layers would contain little visible evidence of above them would contain impressions of a diverseset of jellyfish-like things.

10 Layers still higher would have11creatures with skeletons, appendages, and various organs,such as eyes. Above those would be layers with the firstanimals to have backbones. And so on. The layers with thefirst people would be found higher still. Of course, a singlecolumn containing the entirety of earth history does notexist. Rather, the rocks in each location on earth representonly a small sliver of time. To get the whole picture, weneed to put the pieces together by comparing the rocksthemselves and the fossils inside them, much as if workinga giant jigsaw a column of rocks has a progression of fossil speciesprobably comes as no surprise. Less obvious is that we canmake detailed predictions about what the species in eachlayer might actually look like by comparing them withspecies of animals that are alive today; this informationhelps us to predict the kinds of fossils we will find in ancientrock layers.