The Wild Life of Our Bodies: Predators, Parasites, and Partners That Shape Who We Are Today

by Rob Dunn

  17. Individual scientific meetings can sometimes now be so large that they do not fit into any individual conference centers. The big U.S. meeting for neurobiologists now includes more than 60,000 scientists, nearly all of them focused on some topics sufficiently narrow that at most a few hundred other scientists at the meeting find them interesting.

  6: I Need My Appendix (and So Do My Bacteria)

  1. Even articles that attribute some role to the appendix typically do so in vague terms. A 2001 article in Scientific American concludes that “a growing quantity of evidence indicates that the appendix does in fact have a significant function as a part of the body’s immune system” but then does not go on to even speculate what that “function” might be.

  2. Some have suggested that the appendix cannot go away because a small appendix is more dangerous and likely to burst than a long one, but the presence of small appendices in many, many species makes clear that this is not necessarily true.

  3. Animals have made the evolutionary transition to cave life many tens or even hundreds of times, and each time their eyes have become reduced, their bodies pale. All that is unnecessary and costly has been lost, leaving these creatures like pale ghosts of evolution’s fastidiousness bumping around in the eternal night just under the ground.

  4. William Parker and colleagues have made a recent attempt to reconstruct the evolution of appendices on the mammal evolutionary tree. If you want to take your own stab at trying to discern what the species with appendices share, I direct you to this new paper in which the species are listed. They almost inevitably share something. But what? Two of the species feed on bark, so perhaps they are unique. If one throws them out, then most of the species live in habitats in which diseases might be expected to be a greater than normal threat (e.g., in the dirt or in societies), but there are other organisms in the same habitats with no sign of an appendix. Mysteries remain. Go ahead and have a look yourself. Smith, H. F.; Fisher, R. E.; Everett, A. D.; Thomas, R.; Bollinger, R.; and Parker W. 2009. Comparative Anatomy and Phylogenetic Distribution of the Mammalian Cecal Appendix. Journal of Evolutionary Biology 22: 1984–1999.

  5. Nor is Picasso’s story really so simple as that of the youthful flame. He painted well into his nineties, as did Chagall. Monet painted into his eighties. Similar examples exist for music (Richard Straus), film (John Huston), and, of course, literature (Saul Bellow). For a lovely discussion of the fruits of age see the May 21, 2005, New York Times article by Alan Riding; http://www.nytimes.com/2005/05/21/arts/design/21mati.html?pagewanted=1&_r=1.

  6. This sorting of “us” and “them” is identical to what worker ants or termites do in identifying invaders. Like our antibodies, they make such assessments chemically, in this case using sensors on their antennae and elsewhere on their bodies to cue in on what is foreign and what is not. Foreign species are then, more often than not, mercilessly attacked.

  7. For a delightful (if slightly grumbling) discussion of one aspect of how fictions get recorded as fact in science, see Slobodkin, L. 2001.The Good, the Bad, and the Reified. Evolutionary Ecology Research 3: 1–13. Larry Slobodkin was my adviser’s adviser and a very clever scientist and rhetorician. His rhetoric was so good, in fact, that I think it predisposed his occasional scientific hand waving to going from idea to fact well before being tested. Slobodkin, for example, is the one who suggested that 10 percent of energy goes from primary producers (e.g., grass) to herbivores (cows) and then 10 percent of energy goes from herbivores to predators (e.g., mountain lions). That number, 10 percent, became magic and true, and is reprinted in virtually every textbook of basic biology. It is reprinted even though it is not remotely accurate. Ecological systems vary widely in the percentage of energy that goes from one level in the food chain to the next. And even if we take the average of different systems or species, it does not approach 10 percent. In his last years, Slobodkin railed against this and others of his youthful assertions that had become encodified in science, but to no avail. They remain in textbooks, fiction even though we know otherwise, a complicated legacy of a brilliant man.

  8. Sonnenburg, J. L.; Angenent, L. T.; and Gordon, J. I. 2004. Getting a Grip on Things: How Do Communities of Bacterial Symbionts Become Established in Our Intestine? Nature Immunology 5: 569–573.

  9. Palestrant, D.; Holzknecht, Z. E.; Collins, B. H.; Parker, W.; and Miller, S. E. 2004. Microbial Biofilms in the Gut: Visualization by Electron Microscopy and by Acridine Orange Staining. Ultrastructural Pathology 28: 23–27.

  10. The standard reference on immunology—Atlas of Immunology, by Julius M. Cruse, and Lewis, Robert E. Boca Raton, Fla.: CRC Press, 2004. — does not even list the word “mutualism” in the index. The possibility of cooperation has been expunged from the medical lexicon.

  7: When Cows and Grass Domesticated Humans

  1. Interestingly, although it seems clear that most groups knew many tens and often hundreds of species of plants and animals and their uses, the numbers of known medicinal plants may have been low until agriculture arose. It was with agriculture that the need for medicine to treat disease arose and so too the knowledge.

  2. Denevan, W. 1992. The Aboriginal Population of Amazonia. Pages 205–234 in Denevan, W. M., ed. The Native Population of the Americas in 1492. Madison: University of Wisconsin Press.

  3. The Amazon and its people had long and falsely been assumed “pristine,” but most Amazonian soil bears the marks of charcoal from human burning. In some places, when roads are plowed through the hills, potshards are so dense that they pour out like candy from a piñata.

  4. A time budget for Hadza women, for example, includes just forty-two hours a week of work and that work includes everything—gathering food, preparing food, caring for children, and tending to the repair and construction of homes. More to the point, the Hadza seem to work more than did and do other hunter-gatherers.

  5. Clutton-Brock’s book is a lovely treatise on the biology of those species we depend on disproportionately. It is well worth a read even for someone just casually interested in those few species whose survival we have often depended on. Clutton-Brock, J. 1999. A Natural History of Domesticated Animals. Cambridge, U.K.: Cambridge University Press.

  6. The literature on lactase persistence is growing rapidly. For a clear-headed and comprehensive view of the literature and the more general story of human genetic diversity (particularly in Africa), I recommend Scheinfeldt, L. B.; Soi, S.; and Tishkoff, S. A. 2010. Working Toward a Synthesis of Archaeological, Linguistic, and Genetic Data for Inferring African Population History. Proceedings of the National Academy of Sciences 107: 8931–8938.

  8: So Who Cares If Your Ancestors Sucked Milk from Aurochsen?

  1. With 280,000 deaths a year attributed to obesity in the United States.

  2. Hammer, K., and Khoshbakht, K. 2005. Towards a “Red List” for Crop Plant Species. Genetic Resources and Crop Evolution 52: 249-265.

  3. One piece of evidence in support of this idea is that other primates almost universally have few copies.

  4. Zimmet, P.; Alberti, K. G. M. M.; and Shaw, J. 2001. Global and Societal Implications of the Diabetes Epidemic Lifestyle, Overly Rich Nutrition and Obesity. Nature 414: 782–787.

  5. Yu, C. H. Y., and Zinman, B. 2007. Type 2 Diabetes and Impaired Glucose Tolerance in Aboriginal Populations: A Global Perspective. Diabetes Research and Clinical Practice 78: 159-170.

  6. See, for example, Scheinfeldt, L. B.; Soi, S.; and Tishkoff, S. A. 2010. Working Toward a Synthesis of Archaeological, Linguistic, and Genetic Data for Inferring African Population History. Proceedings of the National Academy of Sciences 107: 8931–8938.

  7. Because race is construed differently in different places, the ways in which we mistakenly use race in medicine differ from country to country. In truth, the differences among peoples relate to either genetics (and hence history) or culture, neither of which is encapsulated by race, particularly as race is often measured in a medical setting by a doctor or nurse’s checkbox asse
ssment. Braun, L.; Fausto-Sterling, A.; Fullwiley, D.; Hammonds, E. M.; Nelson, A.; Quivers, W.; Reverby, S. M.; and Shields A. E. 2007. Racial Categories in Medical Practice: How Useful Are They? PLoS Med 4(9): e271. doi:10.1371/journal.

  9: We Were Hunted, Which Is Why All of Us Are Afraid Some of the Time and Some of Us Are Afraid All of the Time

  1. I gave Bakhul her name. Her real name was lost to history.

  2. Fitzsimons, F. W. 1919. The Natural History of South Africa. New York: Longmans, Green and Co.

  3. Immortalized in several books as well as in two recent films, the most recent of which was the very successful 1996 The Ghost and the Darkness.

  4. Tongue, M. H. 1909. Bushman Paintings. Oxford: Clarendon Press.

  5. There is an old joke in which Johnny and Pete are out in the woods hiking in boots. A grizzly bear starts chasing them. Johnny stops to change into his tennis shoes and Pete yells, “What are you doing, Johnny? You can’t outrun a bear,” to which Johnny responds, “I don’t have to outrun the bear. I just have to outrun you.” This joke cuts to the core of who we are: just another animal who has spent generations figuring out strategies to avoid being the buddy who gets eaten by the bear. Our fear module evolved to allow us to be the one who gets away. Our neocortex, the conscious man’s front brain, evolved to give us the creativity to invent and put on shoes.

  6. McDougal, C. 1991. Man-eaters. In Great Cats: Majestic Creatures of the Wild. John Seidensticker and Susan Lumpkin, consulting editors. Emmaus, Pa.: Rodale Press.

  7. More recent, if gruesome, studies of baboons fed experimentally to leopards confirm that modern leopards consistently leave the heads of their primate prey and regurgitate the other bones. The fingers tend to come back up intact, as was also the case with the bones discovered in the South African caves. Carlson, K. J., and Pickering, T. R. 2007. Intrinsic Qualities of Primate Bones as Predictors of Skeletal Element Representation in Modern and Fossil Carnivore Feeding Assemblages. Journal of Human Evolution 44: 431–450.

  8. This latter study included a drawing with the caption, “Reconstruction of a leopard dragging an . . . ape-manchild. It is suggested that the damage-marks found on the child’s skull could have been caused by the lower canines of the leopard when holding the child’s head in the position shown.” This caption does not seem to actually require a picture. Brian, C. K. 1969. South African Archaeological Bulletin 24: 170–171.

  9. Among them, Agriotherium (a giant, dog-faced bear), Chasmaporthetes (a fast-running, hyena-like carnivore), Machairodus (a saber-toothed cat), Dinofelis (another saber-toothed cat), Homotherium (yet another saber-toothed cat), Pachycrocuta (a group of hyenas, including the giant hyena), and Megantereon (a cat built like a modern jaguar).

  10. Jenny, D., and Zuberbuhler, K. 2005. Hunting Behaviour in West African Forest Leopards. African Journal of Ecology 43: 197–200.

  11. Isbell, L. A. 1994. Predation on Primates: Ecological Patterns and Evolutionary Consequences. Evolutionary Anthropology 3: 61–71. It is perhaps worth noting that some gorillas do occasionally make night nests in trees, but they are the young gorillas, who are still small enough to climb well and/or to be eaten easily.

  12. Alrod, P. L.; Nash, L. T.; Fritz, J.; and Bowen, J. A. 1992. Effects of Management Practices on the Timing of Captive Chimpanzee Births. Zoo Biology 11: 253–260.

  13. Interestingly, not all domesticated animals have become so numbed. Horses remain twitchy, their tendency to flee ever ready, unbroken. In part, these differences reflect the traits we have favored in different domesticated animals. In horses (and other animals used in transportation, such as camels and donkeys), we wanted speed and power. In cows, sheep, and pigs, we wanted more simply milk and meat.

  14. Domestication Effects on Foraging Strategy, Social Behaviour and Different Fear Responses: A Comparison between the Red Junglefowl (Gallus gallus) and a Modern Layer Strain. Applied Animal Behaviour Science 74: 1–14.

  10: From Flight to Fight

  1. Mediterranean tortoises, for example, take around ten years to reach reproductive age. Even limpets and drills take several years. These animals, though once abundant, were slow to recover from being hunted, and so are now abundant almost nowhere in the world. Stiner, M. C.; Munro, N. D.; and Surovell, T. A. 2000. The Tortoise and the Hare: Small Game Use, the Broad Spectrum Revolution, and Paleolithic Demography. Current Anthropology 41:39–73.

  2. Young, R. W. 2003. Evolution of the Human Hand: The Role of Throwing and Clubbing. Journal of Anatomy 202: 165–174.

  3. Corbett went on to kill many “man-eating” tigers, leopards, and lions, but he was also an adamant advocate for the conservation of big cats. To Corbett there seemed in the modern story to be an uneasy truce between big cats and humans, a truce violated by the cats only when they were sick and old but violated by humans at every opportunity.

  11: Vermeij’s Law of Evolutionary Consequences and How Snakes Made the World

  1. Wayne, R. K.; Benveniste, R. E.; Janczewski, D. N.; and O’Brien, S. J. 1989. Molecular and Biochemical Evolution of the Carnivora. In Gittleman, J. L., ed., Carnivore Behavior, Ecology, and Evolution. Ithaca, N.Y.: Cornell University Press, pp. 465–494.

  2. Isbell, L. 1994. Predation on Primates: Ecological Patterns and Evolutionary Consequences. Evolutionary Anthropology. 3: 61–71.

  3. Andersen, P. R.; Barbacid, M.; and Tronick, S. R. 1979. Evolutionary Relatedness of Viper and Primate Endogenous Viruses. Science 204: 318–321.

  4. See Greene’s beautiful treatise on snakes and their sublimity: 1997. Snakes, the Evolution of Mystery in Nature. Berkeley: University of California Press.

  5. The study of the “persistent effects of the idiosyncratic distribution of life” is the bread and butter of my own field, biogeography, where bio means life, geo means Earth, and graphy relates to the story of, and so the field might be described as the story of Earth as conveyed by life. It is one such story, that of humans, that I am revealing here, our story as told by our interactions, across space and time, with the rest of life.

  6. Vermeij, G. J. 1977. Patterns in Crab Claw Size: The Geography of Crushing. Systematic Zoology 26: 138–151.

  7. Notably, if you want to understand a little about what shells were like before crabs with big claws evolved in the ocean, you can look to ponds. In ponds, crushing predators are rare, so one can still find snails with unprotected, simply coiled, shells with wide openings. There they live as if in some more innocent past.

  8. Vermeij first elaborated his idea in 1982 in the paper Unsuccessful Predation and Evolution in the American Naturalist (120: 701–720). Vermeij never refers to his idea as a law. That is my doing.

  9. In fact, hornbills (a large forest bird) can also recognize Diana monkey calls. When Diana monkeys scream, “big cat,” the hornbills do not respond (hornbills are never eaten by leopards). But when Diana monkeys scream, “big bird,” the hornbills begin to scream as well and look for the bird.

  10. Isbell, L. A. 2009. The Fruit, the Tree and the Serpent: Why We See So Well. Cambridge, Mass.: Harvard University Press.

  11. Isbell, for her part, sees fruit consumption and snakes as linked. Once vision began to improve because of the need to detect snakes, she thinks that fruit (which could then also more easily be detected) provided the energy necessary for bigger and bigger brains.

  12. Nor are the effects of snakes on our biology due to venomous snakes alone. Harry Greene, in an e-mail (June 15, 2010) informed me that he was nearing publication of a paper showing that the indigenous Agta people of the Philippines were long plagued by pythons. Of 120 people whose lives were studied, 26 percent of adult males had been attacked by reticulated pythons. Six of those attacks were fatal.

  12: Choosing Who Lives

  1. See Wu, S. V; Rozengurt, N.; Yang, M.; Young, S. H.; Sinnett-Smith, J.; and Rozengurt, E. 2002. Expression of Bitter Taste Receptors of the T2R Family in the Gastrointestinal Tract and Enteroendocrine STC-1 cells. Proceedings of the National Academy of Sciences 99: 23
92–2397. Other species have an even greater diversity of taste bud locations. Sturgeon have taste buds on the outsides of their lips and so, unlike us, are able to taste food before bothering to put it into their mouths. Catfish have taste buds all over their bodies. To them, the whole world is a lunch.

  2. Dean, W. R. J.; Siefried, W. R.; and MacDonald, A. W. 1990. The Fallacy, Fact, and Fate of Guiding Behavior in the Greater Honeyguide. Conservation Biology 4: 99–101.

  3. Leff, B.; Ramankutty, N.; and Foley, J. A. 2004 Geographic Distribution of Major Crops across the World. Global Biogeochemical Cycles 18: GB1009, doi:10.1029/2003GB002108.

  4. Interestingly, this struggle can vary slightly from person to person as a function of our particular histories. Some individuals can taste the chemical compound PTC (it registers as bitter), whereas others cannot. This variation is the result of genetic differences in a series of known genes. This difference may be adaptive. Individuals who can taste PTC are also better able at tasting (and spitting out) plants that contain bitter toxins and so may have done better where toxic plants were diverse. At the same time, in our modern setting this gene has fewer advantages and some disadvantages. Individuals who can taste PTC are much less likely to enjoy some vegetables, such as broccoli, which have an excess of defensive compounds.