Last Ape Standing: The Seven-Million-Year Story of How and Why We Survived (31 page)

Then there are the hundreds of books, articles, and scientific papers I communed with for this project. Each represented years of work and research on the part of their authors, nicely condensed explorations of the corners of human evolution and behavior that I couldn’t hope to cover in a thousand lifetimes. Whether it was global climate, human genetics, evolutionary psychology, anatomy, or history, the work of
these researchers and writers provided the essential vitamins and minerals of the pages that follow. I may not know all of them personally, but I am deeply indebted to each of them.

Jen Szymanski and Frank Harris also deserve my special thanks. Frank for his excellent eye and artwork; Jen for her good nature, unfailing attention to detail, and unshakable reliability.

Books also don’t happen without a publisher and an editor who believe in the book and are willing to accept that an idea can be transformed into something people will want to buy and read. I will be forever and deeply grateful for the insight and generous spirit of George Gibson at Walker/Bloomsbury. In baseball there are “player” managers. George is a “writer’s” publisher, always encouraging, never negative, a fine example of the best that human evolution makes possible. This book’s editor, Jacqueline Johnson, is perhaps the calmest person I have ever met, and no matter what sentences might be flailing around under my hand, what participles might be dangling, what questions I might throw her way, or what deadlines I bent and mangled, she remained as imperturbable as Kilimanjaro. And once again I owe my agent, Peter Sawyer, my deep gratitude for his excellent advice and insights on nearly everything, and for hanging in my corner no matter how cockamamy the ideas are that I bring to his sage ear.

Mostly, though, I owe my gratitude to my family. My daughters, Molly and Hannah, who have, their entire lives, put up with this thing I do, which Molly, when she was two years old, once described to someone as “hitting buttons.” Their smiles and laughter and company place even the toughest days at the desk in perspective. My stepchildren, Steven and Ann, have gamely learned how strange it is to have a writer in the house, and still they haven’t punished me for it or given me up for mad. Above all, though, I thank Cyndy, my incomparable wife and the best human on earth, for her relentless patience, encouragement, and love. How mercilessly I have sometimes bent her beautiful ear, yet we remain married.

1
. Until recently, paleoanthropologists referred to the subfamily of hominoids that consisted of humans and their ancestors as hominids, but even the convoluted argot of science sometimes changes. Today
hominid
refers to all great apes, including gorillas and chimpanzees, but
hominin
refers specifically to ancient and modern humans who split off from a common chimp ancestor seven million years ago, or thereabouts. These include all of the Homo species (
Homo sapiens, H. ergaster, H. rudolfensis
, for example), the australopithecines (
Australopithicus africanus, A. boisei
, etc.), and other ancient forms such as
Paranthropus
and
Ardipithecus
. The important point is that we are the last surviving hominin on earth.

2
. During the writing of this book, two new modern human species were discovered and two move ancient species. For more on these, read the sidebars on pages 90–93, “The Newest member of the Human Family.”

1
. Some scientists have speculated that
tchadensis
and others like him at this time in prehistory could be the offspring of early humans and chimps who mated and brought hybrid “humanzees” into the world in the same way mating female horses and male donkeys conceive mules. Since such a hybrid wouldn’t have been able to produce children of its own, the chances of this rare fossil surviving until the present are exceedingly slim, but in the world of paleoanthropology nearly anything is proving to be possible. For more, read “Human, Chimp Ancestors May Have Mated, DNA Suggests,”
National Geographic News
, May 17, 2006,
http://news.nationalgeographic.com/news/2006/05/humans-chimps.html
.

2
. See chapter 1 of
Thumbs, Toes, and Tears: And Other Traits That Make Us Human
.

3
. For more on this read, “Unlocking the Secrets of Longevity Genes,”
Scientific American
, December 2006.

4
. Additional information on this interesting theory can be found in “How Dietary Restriction Catalyzed the Evolution of the Human Brain,”
Medical Hypotheses
, February 19, 2007.

1
. This is an apt analogue for the situation our species faces today … our own intelligence has put us in a precarious situation that we, too, may not survive. See the epilogue, “The Next Human.”

2
. In one of his more whimsical essays written more than thirty years ago, evolutionary theorist Stephen Jay Gould depicted Mickey Mouse as a perfect example of neoteny in action. The older Mickey got, Gould pointed out, the younger (and cuter) his animators made him look. As he aged, Mickey acquired greater youth. Broadly speaking this is precisely what happened to the line of humans who eventually led to you and me.

3
. See L. Bolk, “On the Problem of Anthropogenesis,”
Proc.Section Sciences Kon. Akad. Wetens
. (Amsterdam) 29 (1926): 465–75.

4
. “In neoteny rates of development slow down and juvenile stages of ancestors become adult features of descendants. Many central features of our anatomy link us with the fetal and juvenile stages of [nonhuman] primates.” Gould,
Ontogeny and Phylogeny
, 1977, 333.

5
. From Barry Bogin, “Evolutionary Hypotheses for Human Childhood,”
Yearbook of Physical Anthropology
(1997), 70. “In Shea’s view, a variety of heterochronic processes are responsible for human evolution. The others may be hypermorphosis, acceleration (defined as an increase in the rate of growth or development), and hypomorphosis (defined as a delay in growth with no delay in the age at maturation) … None of these acting as a single process can produce the human adult size and shape from the human infant size and shape. The same holds true for acceleration and hypomorphosis. In agreement with Schultz, Shea states that ‘we [humans] have extended all of our life history periods, not merely the embryonic or juvenile ones’ (pp. 84–5). Humans have also altered rates of growth from those found in other primates and possible ancestors. To accomplish all this required, in Shea’s view, several genetic changes or adjustments during human evolution. Since the hormones that regulate growth and development are, virtually, direct products of DNA activity, Shea proposes that the best place to look for evidence of the evolution of ontogeny is in the action of the endocrine system. According to Shea and others (e.g., Bogin, 1988) differences in endocrine action between humans and other primates negate neoteny or
hypermorphosis as unitary processes and instead argue for a multiprocess model for human evolution.”

6
. Around this time, our ancestors may also have begun to lose their hair, another neotenic trait, although loss of hair almost certainly also helped to avoid overheating on Africa’s scorching savannas.

7
. Martin, “Human Brain Evolution in an Ecological Context” (fifty–second James Arthur Lecture, American Museum of Natural History, New York, 1983).

8
. The Pleistocene epoch lasted from about 2.5 million years to 11,700 years ago and includes Earth’s recent period of repeated ice ages. The Pleistocene is the first epoch of the Quaternary Period or sixth epoch of the Cenozoic Era. The end of the Pleistocene corresponds with the end of the last glacial period, the one that immediately preceded the blossoming of recorded human history. It also corresponds with the end of the Paleolithic age used in archaeology.

9
. Another reason that children need a special high–energy diet is the rapid growth of their brain. In their research in 1992, Leonard and Robertson estimated that due to this accelerated growth, “a human child under the age of 5 years uses 40–85 percent of resting metabolism to maintain his/her brain [adults use 16–25 percent]. Therefore, the consequences of even a small caloric debt in a child are enormous given the ratio of energy distribution between brain and body.”

10
. Bogin, “Evolutionary Hypotheses for Human Childhood,” 81.

11
. See Gould,
Ontogeny and Phylogeny
, 290–94.

12
. In traditional hunter–gatherer and horticultural societies, studies have found that even without the advantages of modern medicine and sanitation, people manage to raise about 50 percent of their children to adulthood. Monkeys and apes have a success rate between 14 and 36 percent. That means out of every hundred infants born, humans raise at least fourteen more successfully. Over evolutionary time that has made an enormous difference. Even in protected reserves, chimpanzees and gorillas are essentially at zero population growth and their worldwide numbers are dropping. Humans, however, have grown from small clans numbering in the thousands two hundred thousand years ago to seven billion people that live in every conceivable earthly environment, with more coming all the time. The evolutionary “strategy” of a long, if dangerous, human childhood has clearly succeeded, at least for us, for now.

1
. For more detail see
http://users.ecs.soton.ac.uk/harnad/Papers/Py104/pinker.langacq.html
—Steven Pinker’s exploration of human language and its evolution.

2
. Planaria can pass along their personal experience to other flatworms in the
oddest way. Untrained flatworms that eat the ground-up brains of other planaria that have been trained to perform specific tasks will quickly exhibit the same knowledge that the dead flatworms acquired in life. R. Joseph,
The Naked Neuron
, 15.

3
. Only four weeks into gestation the first brain cells begin to form at the astonishing rate of 250,000 every minute. Billions of neurons will forge links with billions of other neurons, and eventually trillions upon trillions of connections will be made between cells.

4
. Research over the past ten years has illustrated exactly how cognitive, emotional, and social capacities are physically connected to behaviors that can affect us throughout our entire lives. Toxic stress damages developing brain architecture, which can lead to lifelong problems in learning, behavior, and physical and mental health. Scientists now know that chronic, unrelenting stress in early childhood, caused by extreme poverty, repeated abuse, or severe maternal depression, for example, can be toxic to the developing brain. On the other hand, so–called positive stress (moderate, short-lived physiological response to uncomfortable experience) is important and necessary to healthy development. Without the buffering protection of adult support, toxic stress can be built into the body largely through epigenetic processes. For more information, see “The Science of Early Childhood Development” and the Working Paper series from the National Scientific Council on the Developing Child.

5
. 
www.developingchild.harvard.edu/content/publications.html
. For more detailed information, see the bibliography, National Scientific Council on the Developing Child, “Children’s Emotional Development is Built into the Architecture of Their Brains,” 2006.

6
. For more on the debate and latest information on exactly how much DNA we have in common with chimpanzees visit
http://news.nationalgeographic.com/news/2002/09/0924_020924_dnachimp_2.html
.

7
. Scientists have found that neurons again overproliferate at a second time in our lives, just before puberty, in a way that they do in the first thirty-six months of life. However, the activity takes place in the prefrontal cortex, not the entire brain. It is almost as if the evolution of the prefrontal cortex required a kind of “second childhood.” Connections made during this time that aren’t used over the long term are also eventually pruned back.

8
. See “A Comparison of Atropine and Patching Treatments for Moderate Amblyopia by Patient Age, Cause of Amblyopia, Depth of Amblyopia, and Other Factors,”
Ophthalmology
110 (8) (August 2003): 1632– 37;discussion, 1637– 38, and L. Kiorpes and J. A. Movshon “Amblyopia: A Developmental Disorder of the Central Visual Pathways,”
Cold Spring Harbor Symposia on Quantitative Biology
61:39–48, for more information about blindness, the visual cortex, and amblyopia.

1
. The same question struck an anthropologist at the University of Southern California, Christopher Boehm, several years ago, so he surveyed fifty previously completed studies of small, nonliterate tribes and bands that live around the world. He wondered if the way these primal communities handled the complexities of ethics, fair play, and morality might offer some insight into the basics of those behaviors in the rest of us. The popular view of nonliterate societies is that they are more prone to violence or war, but Boehm’s research revealed they almost always developed, independently of one another, an egalitarian approach to life; one in which they struggled conscientiously to weigh self–interest and common interest. For example, if a bully acted like a silverback, alpha–male gorilla and attempted to dominate the group, the group responded by shaming, ostracizing, or, in extreme cases, killing the perpetrator to ensure individual rights were protected.

2
. For a summary of Dunbar’s theories, see pages 122–23 of
Thumbs, Toes, and Tears: And Other Traits That Make Us Human
.

3
. For more on this case, see Valerie E. Stone et al., “Selective Impairment of Reasoning About Social Exchange in a Patient with Bilateral Limbic System Damage,”
Proceedings of the National Academy of Sciences of the United States of America
99.17 (2002): 11531–36.