Human Origins and the Fossil Record: A Recap
— Read the Book: Science and Human Origins —
• Part 1: Human Origins and the Fossil Record: What Does the Evidence Say?
Humans, chimps, and all of the organisms leading back to their supposed most recent common ancestor are classified by evolutionary scientists as “hominins.” The discipline of paleoanthropology is devoted to the study of the fossil remains of ancient hominins. Paleoanthropologists face a number of daunting challenges in their quest to reconstruct a story of hominim evolution.
First, hominin fossils tend to be few and far between. It’s not uncommon for long periods of time to exist for which there are few fossils documenting the evolution that was supposedly taking place. As paleoanthropologists Donald Johanson (the discoverer of Lucy) and Blake Edgar observed in 1996, “[a]bout half the time span in the last three million years remains undocumented by any human fossils” and “[f]rom the earliest period of hominid evolution, more than 4 million years ago, only a handful of largely undiagnostic fossils have been found.”3 So “fragmentary” and “disconnected” is the data that in the judgment of Harvard zoologist Richard Lewontin, “no fossil hominid species can be established as our direct ancestor.4
The second challenge faced by paleoanthropologists is the fossil specimens themselves. Typical hominin fossils consist literally of mere bone fragments, making it difficult to make definitive conclusions about the morphology, behavior, and relationships of many specimens. As the late paleontologist Stephen Jay Gould noted, “[m]ost hominid fossils, even though they serve as a basis for endless speculation and elaborate storytelling, are fragments of jaws and scraps of skulls.”5
A third challenge is accurately reconstructing the behavior, intelligence, or internal morphology of extinct organisms. Using an example from living primates, primatologist Frans de Waal observes that the skeleton of the common chimpanzee is nearly identical to its sister species, the bonobo, but they have great differences in behavior. “On the sole basis of a few bones and skulls,” writes de Waal, “no one would have dared to propose the dramatic behavioral differences recognized today between the bonobo and the chimpanzee.”6 He argues this should serve as “a warning for paleontologists who are reconstructing social life from fossilized remnants of long-extinct species.”7 De Waal’s example pertains to a case where the investigators have complete skeletons, but the late University of Chicago anatomist C. E. Oxnard explained how these problems are intensified when bones are missing: “A series of associated foot bones from Olduvai [a locality bearing australopithecine fossils] has been reconstructed into a form closely resembling the human foot today although a similarly incomplete foot of a chimpanzee may also be reconstructed in such a manner.”8
Flesh reconstructions of extinct hominins are likewise often highly subjective. They may attempt to diminish the intellectual abilities of humans and overstate those of animals. For example, one popular high school textbook9 caricatures Neanderthals as intellectually primitive even though they exhibited signs of art, language, and culture,10 and casts Homo erectus as a bungling, stooped form even though its postcranial skeleton is extremely similar to that of modern humans.11 Conversely, the same textbook portrays an ape-like australopithecine with gleams of human-like intelligence and emotion in its eyes — a tactic common in illustrated books on human origins.12 University of North Carolina, Charlotte anthropologist Jonathan Marks warns against this when lamenting the “fallacies” of “humanizing apes and ape-ifying humans.”13 The words of the famed physical anthropologist Earnest A. Hooton of Harvard University still ring true: “alleged restorations of ancient types of man have very little, if any, scientific value and are likely only to mislead the public.”14
Given these challenges, one might expect caution, humility, and restraint from evolutionary scientists when discussing hypotheses about human origins. And sometimes this is indeed found. But as multiple commentators have recognized, we often find precisely the opposite.15 Calm and collected scientific objectivity in the field of evolutionary paleoanthropology can be as rare as the fossils themselves. The fragmented nature of the data, combined with the desire of paleoanthropologists to make confident assertions about human evolution, leads to sharp disagreements within the field, as pointed out by Constance Holden in her article in Science titled “The Politics of Paleoanthropology.” Holden acknowledges that “[t]he primary scientific evidence” relied on by paleoanthropologists “to construct man’s evolutionary history” is “a pitifully small array of bones… One anthropologist has compared the task to that of reconstructing the plot of War and Peace with 13 randomly selected pages.”16 According to Holden, it is precisely because researchers must draw their conclusions from this “extremely paltry evidence” that “it is often difficult to separate the personal from the scientific disputes raging in the field.”17
Make no mistake: The disputes in paleoanthropology are often deeply personal. As Donald Johanson and Blake Edgar admit, ambition and lifelong quests for recognition, funding, and fame, can make it difficult for paleoanthropologists to admit when they are wrong: “The appearance of discordant evidence is sometimes met with a sturdy reiteration of our original views… it takes time for us to give up pet theories and assimilate the new information. In the meantime, scientific credibility and funding for more fieldwork hang in the balance.”18
Indeed, the quest for recognition can inspire outright contempt toward other researchers. After interviewing paleoanthropologists for a documentary in 2002, PBS NOVA producer Mark Davis reported that “[e]ach Neanderthal expert thought the last one I talked to was an idiot, if not an actual Neanderthal.”19
It’s no wonder that paleoanthropology is a field rife with dissent and with few universally accepted theories among its practitioners. Even the most established and confidently asserted theories of human origins may be based upon limited and incomplete evidence. In 2001, Nature editor Henry Gee conceded, “[f]ossil evidence of human evolutionary history is fragmentary and open to various interpretations.”20
Despite the widespread disagreements and controversies just described, there is a standard story of human origins, retold in countless textbooks, newsmedia articles, and coffee table books. A representation of the most commonly believed hominin phylogeny is portrayed below:
Figure: A standard phylogeny of the branch of the hominin tree that includes humans.21
Illustration: Jonathan Jones.
Starting with the early hominins at the bottom left, and moving upwards through the australopithecines, and then into members of the genus Homo, this chapter will review the fossil evidence and assess whether it supports this alleged story of human evolution. As we shall see, the evidence — or lack thereof — often gets in the way of the evolutionary story.
[Editor’s Note: This is an excerpt from Chapter 3, “Human Origins and the Fossil Record,” of the new book Science and Human Origins, co-authored by Ann Gauger, Douglas Axe, and Casey Luskin. For details, see Discovery Institute Press.]
[3.] Donald Johanson and Blake Edgar, From Lucy to Language (New York: Simon & Schuster, 1996), 22-23.
[4.] Richard Lewontin, Human Diversity (New York: Scientific American Library, 1995), 163.
[5.] Stephen Jay Gould, The Panda’s Thumb: More Reflections in Natural History (New York: W. W. Norton & Company, 1980), 126.
[6.] Frans B. M. de Waal, “Apes from Venus: Bonobos and Human Social Evolution,” in Tree of Origin: What Primate Behavior Can Tell Us about Human Social Evolution, ed. Frans B. M. de Waal (Cambridge: Harvard University Press, 2001), 68.
[8.] C. E. Oxnard, “The place of the australopithecines in human evolution: grounds for doubt?,” Nature, 258 (December 4, 1975): 389-95 (internal citation removed).
[9.] See Alton Biggs, Kathleen Gregg, Whitney Crispen Hagins, Chris Kapicka, Linda Lundgren, Peter Rillero, National Geographic Society, Biology: The Dynamics of Life (New York: Glencoe, McGraw Hill, 2000), 442-43.
[10.] See notes 124-139 and accompanying text.
[11.] Sigrid Hartwig-Scherer and Robert D. Martin, “Was ‘Lucy’ more human than her ‘child’? Observations on early hominid postcranial skeletons,” Journal of Human Evolution, 21 (1991): 439-49.
[12.] For example, see Biggs et al., Biology: The Dynamics of Life, 438; Esteban E. Sarmiento, Gary J. Sawyer, and Richard Milner, The Last Human: A Guide to Twenty-two Species of Extinct Humans (New Haven: Yale University Press, 2007), 75, 83, 103, 127, 137; Johanson and Edgar, From Lucy to Language, 82; Richard Potts and Christopher Sloan, What Does it Mean to be Human? (Washington D.C.: National Geographic, 2010), 32-33, 36, 66, 92; Carl Zimmer, Smithsonian Intimate Guide to Human Origins (Toronto: Madison Press, 2005), 44, 50.
[13.] Jonathan Marks, What It Means to be 98% Chimpanzee: Apes, People, and their Genes (University of California Press, 2003), xv.
[14.] Earnest Albert Hooton, Up From The Ape, Revised ed. (New York: McMillan, 1946), 329.
[15.] For a firsthand account of one paleoanthropologist’s experiences with the harsh political fights of his field, see Lee R. Berger and Brett Hilton-Barber, In the Footsteps of Eve: The Mystery of Human Origins (Washington D.C.: Adventure Press, National Geographic, 2000).
[16.] Constance Holden, “The Politics of Paleoanthropology,” Science, 213 (1981): 737-40.
[18.] Johanson and Edgar, From Lucy to Language, 32.
[19.] Mark Davis, “Into the Fray: The Producer’s Story,” PBS NOVA Online (February 2002), accessed March 12, 2012, http://www.pbs.org/wgbh/nova/neanderthals/producer.html.
[20.] Henry Gee, “Return to the planet of the apes,” Nature, 412 (July 12, 2001): 131-32.
[21.] Phylogeny based upon information from multiple sources, including Carl Zimmer, Smithsonian Intimate Guide to Human Origins (Toronto: Madison Books, 2005), 41; Meave Leakey and Alan Walker, “Early Hominid Fossils from Africa,” Scientific American (August 25, 2003), 16; Potts and Sloan, What Does it Mean to be Human?, 32-33; Ann Gibbons, The First Human: The Race to Discover our Earliest Ancestors (New York: Doubleday, 2006); Ann Gibbons, “A New Kind of Ancestor: Ardipithecus Unveiled,” Science, 326 (October 2, 2009): 36-40.