Written in Stone: Evolution, the Fossil Record, and Our Place in Nature

by Brian Switek

  55 Think of doing the breaststroke in a pool. Half the motion is the actual stroke that propels you forward and the other half is a moment of little forward movement in which you bring your limbs back into position for the next stroke.

  56 One hypothesis is that the legs might have been used in nuptial encounters, but just because the structures exist does not mean we need to invent things for them to do. It may be that the small hind limbs were not used for anything; all the more reason for them to be evolved away.

  57 The reasons seals and sea lions (or pinnipeds) swim using their fore-and hindlimbs represent an alternate evolutionary path for aquatically adapted mammals. In April 2009 Natalia Rybczynski, Mary Dawson, and Richard Tedford announced the discovery of Puijila darwini, an otterlike relative of seals and sea lions. A transitional fossil connecting these marine mammals with their terrestrial ancestors, Puijila had very robust arm and leg bones, suggesting that it primarily swam by using its webbed hands and feet. This mode of swimming likely had as much influence over the evolution of pinnipeds as undulation had among early whales.

  58 Other extinct aquatic mammals overcame the buoyancy problem in different ways. During the Miocene and Pliocene there was a genus of giant sloths (Thalassocnus ) that lived along the coast of what is now Peru. They appear to have been at least semi-aquatic, swimming into the shallows to eat algae and other soft plants. They show no sign of using gastroliths or developing bone ballast. Instead they may have held themselves beneath the water by grabbing onto rocks with their massive claws.

  59 Buffon chose iron as the best model metal for Earth, and through his experiments he made the more controversial claim that the earth was much older than the 6,000 and some odd years that Biblical chronologists had frequently come up with.

  60 The moose, said to be about seven feet tall, arrived in Paris in 1787, but by then Buffon had left Paris due to his failing health. The haste with which the carcass was sent caused it to deteriorate rapidly, and despite Jefferson’s wish to see the specimen properly stuffed and displayed in the city’s great natural history museum, many Parisians were probably hoping that Jefferson would send the smelly thing away.

  61 At the time Virginia encompassed a much larger area than it does today. “Big Bone Lick” is currently within the borders of the state of Kentucky.

  62 The imposing teeth and ornery manner of hippos made many early explorers wonder whether they were carnivorous. It would later become known that they are primarily herbivorous, but they will not turn up their noses at meat if an opportunity to scavenge presents itself. In fact, in 2004 it was reported that hippos had become so overcrowded in parks of Uganda that they began to cannibalize each other at a much higher rate, perhaps hastening the spread of a deadly anthrax outbreak that was working its way through the population at that time.

  63 Some, however, thought that the bones belonged to giants that were human in proportion. For a time this was the opinion of Yale president Ezra Stiles, but Jefferson could not accept this conclusion based upon the presence of tusks with the other large bones. After corresponding with Jefferson, Stiles changed his mind.

  64 Thomas Jefferson described the claws of a similar animal in 1797, which he called Megalonyx, but with only the fossil talons to work with he thought it was a kind of enormous lion. The fossils would not be officially named in Jefferson’s honor until 1825, and by this time it was known that the claws had belonged to an enormous ground sloth.

  65 The hypothesis that Amebelodon and Platybelodon used their jaws exclusively to scoop up water plants would later be refuted. These animals lived in terrestrial habitats, and the wear on the enamel of their teeth is inconsistent with the kind of habits paleontologists like H. F. Osborn envisioned. They may have used their teeth and jaws as scoops sometimes, but they also used them to strip bark off trees, saw through tough plants, and gather plant food through other methods.

  66 In his contribution to the Bridgewater Treatises the English naturalist William Buckland would later speculate that Deinotherium used its lower jaw tusks to anchor itself to the riverbank while sleeping, but there is no evidence that it did so.

  67 These names can be a little confusing as they are often derived from common roots and only have different suffixes. Generally, though, any fossil vertebrate group ending in “-formes” contains a wider variety of creatures, or archaic branches closely related to a more specific, specialized group. This latter group is often distinguished by having the suffix “-morpha.” Another example would be the archosaurs close to the ancestry of dinosaurs. The dinosauriformes were a diverse group of early, dinosaurlike animals, while the dinosauramorpha (nested within the dinosauriformes) contains dinosaurs and their closest, non-dinosaurian relatives.

  68 Reptiles do not have this problem, as they constantly replace teeth throughout their lives, but mammals only have two sets: milk teeth that are shed and adult teeth that must last mature animals their entire lives.

  69 I have decided to leave out a discussion of the Pleistocene impact hypothesis for now, as we cannot yet be certain that such an event actually occurred or that it caused an extinction that, by all appearances, was already in progress at the time. Discussing the evidence so far would require an undue amount of speculation on my part. For now I am content to wait for more complete evidence.

  70 In fact, in 2009 a study based upon genetic material preserved in the permafrost of Alaska suggested that there were mammoths living in that location until about 7,000 years ago.

  71 And this is to say nothing of more practical concerns, such as inadvertently introducing new diseases to animals in North America, the threat that some introduced animals might escape, and the cost to maintain the fencing around hypothetical “Pleistocene parks.” Even if agreement could be reached about the effects of such a “rewilding” attempt, the practical, economic, and societal concerns might stall such projects. Then again, there are already many-acre private exotic game ranches and elephant refuges in the United States, so perhaps these problems could be overcome with enough support. Whether it is a project worth undertaking, however, is another question.

  72 Linnaeus also described two other species of Homo. One, Homo troglodytes, was said to be a nocturnal species that only communicated in hisses; while the other, Homo caudatus, was a humanlike inhabitant of the Antarctic that sported a tail. The existence of these species was based on hearsay, but absence of proof was not considered proof of absence. Perhaps there were other humanoids waiting to be found.

  73 The school of biblical analysis called higher criticism, at least partly inspired by Peyrère’s work, was also important to this change. These scholars strove to understand religious documents by finding independent evidence to confirm (or sometimes refute) certain interpretations of scripture. Their conclusions that did not conform to traditional beliefs (like the divine creation of humanity) were decried as heretical, but the controversy higher criticism stirred reaffirmed that Genesis did not have to be read as a history book.

  74 By this time, the Indonesian apes we know as orangutans today had already been placed in their own genus, Pongo. Gorillas (the “Pongo” of Battell) and chimpanzees had also been described, although the species of chimpanzee called the bonobo would not be identified until the 1920s. Historically, though, the same names were often used to refer to several different kinds of primates, and this created a confusing morass of names. Chimpanzees, for instance, were variously referred to as apes, baboons, mandrills, jockos, and orang-outangs, among others.

  75 A later investigation of the skeleton by W. J. Sollas, Buckland’s successor at Oxford, determined that the woman was really a young man. The pelvis is the most useful bone in determining the sex of an individual, as this bone contains several features (like the width of the sciatic notches on the sides of the hips) that allow osteologists to tell the difference between males and females.

  76 Similar skulls were discovered in Gibraltar in 1829 and in Belgium in 1848, but their significance was overlooked u
ntil well after the 1856 discovery was made.

  77 The exact reason why Dubois cut off access to the fossils is unknown. The resentment his actions caused among anthropologists led to wild accusations about getting even with his critics, religious conversion, and other stories. It is more likely attributable to several factors, including Dubois’ difficulty accepting criticism, his annoyance at interruptions when people wanted to see the fossils, and other people publishing descriptive papers about “his” fossils. Even these considerations might not reveal the entire story. In an interview with the anthropologist W. K. Gregory printed in Popular Science in 1931, Gregory said that during this time Dubois was carefully removing the sediment from beneath the skull in order to make a plaster cast of it to show what the brain might have looked like. Even if this is true, though, there were likely other reasons why Dubois was so possessive of the bones.

  78 But their importance to Chinese culture would endure. In communist China, especially, the bones of “Peking Man” were seen as exhibiting the virtue of the worker; it had been through the use of stone tools that humans had pushed their evolution forward. A full study of the importance of these fossils to Chinese culture can be found in Sigrid Schmalzer’s The People’s Peking Man.

  79 Dart almost orphaned his petrified child when he forgot it in the taxi he took back to his hotel. Fortunately, he was able to recover it.

  80 The conference marked a turning point for Leakey. He had been shamed by two scientific mistakes: the identification of a recent burial as the oldest Homo sapiens (“Oldoway Man”) and misidentifying geologically recent Homo sapiens as an even older ancestor (“Homo kanamensis”). He had a reputation as a sloppy field worker, and he was engulfed in personal scandal when he left his wife with child for a young illustrator named Mary Nicol (who later married Leakey). The 1947 conference, in which Leakey could show off on his home turf, did much to rehabilitate his career.

  81 The story of the Piltdown Man forgery requires more space and attention than I can provide here. For a full account, see Piltdown: A Scientific Forgery by Frank Spencer.

  82 But who could have perpetrated such an act of scientific malfeasance? Everyone was a suspect. That Dawson was involved was nearly a certainty, but author Arthur Conan Doyle, paleontologist Teilhard de Chardin, anthropologist Arthur Keith, and several others were not beyond scrutiny as potential accomplices or masterminds. With Dawson dead and no further clues, however, the motives and the identity of any other hoaxers remain mysterious.

  83 Leakey also sent Dian Fossey to study mountain gorillas in Rwanda in 1967 and Biruté Galdikas to study orangutans in Borneo in 1971. These are the most famous women to go on these excursions, but they were not the only ones. Less well known are Rosalie Osborn, who went to study the gorillas in October 1956, and Jill Donisthorpe, who continued the gorilla observations from January 1957 through September of that year. Both had not learned much more than the little that was already known about gorillas, and this general lack of information led George Schaller and his graduate advisor to mount their own scientific expedition in 1958.

  84 In 2008, researchers reported that bone tools associated with Paranthropus were found at the 1.5-2-million-year-old site at Drimolen in South Africa. These were not weapons, but tools that appear to have been used for digging, perhaps to get into termite mounds or uncover tubers in the ground.

  85 As strange as it may seem, the predators that ate our prehistoric relatives often preserved their bones. The “First Family” of Australopithecus afarensis may have been a saber-toothed cat kill; damage to the skull of the “Taung Child” shows that it was a meal for an eagle; the skullcaps of Homo erectus at Dragon Bone Hill are the tablescraps of giant hyenas; and Homo habilis foot bones from Olduvai Gorge show crocodile toothmarks. In fact, in February 2010 a team of scientists led by Chris Brochu discovered a new fossil crocodile from Olduvai Gorge which could have been capable of doing the damage seen on the Homo habilis bones, and so the scientists named it Crocodylus anthropophagus (literally, the “man-eating crocodile”).

  86 The parts of the study based on social behaviors was led by Owen Lovejoy, a locomotion specialist who had previously claimed that the evolution of bipedalism in humans was related to males provisioning females with food to gain sex, thus leading to monogamy, decreased sexual dimorphism, etc. Lovejoy essentially repackaged these assertions, which had generally been panned by other anthropologists, for Ardipithecus ramidus, and the inferences about social structure are the weakest parts of the new study.

  87 In turn this would suggest that gorillas and chimpanzees do not represent the anatomy of our last common ancestors, but instead are specialized apes that have evolved in different ways (such as independently acquiring a knuckle-walking posture). They are still useful for thinking about our own evolution, but we cannot take them to be what our earliest ape ancestors were like.

  88 In April 2010, paleoanthropologists from South Aftica announced the discovery of a new species of australopithecine they named Australopithecus sediba. Although proposed as a possible ancestor of our own genus, Homo, this 1.7-million-year-old hominin is a little too young and a little too different to be one of our direct ancestors. Instead, it seems that A. sediba was a unique, specialized species of human that lived alongside some of the earliest members of our own genus.

  89 There is some dispute about these latter skulls, specifically whether they belong to Homo erectus or a closely related species called Homo georgicus. Further study will hopefully clarify this issue.

  90 And there may have even been another species of human alive during this time. On March 24, 2010, it was announced in the journal Nature that mitochondrial DNA recovered from a 40,000-year-old finger bone found in Siberia’s Altai Mountains differed strongly from both archaic human and Neanderthal DNA. What this means is debatable. The disparity between the DNA samples may signal the existence of an unknown species of human, a Homo sapiens-Neanderthal hybrid, or a population of Neanderthals that had been genetically isolated from their European relatives (which have formed the base of what we know about Neanderthal DNA). Which of these hypotheses, if any, is correct will require further evidence to determine.

  91 Several years later, paleontologist Dougal Dixon presented a more comprehensive vision of the dinosaurs’ “alternative evolution” in his book The New Dinosaurs . (Along with his book After Man, it is one of the most ingenious collections of speculative biology ever written.) Carl Sagan also speculated on this point in his book on the origins of intelligence, The Dragons of Eden, in which he also wondered if a maniraptoran dinosaur might evolve into a highly intelligent species comparable to our own.

  First published in the United States in 2010 by Bellevue Literary Press, New York

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  Copyright © 2010 Brian Switek

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  This book was published with the generous support of Bellevue Literary Press’s founding donor the Arnold Simon Family Trust, the Bernard & Irene Schwartz Foundation, Jan T. and Marica Vilcek, and the Lucius N. Littauer Foundation.

  Cataloging-in-Publication Data is available from the Library of Congress

  Book design and type formatting by Bernard Schleifer

  eISBN : 978-1-934-13736-9

 

 
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