Reading 25


The following passage is adapted from an article entitled “The Mysterious Downfall of the Neanderthals” (2009 Kate Wong).

  1. Ever since the discovery of the first
  2. Neanderthal fossil in 1856,
  3. scientists have debated the place
  4. of these bygone humans on the
  5. family tree and what became of
  6. them. For decades two competing
  7. theories have dominated the
  8. discourse. One holds that
  9. Neanderthals were an archaic
  10. variant of our own species, Homo
  11. sapiens, that evolved into or was
  12. assimilated by the anatomically
  13. modern European population.
  14. The other posits that the
  15. Neanderthals were a separate
  16. species that modern humans
  17. swiftly extirpated on entering the
  18. archaic hominid’s territory.
  19. Over the past decade, however,
  20. two key findings have shifted the
  21. fulcrum of the debate away from
  22. the question of whether
  23. Neanderthals and moderns made
  24. love or war. One is that analyses
  25. of Neanderthal DNA have yet to
  26. yield the signs of interbreeding
  27. with modern humans that many
  28. researchers expected to see. The
  29. other is that improvements in
  30. dating methods show that rather
  31. than disappearing immediately
  32. after the moderns invaded Europe,
  33. starting a little more than 40,000
  34. years ago, the Neanderthals
  35. survived for nearly 15,000 years
  36. after moderns moved in.
  37. These revelations have prompted
  38. a number of researchers to look
  39. more carefully at other factors that
  40. might have led to Neanderthal
  41. extinction. One of the most
  42. informative new lines of evidence
  43. bearing on why the Neanderthals
  44. died out is paleoclimate data.
  45. Scholars have known for some time
  46. that Neanderthals experienced
  47. both glacial conditions and milder
  48. interglacial conditions. In recent
  49. years, however, analysis of
  50. primeval isotopes have enabled
  51. investigators to reconstruct a far
  52. finer-grained picture of the climate
  53. shifts that occurred during a period
  54. known as oxygen isotope stage 3
  55. (OIS-3). Spanning the time
  56. between roughly 65,000 and
  57. 25,000 years ago, OIS-3 began
  58. with moderate conditions and
  59. culminated with the ice sheets
  60. blanketing northern Europe.
  61. Considering that Neanderthals
  62. were the only hominids in Europe
  63. at the beginning of OIS-3 and
  64. moderns were the only ones there
  65. by the end of it, experts have
  66. wondered whether the plummeting
  67. temperatures might have caused
  68. the Neanderthals to perish. Yet
  69. arguing for that scenario has
  70. proved tricky for one essential
  71. reason: Neanderthals had faced
  72. glacial conditions before and
  73. persevered.
  74. In fact, numerous aspects of
  75. Neanderthal biology and behavior
  76. indicate that they were well suited
  77. to the cold. Their barrel chests and
  78. stocky limbs would have conserved
  79. body heat, and their brawny build
  80. seems to have been adapted to
  81. their ambush-style hunting of
  82. large, relatively solitary mammals
  83. that roamed northern and central
  84. Europe during the cold snaps.
  85. But the isotope data reveal that far
  86. from progressing steadily from
  87. mild to frigid, the climate became
  88. increasingly unstable heading into
  89. the last glacial maximum. With that
  90. flux came profound ecological
  91. change. So rapid were these
  92. oscillations that over the course
  93. of an individual’s lifetime, all the
  94. plants and animals that a person
  95. had grown up with could vanish
  96. and be replaced with unfamiliar
  97. flora and fauna. And then, just as
  98. quickly, the environment could
  99. change back again.
  100. It is this seesawing of
  101. environmental conditions that
  102. gradually pushed Neanderthal
  103. populations to the point of no
  104. return, according to scenarios
  105. posited by such experts as
  106. evolutionary ecologist Clive
  107. Finlayson. These shifts would have
  108. demanded that Neanderthals adopt
  109. a new way of life in very short
  110. order. For example, the
  111. replacement of wooded areas with
  112. open grassland would have left
  113. ambush hunters without any trees
  114. to hide behind. To survive, the
  115. Neanderthals would have had
  116. to alter the way they hunted.
  117. Some Neanderthals did adapt to
  118. their changing world, as evidenced
  119. by shifts in their tool types and
  120. prey. But many probably died out
  121. during these fluctuations, leaving
  122. behind ever more fragmented
  123. populations. Under normal
  124. circumstances, these archaic
  125. humans might have been able to
  126. bounce back, as they had previously.
  127. This time, however, the rapidity
  128. of the environmental change left
  129. insufficient time for recovery.
  130. Eventually, the repeated climatic
  131. insults left the Neanderthal
  132. populations so diminished that
  133. they could no longer sustain
  134. themselves.