Reading 34

Dikika Baby

The following passage is adapted from an article about a recent archaeological discovery (© 2009).

  1. Alemseged Zeresenay has two
  2. babies. One is Alula, who spends
  3. most of his time in his mother’s
  4. arms in a cozy bungalow. The
  5. other is a little girl of three,
  6. who spent 3.3 million years
  7. locked in sandstone, until the
  8. Ethiopian scientist and his
  9. team discovered her remains
  10. and painstakingly teased them
  11. out of the rock. It was a long,
  12. slow second birth for a baby
  13. from the dawn of humanity.
  14. Until now all fossils of babies
  15. this ancient could have fit in a
  16. diaper. This new arrival is not
  17. only the most complete ancient
  18. infant but arguably the best
  19. fossil of her species,
  20. Australopithecus afarensis.
  21. That’s the same species as the
  22. superstar fossil called Lucy, a
  23. 3.2-million-year-old adult
  24. female found in 1974. Unlike
  25. Lucy, the baby has fingers, a
  26. foot, and a complete torso.
  27. “But the most impressive
  28. difference between them,”
  29. says Zeresenay, “is that this
  30. baby has a face.” No bigger
  31. than a cantaloupe, the little
  32. bundle of bones may also
  33. bear witness to a key event
  34. in the evolution of hominins,
  35. as humans and their ancestors
  36. are known: the beginning of
  37. our long childhood, when we
  38. grow our large brains.
  39. From the waist down, the
  40. Dikika baby looked like us.
  41. But her upper body had many
  42. apelike features. Her brain
  43. was small, her nose flat like a
  44. chimpanzee’s, and her face
  45. long and projecting. Her finger
  46. bones were curved and almost
  47. as long as a chimp’s. Her
  48. shoulder blades were similar
  49. to those of a young gorilla—a
  50. shape that might have made
  51. it easy for her to climb. A.
  52. afarensis walked on two feet,
  53. but some scientists think this
  54. species also spent time in trees.
  55. Either way, the Dikika baby
  56. was a distinctly different
  57. creature from the apes that her
  58. ancestors had diverged from
  59. several million years earlier. As
  60. apelike feet evolved to support
  61. and propel an upright body,
  62. they could no longer grasp
  63. objects with a thumb-like big
  64. toe, as the feet of chimps can.
  65. For hominin mothers and
  66. infants, the consequences were
  67. momentous: While chimp
  68. babies cling to their mothers’
  69. hair with muscular hands and
  70. grasping toes, a baby hominin
  71. probably had to be carried,
  72. limiting the mother’s ability
  73. to provide for herself. She may
  74. have had to depend on her mate
  75. and the larger group. Brain
  76. evolution expert Dean Falk
  77. speculates that the helplessness
  78. of baby hominins could even lie
  79. at the root of speech, which
  80. could have evolved from
  81. “motherese,” the sounds a
  82. mother makes to comfort her
  83. baby.
  84. The Dikika fossil also hints
  85. that brain development may
  86. already have started to take
  87. longer, a change that prolonged
  88. the dependence of human
  89. young on their parents. From
  90. the Dikika baby’s teeth, the team
  91. estimated her age at three years;
  92. her brain, preserved as a
  93. sandstone cast inside the skull,
  94. had a volume of about 330 cc
  95. —roughly the same as a small
  96. three-year-old chimpanzee’s.
  97. This could mean her brain was
  98. growing no faster than a
  99. chimp’s, so it might have taken
  100. longer to reach its adult size,
  101. slightly larger in an australopith
  102. than in a chimp.
  103. During human evolution, ever
  104. longer brain growth led to the
  105. extended period of dependence
  106. we call childhood. In most other
  107. mammals, including other
  108. primates, the young move on to
  109. forage for themselves after they
  110. finish nursing. In the Dikika
  111. baby, Zeresenay already sees
  112. hints of this uniquely human
  113. life stage. “We’ve captured a
  114. moment in time for an
  115. individual, but also a moment
  116. in the life history of a species,”
  117. he says.
  118. Growing bigger brains had other
  119. consequences. Gray matter is
  120. the gas-hog of our bodies. A
  121. fifth of the calories you consume
  122. go to fuel your brain. Within a
  123. million years of the Dikika baby
  124. our ancestors learned to
  125. supplement the mostly
  126. vegetarian diet of Lucy and her
  127. kin with nutrient-packed meat,
  128. devising stone tools to strip
  129. flesh and crack bones for the
  130. protein-rich marrow. Good
  131. nutrition made even bigger
  132. brains possible. And that led
  133. to more inventions, and then
  134. bigger brains.
  135. The Dikika baby’s biography is
  136. short, but the evolutionary steps
  137. she embodied have had
  138. profound and enduring effects.
  139. Although bipedalism and big
  140. brains carried a high cost,
  141. particularly for the mothers of
  142. our lineage, these traits
  143. ultimately combined to produce
  144. smarter babies who would
  145. eventually be able to master
  146. technologies, build civilizations,
  147. and, yes, explore their own
  148. origins.