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.