Dikika Baby
The following passage is adapted from an article about a recent archaeological discovery (© 2009).
- Alemseged Zeresenay has two
- babies. One is Alula, who spends
- most of his time in his mother’s
- arms in a cozy bungalow. The
- other is a little girl of three,
- who spent 3.3 million years
- locked in sandstone, until the
- Ethiopian scientist and his
- team discovered her remains
- and painstakingly teased them
- out of the rock. It was a long,
- slow second birth for a baby
- from the dawn of humanity.
- Until now all fossils of babies
- this ancient could have fit in a
- diaper. This new arrival is not
- only the most complete ancient
- infant but arguably the best
- fossil of her species,
- Australopithecus afarensis.
- That’s the same species as the
- superstar fossil called Lucy, a
- 3.2-million-year-old adult
- female found in 1974. Unlike
- Lucy, the baby has fingers, a
- foot, and a complete torso.
- “But the most impressive
- difference between them,”
- says Zeresenay, “is that this
- baby has a face.” No bigger
- than a cantaloupe, the little
- bundle of bones may also
- bear witness to a key event
- in the evolution of hominins,
- as humans and their ancestors
- are known: the beginning of
- our long childhood, when we
- grow our large brains.
- From the waist down, the
- Dikika baby looked like us.
- But her upper body had many
- apelike features. Her brain
- was small, her nose flat like a
- chimpanzee’s, and her face
- long and projecting. Her finger
- bones were curved and almost
- as long as a chimp’s. Her
- shoulder blades were similar
- to those of a young gorilla—a
- shape that might have made
- it easy for her to climb. A.
- afarensis walked on two feet,
- but some scientists think this
- species also spent time in trees.
- Either way, the Dikika baby
- was a distinctly different
- creature from the apes that her
- ancestors had diverged from
- several million years earlier. As
- apelike feet evolved to support
- and propel an upright body,
- they could no longer grasp
- objects with a thumb-like big
- toe, as the feet of chimps can.
- For hominin mothers and
- infants, the consequences were
- momentous: While chimp
- babies cling to their mothers’
- hair with muscular hands and
- grasping toes, a baby hominin
- probably had to be carried,
- limiting the mother’s ability
- to provide for herself. She may
- have had to depend on her mate
- and the larger group. Brain
- evolution expert Dean Falk
- speculates that the helplessness
- of baby hominins could even lie
- at the root of speech, which
- could have evolved from
- “motherese,” the sounds a
- mother makes to comfort her
- baby.
- The Dikika fossil also hints
- that brain development may
- already have started to take
- longer, a change that prolonged
- the dependence of human
- young on their parents. From
- the Dikika baby’s teeth, the team
- estimated her age at three years;
- her brain, preserved as a
- sandstone cast inside the skull,
- had a volume of about 330 cc
- —roughly the same as a small
- three-year-old chimpanzee’s.
- This could mean her brain was
- growing no faster than a
- chimp’s, so it might have taken
- longer to reach its adult size,
- slightly larger in an australopith
- than in a chimp.
- During human evolution, ever
- longer brain growth led to the
- extended period of dependence
- we call childhood. In most other
- mammals, including other
- primates, the young move on to
- forage for themselves after they
- finish nursing. In the Dikika
- baby, Zeresenay already sees
- hints of this uniquely human
- life stage. “We’ve captured a
- moment in time for an
- individual, but also a moment
- in the life history of a species,”
- he says.
- Growing bigger brains had other
- consequences. Gray matter is
- the gas-hog of our bodies. A
- fifth of the calories you consume
- go to fuel your brain. Within a
- million years of the Dikika baby
- our ancestors learned to
- supplement the mostly
- vegetarian diet of Lucy and her
- kin with nutrient-packed meat,
- devising stone tools to strip
- flesh and crack bones for the
- protein-rich marrow. Good
- nutrition made even bigger
- brains possible. And that led
- to more inventions, and then
- bigger brains.
- The Dikika baby’s biography is
- short, but the evolutionary steps
- she embodied have had
- profound and enduring effects.
- Although bipedalism and big
- brains carried a high cost,
- particularly for the mothers of
- our lineage, these traits
- ultimately combined to produce
- smarter babies who would
- eventually be able to master
- technologies, build civilizations,
- and, yes, explore their own
- origins.