Studies differ on whether 8-year-old would have reached modern human stature
Philippe Plailly/Science Source
CALGARY, Alberta — A Stone Age boy stands at the center of a controversy over when members of the human evolutionary family first reached heights and weights comparable to those of modern human adults.
All that remains of the ancient, approximately 8-year-old Homo erectus boy today is his nearly complete roughly 1.5-million-year-old skeleton. Excavations in 1984 near Kenya’s Lake Turkana yielded the find, often called Turkana Boy. At the time of the skeleton’s excavation, little was known about adult sizes and growth patterns of H. erectus.
When he died, the child stood roughly 5 feet, 3 inches. A study from 1993 estimated that, had Turkana Boy lived, he would have grown to a height of 6 feet, 1 inch and weight of around 150 pounds. If the boy really was destined for such tallness, then H. erectus would have experienced an adolescent growth spurt on a par with modern humans. A transition to humanlike growth and development would have occurred surprisingly early in hominid evolution.
New comparisons of Turkana Boy’s teeth to those of modern chimpanzees and gorillas at various ages indicate that the child would have reached an adult height of between 5 feet, 9 inches and 5 feet, 11 inches, reported Christopher Ruff at the American Association of Physical Anthropologists annual meeting on April 10.
“That estimate of adult height should be seen as a minimum,” said Ruff, of the Johns Hopkins University School of Medicine. In his view, Turkana Boy demonstrates that H. erectus took a major step toward the extended developmental period of modern humans.
Ruff’s work revises downward only slightly the estimate that he and and Alan Walker of Pennsylvania State University in University Park proposed over 20 years ago. However, the earlier conclusion rested on the assumption that H. erectus grew much as modern humans do, getting considerably taller and heavier during adolescence.
Now, researchers assume that H. erectus growth patterns fell somewhere between those of Homo sapiens and relatively faster-developing chimps.
In line with that view, a team led by Ronda Graves of Florida Atlantic University in Boca Raton estimated in the November 2010 Journal of Human Evolution that Turkana Boy would have reached an adult height of 5 feet, 4 inches, just a tick taller than he stood when he died. That analysis hinged on growth curves for the ancient boy calculated to lie between those of modern humans and chimps.
But between 8 years of age and maturity, even chimps get considerably taller and heavier than Graves and her colleagues say Turkana Boy did, Ruff said, a sign that Graves' team underestimated adolescent development in H. erectus. Growth estimates for chimps and gorillas after tooth development generated Ruff’s new results.
Ruff concluded that Turkana Boy’s height would have fallen within the range of previously estimated heights of adult H. erectus individuals derived from 1.5-million-year-old footprints in Kenya (SN: 3/28/09, p. 14).
In a new set of calculated growth curves for Turkana Boy presented at the anthropology meeting on April 10, Deborah Cunningham of Texas State University in San Marcos — a coauthor of Graves’ 2010 paper — reaffirmed that the child was shorter than Ruff’s estimate and would have weighed between 138 and 147 pounds.
Ruff acknowledged that no modern human or ape populations provide solid comparisons for the growth patterns of H. erectus.
Some anthropologists at the meeting were at a loss to explain the disparity between Ruff’s and Cunningham’s portrayals of Turkana Boy. Bernard Wood of George Washington University in Washington, D.C., commented that he didn’t understand why the growth estimates diverge so greatly.
- C. Ruff. How much more would KNM-WT 15000 have grown? A case study in applying growth trajectories to fossil hominins. American Association of Physical Anthropologists annual meeting, Calgary, Canada, April 10, 2014.
- D. Cunningham et al. New estimates of body mass in KNM-WT 15000. American Association of Physical Anthropologists annual meeting, Calgary, Canada, April 10, 2014.