When humans stopped living in trees, or, how did Lucy die?

UT Austin professor John Kappelman studies 3D printouts of human ancestor Lucy's skeleton
Promo image Marsha Miller, UT Austin

We worry about our kids not getting out into nature enough, but when was the last time you wondered about our ancient ancestors spending time among the trees?

Lucy, one of the oldest (3.18-million-year-old) and most complete specimens of any adult, erect-walking human ancestor has been "at the center of a vigorous debate about whether this ancient species also spent time in the trees" since her discovery in the Afar region of Ethiopia in 1974. New findings on her cause of death may now tip that debate towards a conclusion.

Giving the name 'Lucy' to the collection of bones of the female of the hominin species Australopithecus afarensis known scientifically as AL 288-1 makes her seem more real. But nothing makes a character come alive more than imagining them suffering their last moments. Indeed, you will never think of Lucy quite the same after learning UT Austin professor John Kappelman's theory on how Lucy died.

The evolution of 3D printing has given a boost to the study of fossils, allowing researchers like Dr. Kappelman to re-create the fossil collection AL 288-1 for closer study. His study resembles the TV series that pulls the files on cold cases, using modern scientific techniques to piece together the cause of death based on what remains of a person. And his findings seem hard to dispute: he has built up a robust case for his theory by documenting multiple fractures that consistently tell the same story: Lucy died shortly after a devastating fall.

The "smoking gun" consists of a proximal humerus fracture of Lucy's left shoulder, consistent with the type of broken bones that occur when a conscious person stretches out their arm to break a hard fall. The fractures were sharp, and splintered, not consistent with the usual fractures seen in ancient fossils. Dozens of other compressive fractures, including at the ankle, knee, and pelvis, even a broken rib, all point to a fall from a great height. Because there is no evidence that these fractures started healing, the scientists conclude that the fall occurred shortly before Lucy's death.

Kappelman reflects on how this changed his relationship with Lucy, who he has studied since 2008, when he was part of the team that made the non-destructive scans of the fossils which were used to create the 3D models:

“When the extent of Lucy’s multiple injuries first came into focus, her image popped into my mind’s eye, and I felt a jump of empathy across time and space. Lucy was no longer simply a box of bones but in death became a real individual: a small, broken body lying helpless at the bottom of a tree.”

More importantly, this theory suggests that Lucy represents the evolutionary step at which humans lost the ability to spend time safely in the branches far above the earth. Lucy may have been the "last of the treehuggers" in the most poignant sense of a word that represented a phase in human evolution when holding fast to a tree kept us safe from the predators roaming below.

What's more: you can make up your own mind. For the first time ever, the Ethiopian National Museum provides a set of 3-D files of Lucy’s shoulder and knee for the public to download and print.

When humans stopped living in trees, or, how did Lucy die?
Our most famous ancestor, Lucy, may have still lived in trees - and paid for it with her life

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