Nov 242018
 

On this date in 1974 Donald Johanson and Tom Gray discovered the 40% complete Australopithecus afarensis skeleton, nicknamed “Lucy” (after The Beatles song “Lucy in the Sky with Diamonds” which played constantly at the field site), in the Awash Valley of Ethiopia’s Afar Depression. This makes today something of a coincidence day because on this date in 1859, Charles Darwin published On the Origin of Species, so the date is now celebrated as Evolution Day. The coincidence is not quite perfect since Origin has little to say about human evolution, contrary to popular belief. He had more to say about human evolution in The Descent of Man in 1871, but his speculations are largely wrong because there was almost nothing in the way of fossil evidence to support or oppose them. Both publications did, however, spur research and now we have a much better picture. Finding Lucy was an incredibly important breakthrough in refining the nature of the Australopithecine branch of hominids that led to the genus Homo. I remember the early reports of the discovery of Lucy very well because I was studying human evolution at the time.

Lucy is the common name of AL 288-1. In Ethiopia, the assembly is also known as Dinkinesh, which means “you are marvelous” in the Amharic language. The Lucy specimen is an early australopithecine and is dated to about 3.2 million years ago. The skeleton has a small skull akin to that of non-hominin apes, plus evidence of a walking-gait that was bipedal and upright, akin to that of humans (and other hominins). This combination supports the view that bipedalism preceded increase in brain size in human evolution.

On the morning of 24th November 1974, near the Awash River, Johanson abandoned a plan to update his field notes and joined graduate student Tom Gray to search Locality 162 for bone fossils. By Johanson’s later (published) accounts, both he and Tom Gray spent two hours on the increasingly hot and arid plain, surveying the dusty terrain. On a hunch, Johanson decided to look at the bottom of a small gully that had been checked at least twice before by other workers. At first view nothing was immediately visible, but, as they turned to leave, a fossil caught Johanson’s eye; an arm bone fragment was lying on the slope. Near it lay a fragment from the back of a small skull. They noticed part of a femur (thigh bone) about one meter away. As they explored further, they found more and more bones on the slope, including vertebrae, part of a pelvis, ribs, and pieces of jaw. They marked the spot and returned to camp, excited at finding so many pieces apparently from one individual hominin. In the afternoon, all members of the expedition returned to the gully to section off the site and prepare it for careful excavation and collection, which eventually took three weeks.

Over the next three weeks the team found several hundred pieces or fragments of bone with no duplication, confirming their original speculation that the pieces were from a single individual; ultimately, it was determined that an amazing 40 percent of a hominin skeleton was recovered at the site. Johanson assessed it as female based on the one complete pelvic bone and sacrum, which indicated the width of the pelvic opening.

Lucy was 1.1 m (3 ft 7 in) tall, weighed 29 kg (64 lb), and (after reconstruction) looked somewhat like a chimpanzee. The creature had a small brain like a chimpanzee, but the pelvis and leg bones were almost identical in function to those of modern humans, showing with certainty that Lucy’s species were hominins that had stood upright and had walked erect. Additional finds of A. afarensis were made during the 1970s and forward, gaining for anthropologists a better understanding of the ranges of morphic variability and sexual dimorphism within the species. An even more complete skeleton of a related hominid, Ardipithecus, was found in the same Awash Valley in 1992. “Ardi”, like “Lucy”, was a hominid-becoming-hominin species, but, dated at 4.4 million years ago, it had evolved much earlier than the afarensis species. Excavation, preservation, and analysis of the specimen Ardi was very difficult and time-consuming. Work was begun in 1992, with the results not fully published until October 2009.

Ardi

Initial attempts were made in 1974 by Maurice Taieb and James Aronson in Aronson’s laboratory at Case Western Reserve University to estimate the age of the fossils using the potassium-argon radiometric dating method. These efforts were hindered by several factors: the rocks in the recovery area were chemically altered or reworked by volcanic activity; datable crystals were very scarce in the sample material; and there was a complete absence of pumice clasts at Hadar. (The Lucy skeleton occurs in the part of the Hadar sequence that accumulated with the fastest rate of deposition, which partly accounts for her excellent preservation.)

Fieldwork at Hadar was suspended in the winter of 1976–77. When it was resumed thirteen years later in 1990, the more precise argon-argon technology had been updated by Derek York at the University of Toronto. By 1992 Aronson and Robert Walter had found two suitable samples of volcanic ash—the older layer of ash was about 18 m below the fossil and the younger layer was only one meter below, closely marking the age of deposition of the specimen. These samples were argon-argon dated by Walter in the geochronology laboratory of the Institute of Human Origins at 3.22 and 3.18 million years.

An Ethiopian meal is in order today. I have given a recipe for injera here, http://www.bookofdaystales.com/abebe-bikila/ as well as for beef wat which includes a recipe for berbere spice mix which you will need for many Ethiopian dishes including this lentil dish, misr wat:

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