Monday, 4 December 2017

New evidence on the antiquity of the human race - Homo sapiens is even older than we thought

Up until now, the oldest Homo sapiens fossils were the Omo fossils at Kibish Formation in Ethiopia, dated at 195,000 years. [1] Earlier this year, Nature published two papers in which researchers announced new fossil discoveries from Jebel Irhoud, Morocco, along with analyses of these and previously discovered fossils from the same site, and dating of the strata. At 315,000 years, these are now the oldest Homo sapiens fossils, nearly doubling the previous date of 160,000 years, and extending the age of Homo sapiens by 120,000 years. In retrospect, given the genetic data showing the common ancestor of the lines leading to Homo sapiens and Homo neanderthalensis lived around 400,000 years ago, these revised dates are not surprising. Nonetheless, it's a stunning development in palaeoanthropology, and one which further underscores that YEC assertions about the antiquity and origin of the human race are flat-out wrong.

During the 1960s, two crania, a mandible, and three post-cranial fossils were unearthed at Jebel Irhoud, an archaeological site in western Morocco. Initially dated at 40,000 years, subsequent dates extended that age to 160,000 years. [2] Between 2004 and 2011, sixteen more fossils were unearthed from the site, including a cranium, a maxilla, a mandible, teeth, and other post-cranial data. 

Reconstruction of Irhoud craniun

Irhoud mandible

How old? From Richter et al, in an 8th June paper outlining the dates of the fossils:
A weighted average age places these Middle Stone Age artefacts and fossils at 315 ± 34 thousand years ago. Support is obtained through the recalculated uranium series with electron spin resonance date of 286 ± 32 thousand years ago for a tooth from the Irhoud 3 hominin mandible. [3]
This is 120,000 years older than the previously oldest known Homo sapiens fossil from the Kibish formation in Ethiopia, and makes sense given that genetic data suggests a much earlier date for divergence of the Homo sapiens and Homo neanderthalensis lines.
Hublin et al, in the companion Nature paper are fairly clear in their conclusions as to what this means for palaeoanthropology:
The Irhoud fossils currently represent, to our knowledge, the most securely dated evidence of the early phase of H. sapiens evolution in Africa, and they do not simply appear as intermediate between African archaic Middle Pleistocene forms and RMH. [3]
The reference to early phase of Homo sapiens evolution refers to its morphology which combines a modern human face, with an elongated braincase, which means that the modern human face evolved earlier, with further evolution in the last ~300,000 years affecting the brain case. [5] 

In the commentary on the paper, published in the same edition, Chris Stringer and Julia Galway-Witham note
We agree with Hublin and colleagues that the Jebel Irhoud fossils now represent the best-dated evidence of an early ‘pre-modern’ phase in H. sapiens evolution. These specimens probably constitute an early representative of the H. sapiens lineage that could illuminate the evolution of our species in a way equivalent to how the early Neanderthal Sima de los Huesos fossils from Atapuerca in Spain have provided insight into the development of Neanderthals. [6]
The take-home message? Ann Gibbons, writing at Science notes:
The team doesn’t propose that the Jebel Irhoud people were directly ancestral to all the rest of us. Rather, they suggest that these ancient humans were part of a large, interbreeding population that spread across Africa when the Sahara was green about 300,000 to 330,000 years ago; they later evolved as a group toward modern humans. “H. sapiens evolution happened on a continental scale,” Gunz [one of the contributing authors of the Hublin paper] says. [7]
We've known the human lineage was old. Now it's got even older, and the cradle has got much, much larger.


1. Ian McDougall, Francis H. Brown & John G. Fleagle "Stratigraphic placement and age of modern humans from Kibish, Ethiopia" Nature 433 (2005) 733–736
2. Smith, T. M. et al. Earliest evidence of modern human life history in North African early Homo sapiens. Proc. Natl Acad. Sci. USA (2007) 104:6128–6133
3. Richter, D. et al. The age of the Jebel Irhoud (Morocco) hominins and the origins of the Middle Stone Age. Nature (2017) 546:293-296
4. Hublin, J.-J. et al. New fossils from Jebel Irhoud, Morocco and the pan-African origin of Homo sapiens. Nature (2017) 546:289-292 
5. ibid, p 291
6. Stringer C, Galway-Witham J On the origin of our species Nature (2017):546:212-214
7. Gibbons A World's oldest Homo sapiens fossils found in Morocco. Science. June 7th 2017