A damned close run thing

After Waterloo the Duke of Wellington allegedly said: “It has been a damned nice thing — the nearest run thing you ever saw in your life.” Like many historic quotes it got refined over the years and became: “It was a damned close run thing.

Whichever it is particularly apposite in the light of a recent Nature article (31/8) by Anna Ikarashi on the origins of us homo sapiens.

The article reported on research by a team led by Haipeng Li a University of Chinese Academy of Sciences in Beijing population geneticist.

According to their work human African ancestors almost became extinct around 900,000 years ago with the population of breeding individuals reduced to about 1,280. This didn’t expand for another 117,000 years. A damned close thing indeed for our evolution.

Hapieng Li says “About 98.7% of human ancestors were lost” and the fossil record between 950,000 and 650,000 years ago is patchy and “the discovery of this bottleneck may explain the chronological gap.”

The researchers developed new tools with genome sequencing which have improved scientists’ understanding of population sizes for the period after modern humans emerged but the researchers developed a methodology that enabled them to fill in details about earlier human ancestors.

Serena Tucci, an anthropologist at Yale University in New Haven, Connecticut, told Nature such work was sorely needed. “We still know very little about the population dynamics of early human ancestors for several reasons, including methodological limitations and difficulties in obtaining ancient DNA data from old Homo specimens,” she said.

Nature said: “The researchers’ method allowed them to reconstruct ancient population dynamics on the basis of genetic data from present-day humans. By constructing a complex family tree of genes, the team was able to examine the finer branches of the tree with greater precision, identifying significant evolutionary events.”

They cited Stanley Ambrose, an anthropologist at the University of Illinois at Urbana-Champaign as saying the technique “put the spotlight on the period 800,000 to one million years ago — for which there is much unknown — in a way that hasn’t been done before.”

The period was also a time of far-reaching climate change with droughts and glacial cycles which became longer and more intense.is period was part of the Early-Middle Pleistocene transition — a time of drastic climate change, when glacial cycles became longer and long periods of drought in Africa.

Li argues that this may have wiped out human ancestors and allowed new species to evolve into the last common ancestor of modern humans and humanity’s extinct relatives, the Denisovans and Neanderthals.

Ziqian Hao, a population geneticist at the Shandong First Medical University and a co-author of the paper, says the bottleneck may have has a major impact on human genetic diversity.

“It represents a key period of time during the evolution of humans. So there many important questions to be answered” he told Nature.

Needless to say there are some doubts about all this. A British Museum archaeologist, Nick Ashton, told Nature “this would imply that it occupied a very localised area with good social cohesion for it to survive….Of greater surprise is the estimated length of time that this small group survived. If this is correct, then one imagines that it would require a stable environment with sufficient resources and few stresses to the system.”

He also questioned the findings saying the authors “suggest that the bottleneck was a global crash in population: but the archaeological sites outside Africa suggested this was not the case and that the finding may be a regional phenomenon.

Meanwhile one of our most famous ancestors, Otzi the Iceman is also getting fresh attention thanks to genetic research. Otzi was found in 1991 in an Italian valley near the Austrian border. He died there about 5,300 years ago after being shot with an arrow.

In another Nature article (16/8) Freda Kreier reported on research reported in Cell Genomics saying that Otzi probably had very little hair on his head and much darker skin than previously believed – much darker than modern Sicilians for instance. Yet in 2012 DNA work had suggested that Otzi had pale skin and brown eyes (previously thought to be blue).  But this was a finding in the early days of genetic testing.

Otzi was also believed to come from the steppes but this finding may have stemmed from modern DNA contamination and that, instead, he came from Anatolian farmer ancestors who lived in the lands between the Mediterranean and Black seas.