Researchers said Tuesday they had uncovered fossils showing that complex life on Earth began more than 1.5 billion years ago, nearly a billion years earlier than previously thought.
But the evidence, published in Nature Communications, immediately provoked debate, with some scientists hailing it as rock solid, and others saying they were wholly unconvinced.
After first emerging from the primordial soup, life remained primitive and unicellular for billions of years, but some of those cells eventually congregated like clones in a colony.
Scientists even took to calling the later part of this period the "boring billion", because evolution seemed to have stalled.
But at some point there was another huge leap—arguably second in importance only to the appearance of life itself—towards complex organisms.
This transition progressively gave rise to all the plants and animals that have ever existed.
Exactly when multi-cell eukaryotes—organisms in which differentiated cells each contain a membrane-bound nucleus with genetic material—showed up has inflamed scientific passions for many decades.
The new study is sure to enrich that tradition.
"Our discovery pushes back nearly one billion years the appearance of macroscopic, multicellular eukaryotes compared to previous research," Maoyan Zhu, a professor at the Nanjing Institute of Geology and Palaeontology, told AFP.
The fossils were uncovered in Hebei Province's Yanshan region, where Mao Zedong and his communist army hunkered down during World War II before coming to power.
Zhu and colleagues found 167 measurable fossils, a third of them in one of four regular shapes—an indication of complexity. (...)
What Sparked the Cambrian Explosion? An evolutionary burst 540 million years ago filled the seas with an astonishing diversity of animals. The trigger behind that revolution is finally coming into focus
Diminutive humans that died out on an Indonesian island some 15,000 years ago were not Homo sapiens but a different species, according to a study published Monday that dives into a fierce anthropological debate.
Fossils of Homo floresiensis—dubbed "the hobbits" due to their tiny stature—were discovered on the island of Flores in 2003.
Controversy has raged ever since as to whether they are an unknown branch of early humans or specimens of modern man deformed by disease.
The new study, based on an analysis of the skull bones, shows once and for all that the pint-sized people were not Homo sapiens, according to the researchers.
Until now, academic studies have pointing in one direction or another—and scientific discourse has sometimes tipped over into acrimony.
One school of thought holds that so-called Flores Man descended from the larger Homo erectus and became smaller over hundreds of generations.
The proposed process for this is called "insular dwarfing"—animals, after migrating across land bridges during periods of low sea level, wind up marooned on islands as oceans rise and their size progressively diminishes if the supply of food declines.
An adult hobbit stood a metre (three feet) tall, and weighed about 25 kilos (55 pounds).
Similarly, Flores Island was also home to a miniature race of extinct, elephant-like creatures called Stegodon.
But other researchers argue that H. floresiensis was in fact a modern human whose tiny size and small brain—no bigger than a grapefruit—was caused by a genetic disorder.
One suspect was dwarf cretinism, sometimes brought on by a lack of iodine. Another potential culprit was microcephaly, which shrivels not just the brain and its boney envelope.
Weighing in with a new approach, published in the Journal of Human Evolution, a pair of scientists in France used high-tech tools to re-examine the layers of the "hobbit" skull. (...)
