Where did we come from?

Where Did We Come From? is the title of a book written by Carl Zimmer in the wake of the discovery of the “hobbits” of Flores fifteen years ago. It was a very good popular introduction to human evolution.

According to Zimmer, our African ancestors parted company with the ancestors of chimpanzees and bonobos six or seven million years ago to begin developing an upright posture, tool use and, perhaps most importantly, language. Our own species, Homo sapiens, evolved about 200,000 years ago and began spreading out of Africa 130,000 years ago, through Europe, Asia, Australia and, eventually, America. We lived alongside closely related species until comparatively recent times. Neanderthals reached Europe before we did and coexisted with us there until 28,000 years ago, if not later. The ‘hobbits’ of Flores, by far the most spectacular recent discovery in the field, survived as recently as 18,000 years ago, well after Homo sapiens had migrated through South Asia and the islands to Australia.

Given the pace of discovery in the field, Zimmer’s book is now somewhat outdated. This collection of recent articles introduces research which adds depth and complexity to Zimmer’s account without changing its broad outlines. I have assembled them here in evolutionary order. Each story is represented by its headline and an excerpt, followed by a link to the source. This post (Jan 2021) continues the Australian part of the story up to the era of European colonisation.

Millions of years ago

Ancient fossil skull discovered in Ethiopia fills critical gap in human evolution

• A rare 3.8 million year-old skull found in Ethiopia is rewriting our understanding of the human family tree
• Previously, only fragments had been found of Australopithecus anamensis, the oldest-known member of a group that gave rise to the species made famous by the Lucy skeleton
• Analysis of the skull shows A. anamensis had a mix of features from primitive species as well as Lucy

https://www.abc.net.au/news/science/2019-08-29/ancient-fossil-skull-found-in-ethiopia-fills-human-evolution-gap/11444130

Earliest known skull of Homo erectus unearthed by Australian-led team

The earliest known skull of Homo erectus has been unearthed by an Australian-led team of researchers who have dated the fossil at two million years old …

The lead researcher Prof Andy Herries said the skull was pieced together from more than 150 fragments uncovered at the Drimolen Main Quarry, located about 40km north of Johannesburg in South Africa.

https://www.theguardian.com/science/2020/apr/03/earliest-known-skull-of-homo-erectus-unearthed-by-australian-led-team

Ancestors of Flores ‘hobbits’ may have been pioneers of first ‘human’ migration out of Africa

The Flores hominins were, more clearly than ever, rooted deep in that [family] tree: they could not be descendants of Homo erectus. They came from something more primitive – a close cousin of Homo habilis. But what was an ancient-looking hominin like this doing in Indonesia?

In the most widely accepted model of human evolution today, the first emergence of hominins out of Africa involved Homo erectus, and happened some time after 2m years ago. But Homo floresiensis raises the tantalising possibility of an earlier expansion of hominins – who were probably not-quite-Homo – out of Africa.

https://theconversation.com/ancestors-of-flores-hobbits-may-have-been-pioneers-of-first-human-migration-out-of-africa-76560

More than 100,000 years ago

The Australian Museum has lots more information about the hobbits at  https://australianmuseum.net.au/learn/science/human-evolution/homo-floresiensis/ Here are a couple of key points:

The human remains date from about 100,000 to 60,000 years old, but archaeological evidence (mostly associated stone tools) suggests H. floresiensis lived at Liang Bua from at least 190,000 to 50,000 years ago (recent dates published in Nature, March 2016). These dates make it one of the latest-surviving humans along with Neanderthals, Denisovans and our own species H. sapiens.

Most scientists that accept H. floresiensis as a legitimate species now think its ancestor may have come from an early African dispersal by a primitive Homo species similar in appearance to H. habilis or the Dmanisi hominins. This means that it shared a common ancestor with Asian H. erectus but was not descended from it.

In 2016, scientists announced they had discovered the lower jaw and teeth from at least one adult and possibly two children of what may be an early form of H. floresiensis. These fossils were found at Mata Menge, about 70kms east of Liang Bua cave on Flores and date to 700,000 years old.

A Shocking Find in a Neanderthal Cave in France

A rock structure, built deep underground, is one of the earliest hominin constructions ever found. By measuring uranium levels on either side of the divide, the team could accurately tell when each stalagmite had been snapped off for construction.

Their date? 176,500 years ago, give or take a few millennia.

“When I announced the age to Jacques, he asked me to repeat it because it was so incredible,” says Verheyden. Outside Bruniquel Cave, the earliest, unambiguous human constructions are  just 20,000 years old. Most of these are ruins—collapsed collections of mammoth bones and deer antlers. By comparison, the Bruniquel stalagmite rings are well-preserved and far more ancient.

https://www.theatlantic.com/science/archive/2016/05/the-astonishing-age-of-a-neanderthal-cave-construction-site/484070/

This startling story quickly earned a response in Nature by Prof Chris Stringer, Research Leader in Human Origins at the Natural History Museum, London:

A comment on the ‘Early Neanderthal constructions deep in Bruniquel Cave in southwestern France’

The remarkable discovery of different-sized ‘structures’ made from purposefully broken stalagmites deep within Bruniquel Cave, south west France, would be significant for any period of time, but at around 175,000 years, these must have been made by early Neanderthals, the only known human inhabitants of Europe at this time.

The purpose of the structures and concentrated combustion zones which are mostly on the broken stalagmites rather than on the ground remain enigmatic, but they demonstrate that some Neanderthals, at least, were as much ‘at home’ deep within the cave as at its entrance.

There are examples of human habitation 30 or 40 metres into the dark zones of caves from sites of this or even greater age in Africa , but the Bruniquel occupation is some ten times deeper into the cave, and shows constructions as complex as some made by modern humans only 20 or 30,000 years ago.

https://www.nhm.ac.uk/press-office/press-releases/comment-on-early-neanderthal-constructions-in-brunique-cave.html

Tens of thousands of years ago

Scientists find evidence of ‘ghost population’ of ancient humans

Scientists have found evidence for a mysterious “ghost population” of ancient humans that lived in Africa about half a million years ago and whose genes live on in people today.

Traces of the unknown ancestor emerged when researchers analysed genomes from west African populations and found that up to a fifth of their DNA appeared to have come from the missing relatives.

Geneticists suspect that the ancestors of modern west Africans interbred with the yet-to-be-discovered archaic humans tens of thousands of years ago, much as ancient Europeans once mated with Neanderthals.

https://www.theguardian.com/science/2020/feb/12/scientists-find-evidence-of-ghost-population-of-ancient-humans

Neanderthal-Denisovan ancestors interbred with a distantly related hominin

Previous research has shown that modern Eurasians interbred with their Neanderthal and Denisovan predecessors. We show here that hundreds of thousands of years earlier, the ancestors of Neanderthals and Denisovans interbred with their own Eurasian predecessors—members of a “superarchaic” population that separated from other humans about 2 million years ago. The superarchaic population was large, with an effective size between 20 and 50 thousand individuals. We confirm previous findings that (i) Denisovans also interbred with superarchaics, (ii) Neanderthals and Denisovans separated early in the middle Pleistocene, (iii) their ancestors endured a bottleneck of population size, and (iv) the Neanderthal population was large at first but then declined in size. We provide qualified support for the view that (v) Neanderthals interbred with the ancestors of modern humans.

That’s the “Abstract” (the authors’ summary) of a scientific paper which is rather similar to the one on which the previous story is based. The whole paper can be read at https://advances.sciencemag.org/content/6/8/eaay5483

This is what mysterious ancient humans might have looked like

We know that mysterious ancient humans called Denisovans once lived alongside Neanderthals, thanks to a few bones and teeth recovered from a cave in Siberia. Now, for the first time, researchers have shared what they might have looked like. … the reconstruction is that of a young female Denisovan.

https://edition.cnn.com/2019/09/19/world/denisovan-first-look-scn/index.html

Looking for context

Wikipedia has a beautifully organised and illustrated table of important hominid fossils from 7 million to 5000 years old, i.e., from the last common ancestor we share with chimpanzees, to Otzi the iceman, at https://en.wikipedia.org/wiki/List_of_human_evolution_fossils

In the light of the recent discoveries above, its key lessons seem to be (1) how few pieces of the puzzle we still have and (2) the extent of the overlap between different species of people from 300,000 to 40,000 years ago. Point (1) is, of course, the reason that a single discovery can radically change our understanding of our evolution.

Aside from the purely scientific aspects, our history raises fascinating questions about the borderlines between human animals and other animals – borderlines in consciousness and intelligence, and the ethical borderlines which guide our sense of our proper place in the environment.

11 thoughts on “Where did we come from?”

  1. Burial practices in Africa, 78,000 years ago, and Europe even longer ago ago – https://www.abc.net.au/news/science/2021-05-06/oldest-human-burial-site-in-africa/100065050

    Scientists have uncovered the remains of a three-year-old human child who was buried 78,000 years ago in Kenya. The position of the bones and chemical analyses suggest the child was buried deliberately. While older burial sites have been found in Europe, this is the oldest that has been found in Africa to date.
    …[Excavations] … in Europe [show] that Neanderthals and early modern humans had been formally burying their deceased loved ones near their homes for at least 120,000 years. And in the Es-Skhul and Qafzeh caves in Israel, researchers have found early modern human burials that date back to around 100,000 years.

  2. Archaeologists in Morocco have announced the discovery of North Africa’s oldest hand axe manufacturing site, dating back 1.3 million years. The Stone Age find pushes back the start date of the Acheulian stone tool industry — associated with human ancestor Homo erectus — by hundreds of thousands of years.
    It was made during excavations at a quarry on the outskirts of Casablanca.
    …the beginning of the Acheulian in Morocco was now close to the South and East African start dates of 1.6 million and 1.8 million years ago respectively. Before the find, Morocco’s Acheulian stone tool industry was thought to date back 700,000 years.
    …Mr Mohib said the study also made it possible to attest to “the oldest presence in Morocco of humans” who were “variants of Homo erectus”.
    …In 2017, the discovery of five fossils at Jebel Irhoud in Morocco, estimated at 300,000 years old, overturned evolutionary science when they were designated as Homo sapiens, the same species as modern humans.

    https://www.abc.net.au/news/2021-07-29/morocco-1-3-million-year-old-stone-age-axe-discovery/100332946

  3. “In human populations, changes in genetic variation are driven not only by genetic processes, but can also arise from cultural or social changes. An abrupt population bottleneck specific to human males has been inferred across several Old World (Africa, Europe, Asia) populations 5000–7000 BP. Here, bringing together anthropological theory, recent population genomic studies and mathematical models, we propose a sociocultural hypothesis, involving the formation of patrilineal kin groups and intergroup competition among these groups.”
    https://www.nature.com/articles/s41467-018-04375-6
    This site – https://news.asu.edu/content/researchers-discover-wealth-power-may-have-played-stronger-role-survival-fittest – has a different version of the same story.
    It’s complicated but the basic idea is that, at a particular stage of social development, common conflicts between male-dominated groups led to the extinction of male lineages so that we have fewer male ancestors than female ancestors.

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