Humans

Foreign cells within our bodies help determine our mental states and even contribute to our immune defences – making it tricky to define where you end and the others begin

Humans 9 December 2020
By Graham Lawton

imageBROKER/Alamy

Where are your boundaries?
“Studies show we think of ourselves now and in the future as different people”
DELINEATING where a person begins and ends used to be quite simple. While philosophers might have tied themselves in knots trying to define the self, and biologists still struggle to locate its steering mechanism (see “Where is your self?”), what it encompassed, at least, was more clear-cut.
Their traditional definition comprises three elements, says Thomas Bosch at the University of Kiel, Germany: the mind, the genome and the immune system. Each of us is a self-contained organism defined by our mind and genes, with the immune system patrolling our borders and discriminating between self and non-self. Me, myself and I.
Then we looked more closely, and our relationship status went from “threesome” to “it’s complicated”.
For starters, we are chimeras: some parts of us are human, but genetically not “us”. Most, if not all, of us contain a few cells from our mother, our grandmothers and even elder siblings that infiltrated our bodies in the uterus.
Women who have carried children host such cells too. “Something like 65 per cent of women, even in their 70s, when autopsies were performed, had cells in their brains that were not theirs,” says David Linden at Johns Hopkins University in Maryland. Chimeric cells have been found to contribute to both good and bad health, for example promoting wound healing but also triggering autoimmune disease.
A handful of people even turn out to be true chimeras, created from a merger in the uterus of two non-identical, “fraternal” twins. We don’t know how common this … More

Understanding how individual we all are means grappling with genetics and neuroscience. Unique: The new science of human individuality by David Linden is a great place to start

Humans 9 December 2020
By Clare Wilson
Studying twins has shed light on the heritability of people’s personality
MStudioImages/Getty Images

Unique: The new science of human individuality
David Linden
Hachette
IN 1979, the US public was fascinated by news coverage of the “Jim twins”, a pair of identical twin brothers who were adopted at birth by different families, only to find each other at the age of 39.
The coincidence of their matching first names wasn’t their only similarity. They weren’t mirror duplicates of each other, in looks or temperament, but both worked in law enforcement and their hobby was carpentry. Both owned Chevrolets and took … More

According to the laws of physics, everything we do follows inevitably from what happened before – and yet we’re convinced we can change the world. Can we?

Humans 9 December 2020
By Richard Webb
If you don’t want to read this, put the magazine down now
Getty Images/Image Source

Are you predetermined?
WHAT are you doing right now? Reading these words. Why? Presumably because you chose to. Even if you didn’t – if you are encountering them years in the future lining a forgotten box of crockery in the attic, say – you can always choose to look away now. You possess the nebulous quality of human free will.
Nebulous because, despite debating it for millennia, philosophers have been unable to pin it down – and although we are pretty convinced we have it, at some level it must be an illusion, rather like our sense of self is (see “Are you always the same person?”).
Let’s start with the physics. Whenever you decide something, a certain pattern of neurons fires in your brain to turn your thought into action – moving towards the kitchen to make coffee, perhaps, or formulating an utterance you will come to regret. Ultimately, that is all down to pulses of electrons – fundamental particles that follow the cast-iron laws of physics, under which everything is determined by what happened immediately before.
That doesn’t leave much room for free will, apparently. “Physical laws, if they’re deterministic, tell me that everything that I do, everything that happens in the world, including everything that I do, including every decision I ever made, follows logically from the laws of nature [and] the initial conditions of the universe,” says philosopher of physics Jenann Ismael at Columbia University in New York. Since we control neither the laws of nature nor the initial conditions of the universe, we … More

By Colin Barras
Living in darkness, or even hibernating, could have left ancient humans with bone lesions
gorodenkoff/Getty Images

Some of the ancient humans living in Europe half a million years ago had a remarkable strategy for dealing with winter: they hibernated. At least, that is the claim being made by two researchers. Others dispute the evidence – but ongoing research suggests that it might be possible to induce a hibernation-like state in modern humans.
Sima de los Huesos – the “pit of bones” – lies in northern Spain and is one of the world’s most important sites for studying human evolution. Excavations at … More

By Luke Taylor
The rock art may be 12,500 years old
Courtesy of Jose Iriarte

An extensive collection of ancient rock art and archaeological remains found deep in the Colombian Amazon offers a rare glimpse into the lives of the earliest people to inhabit the region.
The images and remains suggest that people lived in the northern Amazon at the same time as now-extinct mega-mammals. They also show that the ancient humans had a varied diet, indicating that they adapted quickly to their new environment.
The as-yet unnamed site in the Serranía La Lindosa, a large, rocky outcrop in southern Colombia, was found by an international team of researchers investigating the Guaviare region. It is the earliest secure evidence of people in the Colombian Amazon, they say.

Advertisement

A wealth of Indigenous artwork has been documented across Guaviare, particularly in Chiribiquete National Park. The artwork documented at La Lindosa is new to science, and appears to be unknown even to local people, according to the researchers. It is remarkable in both its detail and its scale, the team says. The collage of images includes geometric patterns, handprints, people and animals. It stretches across approximately 5 kilometres of rock face, and could take decades to fully study.

The archaeological team – co-led by Francisco Javier Aceituno at the University of Antioquia, Colombia – was thrilled to find depictions of what appear to be now-extinct megafauna alongside more familiar fish, birds and lizards still alive today.
“We knew that megafauna was in the region and went extinct around 10 to 12,000 years before the present,” says José Iriarte at the University of Exeter, UK, and a member of the research team. If people were depicting them in their art, the humans must have been present in the region at least 12,500 years ago, he argues.
Iriarte says it is “quite clear” that a palaeolama, an extinct stumpy-legged, long-necked camelid, is depicted. Other drawings have been tentatively identified as giant sloths due to their unique proportions, and mastodons – ancient relatives of elephants – due to their trunks.
“The realism for South American standards is really impressive,” says Iriarte.

Others are less sure.
“The horses are clear,” says Hans ter Steege, an expert on Amazonian plant diversity at the Naturalis Biodiversity Center in the Netherlands, who wasn’t involved in the research. “But the palaeolama could be a poor representation of a deer to me.”
Further study will be made of the artwork to gain more certainty of the depictions and their age, say the researchers.

However, additional archaeological evidence makes clear that humans were present in the region 12,500 years ago. The researchers have excavated an area at the base of one section of rock face and uncovered evidence of ancient human activity in the form of processed animal bones. Some of the remains occur in layers of dirt containing charred palms that radiocarbon dating shows are about 12,500 years old. The 12,500-year-old layers also contain fragments of ochre similar to that used to draw the rock art.
Establishing the presence of humans during this period — in which megafauna roamed the region and the climate was warming — is significant, says Aceituno.
“The most important thing has been to obtain good radiocarbon dates to specify the early peopling of the area,” he says.
It shows that humans shared the region with immense beasts, but also helps paint a picture of how their world would have looked.
No megafauna remains have been found at the site, perhaps suggesting that humans didn’t hunt the animals or they were processed elsewhere. There were no remains of medium-sized animals like monkeys either, a staple food for Indigenous groups inhabiting the region today. “It could mean they had not developed blowgun technology at this stage to hunt prey in the treetops,” says Iriarte.
Around half the remains were fish — including piranhas — but diets were broad. Reptiles like iguanas and snakes were consumed as well as rodents like paca and capybara.
There is also evidence that various fruits were eaten. The diversity of animals and plants consumed suggests humans adapted quickly to the Amazon, says ter Steege.
Journal reference: Quaternary International, DOI: 10.1016/j.quaint.2020.04.026
Sign up to Our Human Story, a free monthly newsletter on the revolution in archaeology and human evolution
More on these topics: More

By Donna Lu
Archaeologists have built replica Stone Age rafts to attempt the crossing to the Ryukyu islands
Yosuke Kaifu

Stone Age humans crossed the sea from Taiwan to the Ryukyu islands of south-west Japan tens of thousands of years ago – and it looks like they did so deliberately, even though the islands are too far away to be reliably visible from Taiwan.
Archaeological sites on several of the Ryukyu islands suggest humans had reached the islands by about 30,000 to 35,000 years ago. Yosuke Kaifu at the University of Tokyo and his colleagues suspect the ancient people did so by travelling north-east from Taiwan – a journey that involved ocean crossings of tens to hundreds of kilometres to hop from island to island. The researchers have even repeated some of these ocean crossings themselves using bamboo rafts of the kind that Stone Age humans might have built.
But it hadn’t been clear whether the crossing occurred deliberately or by accident. The Kuroshio current, which flows from Luzon in the Philippines past Taiwan and Japan, is one of the strongest ocean currents in the world, and in some parts is 100 kilometres wide.

Advertisement

“The speed of the Kuroshio in the east of Taiwan is normally 1 to 2 metres per second,” says Kaifu.

To find out if people could have arrived at the islands by drifting on this current, the researchers looked at existing data from 138 satellite-tracked buoys, released into the world’s oceans as part of the Global Drifter Program. The 138 buoys all drifted past Taiwan or Luzon between 1989 and 2017.
Kaifu and his colleagues found that only four buoys travelled to within 20 kilometres of any of the Ryukyu islands. In all four cases this occurred as a result of adverse weather conditions, including a typhoon.
The finding suggests that the Kuroshio current directs drifters away from, rather than towards, the Ryukyu islands. Because the flow of the current is thought to have stayed the same for the past 100,000 years, it seems likely that Stone Age people reached the Ryukyu islands through deliberate voyaging rather than accidental drifting.
“Now we can tell with confidence that Palaeolithic people set sail deliberately even to a remote invisible island,” says Kaifu.

“Most people probably think that Palaeolithic people were just primitive and conservative, but I now see something different from that general image,” he says.
Journal reference: Scientific Reports, DOI: 10.1038/s41598-020-76831-7
More on these topics: More

From The End of Everything by Katie Mack and How to Argue with a Racist by Adam Rutherford to Martha Wells’s Murderbot sc-ifi series, New Scientist’s 2020 gift guide has a book for everyone

Humans 2 December 2020
By New Scientist

Getty Images/Westend61

The End of Everything (Astrophysically Speaking)
by Katie Mack
For a bit of seasonal giving, why not look to the end of the universe? Thankfully, The End of Everything (Scribner) by Katie Mack is no apocalyptic vision but an engrossing and often funny tour of all the ways our cosmos might come to a close. Mack’s enjoyment of physics stands out – and is contagious. She describes primordial black holes as “awfully cute in a terrifying theoretical kind of way”, antimatter as “matter’s annihilation-happy evil twin” and the universe as “frickin’ weird”. All true, and Mack’s explanations … More

In Watch Dogs: Legion you can play as or team up with any of the characters of the game, and strolling around its digital version of London is a real treat, says Jacob Aron

Humans 2 December 2020
By Jacob Aron
Key London landmarks like The Shard appear in Watch Dogs: Legion
Ubisoft

Watch Dogs: LegionUbisoftPC, PlayStation 4 and 5, Xbox One, Series X and S
NEW SCIENTIST closed its offices on 13 March, a week or so before the UK went into national lockdown. Since then, I have spent most of this year in a small radius around my north London flat and have been into the city centre only a handful of times.
As a native Londoner, it is strange to be so cut off from the city, which is why the opening moments of Watch … More