The skull of Homo Erectus, one of our evolutionary ancestors.
- A new study of the genomes of Modern Humans, Neanderthals, and Denisovans suggests the three were interbreeding quite often.
- The study also found DNA from an unidentified, archaic human ancestor which we inherited from the Denisovans.
- Homo Erectus is the most likely source of this DNA.
Modern Humans are the last members of the genus Homo. While we've managed to outlast an extensive list of cousins and genetic ancestors, their genetic heritage lives on through us. More than a few studies have reported that many people today can trace their ancestry back to the Neanderthals and the Denisovans.
A new study suggests that the DNA of an even older ancestor lives in through us, and has some startling implications for the sex lives of our ancient ancestors.
Some of our evolutionary relatives never really left, genetically speaking.
The paper titled "Mapping gene flow between ancient hominins through demography-aware inference of the ancestral recombination graph" was published in PLOS Genetics. It's authors used a new statistical method to analyze the genomes of two Neanderthals, a Denisovan, and two modern humans.
The new method allowed the researchers to determine when segments of one individual's DNA are worked into the chromosomes of another. These occurrences are called "recombination events" and can be used to determine when specific genes entered our genome and provide evidence of where it came from. As an example of how this can be used, if Neanderthal DNA contained genes from another pre-human ancestor that they then passed to us, this method would identify it.
The analysis confirmed previous studies that showed that Modern Humans interbred with Neanderthals and Denisovans. However, this analysis suggests that some of this mixing took place between 200,000 and 300,000 years ago, long before what previous studies had suggested. It also indicates that more instances of interbreeding occurred than previously suspected.
Most interestingly, the researchers noticed that one percent of the DNA in the Denisovans from an even more ancient human ancestor. Fifteen percent of the genes that this ancestor passed onto the Denisovans still exist in the Modern Human genome.
Exactly who this ancestor was remains unknown, but there are some clues. The fact that this ancestor separated from the linage that would lead to modern humans about 1,000,000 years ago is the most useful one we currently have. This led the researchers to suggest Homo Erectus as the most likely candidate.
Who was Homo Erectus?
The bane of all school teachers focusing on human evolution and the original "missing link," Homo Erectus was the first human ancestor to leave Africa. They spread widely throughout the old world, with their remains found from Spain to Java. They resembled modern humans, though they were a tad shorter. They were the first to control fire, made tools, created artwork, and likely had rudimentary language.
It should be repeated that while Homo Erectus is the probable source of this ancient DNA, the jury is still out. Scientists would have to sequence its genome to know for sure.
Studying human evolution leads us down some very strange roads. It is increasingly clear to us that wherever there was an overlap of human species, there was interbreeding and that a considerable amount of the genetic remnants of this endure to this day. While this might get in the way of the old view of evolution as a slow climb to the humanity, the pinnacle of biological achievement, it does provide us a richer view of who we are, where we come form, and where we might be going.
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The “discovery” of dark matter
We can tell how much matter is in the universe by the motions of the stars. In the1920s, physicists attempting to do so discovered a discrepancy and concluded that there must be more matter in the universe than is detectable. How can this be?
In 1933, Swiss astronomer Fritz Zwicky, while observing the motion of galaxies in the Coma Cluster, began wondering what kept them together. There wasn't enough mass to keep the galaxies from flying apart. Zwicky proposed that some kind of dark matter provided cohesion. But since he had no evidence, his theory was quickly dismissed.
Then, in 1968, astronomer Vera Rubin made a similar discovery. She was studying the Andromeda Galaxy at Kitt Peak Observatory in the mountains of southern Arizona when she came across something that puzzled her. Rubin was examining Andromeda's rotation curve, or the speed at which the stars around the center rotate, and realized that the stars on the outer edges moved at the exact same rate as those at the interior, violating Newton's laws of motion. This meant there was more matter in the galaxy than was detectable. Her punch card readouts are today considered the first evidence of the existence of dark matter.
Many other galaxies were studied throughout the '70s. In each case, the same phenomenon was observed. Today, dark matter is thought to comprise up to 27% of the universe. "Normal" or baryonic matter makes up just 5%. That's the stuff we can detect. Dark energy, which we can't detect either, makes up 68%.
Dark energy is what accounts for the Hubble Constant, or the rate at which the universe is expanding. Dark matter on the other hand, affects how "normal" matter clumps together. It stabilizes galaxy clusters. It also affects the shape of galaxies, their rotation curves, and how stars move within them. Dark matter even affects how galaxies influence one another.
Leading theories on dark matter
NASA writes: 'This graphic represents a slice of the spider-web-like structure of the universe, called the "cosmic web." These great filaments are made largely of dark matter located in the space between galaxies.'
Credit: NASA, ESA, and E. Hallman (University of Colorado, Boulder)
Since the '70s, astronomers and physicists have been unable to identify any evidence of dark matter. One theory is it's all tied up in space-bound objects called MACHOs (Massive Compact Halo Objects). These include black holes, supermassive black holes, brown dwarfs, and neutron stars.
Another theory is that dark matter is made up of a type of non-baryonic matter, called WIMPS (Weakly Interacting Massive Particles). Baryonic matter is the kind made up of baryons, such as protons and neutrons and everything composed of them, which is anything with an atomic nucleus. Electrons, neutrinos, muons, and tau particles aren't baryons, however, but a class of particles called leptons. Even though the (hypothetical) WIMPS would have ten to a hundred times the mass of a proton, their interactions with normal matter would be weak, making them hard to detect.
Then there are those aforementioned neutrinos. Did you know that giant streams of them pass from the Sun through the Earth each day, without us ever noticing? They're the focus of another theory that says that neutral neutrinos, that only interact with normal matter through gravity, are what dark matter is comprised of. Other candidates include two theoretical particles, the neutral axion and the uncharged photino.
Now, one theoretical physicist posits an even more radical notion. What if dark matter didn't exist at all? Dr. Melvin Vopson of the University of Portsmouth, in the UK, has a hypothesis he calls the mass-energy-information equivalence. It states that information is the fundamental building block of the universe, and it has mass. This accounts for the missing mass within galaxies, thus eliminating the hypothesis of dark matter entirely.
Information theory
To be clear, the idea that information is an essential building block of the universe isn't new. Classical Information Theory was first posited by Claude Elwood Shannon, the "father of the digital age" in the mid-20th century. The mathematician and engineer, well-known in scientific circles—but not so much outside of them, had a stroke of genius back in 1940. He realized that Boolean algebra coincided perfectly with telephone switching circuits. Soon, he proved that mathematics could be employed to design electrical systems.
Shannon was hired at Bell Labs to figure out how to transfer information over a system of wires. He wrote the bible on using mathematics to set up communication systems, thereby laying the foundation for the digital age. Shannon was also the first to define one unit of information as a bit.
There was perhaps no greater proponent of information theory than another unsung paragon of science, John Archibald Wheeler. Wheeler was part of the Manhattan Project, worked out the "S-Matrix" with Niels Bohr and helped Einstein develop a unified theory of physics. In his later years, he proclaimed, "Everything is information." Then he went about exploring connections between quantum mechanics and information theory.
He also coined the phrase "it from bit" or that every particle in the universe emanates from the information locked inside it. At the Santa Fe Institute in 1989, Wheeler announced that everything, from particles to forces to the fabric of spacetime itself "… derives its function, its meaning, its very existence entirely … from the apparatus-elicited answers to yes-or-no questions, binary choices, bits."
Part Einstein, part Landauer
Vopson takes this notion one step further. He says that not only is information the essential unit of the universe but also that it is energy and has mass. To support this claim, he unifies and coordinates special relativity with the Landauer Principle. The latter is named after Rolf Landauer. In 1961, he predicted that erasing even one bit of information would release a tiny amount of heat, a figure which he calculated. Landauer said this proves information is more than just a mathematical quantity. This connects information to energy. Through experimental testing over the years, the Landauer Principle has held up.
Vopson says, "He [Landauer] first identified the link between thermodynamics and information by postulating that logical irreversibility of a computational process implies physical irreversibility." This indicates that information is physical, Vopson says, and demonstrates the link between information theory and thermodynamics.
In Vopson's theory, information, once created has "finite and quantifiable mass." It so far applies only to digital systems, but could very well apply to analogue and biological ones too, and even quantum or relativistic-moving systems. "Relativity and quantum mechanics are possible future directions of the mass-energy-information equivalence principle," he says.
In the paper published in the journal AIP Advances, Vopson outlines the mathematical basis for his hypothesis. "I am the first to propose the mechanism and the physics by which information acquires mass," he said, "as well as to formulate this powerful principle and to propose a possible experiment to test it."
The fifth state of matter
To measure the mass of digital information, you start with an empty data storage device. Next, you measure its total mass with a highly sensitive measuring apparatus. Then, you fill it and determine its mass. Next, you erase one file and evaluate it again. The trouble is, the "ultra-accurate mass measurement" device the paper describes doesn't exist yet. This would be an interferometer, something similar to LIGO. Or perhaps an ultrasensitive weighing machine akin to a Kibble balance.
"Currently, I am in the process of applying for a small grant, with the main objective of designing such an experiment, followed by calculations to check if detection of these small mass changes is even possible," Vopson says. "Assuming the grant is successful and the estimates are positive, then a larger international consortium could be formed to undertake the construction of the instrument." He added, "This is not a workbench laboratory experiment, and it would most likely be a large and costly facility." If eventually proved correct, Vopson will have discovered the fifth form of matter.
So, what's the connection to dark matter? Vopson says, "M.P. Gough published an article in 2008 in which he worked out … the number of bits of information that the visible universe would contain to make up all the missing dark matter. It appears that my estimates of information bit content of the universe are very close to his estimates."
As he described it, “In my mind's eye I saw many, many things: children that I hadn't even had yet, friends that I had never seen but are now my friends. The thing that really stuck in my mind was playing an instrument". Then Tony landed on his head and lost consciousness.
When he came to at the hospital, he felt like a different person and didn't want to return to his previous life. Over the following weeks, the images kept flashing back into his mind. He felt that he was “being shown something" and that the images represented his future.
Later, Tony saw a picture of a saxophone and recognized it as the instrument he'd seen himself playing. He used his compensation money from the accident to buy one. Now, Tony Kofi is one of the UK's most successful jazz musicians, having won the BBC Jazz awards twice, in 2005 and 2008.
Though Tony's belief that he saw into his future is uncommon, it's by no means uncommon for people to report witnessing multiple scenes from their past during split-second emergency situations. After all, this is where the phrase “my life flashed before my eyes" comes from.
But what explains this phenomenon? Psychologists have proposed a number of explanations, but I'd argue the key to understanding Tony's experience lies in a different interpretation of time itself.
When life flashes before our eyes
The experience of life flashing before one's eyes has been reported for well over a century. In 1892, a Swiss geologist named Albert Heim fell from a precipice while mountain climbing. In his account of the fall, he wrote is was “as if on a distant stage, my whole past life [was] playing itself out in numerous scenes".
More recently, in July 2005, a young woman called Gill Hicks was sitting near one of the bombs that exploded on the London Underground. In the minutes after the accident, she hovered on the brink of death where, as she describes it: “my life was flashing before my eyes, flickering through every scene, every happy and sad moment, everything I have ever done, said, experienced".
In some cases, people don't see a review of their whole lives, but a series of past experiences and events that have special significance to them.
Explaining life reviews
Perhaps surprisingly, given how common it is, the “life review experience" has been studied very little. A handful of theories have been put forward, but they're understandably tentative and rather vague.
For example, a group of Israeli researchers suggested in 2017 that our life events may exist as a continuum in our minds, and may come to the forefront in extreme conditions of psychological and physiological stress.
Another theory is that, when we're close to death, our memories suddenly “unload" themselves, like the contents of a skip being dumped. This could be related to “cortical disinhibition" – a breaking down of the normal regulatory processes of the brain – in highly stressful or dangerous situations, causing a “cascade" of mental impressions.
But the life review is usually reported as a serene and ordered experience, completely unlike the kind of chaotic cascade of experiences associated with cortical disinhibition. And none of these theories explain how it's possible for such a vast amount of information – in many cases, all the events of a person's life – to manifest themselves in a period of a few seconds, and often far less.
Thinking in 'spatial' time
An alternative explanation is to think of time in a “spatial" sense. Our commonsense view of time is as an arrow that moves from the past through the present towards the future, in which we only have direct access to the present. But modern physics has cast doubt on this simple linear view of time.
Indeed, since Einstein's theory of relativity, some physicists have adopted a “spatial" view of time. They argue we live in a static “block universe" in which time is spread out in a kind of panorama where the past, the present and the future co-exist simultaneously.
The modern physicist Carlo Rovelli – author of the best-selling The Order of Time – also holds the view that linear time doesn't exist as a universal fact. This idea reflects the view of the philosopher Immanuel Kant, who argued that time is not an objectively real phenomenon, but a construct of the human mind.
This could explain why some people are able to review the events of their whole lives in an instant. A good deal of previous research – including my own – has suggested that our normal perception of time is simply a product of our normal state of consciousness.
In many altered states of consciousness, time slows down so dramatically that seconds seem to stretch out into minutes. This is a common feature of emergency situations, as well as states of deep meditation, experiences on psychedelic drugs and when athletes are “in the zone".
The limits of understanding
But what about Tony Kofi's apparent visions of his future? Did he really glimpse scenes from his future life? Did he see himself playing the saxophone because somehow his future as a musician was already established?
There are obviously some mundane interpretations of Tony's experience. Perhaps, for instance, he became a saxophone player simply because he saw himself playing it in his vision. But I don't think it's impossible that Tony did glimpse future events.
If time really does exist in a spatial sense – and if it's true that time is a construct of the human mind – then perhaps in some way future events may already be present, just as past events are still present.
Admittedly, this is very difficult to make sense of. But why should everything make sense to us? As I have suggested in a recent book, there must be some aspects of reality that are beyond our comprehension. After all, we're just animals, with a limited awareness of reality. And perhaps more than any other phenomenon, this is especially true of time.
Steve Taylor, Senior Lecturer in Psychology, Leeds Beckett University
This article is republished from The Conversation under a Creative Commons license. Read the original article.
