Showing posts with label BBC Earth. Show all posts
Showing posts with label BBC Earth. Show all posts
Sunday, June 20, 2021
Monday, January 11, 2021
An interesting fact: Birds, including the chickens I eat every day, evolved from the one branch of dinosaurs that survived 66 million years ago after an asteroid wiped out all the other dinosaurs.
BBC Earth
A chicken embryo with a dinosaur-like snout instead of a beak has been developed by scientists
By Melissa Hogenboom
13 May 2015
Sixty-five million years ago, an asteroid is believed to have crashed into Earth. The impact wiped out huge numbers of species, including almost all of the dinosaurs.
One group of dinosaurs managed to survive the disaster. Today, we know them as birds.
The idea that birds evolved from dinosaurs has been around since the 19th century, when scientists discovered the fossil of an early bird called Archaeopteryx. It had wings and feathers, but it also looked a lot like a dinosaur. More recent fossils look similar.
But these early birds didn't look the same as modern ones. In particular, they didn't have beaks: they had snouts, like those of their dinosaur ancestors.
To understand how one changed into another, a team has been tampering with the molecular processes that make up a beak in chickens.
By doing so, they have managed to create a chicken embryo with a dinosaur-like snout and palate, similar to that of small feathered dinosaurs like Velociraptor. The results are published in the journal Evolution.
The team's aim was to understand how the bird beak evolved, because the beak is such a vital part of bird anatomy. It has been crucial for their success. The 10,000 or more bird species occupy a wide range of habitats, and many have specialised beaks to help them survive.
But they did not set out to create a "dino-chicken", say lead authors Bhart-Anjan Bhullar of Yale University in New Haven and Arkhat Abzhanov of Harvard University in Cambridge, US.
"Whenever you examine an important evolutionary transformation, you want to learn the underlying mechanism," says Bhullar.
The beak is also the part of the avian skeleton that has "diversified most extensively and most radically", says Bhullar.
Despite this diversity – ranging from flamingos to pelicans - very little work has been done to figure out "what the heck a beak actually is", he adds.
"I wanted to know what the beak was skeletally, functionally and when this major transformation occurred from a normal vertebrate snout to the very unique structures used in birds."
To begin to understand this, the team trawled though changes in the ways genes are expressed in the embryos of chickens and several other animals. They looked at the embryos of mice, emus, alligators, lizards and turtles, representing many of the major animal groups.
They found that birds have a unique cluster of genes related to facial development, which the non-beaked creatures lacked.
When they silenced these genes, the beak structure reverted back to its ancestral state. So too did the palatal bone in the roof of the mouth.
To make this genetic tweak, Bhullar and his colleagues isolated the proteins that would have gone on to develop beaks. Then they suppressed them using tiny beads coated with an inhibiting substance.
When their skeletons started to develop inside the eggs, these animals had short, rounded bones instead of elongated, fused beaks that bird skeletons have.
"By affecting this early protein you are actually altering gene expression," added Bhullar.
The work highlights that beaks develop very differently from snouts, using a different set of genes, says Michael Benton of Bristol University in the UK. "That's what proves the beak is a real adaptation or 'thing', not just a slightly different nose shape."
The shift from snouts to beaks happened well into the evolution of birds, 40-50 million years after Archaeopteryx, says Benton.
For now Bhullar has no plans, or ethical approval, to hatch the snouted chickens. But he believes they would have been able to survive "just fine".
"These weren't drastic modifications," says Bhullar. "They are far less weird than many breeds of chicken developed by chicken hobbyists and breeders."
"The rest of the animal looked OK, but one needs to think about this carefully from an ethical point of view."
Follow Melissa Hogenboom and BBC Earth on twitter.
Monday, December 28, 2020
Sunday, December 20, 2020
Scientists have figured out why is there something rather than nothing. A magic god fairy was not required.
BBC Earth BBC Earth
Some physicists think they can explain why the universe first formed. If they are right, our entire cosmos may have sprung out of nothing at all.
By Robert Adler
November 6, 2014
People have wrestled with the mystery of why the universe exists for thousands of years. Pretty much every ancient culture came up with its own creation story - most of them leaving the matter in the hands of the gods - and philosophers have written reams on the subject. But science has had little to say about this ultimate question.
However, in recent years a few physicists and cosmologists have started to tackle it. They point out that we now have an understanding of the history of the universe, and of the physical laws that describe how it works. That information, they say, should give us a clue about how and why the cosmos exists.
Their admittedly controversial answer is that the entire universe, from the fireball of the Big Bang to the star-studded cosmos we now inhabit, popped into existence from nothing at all. It had to happen, they say, because "nothing" is inherently unstable.
This idea may sound bizarre, or just another fanciful creation story. But the physicists argue that it follows naturally from science's two most powerful and successful theories: quantum mechanics and general relativity.
Here, then, is how everything could have come from nothing.
Particles from empty space
First we have to take a look at the realm of quantum mechanics. This is the branch of physics that deals with very small things: atoms and even tinier particles. It is an immensely successful theory, and it underpins most modern electronic gadgets.
Quantum mechanics tells us that there is no such thing as empty space. Even the most perfect vacuum is actually filled by a roiling cloud of particles and antiparticles, which flare into existence and almost instantaneously fade back into nothingness.
These so-called virtual particles don't last long enough to be observed directly, but we know they exist by their effects.
Space-time, from no space and no time
From tiny things like atoms, to really big things like galaxies. Our best theory for describing such large-scale structures is general relativity, Albert Einstein's crowning achievement, which sets out how space, time and gravity work.
Relativity is very different from quantum mechanics, and so far nobody has been able to combine the two seamlessly. However, some theorists have been able to bring the two theories to bear on particular problems by using carefully chosen approximations. For instance, this approach was used by Stephen Hawking at the University of Cambridge to describe black holes.
In quantum physics, if something is not forbidden, it necessarily happens
One thing they have found is that, when quantum theory is applied to space at the smallest possible scale, space itself becomes unstable. Rather than remaining perfectly smooth and continuous, space and time destabilize, churning and frothing into a foam of space-time bubbles.
In other words, little bubbles of space and time can form spontaneously. "If space and time are quantized, they can fluctuate," says Lawrence Krauss at Arizona State University in Tempe. "So you can create virtual space-times just as you can create virtual particles."
What's more, if it's possible for these bubbles to form, you can guarantee that they will. "In quantum physics, if something is not forbidden, it necessarily happens with some non-zero probability," says Alexander Vilenkin of Tufts University in Boston, Massachusetts.
A universe from a bubble
So it's not just particles and antiparticles that can snap in and out of nothingness: bubbles of space-time can do the same. Still, it seems like a big leap from an infinitesimal space-time bubble to a massive universe that hosts 100 billion galaxies. Surely, even if a bubble formed, it would be doomed to disappear again in the blink of an eye?
If all the galaxies are flying apart, they must once have been close together
Actually, it is possible for the bubble to survive. But for that we need another trick: cosmic inflation.
Most physicists now think that the universe began with the Big Bang. At first all the matter and energy in the universe was crammed together in one unimaginably small dot, and this exploded. This follows from the discovery, in the early 20th century, that the universe is expanding. If all the galaxies are flying apart, they must once have been close together.
Inflation theory proposes that in the immediate aftermath of the Big Bang, the universe expanded much faster than it did later. This seemingly outlandish notion was put forward in the 1980s by Alan Guth at the Massachusetts Institute of Technology, and refined by Andrei Linde, now at Stanford University.
As weird as it seems, inflation fits the facts
The idea is that, a fraction of a second after the Big Bang, the quantum-sized bubble of space expanded stupendously fast. In an incredibly brief moment, it went from being smaller than the nucleus of an atom to the size of a grain of sand. When the expansion finally slowed, the force field that had powered it was transformed into the matter and energy that fill the universe today. Guth calls inflation "the ultimate free lunch".
As weird as it seems, inflation fits the facts rather well. In particular, it neatly explains why the cosmic microwave background, the faint remnant of radiation left over from the Big Bang, is almost perfectly uniform across the sky. If the universe had not expanded so rapidly, we would expect the radiation to be patchier than it is.
The universe is flat and why that's important
Inflation also gave cosmologists the measuring tool they needed to determine the underlying geometry of the universe. It turns out this is also crucial for understanding how the cosmos came from nothing.
Einstein's theory of general relativity tells us that the space-time we live in could take three different forms. It could be as flat as a table top. It could curve back on itself like the surface of a sphere, in which case if you travel far enough in the same direction you would end up back where you started. Alternatively, space-time could curve outward like a saddle. So which is it?
There is a way to tell. You might remember from maths class that the three angles of a triangle add up to exactly 180 degrees. Actually your teachers left out a crucial point: this is only true on a flat surface. If you draw a triangle on the surface of a balloon, its three angles will add up to more than 180 degrees. Alternatively, if you draw a triangle on a surface that curves outward like a saddle, its angles will add up to less than 180 degrees.
So to find out if the universe is flat, we need to measure the angles of a really big triangle. That's where inflation comes in. It determined the average size of the warmer and cooler patches in the cosmic microwave background. Those patches were measured in 2003, and that gave astronomers a selection of triangles. As a result, we know that on the largest observable scale our universe is flat.
It turns out that a flat universe is crucial. That's because only a flat universe is likely to have come from nothing.
Everything that exists, from stars and galaxies to the light we see them by, must have sprung from somewhere. We already know that particles spring into existence at the quantum level, so we might expect the universe to contain a few odds and ends. But it takes a huge amount of energy to make all those stars and planets.
The energy of matter is exactly balanced by the energy of the gravity the mass creates
Where did the universe get all this energy? Bizarrely, it may not have had to get any. That's because every object in the universe creates gravity, pulling other objects toward it. This balances the energy needed to create the matter in the first place.
It's a bit like an old-fashioned measuring scale. You can put a heavy weight on one side, so long as it is balanced by an equal weight on the other. In the case of the universe, the matter goes on one side of the scale, and has to be balanced by gravity.
Physicists have calculated that in a flat universe the energy of matter is exactly balanced by the energy of the gravity the mass creates. But this is only true in a flat universe. If the universe had been curved, the two sums would not cancel out.
Universe or multiverse?
At this point, making a universe looks almost easy. Quantum mechanics tells us that "nothing" is inherently unstable, so the initial leap from nothing to something may have been inevitable. Then the resulting tiny bubble of space-time could have burgeoned into a massive, busy universe, thanks to inflation. As Krauss puts it, "The laws of physics as we understand them make it eminently plausible that our universe arose from nothing - no space, no time, no particles, nothing that we now know of."
So why did it only happen once? If one space-time bubble popped into existence and inflated to form our universe, what kept other bubbles from doing the same?
There could be a mind-boggling smorgasbord of universes
Linde offers a simple but mind-bending answer. He thinks universes have always been springing into existence, and that this process will continue forever.
When a new universe stops inflating, says Linde, it is still surrounded by space that is continuing to inflate. That inflating space can spawn more universes, with yet more inflating space around them. So once inflation starts it should make an endless cascade of universes, which Linde calls eternal inflation. Our universe may be just one grain of sand on an endless beach.
Those universes might be profoundly different to ours. The universe next door might have five dimensions of space rather than the three – length, breadth and height – that ours does. Gravity might be ten times stronger or a thousand times weaker, or not exist at all. Matter might be built out of utterly different particles.
So there could be a mind-boggling smorgasbord of universes. Linde says eternal inflation is not just the ultimate free lunch: it is the only one at which all possible dishes are available.
As yet we don't have hard evidence that other universes exist. But either way, these ideas give a whole new meaning to the phrase "Thanks for nothing".
Some physicists think they can explain why the universe first formed. If they are right, our entire cosmos may have sprung out of nothing at all.
By Robert Adler
November 6, 2014
People have wrestled with the mystery of why the universe exists for thousands of years. Pretty much every ancient culture came up with its own creation story - most of them leaving the matter in the hands of the gods - and philosophers have written reams on the subject. But science has had little to say about this ultimate question.
However, in recent years a few physicists and cosmologists have started to tackle it. They point out that we now have an understanding of the history of the universe, and of the physical laws that describe how it works. That information, they say, should give us a clue about how and why the cosmos exists.
Their admittedly controversial answer is that the entire universe, from the fireball of the Big Bang to the star-studded cosmos we now inhabit, popped into existence from nothing at all. It had to happen, they say, because "nothing" is inherently unstable.
This idea may sound bizarre, or just another fanciful creation story. But the physicists argue that it follows naturally from science's two most powerful and successful theories: quantum mechanics and general relativity.
Here, then, is how everything could have come from nothing.
Particles from empty space
First we have to take a look at the realm of quantum mechanics. This is the branch of physics that deals with very small things: atoms and even tinier particles. It is an immensely successful theory, and it underpins most modern electronic gadgets.
Quantum mechanics tells us that there is no such thing as empty space. Even the most perfect vacuum is actually filled by a roiling cloud of particles and antiparticles, which flare into existence and almost instantaneously fade back into nothingness.
These so-called virtual particles don't last long enough to be observed directly, but we know they exist by their effects.
Space-time, from no space and no time
From tiny things like atoms, to really big things like galaxies. Our best theory for describing such large-scale structures is general relativity, Albert Einstein's crowning achievement, which sets out how space, time and gravity work.
Relativity is very different from quantum mechanics, and so far nobody has been able to combine the two seamlessly. However, some theorists have been able to bring the two theories to bear on particular problems by using carefully chosen approximations. For instance, this approach was used by Stephen Hawking at the University of Cambridge to describe black holes.
In quantum physics, if something is not forbidden, it necessarily happens
One thing they have found is that, when quantum theory is applied to space at the smallest possible scale, space itself becomes unstable. Rather than remaining perfectly smooth and continuous, space and time destabilize, churning and frothing into a foam of space-time bubbles.
In other words, little bubbles of space and time can form spontaneously. "If space and time are quantized, they can fluctuate," says Lawrence Krauss at Arizona State University in Tempe. "So you can create virtual space-times just as you can create virtual particles."
What's more, if it's possible for these bubbles to form, you can guarantee that they will. "In quantum physics, if something is not forbidden, it necessarily happens with some non-zero probability," says Alexander Vilenkin of Tufts University in Boston, Massachusetts.
A universe from a bubble
So it's not just particles and antiparticles that can snap in and out of nothingness: bubbles of space-time can do the same. Still, it seems like a big leap from an infinitesimal space-time bubble to a massive universe that hosts 100 billion galaxies. Surely, even if a bubble formed, it would be doomed to disappear again in the blink of an eye?
If all the galaxies are flying apart, they must once have been close together
Actually, it is possible for the bubble to survive. But for that we need another trick: cosmic inflation.
Most physicists now think that the universe began with the Big Bang. At first all the matter and energy in the universe was crammed together in one unimaginably small dot, and this exploded. This follows from the discovery, in the early 20th century, that the universe is expanding. If all the galaxies are flying apart, they must once have been close together.
Inflation theory proposes that in the immediate aftermath of the Big Bang, the universe expanded much faster than it did later. This seemingly outlandish notion was put forward in the 1980s by Alan Guth at the Massachusetts Institute of Technology, and refined by Andrei Linde, now at Stanford University.
As weird as it seems, inflation fits the facts
The idea is that, a fraction of a second after the Big Bang, the quantum-sized bubble of space expanded stupendously fast. In an incredibly brief moment, it went from being smaller than the nucleus of an atom to the size of a grain of sand. When the expansion finally slowed, the force field that had powered it was transformed into the matter and energy that fill the universe today. Guth calls inflation "the ultimate free lunch".
As weird as it seems, inflation fits the facts rather well. In particular, it neatly explains why the cosmic microwave background, the faint remnant of radiation left over from the Big Bang, is almost perfectly uniform across the sky. If the universe had not expanded so rapidly, we would expect the radiation to be patchier than it is.
The universe is flat and why that's important
Inflation also gave cosmologists the measuring tool they needed to determine the underlying geometry of the universe. It turns out this is also crucial for understanding how the cosmos came from nothing.
Einstein's theory of general relativity tells us that the space-time we live in could take three different forms. It could be as flat as a table top. It could curve back on itself like the surface of a sphere, in which case if you travel far enough in the same direction you would end up back where you started. Alternatively, space-time could curve outward like a saddle. So which is it?
There is a way to tell. You might remember from maths class that the three angles of a triangle add up to exactly 180 degrees. Actually your teachers left out a crucial point: this is only true on a flat surface. If you draw a triangle on the surface of a balloon, its three angles will add up to more than 180 degrees. Alternatively, if you draw a triangle on a surface that curves outward like a saddle, its angles will add up to less than 180 degrees.
So to find out if the universe is flat, we need to measure the angles of a really big triangle. That's where inflation comes in. It determined the average size of the warmer and cooler patches in the cosmic microwave background. Those patches were measured in 2003, and that gave astronomers a selection of triangles. As a result, we know that on the largest observable scale our universe is flat.
It turns out that a flat universe is crucial. That's because only a flat universe is likely to have come from nothing.
Everything that exists, from stars and galaxies to the light we see them by, must have sprung from somewhere. We already know that particles spring into existence at the quantum level, so we might expect the universe to contain a few odds and ends. But it takes a huge amount of energy to make all those stars and planets.
The energy of matter is exactly balanced by the energy of the gravity the mass creates
Where did the universe get all this energy? Bizarrely, it may not have had to get any. That's because every object in the universe creates gravity, pulling other objects toward it. This balances the energy needed to create the matter in the first place.
It's a bit like an old-fashioned measuring scale. You can put a heavy weight on one side, so long as it is balanced by an equal weight on the other. In the case of the universe, the matter goes on one side of the scale, and has to be balanced by gravity.
Physicists have calculated that in a flat universe the energy of matter is exactly balanced by the energy of the gravity the mass creates. But this is only true in a flat universe. If the universe had been curved, the two sums would not cancel out.
Universe or multiverse?
At this point, making a universe looks almost easy. Quantum mechanics tells us that "nothing" is inherently unstable, so the initial leap from nothing to something may have been inevitable. Then the resulting tiny bubble of space-time could have burgeoned into a massive, busy universe, thanks to inflation. As Krauss puts it, "The laws of physics as we understand them make it eminently plausible that our universe arose from nothing - no space, no time, no particles, nothing that we now know of."
So why did it only happen once? If one space-time bubble popped into existence and inflated to form our universe, what kept other bubbles from doing the same?
There could be a mind-boggling smorgasbord of universes
Linde offers a simple but mind-bending answer. He thinks universes have always been springing into existence, and that this process will continue forever.
When a new universe stops inflating, says Linde, it is still surrounded by space that is continuing to inflate. That inflating space can spawn more universes, with yet more inflating space around them. So once inflation starts it should make an endless cascade of universes, which Linde calls eternal inflation. Our universe may be just one grain of sand on an endless beach.
Those universes might be profoundly different to ours. The universe next door might have five dimensions of space rather than the three – length, breadth and height – that ours does. Gravity might be ten times stronger or a thousand times weaker, or not exist at all. Matter might be built out of utterly different particles.
So there could be a mind-boggling smorgasbord of universes. Linde says eternal inflation is not just the ultimate free lunch: it is the only one at which all possible dishes are available.
As yet we don't have hard evidence that other universes exist. But either way, these ideas give a whole new meaning to the phrase "Thanks for nothing".
Friday, October 9, 2020
Thursday, October 8, 2020
An interesting fact: Human apes need less sleep than any other primate.
 | ||
Babies need far more sleep than adults
|
 |
| Homo erectus (right) was bigger brained than earlier hominins (left) |
 |
| H. erectus was starting to build better tools. Technologies like the Acheulean hand-axes pictured above were more advanced than older stone tools. This knowledge was widely shared, so they must have learned it quickly. |
 |
| Gorillas build new sleeping nests each night |
 |
| Sleeping in trees means there is a risk of falling |
 |
| Hadza hunter-gatherers do not need much sleep |
 |
| Our closest living relatives sleep for longer than we do |
 |
| Dolphins never completely switch off |
BBC Earth
Why humans need less sleep than any other primate
Most of us feel like we need more sleep, but as a species we have actually evolved to sleep less than our ape and monkey relatives. Could that be the key to our success?
By Melissa Hogenboom
21 January 2016
I have always been envious of people who can get by with only six hours' sleep. I prefer eight, sometimes more. I can function on six, but after a few days my brain will be way below full capacity.
How much sleep we get affects us all. Too much sleep makes us groggy and disorientated. Sleep too little and our mood and concentration suffer. If this carries on it can also cause serious health issues, heightening the risk of diabetes, obesity and high blood pressure.
Most of us sleep between six to nine hours a night, meaning we spend about a third of our lives asleep. This may seem like a long time, but we actually sleep the least among all the primates – the group that includes monkeys, apes and us.
So says a new analysis looking at the impact sleep has had on our evolution. The new research suggests that humans have evolved to sleep less, but also to sleep very deeply. This may help explain our success as a species.
But by two million years ago, hominins had become fully upright. Homo erectus spent its life on the ground, and may have been the first hominin to make beds there. If that is true, we have been sleeping on the ground for a long time.
Sleeping on the ground may have gifted H. erectus with a higher-quality, more restful sleep.
For one thing, they did not have to worry about falling out of the trees. What's more, while the risk from predators was higher on the ground, they had ways to protect themselves.
In particular, H. erectus may have mastered the use of fire. The flames and smoke would have scared away both mosquitoes and larger predators, keeping them safe. They may also have hidden away in sheltered places like caves.
We do not have direct evidence that H. erectus used fire at this time. But 10 years ago, Richard Wrangham of Harvard University proposed that our ancestors must have eaten cooked food to get enough calories to fuel their bigger brains.
As BBC Earth has covered before, fuelling our energy-hungry brains with enough calories has been crucial to our evolution. If our ancestors did not cook, Wrangham argued, they would have had to spend too much time chewing and digesting.
There is also evidence that at the same time hominins came down from the trees, they became smarter and acquired better weapons.
Group sizes also increased around this time, perhaps aided by better weaponry and communication skills.
According to David Samson and Charles Nunn of Duke University in North Carolina, US, all these changes – from larger groups to more advanced tools – can be linked to a change in the way our ancestors slept.
They have set out their ideas in a new study published in the journal Evolutionary Anthropology.
They argue that moving from the trees to the ground allowed our ancestors to sleep more deeply – "which could in turn have affected cognition", says Samson.
The theory goes that although we sleep for fewer hours than other primates, the sleep that we have is of high quality so we do not need as much.
To understand whether human sleep is unique, Samson and Nunn compared the sleep patterns of 21 primates, whose slumber patterns had already been analyzed.
As well as noting how long the animals slept for, they looked at how much time they spent in rapid-eye movement (REM) sleep. This is when we dream, and when our brain consolidates our memories into long-term storage.
Humans slept the least. The sleepiest primates were grey mouse lemurs and night monkeys, which slept for 15 and 17 hours respectively.
But in contrast, humans spent the highest proportion of their sleep in an REM state: almost 25%. "Humans therefore have the deepest sleep of any primate," says Samson.
Other primates get much less REM sleep, between 5-10%.
Samson previously compared ape and monkey sleep, and found a similar pattern: apes seem to have better-quality sleep than monkeys.
This may be because apes sleep in specially-built nests in the trees. Monkeys do not, and their environment is often less secure. That means they have to sleep more lightly, allowing them to wake quickly if a predator approaches.
Just as apes get better sleep than monkeys, so we get better sleep than apes. "From an evolutionary perspective, just as the transition from tree branches to sleeping platforms had adaptive benefits, so too did the early hominin transition from sleeping platforms to secure ground sleep," Samson previously told BBC Earth.
He argues that we could not have slept so deeply until we found ways to sleep safely. During REM sleep, you are "essentially as close to dead in the outside world as you'll ever be", says Samson. "You need to have a unique sleep environment to be able to pull this off."
The idea that humans have evolved to sleep briefly but deeply runs counter to a cherished folk belief. Surely modern technologies like artificial lighting have disrupted our natural sleep patterns? Isn't that why we are all so sleep-deprived?
Surprisingly, this may not be entirely true.
A study published in November 2015 looked at the sleep habits of three preindustrial societies: two hunter-gatherer groups from Africa and one horticultural group from Bolivia.
All three groups slept for an average of 6.4 hours per night, ranging from 5.7–7.1 hours. That is even less than the average for an industrial society.
The people in the study woke before sunrise and went to bed several hours after sunset, suggesting that the natural light and dark cycles were not determining when they went to sleep.
What's more, getting less sleep did not appear to reduce their cognitive abilities, and they were all generally healthy, says lead author Jerome Siegel of the University of California, Los Angeles in the US. This suggests they were sleeping enough.
Siegel's study does not tell us anything about ancestral species like H. erectus. But it does suggest that the earliest modern humans, who lived in similar environments to the people in the study, also needed surprisingly little sleep.
It is tricky to be sure about this, because some people need more sleep than others. There could even be population-level patterns: certain groups of people may have inherited genes that allow them to get by on less sleep.
Samson and Nunn's study focused on average amounts of sleep, taken across entire populations. But that might be missing the point, says sleep specialist Jeffrey Durmer of Georgia State University in Atlanta, US.
Sleep is particularly important when we are very young, especially REM sleep. Infants spend far more time in REM sleep than children or adults.
If you compare a child's REM sleep to that of an adult, the difference is much greater than it is between humans and chimpanzees, he says. This might mean that getting enough quality sleep early on in life was more important in helping our ancestors develop into ever big-brained hominins.
"REM sleep is very important in the development of the nervous system," says Durmer. "That means that cognition in particular is ultimately very reliant on REM sleep."
The biggest problem with Samson and Nunn's idea is that we do not yet understand all the functions of sleep, so we cannot say for sure what benefits we might get from extra REM sleep.
In particular, we periodically switch from REM sleep to other kinds of sleep. We do not know why these transitions happen, or how important they are, says Derk-Jan Dijk of the University of Surrey in the UK. "There may be a little secret there."
The picture gets even muddier when we start to compare our own REM sleep to that of other animals, beyond our close relatives the primates.
Siegel thinks that REM sleep is not that important to humans after all.
He argues that we should consider all mammals, not just primates. When we do so, humans do not stand out as needing a particularly large proportion of REM sleep.
The link between REM sleep and intelligence also fades away. For example, dolphins are intelligent and have large brains, yet they do not need any REM sleep. Meanwhile opossums, which are not noted for their deep thinking, need over six hours.
Samson disagrees. He points out that species' distinct lifestyles can result in differing needs for sleep.
Famously, dolphins only sleep on one side of their brain at a time. The reason for this is simple: if they switched off completely they would drown. Looked at in that light, it makes sense that dolphins do not sleep deeply.
"When you use animal studies to compare to humans we aren't comparing apples to apples," agrees Durmer. "We may have a very different use of REM sleep compared to other species."
Regardless of why it happened, the fact remains that human sleep is strange compared to our closest living relatives. This suggests that we have evolved to need less of it.
Obviously, we cannot ever study how long our hominin ancestors slept for, because they have gone extinct. The best we can do is to compare ourselves to other living animals.
It seems that, at some point, bigger-brained hominins became more efficient sleepers. The bad news for above-average sleepers like me is that we may be genetically predisposed to need more of it.
But the third of our lives we spend doing so is certainly not wasted. Our big brains took millions of years of evolution to get there, so it's only fair that we reward ourselves with a lifetime of adequate rest.
Melissa Hogenboom is BBC Earth's feature writer. She is @melissasuzanneh on Twitter.
Follow BBC Earth on Facebook, Twitter, and Instagram
Sunday, August 30, 2020
Tuesday, August 11, 2020
Wednesday, April 1, 2020
Saturday, December 28, 2019
Blue Planet II Official Trailer 2 - BBC Earth
In 2001, The Blue Planet opened our eyes to the worlds beneath the waves. A generation on, new science and technology allow us to journey deeper than ever before at the most crucial time in our ocean’s history. This is Blue Planet II. Take a deep breath. Subscribe to BBC Earth for more amazing animal videos: http://bit.ly/BBCEarthSub Watch more videos from BBC Earth: Blue Planet: http://bit.ly/BluePlanetPlaylist Planet Earth: http://bit.ly/PlanetEarthPlaylist Planet Earth II: http://bit.ly/PlanetEarthIIPlaylist Planet Dinosaur: http://bit.ly/PlanetDinoPlaylist Blue Planet II is narrated by Sir David Attenborough and features an original score by legendary composer Hans Zimmer. The series is set for UK broadcast on BBC One on October 29th and coming soon to BBC America in 2018. A BBC Studios Natural History Unit production, co-produced with BBC America, Tencent, WDR, France Télévisions and CCTV9. A BBC Open University Partnership. Check out the other two channels in the BBC Earth network: BBC Earth Unplugged: http://bit.ly/BBCEarthUnplugged BBC Earth Lab: http://bit.ly/BBCEarthLabYouTubeChannel About BBC Earth: The world is an amazing place full of stories, beauty and natural wonder. Jump in to BBC Earth's YouTube channel and meet your planet. You'll find 50 years worth of astounding, entertaining, thought-provoking and educational natural history content on here. Dramatic, rare, and exclusive, nature doesn't get more exciting than this. Subscribe to be the first to view new videos. And you can become part of the BBC community by checking out our BBC Earth Facebook page. Here you'll find the best natural history content from the web, exclusive videos and images and a thriving, vibrant community.
Monday, October 28, 2019
BBC Earth - Some evidence for evolution. July 2015.
BBC Earth - How do we know evolution is really happening?
The idea that species gradually change over many generations is the cornerstone of biology. This is how we know it's true
By Chris Baraniuk
30 July 2015
The idea that species gradually change over many generations is the cornerstone of biology. This is how we know it's true
By Chris Baraniuk
30 July 2015
Evolution is one of the greatest theories in all of science. It sets out to explain life: specifically, how the first simple life gave rise to all the huge diversity we see today, from bacteria to oak trees to blue whales.
For scientists, evolution is a fact. We know that life evolved with the same certainty that we know the Earth is roughly spherical, that gravity keeps us on it, and that wasps at a picnic are annoying.
Not that you would know that from the media in some countries, where evolution is ferociously argued about – put down as "just a theory" or dismissed as a flat-out lie.
Why are biologists so certain about this? What is the evidence? The short answer is that there is so much it's hard to know where to start. But here is a very cursory summary of the evidence that life has, indeed, evolved.
It might help to first spell out quickly what Darwin's theory of evolution actually says. Most of us have the general idea: species change over time, only the fittest survive, and somehow a monkey-like creature gave rise to human beings.
It is hard to accept that you are descended, through countless generations, from a worm
Darwin's theory of evolution says that each new organism is subtly different from its parents, and these differences can sometimes help the offspring or impede it. As organisms compete for food and mates, those with the advantageous traits produce more offspring, while those with unhelpful traits may not produce any. So within a given population, advantageous traits become common and unhelpful ones disappear.
Given enough time, these changes mount up and lead to the appearance of new species and new types of organism, one small change at a time. Step by step, worms became fish, fish came onto land and developed four legs, those four-legged animals grew hair and – eventually – some of them started walking around on two legs, called themselves "humans" and discovered evolution.
This can be hard to believe. It's one thing to realise that you are not identical to our parents: perhaps your hair is a different colour, or you are taller, or have a more cheerful nature. But it is much harder to accept that you are descended, through countless generations, from a worm.
Plenty of people certainly don't accept this. But forget all the drama for a moment. Instead, begin as Charles Darwin did: on your doorstep.
Darwin's book On the Origin of Species, first published in 1859, begins by asking the reader to look around at the familiar. Not unexplored tropical islands or faraway jungles, but the farmyard and garden. There, you can easily see that organisms pass on characteristics to their offspring, changing the nature of that organism over time.
These changes from generation to generation are called "descent with modification"
Darwin was highlighting the process of cultivation and breeding. For generations, farmers and gardeners have purposefully bred animals to be bigger or stronger, and plants to yield more crops.
Breeders work just like Darwin imagined evolution worked. Suppose you want to breed chickens that lay more eggs. First you must find those hens that lay more eggs than the others. Then you must hatch their eggs, and ensure that the resulting chicks reproduce. These chicks should also lay more eggs.
If you repeat the process with each generation, eventually you'll have hens that lay far more eggs than wild chickens do. A female jungle fowl – the closest wild relative of the domestic chicken – might lay 30 eggs in a year, whereas farm hens may well produce ten times as many.
These changes from generation to generation are called "descent with modification".
Our oldest domesticated animals are still capable of rapid improvement or modification
A young chick will in many ways be similar to its parents: it will be recognisably a chicken, and definitely not an aardvark, and it will probably be more similar to its parents than it is to other chickens. But it won't be identical.
"That's what evolution is," says Steve Jones of University College London in the UK. "It's a series of mistakes that build up."
You might think that breeding can only make a few changes, but there seems to be no end to it. "No case is on record of a variable being ceasing to be variable under cultivation," wrote Darwin. "Our oldest cultivated plants, such as wheat, still often yield new varieties: our oldest domesticated animals are still capable of rapid improvement or modification."
Breeding, Darwin argued, is essentially evolution under human supervision. It shows us that the tiny changes from generation to generation can add up. "It's inevitable," says Jones. "It's bound to happen."
Still, it's quite a step from carefully breeding chickens that lay more eggs to the natural evolution of new species. According to evolutionary theory, those chickens are ultimately descended from dinosaurs, and if you go further back, from fish.
The answer is simply that evolution takes a long time to make big changes. To see evidence of that, you have to look at older records. You have to look at fossils.
Fossils are the remains of long-dead organisms, preserved in rock. Because rocks are laid down in layers, one on top of the other, the fossil record is generally set out in date order: the oldest fossils are at the bottom.
I always think that the most convincing case for evolution is in the fossil record
Running through the fossil record makes it clear that life has changed over time.
The oldest fossils of all are the remains of single-celled organisms like bacteria, with more complicated things like animals and plants only appearing much later. Among the animal fossils, fish appear much earlier than amphibians, birds or mammals. Our closest relatives the apes are only found in the shallowest – youngest – rocks.
"I always think that the most convincing case for evolution is in the fossil record," says Jones. "It's noticeable that one page in every six in the Origin of Species is to do with the fossil record. [Darwin] knew that that was an irrefutable case that evolution had taken place."
How do we really know that one species evolved into another?
By carefully studying fossils, scientists have been able to link many extinct species with ones that survive today, sometimes indicating that one descended from another.
For example, in 2014 researchers described the fossils of a 55-million year old carnivore called Dormaalocyon, which may be a common ancestor of all today's lions, tigers and bears. The shapes of Dormaalocyon's teeth gave it away.
Still, you may not be convinced. Those animals may all have similar teeth, but lions, tigers and Dormaalocyons are still distinct species. How do we really know that one species evolved into another?
The fossil record is only so much help here, because it is incomplete. "If you look at most fossil records, what you actually see is one form that lasts quite a long time and then the next bunch of fossils that you've got is quite different from what you had before," says Jones.
It is also possible to observe the evolution of a new species as it happens
But as we have dug up more and more remains, a wealth of "transitional fossils" has been discovered. These "missing links" are halfway houses between familiar species.
For instance, earlier we said that chickens are ultimately descended from dinosaurs. In 2000 a team led by Xing Xu of the Chinese Academy of Sciences described a small dinosaur called Microraptor, which had feathers similar to modern birds and may have been able to fly.
It is also possible to observe the evolution of a new species as it happens.
In 2009, Peter and Rosemary Grant of Princeton University in New Jersey described how a new species of finch came into being on one of the Galápagos Islands: the same islands visited by Darwin.
This little group of birds had formed a new species
In 1981, a single medium ground finch arrived on an island called Daphne Major. He was unusually large and sang a somewhat different song to the local birds.
He managed to breed, and his offspring inherited his unusual traits. After a few generations, they were reproductively isolated: they looked different from the other birds, and sang different songs, so could only breed among themselves. This little group of birds had formed a new species: they had "speciated".
This new species is only subtly different from its forebears: their beaks are different and they sing an unusual song. But it is possible to watch far more dramatic changes as they happen.
Richard Lenski of Michigan State University is in charge of the world's longest-running evolution experiment.
It's a very direct demonstration of Darwin's idea of adaptation by natural selection
Since 1988, Lenski has been tracking 12 populations of Escherichia coli bacteria in his lab. The bacteria are left to their own devices in storage containers, with nutrients to feed on, and Lenski's team regularly freezes small samples.
The E. coli are no longer the same as they were in 1988. "In all 12 populations, the bacteria have evolved to grow much faster than did their ancestor," says Lenski. They have adapted to the specific mix of chemicals he gives them.
"It's a very direct demonstration of Darwin's idea of adaptation by natural selection. Now, 20-some years into the experiment, the typical lineage grows about 80% faster than did the ancestor."
In 2008, Lenski's team reported that the bacteria had made a huge leap forward. The mixture they live in includes a chemical called citrate, which E. coli cannot digest. But 31,500 generations into the experiment, one of the 12 populations started feeding on citrate. This would be like humans suddenly developing the ability to eat tree bark.
All living things carry genes, in the form of DNA
The citrate was always there, says Lenski, "so all of the populations have [had] the opportunity in a sense to evolve the ability to use this... But only one of the 12 populations has found their way to do this."
At this point, Lenski's habit of regularly freezing samples of the bacteria proved crucial. He was able to go back through older samples, and trace the changes that led to the E. coli eating citrate.
To do this, he had to look under the hood. He used a tool that wasn't available in Darwin's day, but which has revolutionised our understanding of evolution as a whole: genetics.
All living things carry genes, in the form of DNA.
Genes control how an organism grows and develops, and they are passed on from parent to offspring. When a mother chicken lays lots of eggs, and passes that trait onto her offspring, she does so through her genes.
All modern life has descended from a single common ancestor
Over the last century scientists have catalogued the genes from different species. It turns out that all living things store information in their DNA in the same way: they all use the same "genetic code".
What's more, organisms also share many genes. Thousands of genes found in human DNA may also be found in the DNA of other creatures, including plants and even bacteria.
These two facts imply that all modern life has descended from a single common ancestor, the "last universal ancestor", which lived billions of years ago.
By comparing how many genes organisms share, we can figure out how they are related. For instance, humans share more genes with apes like chimps and gorillas than other animals, as much as 96%. That suggests they are our closest relatives.
We have a common ancestor with chimpanzees
"Try to explain that in any other way than the fact that those relationships are based on a sequence of changes through time," says Chris Stringer of the Natural History Museum in London. "We have a common ancestor with chimpanzees, and we and they have diverged since then from that common ancestor."
We can also use genetics to track the detail of evolutionary changes.
"You can compare different types of bacteria and find the genes that they share," says Nancy Moran at the University of Texas at Austin. "Once you recognise these genes… you can look at how they have evolved in different kinds of populations."
When Lenski went back through his E. coli samples, he found that the citrate-eating bacteria had several changes to their DNA that the other bacteria didn't. These changes are called mutations.
Lenski's E. coli show us that evolution can give organisms radically new abilities
Some of them had happened long before the bacteria developed their new ability. "In and of themselves, [these mutations] did not confer the ability to grow on citrate, but set the stage for subsequent mutations that then conferred that ability," says Lenski.
This complex chain of events helps explain why only one population evolved the ability.
It also illustrates an important point about evolution. A particular evolutionary step may seem extremely unlikely, but if there are enough organisms being pushed to take it, one of them probably will – and it only takes one.
Lenski's E. coli show us that evolution can give organisms radically new abilities. But evolution doesn't always make things better. Its effects are often, to our eyes at least, rather random.
The mutations that lead to changes in an organism are very rarely for the better, says Moran. In fact, most mutations have either no impact, or a negative impact, on the way an organism functions.
Animals that live in dark caves often lose their eyes
When bacteria are confined to isolated environments, they sometimes pick up unwelcome genetic mutations that get passed on directly to every generation. Over time, this gradually hampers the species.
"It really shows the process of evolution," says Moran. "It's not all just adaptation and things getting better, there's also this big potential for things to get worse."
What's more, organisms sometimes lose abilities. For instance, animals that live in dark caves often lose their eyes.
This may seem odd. We tend to think of evolution as a process of biological betterment, of species improving and becoming less primitive. But this is not necessarily what happens.
The notion of betterment can be traced back to a scientist named Jean-Baptiste Lamarck, who was pushing the idea that organisms evolve before Darwin was. His contributions were vital.
What did he mean they wanted to improve? How would you test that?
But unlike Darwin, Lamarck thought that organisms got better at living in their environments as a deliberate reaction to those environments, as though they inherently wanted to improve.
Lamarck's theory would say that giraffes have long necks because their ancestors stretched to reach tall trees, and then passed their newly-acquired long necks on to their offspring.
"Darwin wrote about Lamarck privately and said his theory is complete nonsense, it's untestable," says Jones. "What did he mean they wanted to improve? How would you test that?"
Darwin had an alternative theory: natural selection. It offers a completely different explanation for giraffes' long necks.
Imagine an ancestor of modern giraffes, something a bit like a deer or antelope. If there were lots of tall trees where this animal lived, the animals with the longest necks would get more food, and do better than those with shorter necks.
Animals like giraffes are so striking because they appear so perfectly adapted
After a few generations, all the animals would have slightly longer necks than their ancestors did. Again, those with the longest would do best, so over many years, giraffes' necks would gradually get longer, because those with short necks tended not to have offspring.
The mutations underlying this all happened at random, and were just as likely to produce short necks as long ones. But those short-neck mutations didn't tend to last.
Animals like giraffes are so striking because they appear so perfectly adapted. They live in areas where the trees are tall and only have leaves high off the ground, so of course they have long necks to reach them.
"That kind of image is actually what confuses people, I think, because it looks so perfect, it looks designed," says Moran. But if you look closer, it is the result of a long chain of little changes. "You realise, oh, it's not designed, it's actually one odd event that might have spread and led to another odd event."
We now have all the pieces of evidence that, when put together, show that life has evolved.
Human evolution has always been a concept difficult for some to stomach
Descent with modification, which is caused by random mutations in genes, ultimately leads to gradual changes and the formation of new species – much of it driven by natural selection, which weeds out those organisms that are less suited to their environments.
Finally, let's apply all this to ourselves.
Human evolution has always been a concept difficult for some to stomach, but it's impossible to turn a blind eye to it now, says Stringer.
Homo sapiens is believed to have evolved in Africa before spreading all over the world.
People of European and Asian descent carry Neanderthal genes in their DNA
The fossil record shows a gradual change from ape-like animals walking on all fours to bipedal creatures that gradually developed bigger brains.
The first humans to leave Africa interbred with other hominin species, such as the Neanderthals. As a result, people of European and Asian descent carry Neanderthal genes in their DNA, but people of African descent don't.
This all happened thousands of years ago, but the story is not over. We are still evolving.
For instance, in the 1950s a British doctor called Anthony Allison was studying a genetic disorder called sickle-cell anaemia, which is common in some African populations. People with the disorder have misshapen red blood cells, which don't carry oxygen around the body as well as they might.
For those people, it was worth carrying the sickle-cell mutation
Allison discovered that the east African populations were divided into groups of lowland-dwelling people, who were prone to the disease, and people who lived in the highlands, who were not.
It turned out that people carrying the sickle-cell trait got an unexpected benefit. It protected them from malaria, which was only really a threat in the lowlands. For those people, it was worth carrying the sickle-cell mutation, even if their children might be anaemic.
By contrast, people living in highland areas were not at risk from malaria. That meant there was no advantage to carrying the sickle-cell trait, so its otherwise-harmful nature had meant it disappeared.
Of course, there are all sorts of questions about evolution that we still haven't answered.
Their ancestors go back in an unbroken line for over 3 billion years
Stringer offers a simple one: what was the genetic change that allowed humans to walk upright, and why was that mutation so successful? Right now we don't know, but with more fossils and better genetics, we might someday.
What we do know is that evolution is a fact of nature. It is the basis for life on Earth as we know it.
So next time you're out and about, whether it's in your garden or on a farm or just walking down a road, take a look at the animals and plants around you and think about how they all got there.
Each of the organisms you see, whether it's a tiny insect or a great big elephant, is the latest member of an ancient family. Their ancestors go back in an unbroken line for over 3 billion years, to the dawn of life itself. So do yours.
Subscribe to:
Posts (Atom)