The inside of the body is an environment just like the outside environment.

There's a whole universe inside, a planet in every cell.

You have 37 trillion cells in your body.

Do you realise that you are such a part of the universe that you have entire ecosystems inside you.

It all happens in total darkness.

How a body grows

Vertebrates vs Invertebrates

There are two competing models.

Vertebrates (I.e. fish, amphibians, reptiles, birds, mammals) have their hard, structural components on the inside of their bodies (bones). This means that their exterior is softer and more prone to damage, but it is also easier to grow larger when abundant food sources are available. Their bodies can also expand and contract, which means that they can draw large amounts of oxygen directly into their bodies through breathing.

Invertebrates (I.e. crustaceans, insects, arachnids) have their hard, structural components on the outside of their bodies (exoskeletons). This means that their exterior is hard and impervious to damage, but they are also fundamentally constrained by it. To grow, many must go through phases of metamorphosis where their bodies are effectively dissolved and remade, and then in adulthood must periodically shed their exoskeleton in order to grow incrementally larger. They cannot have lungs as their bodies are rigid and unable to contract; instead they must have tiny pore-like holes in their exoskeletons down into their bodies, called spiracles, through which oxygen can be exchanged. It is in particular this second factor that prevents invertebrates from growing to the size of vertebrates, unless the oxygen content of the atmosphere is drastically high (as it has been in the past). Also, more body types and shapes are available to invertebrates.


Say hey to Owlbert Einstein

Curator of the Big Ideas Network

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The senses

Our senses are our ways of detecting the universe.

Perhaps there is another 'dirty glass' in addition to language and I think the other was culture.

Biology. The limited spectrum that we see, and perhaps our perception of time and other phenomena.

Perhaps the rate at which we experience time comes not from anything intrinsic or objective, but rather from our midworld perspective, which also may be connected to the rate of decay of our complex chemical bodies.

We judge something as taking a long time by how much of a percentage of our lifetime it takes up.

If we were sentient, long lived robots, or more complex biological bodies, perhaps we would perceive the lifetimes of stars as quick and transient, and we'd watch constellations dance. But they seem so long lived compared to us- because they are, compared to our bodies that decay.

Shakespeare, King Henry IV

O God! That one might read the book of fate,

And see the revolution of the times

Make mountains level, and the continents,

Weary of solid firmness, melt itself

Into the sea!

The systems



These are cells which line the trachea. It's a weird world down there.


Blood vessels

The blood in a human body would just about fill a basketball.

If you could visualise the shape of what you last ate, it may now be the shape of your capillaries, as your food has been broken down and distributed throughout your bloodstream.

The tiny capillaries on your tongue



Bodies are transformed food.

Your pets are simply the food that you've given them, that has been transformed. The same applies to you.

You could also say that, at least in the natural environment, organisms are an extension of their surrounding nutrient cycles.

Question: How long does it take us to eat our own body weight in food?

Nutrient cycles

In nature, you can see that energy and nutrients come from the soil, move up into animals, then waste from food scraps or from animals all gets reused. Sustainability is implicit.

How do ants, one of the most successful and prolific species on the planet, practice sustainability?

The total yield or biomass of any organism will be determined by the nutrient present in the lowest (minimum) concentration in relation to the requirements of that organism.

"The limiting nutrient is the one in least abundance."

Why is Nitrogen commonly a limiting nutrient in terrestrial ecosystems?

Ammonium and nitrate ions are highly soluble in water and easily leached from the soil

In aquatic ecosystems, it's Phosphorous that is usually limiting.

You ARE what you eat

Excerpt from* ***YOUR ATOMIC SELF: The Invisible Elements That Connect You to Everything Else in the Universe*** *by Curt Stager.

When you take a sip of water it doesn’t just slake your thirst. It literally becomes you. The water that runs down your gullet will, within minutes and without processing of any kind, become some of the dominant fluid in your veins and your flesh. Most of your blood is simply tap water with cells, salts, and organic molecules floating in it. Some of the rubbery squishiness of your earlobe poured out of a bottle or a can just a short time ago. And much of the moisture in your eyes only recently fell from rainclouds.

Your mouth is the portal through which water normally enters your body, but you are quite a leaky vessel. A hydrogen isotope study published in the *British Journal of Sports Medicine* reported that the sedentary men under examination consumed and lost about seven pints of body water per day, with four pints leaving through urine and two or three pints through sweat and breath moisture. Vigorous exercise can boost non-urine water losses to one or two pints per hour.

Now let’s see what logic can do with those facts. Nearly two-thirds of your weight comes from water, and your body is an eddy in a stream of that common fluid. Surely the liquid that you slurp from a fountain is not alive, and you don’t consider it murder to stomp on a puddle of water. Therefore most of you is not alive at all, nor is it even permanent or unique enough to merit a personal name.

  • Long, Beautiful Hair**

Next let’s consider your hair. It is a slow-motion shower of lifeless protein that sprays out of your head at roughly half an inch per month or six inches per year. Each filament is a tangle of carbon and oxygen atoms that are outnumbered two to one by hydrogen and sprinkled with nitrogen along with a dash of sulfur. The atoms in the roots are derived from meals that you ate within the last few days, along with some drinks, metabolic water, and your own recycled cells.

Your fingernails are also full of keratin, and they roll out of your fingertips at three to four millimeters per month, on average. Your toenails grow half as fast but they, too, release atoms from their leading edges as you cut or wear them away, and you also shed millions of microscopic keratinous skin flakes every day. If you could fast-forward a video of your hair, nail, and epidermal growth, you would seem to smolder with skin dust while jungles of protein poured from your hairy parts and curly peels of keratin shot from your fingertips and toes. Even at the usual slow pace, that’s a lot of atoms, all of which must be replaced if you are to resemble yourself for very long.

One way of summarizing this unusual time-lapse view of yourself is that you are a walking fountain of carbonated water vapor, liquid water, and protein. Much of it trails off behind you in an invisible mist of exhalations and exfoliations, ending up in the dust bunnies beneath your bed or, should you misbehave badly enough, in the nostrils of a bloodhound. If you ever do become a fugitive of that sort, then perhaps you might attempt a plea of atomic innocence should you be brought before a court of law. “It wasn’t I, Your Honor,” you can truthfully say (and perhaps with excessive grammatical propriety), thanks to the rapid turnover of matter in your body.

  • The Sum of Your Parts**

There is a lot more to your body now than there was when you could still fit inside your mother’s womb, and that fact alone makes it obvious that most of your body is younger than you are. But imagining yourself as a temporary collection of cells can also make the transitory nature of your body more apparent, too.

A study by the Italian researcher Eva Bianconi and her colleagues recently put the average number of cells in an adult human body at thirty-seven trillion. They vary wildly in shape and size, with diameters ranging from eight microns for a red blood cell and about twenty-two microns for a liver cell to roughly one hundred microns for a mature egg cell (five hundred microns would span a grain of salt). Some of them may last for a few days or weeks before being recycled and replaced, while others may last a lifetime. How can you tell which is which?

One way to estimate the turnover rates of human cells is to measure the amount of carbon-14 in them. During the Cold War, atmospheric testing of thermonuclear weapons turned atmospheric nitrogen atoms into radioactive carbon-14 that still contaminates air and oceans today. Moving into plants as carbon dioxide, the unstable atoms of bomb carbon have worked their way through food chains and lodged in the bodies of everyone on Earth, including you. Since 1963 when above-ground testing was banned, radiocarbon concentrations have declined as carbon-rich organic matter has been buried in ocean sediments, and the change is reflected in our bodies. If there is any bright side to thermonuclear pollution, it may be this shifting concentration of bomb carbon that provides a global isotopic tracer for determining the ages of our cells.

Olaf Bergmann, a cell biologist at the Karolinska Institute in Stockholm, recently coauthored a paper in *Science* that used this technique to document the growth of new cells in heart muscle. His approach resolved a long-standing conflict between experts who believed that the heart is renewed as many as four times during a lifetime and those who believed that we die with essentially the same heart we were born with. By measuring the radiocarbon contents of cardiomyocyte cells from which heart muscle is made, Bergmann’s team found that the cardiac tissues of relatively young people who spent their entire lives amid the earth’s contaminated carbon reservoir were far more radioactive overall than those of older people who were born before the nuclear tests began.

From these and similar findings, it appears that you do continue to form some new heart tissue throughout your life, and that you do so at different rates as you age. According to Bergmann’s calculations, you replace about 1 percent of your cardiac muscle cells per year at age twenty and half as many at age seventy-five. Nevertheless, you still keep most such cells with you throughout your adult life.

Similar radiocarbon tracer studies suggest that the average replacement rate of most cells in your body is between seven and ten years, but some cells fall well outside that range. Your heart, for example, is full of connective tissue, blood vessels, and other structures that are replaced more often than your cardiomyocytes. A median annual turnover rate of 18 percent for those components suggests that most of your heart is less than five years old.

In a follow-up paper in *Science*, Bergmann and the biologist Jonas Frisén reported that nerve cells within the olfactory bulb and hippocampus of a human brain are continuously regenerated. This means that when a whiff of something sparks a memory, be it a smoky campfire or a familiar perfume, the neurons that originally encoded those sensations may no longer be with you, and the memories may now be preserved by cells that never experienced them. Most of your other brain cells date back to your infancy, but tracer studies now show that some fresh neurons can also appear within your cerebral cortex, perhaps registering new experiences from day to day.

  • Cellular Churn**

Cells that line your digestive tract are replaced every few days, which is not surprising considering the abuse they take from stomach acids, bile, and erosion by the passage of food and waste. Work by the physiologist Bernd Lindemann posits a lifespan of about ten days for the taste cells in your mouth, and the dermatologist Gerald Weinstein and his colleagues estimate a mean turnover time of thirty-nine days for skin cells, which spend only a couple of weeks in your outermost layers before flaking off by the hundreds of millions. This continuous shedding gives you a new wrapper of skin once or twice a month and a steady supply of house dust to keep up with.

The lives of your red blood cells are rather “nasty brutish and short.” After tumbling through hundreds of miles of aortic rapids and hard-to-squeeze-through capillaries, and after repeatedly swelling and shrinking in thousands of transits through the osmotic jungles of your kidneys, most of them wear out within four months or so and must be replaced by progenitor cells in your spleen and bone marrow. And according to the science journalist Nicholas Wade, the replacement times of three hundred to five hundred days that liver cells enjoy can grow you a whole new liver every year or two.

The Swedish biologist Kirsty Spalding and others have found that your fat-storage cells persist for about a decade, which is good news for people who struggle to lose weight. It was long thought that starvation merely deflates fat cells rather than killing them off, leaving them to fill up again like grocery bags when a dieter tires of feeling hungry. But if you can stick to a healthy regimen for long enough, it seems that you can help to stabilize your weight by outliving some of your fat cells.

Your bones and muscles are constantly remodeled. About 3 percent of the dense outermost layers of your skeleton and up to a quarter of the porous bone in the knobby parts of your limb joints are recycled every year, and experts calculate an average life cycle of a decade or so for your skeleton as a whole. The muscle cells between your ribs live for about fifteen years, according to Nicholas Wade, and the collagen cores of your tendons are essentially permanent once they finish developing during your late teens.

Recent isotopic analyses by researchers in Denmark and Sweden show that the oldest easily identifiable structures in your body are the crystalline lens proteins of your eyes and the enamel of your teeth. If you carry healthy ovaries, then you may also carry thousands to millions of microscopic oocytes that formed while you were still in your mother’s womb, making the initial cells of your potential future children nearly as old as you are. And as for tattoos, although younger than you they are permanent because the ink is not cellular and therefore not recycled; it is more like the persistent pebbles in a cornfield than the ephemeral crops of skin.

In sum, your tissues are a mishmash of newborn, persistent, and dying cells, most of which are relatively new. Therefore, whatever you have supposedly done to deserve credit or blame, it really wasn’t *you* after all, was it? In this mad worldview the most likely culprits would be your eyes, your teeth, some brain matter, and perhaps the seeds of your unborn children.


Small differences in body shape and function can have drastic effects on a species


Body size scales

One of the reasons that life is so robust is because it is size scalable. On the whole, it can adapt to availability of energy and nutrients on a logarithmic scale.


I also read somewhere that it's relatively easy for a species to becomes significantly bigger or smaller in a few generations, with selective pressure.

Cold blooded animals might be a bit different

The Brain

Ed Boyden, Neuroscientist at MIT, A new way to study the brain's invisible secrets

The density of the brain is incredible. In a cubic millimeter of your brain, there are about 100,000 of these neurons and maybe a billion connections.

A huge hierarchy of pattern recognisers

Ray Kurzweil, How To Create A Mind: Ray Kurzweil at TEDxSiliconAlley

A lot of the methods used in Watson in fact are very similar to the mathematics of what the human brain does, which is to build up ideas and concepts - patterns, if you will in a hierarchical fashion.

So let me quickly describe how this works - we have 300 million little pattern recognizers. So I have a number that recognizes the crossbar in a capital A and that's really all it cares about. A pretty girl can walk by, a beautiful song can play; it doesn't care. But when it sees the crossbar a capital A gets very excited and fires 'Wow! Crossbar' and that goes up to a higher level.

Another pattern recognizer that's getting that input as well as other primitive feature detectors and goes "Ah, capital A." And it fires with a high probability. That goes to a higher level. That might go up to the printed word "Apple" in another part of the visual cortex that might be recognized and it goes "An actual apple!". That because an actual apple in the auditory cortex that might be one that fires it says "Oh, somebody just said Apple."

Go up another 20 levels and its now sitting at a very high point of a hierarchy and that below it is getting input - from the visual system, the auditory systems, the olfactory system, and it smells certain perfume and sees a certain fabric it has a certain voice and goes "uh-huh my friend just entered the room." Go up another 20 levels and you've got pattern recognizers that might say "oh she's pretty," "that was ironic," "that's funny"…

So you probably think that those high level pattern recognizers - beauty, humor; are much more complicated than the ones just recognize the edge of an object or a crossbar in a capital A but they're actually the same, except that the high level ones are used to sitting in a different position in that grand hierarchy.

I talk about in the book, this girl had to have brain surgery and she was conscious - you can be conscious during brain surgery because there's no pain receptors in the brain - and whenever the surgeons triggered a particular spot in our neocortex she would laugh, and they thought 'maybe they're triggering some laugh reflex', but they quickly discovered no, they're actually triggering the perception of humor. She just found everything hilarious whenever they triggered the spot; "you guys are so funny just standing there" was a typical remark. And these guys were not funny. So she obviously has more than one spot that recognizes humor; we have tremendous redundancy in general.

I've got lots of pattern recognizers that recognize the crossbar and a capital A but they're all organized in this grand hierarchy - so where does this hierarchy come from? We’re not born with it. The subtitle of the book is: "a secret of human thought revealed" and that is the secret - the neocortex recognizes these patterns and actually sees, and its own experience and then wires itself up in this hierarchy. I have a one year old grandson now and he's already laid down several layers of this hierarchy - we can actually learn one conceptual level at a time, that's why it takes a long time to get up to high-level concepts like irony. And many civilizations actually never got to understanding irony which is unfortunate. But, so we create this, our brain creates our thoughts, our thoughts create our brain, we can actually see this on brain scans and all of these recognizes all the same.

Some of the best evidence for that came out just as I was sending the book out, for example what happens to the visual cortex, which is this region that processes visual information - actually the one particular region that's the first region that handles the lowest level patterns in visual images, like the crossbar in a capital A or the edge of an object - what happens to that in the congenitally blind person, who's not getting any visual information? It actually gets taken over by the frontal cortex which deals with high-level language concepts like beauty and irony to help it with those high-level concepts, showing that the these low-level pattern recognizers are actually the same thing.

They are capable of handling high or low level features as the case may be it just depends on where they actually wire themselves to be in the in this hierarchy; that's why you can learn a new skill that may be wiped out in a stroke or our brain accident - you actually learn it with another region of the neocortex.

What's inside the neuron?

Ed Boyden, Neuroscientist at MIT, A new way to study the brain's invisible secrets

If you could zoom in to a neuron, and, of course, this is just our artist's rendition of it. What you would see are thousands and thousands of kinds of biomolecules, little nanoscale machines organized in complex, 3D patterns, and together they mediate those electrical pulses, those chemical exchanges that allow neurons to work together


Old age

Richard Dawkins, The Selfish Gene

Senile decay is simply a by product of the accumulation in the gene pool of late acting lethal and semi lethal genes, which have been allowed to slip through the net of natural selection simply because they are late acting…

If we wanted to increase the human lifespan, there are two general ways in which we could do it. Firstly, we could ban reproduction before a certain age, say 40. After some centuries of this the  minimum age limit would be raised 50, and so on. It is conceivable that human longevity could be pushed up to several centuries by this means. I can't imagine that anyone would seriously want to institute such a policy.

Secondly we could try to fool genes into thinking that the body they are sitting in is younger than it really is. In practice this will mean identify changes in the internal chemical environment of a body which takes place during aging. Any of these could be the cues which turn on late acting lethal genes. By stimulating the superficial chemical properties of your body it may be possible to prevent the turning on of late acting deleterious genes.

In the actual duration of his life, the individual ranges from the bacterium's hour to the big tree's five thousand years.

  • Julian Huxley


Eventually the inanimate world will retake our bodies and minds.

The process may not be easy. It can be a slow process that takes hours or days. But it will happen.