homeaboutarchives + tagsshopmembership!
aboutarchivesshopmembership!
aboutarchivesmembers!

kottke.org posts about biology

Body of Theseus

posted by Jason Kottke   Jun 29, 2016

How old are different parts of our bodies? Does anything stick around the entire time? The hair on our bodies lasts only a few years. Fingernails are fully replaced every six months. Your skin lasts 2-4 weeks. Even your blood and bones regenerate every so often. There’s at least one part of your body with lasts the whole time you’re alive, which I found somewhat surprising. See the ship of Theseus paradox.

The ship wherein Theseus and the youth of Athens returned from Crete had thirty oars, and was preserved by the Athenians down even to the time of Demetrius Phalereus, for they took away the old planks as they decayed, putting in new and stronger timber in their places, in so much that this ship became a standing example among the philosophers, for the logical question of things that grow; one side holding that the ship remained the same, and the other contending that it was not the same.

How do we know the lifespans of different cells in the body? Carbon-14 levels from nuclear testing done in the 50s and 60s.

Analysis of growth rings from pine trees in Sweden shows that the proliferation of atomic tests in the 1950s and 1960s led to an explosion in levels of atmospheric carbon 14. Now, Jonas Frisen and colleagues at the Karolinska Institute in Stockholm have taken advantage of this spike in C14 to devise a method to date the birth of human cells. Because this test can be used retrospectively, unlike many of the current methods used to detect cell proliferation, and because it does not require the ingestion of a radioactive or chemical tracer, the method can be readily applied to both in vivo and postmortem samples of human tissues.

Increasing the efficiency of photosynthesis

posted by Jason Kottke   Mar 28, 2016

Stewart Brand wrote a summary of a seminar given by Jane Langdale about how the efficiency of photosynthesis might be improved for some of the world’s plants, particularly rice.

Most plants use what’s called C3 photosynthesis to produce sugars and starch, but the process is not very efficient. Some plants, like corn and sugarcane, have evolved the capability to produce sugars and starch using the much more efficient C4 photosynthesis process. So if you could modify rice to use C4 instead of C3, yields would increase dramatically.

Rice is a C3 plant — which happens to be the staple food for half the world. If it can be converted to C4 photosynthesis, its yield would increase by 50% while using half the water. It would also be drought-resistant and need far less fertilizer.

You can read more about the efforts in developing C4 photosynthesis in Technology Review.

CRISPR, a cheap and accurate copy/paste for DNA

posted by Jason Kottke   Nov 13, 2015

Michael Specter has a truly fascinating piece in the New Yorker about CRISPR, a relatively new genetic tool for editing genes that geneticists are very excited about.

With CRISPR, scientists can change, delete, and replace genes in any animal, including us. Working mostly with mice, researchers have already deployed the tool to correct the genetic errors responsible for sickle-cell anemia, muscular dystrophy, and the fundamental defect associated with cystic fibrosis. One group has replaced a mutation that causes cataracts; another has destroyed receptors that H.I.V. uses to infiltrate our immune system.

The story has everything: the cheap copy/paste of DNA, easily editable mice, pig Hitler, “destroyer of worlds” overtones, and an incredible tale of science that could actually revolutionize (or ruin, depending on who you talk to) the world. I was shocked at how easy it is to do genetic research nowadays.

Ordering the genetic parts required to tailor DNA isn’t as easy as buying a pair of shoes from Zappos, but it seems to be headed in that direction. Yan turned on the computer at his lab station and navigated to an order form for a company called Integrated DNA Technologies, which synthesizes biological parts. “It takes orders online, so if I want a particular sequence I can have it here in a day or two,” he said. That is not unusual. Researchers can now order online almost any biological component, including DNA, RNA, and the chemicals necessary to use them. One can buy the parts required to assemble a working version of the polio virus (it’s been done) or genes that, when put together properly, can make feces smell like wintergreen. In Cambridge, I.D.T. often makes same-day deliveries. Another organization, Addgene, was established, more than a decade ago, as a nonprofit repository that houses tens of thousands of ready-made sequences, including nearly every guide used to edit genes with CRISPR. When researchers at the Broad, and at many other institutions, create a new guide, they typically donate a copy to Addgene.

And CRISPR in particular has quickened the pace. A scientist studying lung cancer mutations said of her research:

“In the past, this would have taken the field a decade, and would have required a consortium,” Platt said. “With CRISPR, it took me four months to do it by myself.”

Also recommended: Radiolab’s podcast on CRISPR from back in June.

Scaling laws and the speed of animals

posted by Jason Kottke   Oct 19, 2015

Animal Speed Scaling

A recent paper found that the time it takes for an animal to move the length of its own body is largely independent of mass. This appears to hold from tiny bacteria on up to whales — that’s more than 20 orders of magnitude of mass. The paper’s argument as to why this happens relies on scaling laws. Alex Klotz explains.

A well-known example is the Square-Cube Law, dating back to Galileo and described quite well in the Haldane essay, On Being the Right Size. The Square-Cube Law essentially states that if something, be it a chair or a person or whatever, were made twice as tall, twice as wide, and twice as deep, its volume and mass would increase by a factor of eight, but its ability to support that mass, its cross sectional area, would only increase by a factor of four. This means as things get bigger, their own weight becomes more significant compared to their strength (ants can carry 50 times their own weight, squirrels can run up trees, and humans can do pullups).

Another example is terminal velocity: the drag force depends on the cross-sectional area, which (assuming a spherical cow) goes as the square of radius (or the two-thirds power of mass), while the weight depends on the volume, proportional to the cube of radius or the first power of mass. As Haldane graphically puts it

“You can drop a mouse down a thousand-yard mine shaft; and, on arriving at the bottom, it gets a slight shock and walks away, provided that the ground is fairly soft. A rat is killed, a man is broken, a horse splashes.”

Scaling laws also come into play in determining the limits of the size of animals: The Biology of B-Movie Monsters.

When the Incredible Shrinking Man stops shrinking, he is about an inch tall, down by a factor of about 70 in linear dimensions. Thus, the surface area of his body, through which he loses heat, has decreased by a factor of 70 x 70 or about 5,000 times, but the mass of his body, which generates the heat, has decreased by 70 x 70 x 70 or 350,000 times. He’s clearly going to have a hard time maintaining his body temperature (even though his clothes are now conveniently shrinking with him) unless his metabolic rate increases drastically.

Luckily, his lung area has only decreased by 5,000-fold, so he can get the relatively larger supply of oxygen he needs, but he’s going to have to supply his body with much more fuel; like a shrew, he’ll probably have to eat his own weight daily just to stay alive. He’ll also have to give up sleeping and eat 24 hours a day or risk starving before he wakes up in the morning (unless he can learn the trick used by hummingbirds of lowering their body temperatures while they sleep).

Mother Nature invented the gear

posted by Jason Kottke   Sep 23, 2015

Nature Gears

Scientists have discovered that an insect has evolved something like a gearbox to coordinate its leg movements while jumping. That’s right, nature invented mechanical gears before man got around to it.

The gears in the Issus hind-leg bear remarkable engineering resemblance to those found on every bicycle and inside every car gear-box.

Each gear tooth has a rounded corner at the point it connects to the gear strip; a feature identical to man-made gears such as bike gears — essentially a shock-absorbing mechanism to stop teeth from shearing off.

The gear teeth on the opposing hind-legs lock together like those in a car gear-box, ensuring almost complete synchronicity in leg movement — the legs always move within 30 ‘microseconds’ of each other, with one microsecond equal to a millionth of a second.

This is critical for the powerful jumps that are this insect’s primary mode of transport, as even minuscule discrepancies in synchronisation between the velocities of its legs at the point of propulsion would result in “yaw rotation” — causing the Issus to spin hopelessly out of control.

“This precise synchronisation would be impossible to achieve through a nervous system, as neural impulses would take far too long for the extraordinarily tight coordination required,” said lead author Professor Malcolm Burrows, from Cambridge’s Department of Zoology.

Tree of 40 Fruit

posted by Jason Kottke   Jul 24, 2015

Artist Sam Van Aken is using grafting to create trees that bear 40 different kinds of fruit. National Geographic recently featured Van Aken’s Tree of 40 Fruit project:

The grafting process involves slicing a bit of a branch with a bud from a tree of one of the varieties and inserting it into a slit in a branch on the “working tree,” then wrapping the wound with tape until it heals and the bud starts to grow into a new branch. Over several years he adds slices of branches from other varieties to the working tree. In the spring the “Tree of 40 Fruit” has blossoms in many hues of pink and purple, and in the summer it begins to bear the fruits in sequence — Van Aken says it’s both a work of art and a time line of the varieties’ blossoming and fruiting. He’s created more than a dozen of the trees that have been planted at sites such as museums around the U.S., which he sees as a way to spread diversity on a small scale.

(via colossal)

Copy and paste, but for DNA

posted by Jason Kottke   Jul 22, 2015

No hunger. No pollution. No disease. Wired’s Amy Maxmen welcomes you to the age of copy and paste DNA editing and the end of life as we know it.

Genome editing started with just a few big labs putting in lots of effort, trying something 1,000 times for one or two successes. Now it’s something that someone with a BS and a couple thousand dollars’ worth of equipment can do. What was impractical is now almost everyday. That’s a big deal.

[I recently listened to Radiolab’s show on Crispr. Recommended. -jkottke]

Bacterial handprint

posted by Jason Kottke   Jun 08, 2015

Tasha Sturm, a lab technician at Cabrillo College, had her 8-year-old son put his handprint on a prepared petri dish and then incubated it for several days. This was the result:

Bacteria Handprint

If you’ll excuse me, I have to go wash my hands about 4,000 times. Bacteria is cooooool though:

Bacteria Handprint Closeup

(via colossal)

Superwolves, pizzly bears, emerging hybrid species, and climate change

posted by Jason Kottke   Jun 04, 2015

Because of climate change and other activities caused by humans (invasive species, habitat loss), hybridization of species is resulting in things like super-sized coyotes, pizzly bears (grizzly/polar bear hybrids), and other animals that may not be ideally suited to survive.

Some scientists and conservationists see the coywolf as a nightmare of the Anthropocene — a poster child of mongrelization as plants and animals reshuffle in response to habitat loss, climate change and invasive species. Golden-winged warblers increasingly cross with blue-winged warblers in the U.S. Northeast and eastern Canada. Southern flying squirrels hybridize with northern flying squirrels as the southern species presses northward in Ontario. Polar bears mate with grizzlies in the Canadian Arctic along the Beaufort Sea to produce “pizzly bears.”

All of this interbreeding upsets the conventional notion of species as discrete, inviolable entities. Moreover, some scientists and conservationists warn that hybridization will degrade biodiversity as unusual species are lost to genetic homogenization.

Partly scientists fear hybrids will be less fit than organisms that have evolved in place over eons. And often that is true, but the problem solves itself over time as hybrids lose out in the competitive race for survival.

Teaching evolution to religious students

posted by Jason Kottke   Mar 27, 2015

James Krupa teaches a mandatory biology class at the University of Kentucky and some students have a difficult time because Krupa refuses to shy away from evolution.

Rarely do I have a Kentucky student who learned about human evolution in high school biology. Those who did usually attended high schools in large urban centers like Louisville or Lexington. Given how easily it can provoke parents, the teaching of human evolution is a rarity in high school, so much so in Kentucky that it startled me when I first arrived.

The story of our evolutionary history captivates many of my students, while infuriating some. During one lecture, a student stood up in the back row and shouted the length of the auditorium that Darwin denounced evolution on his deathbed — a myth intentionally spread by creationists. The student then made it known that everything I was teaching was a lie and stomped out of the auditorium, slamming the door behind him. A few years later during the same lecture, another student also shouted out from the back row that I was lying. She said that no transitional fossil forms had ever been found — despite my having shared images of many transitional forms during the semester. Many of her fellow students were shocked by her combativeness, particularly when she stormed out, also slamming the door behind her. Most semesters, a significant number of students abruptly leave as soon as they realize the topic is human evolution.

I personally don’t understand the compatibility of evolutionary biology and Christianity Krupa emphasizes in his class, but I guess it helps to meet people halfway?

God, Darwin, and biology class

posted by Jason Kottke   Oct 01, 2014

Every year, evolutionary biologist and professor David Barash gives his students The Talk about how evolution and religion do and do not get along.

It’s irresponsible to teach biology without evolution, and yet many students worry about reconciling their beliefs with evolutionary science. Just as many Americans don’t grasp the fact that evolution is not merely a “theory,” but the underpinning of all biological science, a substantial minority of my students are troubled to discover that their beliefs conflict with the course material.

Until recently, I had pretty much ignored such discomfort, assuming that it was their problem, not mine. Teaching biology without evolution would be like teaching chemistry without molecules, or physics without mass and energy. But instead of students’ growing more comfortable with the tension between evolution and religion over time, the opposite seems to have happened. Thus, The Talk.

This is the sort of thing Barash talks about:

The more we know of evolution, the more unavoidable is the conclusion that living things, including human beings, are produced by a natural, totally amoral process, with no indication of a benevolent, controlling creator.

(via @TomJunod)

A Disappearing Planet

posted by Jason Kottke   Jul 15, 2014

From ProPublica, an alarming series of graphs and charts on animal extinction: A Disappearing Planet.

Animal species are going extinct anywhere from 100 to 1,000 times the rates that would be expected under natural conditions. According to Elizabeth Kolbert’s The Sixth Extinction and other recent studies, the increase results from a variety of human-caused effects including climate change, habitat destruction, and species displacement. Today’s extinction rates rival those during the mass extinction event that wiped out the dinosaurs 65 million years ago.

(via @SrikarDR)

The leaf that hates water

posted by Jason Kottke   Jun 20, 2014

Aatish Bhatia noticed a plant in his backyard whose leaves naturally repelled water. He took a sample to a friend who had access to a high-speed camera and an electron microscope to investigate what made the leaves so hydrophobic.

But how does a leaf become superhydrophobic? The trick to this, Janine explained, is that the water isn’t really sitting on the surface. A superhydrophobic surface is a little like a bed of nails. The nails touch the water, but there are gaps in between them. So there’s fewer points of contact, which means the surface can’t tug on the water as much, and so the drop stays round.

The leaf is so water repellant that drops of water bounce right off of it:

Immigrant life on Mars

posted by Jason Kottke   May 20, 2014

If there wasn’t life on Mars before, there might be now. Before NASA sent Curiosity to Mars, it was thoroughly cleaned of all traces of contaminants. But swabs of rover’s surfaces taken before it was sent to Mars have revealed 377 different strains of bacteria that potentially could have made the trip. Some of them may have even survived.

A study that identified 377 strains found that a surprising number resist extreme temperatures and damage caused by ultraviolet-C radiation, the most potentially harmful type. The results, presented today at the annual meeting of the American Society for Microbiology, are a first step towards elucidating how certain bacteria might survive decontamination and space flight.

The anternet

posted by Jason Kottke   Apr 04, 2014

Researchers at Stanford have observed that foraging harvester ants act like TCP/IP packets, so much so that they’re calling the ants’ behavior “the anternet”.

Transmission Control Protocol, or TCP, is an algorithm that manages data congestion on the Internet, and as such was integral in allowing the early web to scale up from a few dozen nodes to the billions in use today. Here’s how it works: As a source, A, transfers a file to a destination, B, the file is broken into numbered packets. When B receives each packet, it sends an acknowledgment, or an ack, to A, that the packet arrived.

This feedback loop allows TCP to run congestion avoidance: If acks return at a slower rate than the data was sent out, that indicates that there is little bandwidth available, and the source throttles data transmission down accordingly. If acks return quickly, the source boosts its transmission speed. The process determines how much bandwidth is available and throttles data transmission accordingly.

It turns out that harvester ants (Pogonomyrmex barbatus) behave nearly the same way when searching for food. Gordon has found that the rate at which harvester ants — which forage for seeds as individuals — leave the nest to search for food corresponds to food availability.

A forager won’t return to the nest until it finds food. If seeds are plentiful, foragers return faster, and more ants leave the nest to forage. If, however, ants begin returning empty handed, the search is slowed, and perhaps called off.

(via wordspy)

Neil deGrasse Tyson explains evolution

posted by Jason Kottke   Mar 23, 2014

The reboot of Cosmos has been solid but not spectacular so far, but the second episode contains as solid and clear an explanation of evolution as I’ve ever seen.

Even if evolution clashes with your world view, this is worth watching if only to understand what you’re aligned against (per Bret Victor’s advice). The third episode airs on Fox tonight and is about the creation of the scientific method.

There are lots of fish in the sea

posted by Jason Kottke   Mar 05, 2014

A group of marine biologists that has been recently studying mesopelagic fish (“fish that live between 100 and 1000m below the surface”) believes that 95% of fish biomass is unknown to humans. Marine dark matter. The problem lies with how fish have traditionally been counted and the enhanced visual and pressure senses of these fish.

He says most mesopelagic species tend to feed near the surface at night, and move to deeper layers in the daytime to avoid birds.

They have large eyes to see in the dim light, and also enhanced pressure-sensitivity.

“They are able to detect nets from at least five metres and avoid them,” he says.

“Because the fish are very skilled at avoiding nets, every previous attempt to quantify them in terms of biomass that fishing nets have delivered are very low estimates.

“So instead of different nets what we used were acoustics… sonar and echo sounders.”

A not-so-difficult prediction to make is that humans will find a way to catch these wary creatures, we’ll eat most of them, and then we’ll be back to where we are now: the world’s oceans running low on fish. (via @daveg)

Plant intelligence

posted by Jason Kottke   Dec 17, 2013

Plants eat light, grow almost everywhere on Earth, and make up 99% of the planet’s biomass. But do what extent do plants think? Or feel? Michael Pollan tackles the question of plant intelligence in a thought-provoking article for the New Yorker (sadly behind their paywall).

Indeed, many of the most impressive capabilities of plants can be traced to their unique existential predicament as beings rooted to the ground and therefore unable to pick up and move when they need something or when conditions turn unfavorable. The “sessile life style” as plant biologists term it, calls for an extensive and nuanced understanding of one’s immediate environment, since the plant has to find everything it needs, and has to defend itself, while remaining fixed in place. A highly developed sensory apparatus is required to locate food and identify threats. Plants have evolved between fifteen and twenty different senses, including analogues of our five: smell and taste (they sense and respond to chemicals in the air or on their bodies); sight (they react differently to various wavelengths of light as well as to shadow); touch (a vine or root “knows” when it encounters a solid object); and, it has been discovered, sound.

In a recent experiment, Heidi Appel, a chemical ecologist at the University of Missouri, found that, when she played a recording of a caterpillar chomping a leaf for a plant that hadn’t been touched, the sound primed the the plant’s genetic machinery to produce defense chemicals. Another experiment, dome in Mancuso’s lab and not yet published, found that plant roots would seek out a buried pipe through which water was flowing even if the exterior of the pipe was dry, which suggested that plants somehow “hear” the sound of flowing water.

One of the researchers featured in the article, Stefano Mancuso, has a TED talk available in which he outlines his case for plant intelligence:

The article also discusses if plants have feelings. If so, should we feel bad that our wifi routers might kill plants?

Update: Mancuso and Alessandra Viola have collaborated on a new book about the intelligence of plants, Brilliant Green: The Surprising History and Science of Plant Intelligence.

Dog breed “improvement”

posted by Jason Kottke   Dec 04, 2013

From a blog about the science of dogs, a comparison of photos of purebred dogs from 1915 to those of today. You can see how much the dogs have changed in just under 100 years, in some cases for the worse. For instance, the difference in the Bull Terrier (aka the Spuds MacKenzie dog) is marked and a bit disturbing:

Bull Terrier

Pure breeding has also introduced medical problems for some breeds.

The English bulldog has come to symbolize all that is wrong with the dog fancy and not without good reason; they suffer from almost every possible disease. A 2004 survey by the Kennel Club found that they die at the median age of 6.25 years (n=180). There really is no such thing as a healthy bulldog. The bulldog’s monstrous proportions makes them virtually incapable of mating or birthing without medical intervention.

(via @mulegirl)

Iconic insects are disappearing

posted by Jason Kottke   Nov 25, 2013

The monarchs are late. Usually by the 1st of November, the forests of central Mexico are swarming with them. Last year, they came in record low numbers, only 60 million. This year? A week late and only 3 million. And this happening to insects across the spectrum.

A big part of it is the way the United States farms. As the price of corn has soared in recent years, driven by federal subsidies for biofuels, farmers have expanded their fields. That has meant plowing every scrap of earth that can grow a corn plant, including millions of acres of land once reserved in a federal program for conservation purposes.

Another major cause is farming with Roundup, a herbicide that kills virtually all plants except crops that are genetically modified to survive it.

As a result, millions of acres of native plants, especially milkweed, an important source of nectar for many species, and vital for monarch butterfly larvae, have been wiped out. One study showed that Iowa has lost almost 60 percent of its milkweed, and another found 90 percent was gone. “The agricultural landscape has been sterilized,” said Dr. Brower.

The Human Body

posted by Jason Kottke   Aug 16, 2013

My friends at Tinybop have released their first app, The Human Body, in which “curious kids ages 4+ can see what we’re made of and how we work, from the beating heart to gurgling guts”. Kelli Anderson did the illustrations for the app and they look amazing. Can’t wait to try this out with Ollie and Minna.

The trees of Chernobyl

posted by Jason Kottke   Aug 09, 2013

This is what the trees look like near Chernobyl when you cut them down. It’s a biiiit tricky but see if you can spot when the nuclear plant disaster happened…

Chernobyl trees

Not surprisingly, researchers have found evidence that the radiation has affected the growth of trees near the accident site. From the paper:

Mean growth rate was severely depressed and more variable in 1987-1989 and several other subsequent years, following the nuclear accident in April 1986 compared to the situation before 1986. The higher frequency of years with poor growth after 1986 was not caused by elevated temperature, drought or their interactions with background radiation. Elevated temperatures suppressed individual growth rates in particular years. Finally, the negative effects of radioactive contaminants were particularly pronounced in smaller trees. These findings suggest that radiation has suppressed growth rates of pines in Chernobyl, and that radiation interacts with other environmental factors and phenotypic traits of plants to influence their growth trajectories in complex ways.

Liquid mammoth blood found

posted by Jason Kottke   May 29, 2013

A mammoth recently found in Siberia was so well preserved that when researchers were chipping it out of the ice, liquid blood flowed out.

Semyon Grigoriev, chairman of the university’s Museum of Mammoths and head of the expedition, said: “The fragments of muscle tissues, which we’ve found out of the body, have a natural red colour of fresh meat. The reason for such preservation is that the lower part of the body was underlying (sic) in pure ice, and the upper part was found in the middle of tundra. We found a trunk separately from the body, which is the worst-preserved part.”

The temperature was ten degrees celsius below zero when the mammoth was found, so the discovery of liquid blood was a shock. “It can be assumed that the blood of mammoths had some cryo-protective properties,” Grigoriev said. “The blood is very dark, it was found in ice cavities below the belly and when we broke these cavities with a pick, the blood came running out.”

More photos and information here. Bring on the mammoth clones, John Hammond. (via @carlzimmer)

Bees still dying at a fantastic rate

posted by Jason Kottke   Apr 01, 2013

Despite progress in recent years on causes and cures, colony collapse disorder has wreaked havoc on honeybee colonies across the country.

A mysterious malady that has been killing honeybees en masse for several years appears to have expanded drastically in the last year, commercial beekeepers say, wiping out 40 percent or even 50 percent of the hives needed to pollinate many of the nation’s fruits and vegetables.

Which is like, yeah, big whoop, it’s just bees, right? Except that:

The Agriculture Department says a quarter of the American diet, from apples to cherries to watermelons to onions, depends on pollination by honeybees.

Possible fossils found in meteorite fragments?

posted by Jason Kottke   Mar 11, 2013

Well, here’s something potentially interesting: researchers at Cardiff University think they have found fossils in meteorite fragments from Sri Lanka.

The most startling claims, however, are based on electron microscope images of structures within the stones (see above). Wallis and co say that one image shows a complex, thick-walled, carbon-rich microfossil about 100 micrometres across that bares similarities with a group of largely extinct marine dinoflagellate algae.

They say another image shows well-preserved flagella that are 2 micrometres in diameter and 100 micrometres long. By terrestrial standards, that’s extremely long and thin, which Wallis and co interpret as evidence of formation in a low-gravity, low-pressure environment.

Gotta take this with a massive grain of salt, but it will be interesting to see how this one plays out.

Update: One of the authors of this study holds some unusual views about life on Earth.

On May 24, 2003 The Lancet published a letter from Wickramasinghe, jointly signed by Milton Wainwright and Jayant Narlikar, in which they hypothesized that the virus that causes Severe Acute Respiratory Syndrome (SARS) could be extraterrestrial in origin and not originated from chickens.

Wickramasinghe and his mentor Fred Hoyle have also used their data to argue in favor of cosmic ancestry, and against evolution.

Like I said, big grain of salt. (thx, onno)

Does every species get a billion heartbeats per lifetime?

posted by Jason Kottke   Feb 08, 2013

There’s an assumption that because of the relationship between metabolic rates, volume, and surface area, animals get an average of one billion heartbeats out of their bodies before they expire. Turns out there’s some truth to it.

One Billion Heartbeats

As animals get bigger, from tiny shrew to huge blue whale, pulse rates slow down and life spans stretch out longer, conspiring so that the number of heartbeats during an average stay on Earth tends to be roughly the same, around a billion.

Mysteriously, these and a large variety of other phenomena change with body size according to a precise mathematical principle called “quarter-power scaling”.

It might seem that because a cat is a hundred times more massive than a mouse, its metabolic rate, the intensity with which it burns energy, would be a hundred times greater. After all, the cat has a hundred times more cells to feed.

But if this were so, the animal would quickly be consumed by a fit of spontaneous feline combustion, or at least a very bad fever. The reason: the surface area a creature uses to dissipate the heat of the metabolic fires does not grow as fast as its body mass.

To see this, consider a mouse as an approximation of a small sphere. As the sphere grows larger, to cat size, the surface area increases along two dimensions but the volume increases along three dimensions. The size of the biological radiator cannot possibly keep up with the size of the metabolic engine.

Humans and chickens are both outliers in this respect…they both live more than twice as long as their heart rates would indicate. Small dogs live about half as long.

Immortality lessons from the humble jellyfish

posted by Jason Kottke   Nov 28, 2012

Looking to live forever? You might want to take a close look at the immortal jellyfish. This death-defying creature ages, but researchers studying the jellyfish found that, instead of dying, it started “to age in reverse, growing younger and younger until it reached its earliest stage of development, at which point it began its life cycle anew.” (If beginning the life cycle anew means another trip through junior high, count me out.) From NYT Magazine: Can a Jellyfish Unlock the Secret of Immortality?

Some birds have a heads-up display compass

posted by Jason Kottke   Mar 15, 2012

Birds can detect the magnetic field of the Earth, which gives them an incredible sense of direction. Curiously, this sense of direction doesn’t work in darkness. This led scientists to discover that some birds can actually see the directions overlaid on their normal vision, like a heads-up display.

According to the new model, when a photon of light from the Sun is absorbed by a special molecule in the bird’s eye, it can cause an electron to be kicked from its normal state into an alternative location a few nanometres away. Until the electron eventually relaxes back, it creates an ‘electric dipole field’ which can augment the bird’s vision - for example altering colours or brightness.

Crucially, the alignment of the molecule compared to the Earth’s magnetic field controls the time it takes for the electron to relax back, and so controls the strength of the effect on the bird’s vision.

There are many such molecules spread throughout the eye, with different orientations. So from the patterns on top of its vision, and the change of these patterns as it moves its head, the bird learns about the direction of Earth’s magnetic field.

(via @daveg)

The human body’s microbial ecosystem

posted by Jason Kottke   Jan 27, 2012

In this transcript of a talk given to the attendees of the Joint Summits on Translational Science, Carl Zimmer highlights an important aspect of understanding the human body and how to treat its many maladies: the ecosystem of microbes.

The microbes in your body at this moment outnumber your cells by ten to one. And they come in a huge diversity of species — somewhere in the thousands, although no one has a precise count yet. By some estimates there are twenty million microbial genes in your body: about a thousand times more than the 20,000 protein-coding genes in the human genome. So the Human Genome Project was, at best, a nice start. If we really want to understand all the genes in the human body, we have a long way to go.

Now you could say “Who cares? They’re just wee animalcules.” Those wee animacules are worth caring about for many reasons. One of the most practical of those reasons is that they have a huge impact on our “own” health. Our collection of microbes-the microbiome-is like an extra organ of the human body. And while an organ like the heart has only one function, the microbiome has many.

When food comes into the gut, for example, microbes break some of them down using enzymes we lack. Sometimes the microbes and our own cells have an intimate volley, in which bacteria break down a molecule part way, our cells break it down some more, the bacteria break it down even more, and then finally we get something to eat.

Another thing that the microbiome does is manage the immune system. Certain species of resident bacteria, like Bacteroides fragilis, produce proteins that tamp down inflammation. When scientists rear mice that don’t have any germs at all, they have a very difficult time developing a normal immune system. The microbiome has to tutor the immune system in how to do its job properly. It also acts like an immune system of its own, fighting off invading microbes, and helping to heal wounds.

While the microbiome may be an important organ, it’s a peculiar one. It’s not one solid hunk of flesh. It’s an ecosystem, made up of thousands of interacting species.

Meet LUCA, our distant Earth-sized ancestor

posted by Jason Kottke   Nov 25, 2011

Here’s an interesting hypothesis: that all current life on Earth originated from a planet-wide super-organism named LUCA.

The latest results suggest LUCA was the result of early life’s fight to survive, attempts at which turned the ocean into a global genetic swap shop for hundreds of millions of years. Cells struggling to survive on their own exchanged useful parts with each other without competition — effectively creating a global mega-organism.

It was around 2.9 billion years ago that LUCA split into the three domains of life: the single-celled bacteria and archaea, and the more complex eukaryotes that gave rise to animals and plants (see timeline). It’s hard to know what happened before the split. Hardly any fossil evidence remains from this time, and any genes that date that far back are likely to have mutated beyond recognition.

(via @daveg)