Organs lifespan out of the body

Organs lifespan out of the body

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What organ can be conserved outside of the body for the longest time and still function when reimplanted?

Depends what you consider an organ. Typically though it's the cells which require the most metabolic activity which have the shortest life span. The kidney is the most of the major internal organs with up to 36 hours with liver coming second at up to 16 hours.

How Long Can Organs Stay Outside the Body Before Being Transplanted?

Depending on the organ, the time can range from a few hours to a day and a half.

When it comes to organ transplant surgery, doctors are racing against the clock — and time is not on their side.

A team of clinicians must first remove the organ from its donor, sets of gloved hands coordinating to deftly cleave tissue from the body. Doctors then prep the harvested organ for transport to its recipient, who may be hours away by plane. Once the organ reaches its destination, the transplant operation can finally commence again, surgeons must work swiftly to ensure both the patient's safety and the organ's viability.

This description may make organ transplant surgery sound like a TV drama, with medical personnel sprinting through hospital corridors carrying coolers packed with body parts. But all the rushing about raises a question that's much more important than a TV show: How long can an organ last outside the body and remain fit for transplantation?

It depends on the organ. For now, the time window can be between 4 and 36 hours. But someday, doctors hope to be able to maintain organs for weeks on end.

9 thoughts on &ldquo No, the body doesn’t just wear out as we get older. &rdquo

Hi Josh and thank you for your great blog and many insightful posts. I’ve been an avid reader for some time now.

Did you notice the recent publication of this study about biomarkers that seem to accurately predict mortality?

Would love to hear your comments. All the best, Mika

Thank you, Mika – no I wasn’t aware of this, and I’m very interested. I believe there exists the possibility that just “treating the symptom” by re-adjusting some of these blood factors may in itself be a strategy for driving down mortality. I’m going to pass this around, learn more about it, and I’ll let you know what I find.

This makes so much sense. It explains why people who have made a habit out of exercising tend to look much younger than their peers who happen to be the same age as them but are less fond of the idea of exercising. We live in such a technical world, so much so that we have developed an expectation for human beings to be some sort of machines forgetting that humans are actually living beings. I see, one cannot eliminate aging completely, there is just no getting around it, however, one can most certainly slow it down. The secret to doing so is STAYING ACTIVE ! As you have already mentioned aging is more of a self-destruction mechanism than it is a wearing out mechanism, I suppose it is safe to say that healthy eating can have just as big an impact as exercise right ? By eating healthy food we boost the functioning and the repair of the components of our bodies that tend to self-destruct, right ? I must say, this article was very interesting, as a matter of fact I’m thinking of joining a gym …

Josh: Would love to know what some of your contributors think of this product from Dr. Al Sears (not Barry Sears), who is out there hawking a telomere regeneration/rejuvenation formula. A look at the product ingredients is….interesting. I am skeptical, wonder if you and some of your contributors are for the same reason.

Thanks for sending this, George. In the ingredients list, I see a lot of expected ones – overlap with Product B. (Product B is my reference because primary data on telomerase activation is so scarce, and at least I understand how Product B was vetted, and I trust Sierra Sciences, which did the research behind it.)

Comments on specific ingredients:
Alpha Ketoglutarate is a muscle-building supplement.
N-Acetyl Cysteine is a supplement that increases glutathione levels, which I think is a good idea, though unrelated to telomerase.
I’ve seen nothing in the primary literature relating Kudzu to telomerase. The only references I’ve been able to find go back to Sears himself.
There is some literature concerning ginseng as as a telomerase inhibitor.
Stilbenes are chemical cousins of resveratrol.
Half the recommended dose (11 g) is unaccounted for in the ingredient list.
Vitamin C is the largest single ingredient, 14% of the total dosage.
Citrulline is an amino acid.
Nothing in the mix would seem to justify the price Sears is charging.

“So yes, some loss of information is inevitable over long enough times but no, this is not relevant to aging.”

Not to mention if this was true, how to explain life itself lasting for so many millions of years… every generation would eventually produce mostly deleterious mutations and only the few who mutated just at the right place to generate something either beneficial (which is rare) OR neutral (which would make the prospects for the next generation even direr) would survive. Eventually there would be not enough resources (either energy, matter or time) to generate “young youngsters” (sorry for the pun =)) before the progenitor aged itself and died.

Ever looked at an adult human lung? There is a significant amount of material that is deposited from the air we breathe into the lungs. It shows up as many black spots, and remains even after using a detergent to remove the cells. The body simply doesn’t have any mechanism to remove this material. This sort of damage occurs all over the body. Molecules and material build up that just simply cannot be expelled and it ends up causing all sorts of problems that can lead to death. Similarly, material (such as plaque) builds up naturally. The body simply can’t get rid of it. While it may be possible to engineer the body to clean up some of this material, or to prevent “self destruction”, this is quite a difficult task and it is unlikely to be successful to extend lifespan with our lifetimes… certainly yours.

I agree that there is more to aging than simply wearing out, but wearing out is a major portion of the problem. Consider also that stem cell derived replacement tissues would likely be younger tissues with greater regenerative capacity. Growing replacement parts is the most feasible and immediate route to significantly extending lifespan. Certainly, it isn’t the only solution. You can’t simply make a replacement brain. Replacement parts would nevertheless solve many medical problems that would ultimately lead to death.

-B.S. Cell and Molecular Biology
-Grad Student Biomedical Engineering
-3 years stem cell/dev bio/tissue engineering research 3 years synthetic biology research
-Been interested in aging, replacement parts, and life extension for about 15 years now. Interesting blog. I do recall coming across it several times over the years.

Do you work at SENS or something? Do you have a ‘skin in the game’ (pun intended) of aging paradigms (wear&tear vs programmed)? If not, why are you being so cruel? Hope is much more productive than doom&gloom. Technology is progressing faster and faster, our illusion of knowledge may change sooner than we think.. well, certainly mine will.

Your not making any sense . We are meant to die from organ expiration not diseases . Everyone has to die but not from diseases like heart attacks, cancer, diabetes if you eat right chemical free whole foods . Go back in biblical times in Genesis none of the great men died from diseases but from organ expiration [ organs gave out ] . So you have to die and if you don’t die from diseases then it would be your organs get weak and stop working natural causes .

What are the organs of the body?

In the human body, there are five vital organs that people need to stay alive. These are also a number of other organs that work together with these vital organs to ensure that the body is functioning well.

Keep reading to learn more about the organs of the body, the various organ systems, and some guidelines on how to maintain optimum health.

The interactive body map below shows the organs of the body and which systems they play a role in. Click on the map to learn more.

The vital organs are those that a person needs to survive. A problem with any of these organs can quickly become life threatening.

It is not possible to live without these organs. That said, in the case of the paired kidneys and lungs, a person can live without one of the pair.

The sections below will look at the five vital organs in more detail.


The brain is the body’s control center. It forms the core of the central nervous system by creating, sending, and processing nerve impulses, thoughts, emotions, physical sensations, and more.

The skull encloses the brain, protecting it from injury.

Neurologists are doctors who study the nervous system. Over time, they have identified numerous parts of the brain, including systems within the brain that function similarly to independent organs.

The brain is made up of three main subparts: the cerebrum, the cerebellum, and the brainstem. Within these areas, there are several key components of the brain that, together with the spinal cord, comprise the central nervous system.

The major areas of the central nervous system include:

  • The medulla: This is the lowest part of the brainstem. It helps control heart and lung function.
  • The pons: Located above the medulla in the brainstem, this area helps control eye and facial movement.
  • The spinal cord: Extended from the base of the brain and down the center of the back, the spinal cord helps with many automatic functions, such as reflexes. It also sends messages to and from the brain.
  • The parietal lobe: Situated in the middle of the brain, the parietal lobe supports the identification of objects and spatial reasoning. It also plays a role in interpreting pain and touch signals.
  • The frontal lobe: The frontal lobe, which is located in the front of the head, is the largest section of the brain. It plays a role in many conscious functions, including personality and movement. It also helps the brain interpret smells.
  • The occipital lobes: Positioned near the back of the brain, the occipital lobe primarily interprets vision signals.
  • The temporal lobes: Located on either side of the brain, the temporal lobes play a role in numerous functions, including speech, scent recognition, and short-term memory.

The brain’s two halves are called the right and left hemispheres. The corpus callosum connects these two hemispheres.


The heart is the most important organ of the circulatory system, which helps deliver blood to the body. It works with the lungs to add oxygen to blood and pump this freshly oxygenated blood through the blood vessels and around the body.

The heart also has an electrical system within. Electrical impulses within the heart help ensure that it beats with a consistent rhythm and proper rate.

The heart rate increases when the body needs more blood, such as during intense exercise. It decreases during times of rest.

The heart has four chambers. The two upper chambers are called atria, and the two lower chambers are called ventricles.

Blood flows into the right atrium from the veins of the heart and body (except the lungs), then it flows into the right ventricle. From there, it flows into the pulmonary artery, which has branches that reach the lungs. The lungs then oxygenate the blood.

This oxygenated blood travels from the lungs, through pulmonary veins that lead back and join together, to the left atrium, and then through the left ventricle. From there, the heart pumps the blood through an artery that branches to distribute blood to itself and other body parts (except the lungs).

The heart has four valves that ensure that blood flows in the right direction. The heart valves are:

  • the tricuspid valve
  • the pulmonary valve
  • the mitral valve
  • the aortic valve


The lungs work with the heart to oxygenate blood. They do this by filtering the air a person breathes, then removing excess carbon dioxide in exchange for oxygen.

Several parts of the lungs help the body take in air, filter it, and then oxygenate the blood. These are:

  • The left and right bronchi: The trachea splits into these tubes, which extend into the lungs and have branches. These smaller bronchi split into even smaller tubes called bronchioles.
  • The alveoli: The alveoli are tiny air sacs at the end of the bronchioles. They work like balloons, expanding when a person inhales and contracting when they exhale.
  • The blood vessels: There are numerous blood vessels in the lungs for carrying blood to and from the heart.

With extensive medical care, a person can live without one lung, but they cannot survive with no lungs.

The diaphragm, which is a thick band of muscle directly under the lungs, helps the lungs expand and contract when a person breathes.


The liver is the most important organ of the metabolic system. It helps convert nutrients into usable substances, detoxifies certain substances, and filters blood coming from the digestive tract through a vein before it joins venous blood flow from other parts of the body. Oxygenated blood reaches the liver via an artery.

The majority of liver mass is in the upper right side of the abdomen, just under the rib cage.

The liver plays many roles in digestion and filtering the blood, including:

  • producing bile
  • helping the body filter out toxic substances, including alcohol, drugs, and harmful metabolites
  • regulating blood levels of various important chemicals, including amino acids
  • making cholesterol
  • removing some bacteria from the blood
  • making some immune factors
  • clearing bilirubin from the blood
  • regulating the process of blood clotting, so that a person does not bleed too much and does not develop dangerous blood clots

The liver partners with the gallbladder to deliver bile to the small intestine. The liver pours bile into the gallbladder, which then stores and later releases the bile when the body needs it to help with digestion.

A person can live without portions of their liver, but the liver itself is vital for life.


The kidneys are a pair of bean shaped organs, and each is about the size of a fist. They are located on either side of the back, protected inside of the lower part of the rib cage. They help filter blood and remove waste from the body.

Blood flows from the renal artery into the kidneys. Each kidney contains about a million tiny units for filtration known as nephrons. They help filter waste to the urine and then return the filtered blood to the body through the renal vein.

The kidneys also produce urine when they remove waste from the blood. Urine flows out of the kidneys through the ureters, then down to the urinary bladder.

A person can live with just one kidney. When a person is experiencing severe kidney failure, dialysis can filter the blood until they get a kidney transplant or their kidney recovers some function. Some people need to undergo hemodialysis long term.

Felt Human Organs

Don’t want to make your own? Grab these cool felt human organs.

How does the body create urine to expel waste?

See which organs play a major role in the endocrine system.

What are these systems made of? Different organs with very specific jobs but each of those organs is made up of cells.

Color the organelles in the cell so you can label them. What does each one do?

More Science Activities for Kids

Want more anatomy activities? Try our bundle – Anatomy for Kids! Following this hands-on anatomy unit study, children get to build life-size anatomy models of themselves, play with anatomy dress-up dolls, complete anatomy puzzles, build organs from play-dough, colour, draw and play games! The anatomy bundle is full of creative activities for young scientists.

Animal Trivia for kids is a printable game that introduces players to the amazing animal diversity on our planet. Challenge each other to a battle of wits and learn together!

Complete animal habitat projects with LEGO bricks. With our printable pack, you can study eight principle biomes, design them and play with them!

When you make your own anatomy model, we’d be delighted to see it! Tag us on facebook or instagram (@adventureinabox).

DNA repair: a cause of aging

Genome: the genome is the sum of the genetic information of a person or species. The information is mostly stored in the cell’s nucleus, and the genome is the map to build the whole organism. It contains all the information that allow our cells to build and maintain our bodies, which is stored as DNA. Every fraction of DNA represents a specific characteristic of an individual (a gene). The human genome contains between 25,000 and 30,000 genes. The DNA contained in the nucleus is wrapped around proteins called histones. It is the combination of histones and DNA that makes up chromosomes. The chromosomes contain all of our genetic information and are replicated with every cell division in order to transmit the information to the newly created daughter cell.

Throughout life, our cells get to divide a great number of times. In older people, genetic anomalies can be observed [1]. Those mutations mostly happen during DNA replication and can affect important genes, or cause genetic transcription issues. These mutations cause the cell to malfunction and can affect the remaining tissue if the cell isn’t eliminated through apoptosis (cellular death) or through senescence (degradation of the cell’s functions).

Recent studies have shown that the DNA repair system could play a part in the aging process. A control system is in place to repair DNA that was modified during replication. The system uses proteins and enzymes in order to reprogram the modified cell. On top of correcting the corrupted DNA, these proteins have other effects, such as NAD+ consumption (see definition) and links to the mitochondrial functions [2]. Studies have shown that more DNA-repairing proteins (PARP) can be found in aged subjects [3]. Too much activation leads to the exhaustion of NAD+ stocks (although is it necessary to activate many NAD-dependent molecules such as sirtuins), and can induce cell apoptosis (death of the cell) if the DNA damage is too serious [4]. With age, there is an increase in the number of dead cells and in senescence, which can explain the degradation of organs.

DNA strand

Another part of the cell control system can have a negative effect over time: the protein P53 is responsible for elimination of carcinogenic cells, and allows to prolong the life of the organs by preventing the development of cancerous cells. However, the more that protein gets activated, the more it accelerates the aging process. Too many cells get destroyed and the tissues lose homogeneity[4]. Activation of the PARP enzyme can induce overexpression of the protein P53. [5]

Both processes are beneficial to the body, but as the body ages, their action becomes detrimental.

One interpretation is that the damage sustained by the DNA can grow exponentially because of the mutations that can affect the genes responsible for replication, or the DNA repair system. PARP activation protects the body from DNA damage within the cells, and is linked to the exhaustion of NAD+ in cells. The coenzyme NAD+ is needed to activate all NAD-dependent enzymes (sirtuins). That exhaustion causes cells to dysfunction.

Life Cycle, Human

The human life cycle begins at fertilization, when an egg cell inside a woman and a sperm cell from a man fuse to form a one-celled zygote . Over the next few days, the single, large cell divides many times to form a hollow ball of smaller cells. On the sixth day after fertilization, this hollow ball burrows into the wall of the mother's uterus, or womb. The cells then form three layers that fold and bend into the more complex shape of an early embryo. Gradually, the cells begin to become different from one another, forming, for example, the nervous system and the circulatory system.

On the twenty-second day after fertilization, a simple tubelike heart begins to beat. The embryo has no other working organs: the first brain activity will not begin for five more months. But in just one more month, all the major organs will have formed in miniature, including tiny eyes and ears, liver, and kidneys. These organs do not work, but they are there. Once all the organs have formed, the individual is called a fetus. During the fetal period, all the organs begin to mature. Cells from the embryo and its mother also combine to form a placenta, an organ in the uterus that connects the embryo to the mother's blood supply.

Biologists count the days of development starting from fertilization, but medical doctors count from the first day from the last menstrual period, which is about two weeks before fertilization. So, where a biologist would say the embryo's heart begins beating at three weeks, a medical doctor would say the heart begins beating at five weeks. The total time from fertilization to birth is about thirty-eight weeks. At the end of the embryonic period (eight weeks), the embryo is about 30 millimeters (just over 1 inch) long. Between three months and nine months the fetus grows until it is about twenty times as long.

At birth, the muscles of the mother's uterus begin to contract and push the baby out through the vagina. This process is called "labor," because it is hard work and can take a long time. In the first stage, called dilation , the lower end of the uterus, called the cervix, opens to about the same diameter as the baby's head. Dilation takes from eight to twenty-four hours in a woman who has never given birth before. In the second stage, called expulsion, the baby is pushed out of the uterus, into the vagina, and out of the body. Expulsion takes about half an hour the first time a woman gives birth. In the third stage, the mother expels the placenta. A few hours later, her uterus begins to contract to a smaller size, and her breasts begin to synthesize milk.

Within a few minutes after the baby is born, it may begin to nurse. The mother and baby can nurse as many months as they like. Women in traditional cultures may nurse for several years, but most American women nurse for about six months. Human milk is better for babies than bottled formula or other alternatives. For example, human milk contains antibodies and immune cells that protect the infant from infections. Babies who eat solid foods too early seem to be more subject to allergies later in life.

During infancy, between birth and one year, the brain continues to develop and grow. In this respect, human infants differ from other primate infants, whose brains stop growing at birth. Indeed, the human brain continues to grow new neurons until the child is two years old.

Infants' bodies also grow and develop rapidly, though not as fast as the brain. A one-year-old human typically weighs three times what he or she did at birth, has several teeth, and has begun to walk. At about two years, most humans begin to speak in sentences. During childhood (one to thirteen years), humans develop their first set of teeth, lose them, and begin to develop a second, or adult, set of teeth.

Between eleven and thirteen, children enter puberty. After puberty, adolescent humans can produce viable eggs and sperm, and many girls can carry a baby to term. Girls and boys develop secondary sexual characteristics, including body hair, deeper voices (especially in boys), breasts (in girls), and larger external genitalia (in both girls and boys). Boys begin to produce fertile sperm for the first time. Girls begin a monthly cycle of ovulation (releasing eggs) and menstruation (shedding the uterine lining) that will continue until they are in their fifties.

The changes that adolescents go through are so dramatic that many biologists compare puberty to the metamorphosis that tadpoles go through when they become frogs. For example, before puberty, boys and girls have the same amount of muscle mass, bone mass, and body fat. After puberty, men have 1.5 times as much bone and muscle mass as women, and women have twice as much body fat as men. Changes in the brain and in behavior also occur. By their early to mid-twenties, humans have reached their adult size. The bones stop growing and the brain is fully mature.

Humans in their twenties are in their peak reproductive years. Women who reproduce at this time have the least-complicated pregnancies. For males, the late teens and twenties are a time of peak death rates from accidents and other misfortunes, most likely due to the behavioral effects of high testosterone levels.

After age thirty, human beings begin to age noticeably. Hormone levels decline, skin becomes thinner and less flexible, gray hair and wrinkles appear, muscle mass decreases, bones lose calcium, blood vessels stiffen, and brain cells begin to die. Starting around age thirty-five, humans may lose one hundred thousand brain cells per day. The ears, the eyes, and other sensory organs also become less sensitive. Women gradually stop ovulating and menstruating in their fifties, and men experience a slow decline in testosterone levels that is most often noticed in the fifties.

Why people age is not completely understood. But some aspects of aging result when cells can no longer divide and replace themselves as they die. Some cells also begin to lose their ability to repair mistakes in the DNA (deoxyribonucleic acid), which leads to abnormalities, including, sometimes, cancer. Another cause of aging may be destructive molecular fragments known as free radicals, which damage DNA, proteins , and lipids . The average American woman lives seventy-nine years, and the average man lives seventy-two years. But despite advances in health care and healthier lifestyles, few people live beyond age one hundred.

Get introduced to the major organ systems of the human body with gamification. Play this anatomy game for the organs and quickly memorize all the organ names and locations in the body.

The internal organs practiced are:

Lung, liver, heart, large intestine, small intestine, gallbladder, brain, appendix, stomach, pancreas, gall bladder, esophagus, spleen, kidney, larynx, thyroid gland.

Level 1 to 3

Image markups - At each level, you can see a picture with up to 10 questions. Each question should be answered by selecting the correct dot in the image. Only one of the dots is correct. It is for you to find the right dot in the picture. If your guess is wrong, you may try again, but you will not get any knowledge points for that round.

Level 4

Letter grid - At each level, you get up to ten words to find on a board consisting of letters in a grid. You'll click and drag with the mouse or use your finger and swipe until the sought word is found. You may find words in any order you want. Once you find all the words you get a knowledge point. If you get stuck, you may click on the Give up button. The game creator has chosen how the words should be placed on the board, which can be readable words, one line words, curved words or unreadable words. In addition, the game creator may have chosen that the list with the requested words should have shuffled letters. Then you should start by identifying the correct word, which you then should mark on the board as described above. Sometimes clues are shown instead of the words in the list and sometimes there's only masked letters in the list.

Level 5 to 6

Multiple choice - On each level you will get up to ten questions with or without images, video and audio tracks. For each question you will get two or three possible answers. Only one of these is correct. It's up to you to find the right answer. If you guess incorrectly, you may try again, but you will not get any knowledge points for that round.

Level 7

Memory - Find the two cards that belongs to each other. Sometimes it's the same card and sometimes there are different cards that belong together, which depends on how this memory was created. The game is finished when all card pairs have been found and the memory has no more cards left.

Level 8

Questions with text answers - On each level you will get up to ten questions with or without images, videos and audio files. You must type the correct answer by yourself. If you make a mistake, you get to try again until you find the searched word or phrase. Once you figure out the correct answer, you will get knowledge points. If you're having trouble figuring out the correct answer, you can click on the button labelled 'Give Up'. It will reveal the correct answer, but you will not get any knowledge points for that round.

The game creator may have allowed you to get feedback on your typing. If so, the textbox, where you type your answer, will turn red or green as you type. The game creator has also decided if the answer is case sensitive, ie if it is important that you type in correct case. Both of these settings may vary between the levels, which you'll be noticed of when you play a level. You may misspell a maximum of three times per question. On your fourth misspelling, the question will be classified as incorrectly answered.

Level 9

Guess word - Here you have to figure out the hidden word or sentence by choosing letters in the alphabet. If the chosen letter is in the requested word, the letter is shown in all the correct places in the letter slots. If the letter is not in the word, either a balloon bursts or a heart is broken, depending on game settings by the creator. If you manage to guess the right letters and find the word before you run out of balloons / hearts, you've won the game round. Sometimes there are clues that may help you guess the word and sometimes you need to find the word within a certain amount of time.

What's the Least Useful Body Part?

We’re all familiar with the flashy, big-ticket organs: the heart, the brain, the lungs. Their celebrity often obscures the work—humbler, less heroic, but often no less essential to the maintenance of a life—performed by those organs only doctors know about: the body’s back-up players, pulsing and pumping in relative obscurity. Not to mention the mid-tier organs, like the gallbladder, whose functions most of us only dimly comprehend, unless—or until—they start acting up.

Still, however crucial some of these organs and other body parts might be, there is a hierarchy—which means, inevitably, that one of them is at the bottom, expendable in a pinch. To find out which piece of the body that happens to be—what, in other words, the least essential chunk is—for this week’s Giz Asks we reached out to a number of anatomists and evolutionary biologists.

Elizabeth Brainerd

Professor of Biology and Medical Science at Brown University and head of the Brainerd Lab, which integrates studies of anatomy, physiology and biomechanics toward a more complete understanding of vertebrate morphology and evolution

The first organ I’d give up would be the gallbladder. Gallbladder removal (due to gallstones) is one of the most common surgeries, and people do fine without a gallbladder. The liver makes bile, and bile can drain directly into the intestine to help digest fats. The gallbladder acts as extra storage space for bile and it contracts to add more bile when we eat a particularly fatty meal. People without a gallbladder have to be careful not to eat too much fat at one time or they may experience abdominal pain, nausea and vomiting.

After that I’d go with the spleen, which is part of the lymphatic system of the body and helps fight infections. Sometimes it gets damaged, such as in a car accident, and has to be removed. People do well after spleen removal, but may be more susceptible to serious infections.

Next: One kidney. Healthy people do not need two kidneys.

Lastly, the left lung. Lung capacity in healthy people is greater than is needed, even during exercise. The left lung is the smaller of the two, so it is more expendable. But living with only a right lung may decrease exercise capacity.

After that I begin to feel quite possessive of the remainder of my organs.

Nathan Lents

It’s hard to pick just one! The human wrist is a clunky hodgepodge of unnecessary bones. If we could design that joint from scratch, there is no way we would stick eight small, fixed, and mostly useless bones in there. We also have the stump of a tail that we could totally do without. It does nothing for us except occasionally gets injured or develops cancer.

I think my favorite useless body part is the pyramidalis muscle, which is located in our pelvic floor and attaches to the pelvis and some other connective tissue in our nether regions. What does it do? Well, when you flex this muscle, you can sort of squish the tissue in that area around pointlessly, but in monkeys and other mammals, it helps to manipulate the tail. So useless is this muscle that at least 20% of us don’t even have one and we don’t even miss it. I always enjoy telling people that, although humans and other apes don’t have tails, we still have the muscles to flex them!

David Green

Associate Professor, Anatomy, Campbell University School of Osteopathic Medicine

My mind immediately goes to a few muscles that are so tiny, they are effectively useless. In our forearm, there is a muscle called palmaris longus. It spans from the base of our arm (humerus), crosses the elbow and the wrist and inserts onto a thick band of tissue in the palm of our hand called the palmar aponeurosis. It technically can help flex our forearm at the elbow and hand at the wrist, but it is so puny—most times it is just a thin ribbon of tendon—that its contribution to these actions must be negligible. In fact, about 15% of people won’t even have it—if you flex your wrist and cup your hand, you may see two prominent tendons pop out in front of your forearm just before the wrist. On the side closer to your thumb, you should see the prominent tendon of flexor carpi radialis. If you don’t see a tendon next to it on the pinky side, you may not have palmaris longus.

In our leg, there is a little muscle called plantaris. This muscle comes off of the base of our thigh bone—the femur—and joins the rest of our calf muscles to contribute to the Achille’s tendon. It has a small muscle belly behind the knee, but for the most part, this muscle exists as a tiny tendon sandwiched between the much larger calf muscles—gastrocnemius and soleus. It is so uninspiring that surly professors call it the “freshman nerve,” because it is often misidentified by first year medical students as a nerve.

That said, I shouldn’t be so negative towards these muscles, which may serve a purpose after all: they are often harvested by surgeons for tendon or ligament reconstruction surgery.

Melissa Wilson

Assistant Professor, Life Sciences, Arizona State University, whose research focuses on evolutionary biology, specifically sex-based biology

All organs are useful! But as for which are the most useful, and which are the least: From an evolutionary perspective, we think about survival. If the organ were removed, how would it affect our ability to function, and to survive? We often talk about positive selection (something that makes you better at survival and reproduction), but turns out that most selection is negative selection (that is, something it would be very, very bad to lose, and so is kept around). For example, most every organ is maintained in the body because without it, we have poorer chances of survival. This is all that negative (or purifying) selection is.

It’s like your car. There are a lot of ways your car can break, so you spend time maintaining everything and just keeping it going—this is similar to purifying selection on features in the human body. We spend time trying to maintain things, and that depends on the environment. Do I need snow tires in Arizona? Nope, so cars here won’t have snow tires. But is having snow tires useful in Minnesota? You betcha. And cars without engines won’t work in any environment, and won’t go on to having baby cars. well, you know what I mean.

It’s easy to say which organs are the most useful, because without them we won’t function as humans in any environment. But the least useful organ in the human body depends entirely on your environment. So, maybe sweat glands are less useful for someone who lives their whole life in the arctic, but essential for a person in the Savannah. And, maybe tonsils, which are part of the body’s immune system, are less useful when we have a wide array of antibiotics, but in regions where people don’t have access to antibiotics, tonsils could be extremely useful. We could think about hair (which grows out of our skin, a HUGE organ) we can survive without it, but is it useful? Yes. Hair plays both a role in warmth, keeping particles at bay (eyelashes and nose hairs!), skin protection, or even mate choice (how we get huge societal differences). So, I think it’s actually far easier to say which is the most important organ, and far more messy to say which is the least important.