How Two Biologists Put A Killer Whale Back Together, Bone by Bone

It might have been the splashing of harbor seals that caught his attention.

Without making a sound, the bullet-shaped killer whale named T44 might have turned and accelerated toward the seals through the clear, cold waters of British Columbia’s Johnstone Strait, gaining speed with each thrust of his powerful tail. He wouldn’t have been alone—several female whales and their calves, also part of northern Vancouver Island’s T pod, swam alongside him, and when they reached the group of plump harbor seals, they struck.

T44's black-and-white head would have shot out of the sea, veered in a half-turn to catch the flipper of the panicked seal in its teeth, and dragged it down below the surface. Using his paddle-shaped flippers like rudders, the orca might have breached again with the seal still in his jaws, arcing clear of the water before falling back.

We don’t know for sure—no one witnessed T44’s final hunt. But we do know that at some point, T44 swallowed the 100-pound seal, claws and all. He had chased down about 15 harbor seals in the week before this catch.

But this one, in March 2009, would be T44's last.

Not long after, fishermen found T44’s body floating in the strait, a narrow channel separating the rocky coasts of northeastern Vancouver Island and mainland British Columbia. The whale had been born there about 30 years earlier, and had never left the area.

T44's story wasn’t over, though. Its huge body would be salvaged and its bones stripped of flesh and oil. Mike DeRoos and Michi Main, two of the world's top skeleton articulators—people who rebuild an animal's bones into a scientifically accurate skeleton—would reassemble the cleaned bones in their workshop. From an inert puzzle of bone and steel, the couple would resurrect T44 in a true-to-nature pose for a local museum, giving the killer whale a second life.

 

Humans have been fascinated by killer whales’ savage intelligence for centuries. The Roman historian Pliny the Elder wrote that “their Likeness cannot be represented by any other Figure than that of a mighty Lump of Flesh, armed with terrible Teeth.” As the sea’s apex predators, orcas inspired legends among Pacific Northwest whaling peoples like the Makah and Nuu-Chah-Nulth. In the 18th century, naturalist Carl Linnaeus named them Delphinus orca, or “demon dolphin.” Their current scientific name, Orcinus orca, translates to “demon from hell.”

Telegraph Cove British Columbia
Telegraph Cove on Vancouver Island, British Columbia
David Stanley, Flickr // CC BY 2.0

Modern scientists are just beginning to study and understand the animals' culture. The northern Pacific Ocean is home to three killer whale ecotypes—populations that are genetically, behaviorally, and geographically distinct from one another. Endangered resident killer whales mainly eat salmon, while little is known about offshore killer whales, which prowl the edge of the continental shelf.

T44 was a transient killer whale, the ecotype that specializes in hunting marine mammals. (In the 1970s, marine biologist Michael Bigg noted they had taller dorsal fins and didn’t interact with the residents, leading him to conclude that they were just passing through—transients, in other words. They're also called "Bigg’s killer whales.") They roam the coastal waters of British Columbia, where the channels and bays of the Inside Passage brim with seals, sea lions, porpoises, dolphins, and baleen whales. Groups of transients are known to take on gray whale calves and minke whales. Humpback whales, twice as long and five times heavier than a fully grown orca, have been seen with rake marks on their flukes and flippers from the transients’ teeth.

T44 killer whale at Telegraph Cove, British Columbia in 2007
T44, identified by his distinctive dorsal fin shape, swims by Telegraph Cove in 2007.
Jared Towers

When hunting, transients rely on stealth. Traveling in small groups of four or five, they passively listen for the splash of a seal, the whoosh of a minke surfacing to exhale, or the call of a mother gray whale to her calf. One transient group may signal other transients with quiet clicks at specific intervals, inviting them to join the hunting party; biologists believe transients share a limited vocabulary to aid communication between unrelated groups. Then, the killers attack with shocking ferocity. They seem to like playing with their prey before tearing it to pieces. “If people see them hunting, there’s often red blood in the water, and it can be kind of gruesome,” DeRoos, the skeleton articulator, tells Mental Floss. A soft-voiced biologist who speaks thoughtfully about cetacean murder, DeRoos has been studying orcas and rebuilding their bones for more than 15 years. “They’re the real killer whale,” he adds.

Born in 1978, T44 was the 44th identified whale in the transient population around the northern end of Vancouver Island. He spent almost all of his life in the waters around Telegraph Cove, a tiny settlement on the island’s east coast. Crowded by dense cedar forest on one side and Johnstone Strait on the other, the former fishing and cannery village is now a seasonal hub for eco-tourism. Between May and October, thousands of visitors come to see the strait’s humpback whales blow prismatic jets of vapor and Steller sea lions pose on the rocks. Most tourists hope to glimpse the orcas as they chase 30-pound Chinooks or punt hapless dolphins into the air.

Killer whale T44 towed to Telegraph Cove harbor in British Columbia
Jim Borrowman and Graeme Ellis tow the body of T44 to Telegraph Cove so biologists can perform a necropsy on the killer whale.
Courtesy of Mary Borrowman

Jim Borrowman, one of about 12 year-round residents of Telegraph Cove, opened the village’s Whale Interpretive Centre in 2002 after co-founding British Columbia’s first whale watching company in 1980. The center exhibits skeletons of cetaceans common to local waters, including a 60-foot fin whale and a gray whale, whose carcasses were found floating near Telegraph Cove.

It was Borrowman who received the phone call on March 31, 2009, about a dead killer whale in Johnstone Strait. The Canadian Coast Guard had identified it as an orca and called Graeme Ellis, a local killer whale researcher and Borrowman's friend. “Graeme called me up and said, ‘We’ve got this dead killer whale. The [Coast Guard] ship tied it up in a bay on the north end of the island,’” Borrowman, a garrulous old salt, tells Mental Floss. “Graeme said he wanted to try and figure out if we could identify it still—once these whales die, they lose their skin quite quickly and all their identifying marks. But he definitely wanted to do a necropsy [to find the cause of death]. These are very rare finds and very important finds.”

“I really wanted a bigger killer whale for the museum; I have a juvenile already,” Borrowman adds. “Graeme said, ‘If you can tow it down, you can have it.’ I said, ‘Hurry and get here!’”

From Telegraph Cove, the two men drove Borrowman’s whale-watching boat to where the Coast Guard ship had secured the orca. Major decomposition had yet to set in, and Ellis recognized it right away. “We knew it was a Bigg’s type. T44 had a big nick on the back edge of the dorsal fin. And there were a few scratches left on the saddle patch area, some marks there, so Graeme could positively identify it,” Borrowman says.

They worked quickly to tie a thick nylon line around the whale’s flukes as gale-force winds whipped up. As they towed T44 behind the boat toward Telegraph Cove, the 7-ton whale snapped the tow line, but Borrowman managed to rehook it. They waited out the storm overnight on shore. A light snow was falling the following morning when they arrived in Telegraph Cove, where 18 scientists were waiting with flensing knives in hand.

 

The first step in preparing T44 for his second life took days. First, the scientists, who came from the island's Pacific Biological Station, "spent all day cutting all the bones completely apart and trimmed as much of the meat off as we could. During this time, [biologist] Steven Rafferty took measurements and collected all the samples he needed,” Borrowman says.

Killer whale skull and vertebrae in skeleton articulation workshop
T44's skull rests on a workbench while the vertebrae are mounted on the steel bar.
Mike DeRoos

T44 appeared to be a healthy, mature 31-year-old male, about 25.5 feet long and roughly 15,000 pounds, with no bruising or obvious signs of a ship strike. (The average lifespan of a male orca is about 30 years, while females live for an average of 50 years, and some much longer.) There were more than 300 seal claws in T44’s stomach, indicating that he ate roughly 15 to 20 harbor seals in his final week, along with two yellow plastic flipper tags from juvenile elephant seals. Researchers were unable, however, to point to a cause of death based on tissue samples. “It could simply be that he lived and died a fairly normal life,” Borrowman says.

When the necropsy was complete, the biologists turned the carcass over to Borrowman. He and a few others continued cutting the skeleton apart for several more days. Now, the months-long process of cleaning and degreasing T44’s skeleton for display in the Whale Interpretive Centre began. Every morsel of rotting muscle and blubber, every cartilaginous tendon and bit of skin, would need to be removed from the exterior of the bones. Every pint of oil, which helps keep live whales buoyant, would have to be drained from their porous tissue.

From his earlier experience denuding the 60-foot, 60-ton fin whale, Borrowman had determined that sea scavengers—fish, crabs, shrimp, and microbes—are the best cleaners for the job. The fish and crustaceans pick off the flesh, while marine bacteria burrow into the bone. In the cold waters of Johnstone Strait, the oil would solidify into a wax for them to devour.

The crew put T44’s skull in netting to hang it from a dock, while the mandibles, including the teeth, went into large apple juice barrels with holes punched in the lids. Pectoral fins—which were so heavy it took four men to lift them—were secured in large fish totes and weighted down. They tied all of the loose ribs together in bundles and strung about three dozen star-shaped vertebrae on lines. Then, they heaved everything into Telegraph Cove harbor.

“The meat goes quickly,” Borrowman says. “The problem is that every species, and every age of every species, has a different amount of oil in it and time period that it takes to get it out. And there’s no book on that.” Any oil that remains in the bones will ooze out, drop by drop, sometimes for decades.

T44’s bones remained underwater for a year. In the spring of 2010, Borrowman brought up the bundles and barrels, encrusted with barnacles and anemones, and pried off the lids. He spread the cleaned bones on Telegraph Cove’s dock so the sun’s heat could liquify most of the remaining oil, which took several months to drain out. Later, he put some of the individual bones on display in the Whale Interpretive Centre for a few years.

Then, he hired Mike DeRoos and Michi Main to put T44 back together.

 

DeRoos and Main, a husband-and-wife skeleton articulating team, operate from their home and workshop on Salt Spring Island, just down the main highway from Telegraph Cove. Both are trained as biologists; DeRoos learned the art of putting skeletons together as one of the first student workers hired at the Whale Interpretive Centre in 2002. “I grew up working with my dad, building things. I’ve always loved working with my hands and figuring out how to put things together. Building skeletons just seemed like the extension of that,” DeRoos says. “If I hadn’t become a biologist, I probably would have gone into engineering.”

Killer whale skull, vertebrae, and ribs mounted on steel supports
T44's skull and ribs are mounted on to the backbone.
Mike DeRoos

In September 2017, Borrowman delivered T44 to the workshop. The bones would need no further degreasing, but that hasn’t been the case with every project DeRoos and Main have worked on. After the marine scavengers and the sun’s rays do their jobs, DeRoos will often bury skeletons in big piles of horse manure for up to six months. The heat of the composting process transforms the oil from a viscous, coconut-oil consistency to a flowing liquid, and microbes in the manure will consume most of it. To get bones completely oil-free, DeRoos will employ an industrial-strength vapor degreaser—a type of machine originally used in aerospace manufacturing facilities to clean out aircraft engines. The degreaser uses solvents to dissolve any remaining oil in the bones in a few hours.

Cleaning the bones of every speck of oil and tissue is essential, because whale guts in any stage of decomposition are not pleasant. “It can have a really rancid, fishy, rotting flesh smell—or, if it’s really fresh, it just has sort of a warm, semi-sweet, bloody fish smell,” DeRoos says. “If you get the tiniest little bit of rotten whale guts on your clothing or on your body, the smell will really follow you. The worst thing, the very worst thing, is when it’s late at night, after you’ve cleaned up from working, it follows you into your house, into places where it shouldn’t be.”

“Some people naturally have a stronger stomach than others,” he adds. “Mine is able to handle a lot of pretty bad stuff.”

By early 2018, the fully degreased, cream-colored pieces of T44 lay in piles around DeRoos’s workshop. The tusk-like ribs spooned on a tarp. The whale’s massive skull was propped on a workbench, seeming to watch DeRoos and Main as they planned T44’s next phase.

Long before the couple begins articulating an animal’s skeleton, they conduct hours of research to learn as much as they can about the species’ natural history. As biologists, they have spent the summer months out on boats in the glacier-hewn channels and straits of British Columbia, monitoring marine mammals and watching how they behave. They’ll consult other scientists and browse their photos of the species from the field. And they'll also watch videos of the animals underwater to understand the nuances of their movement—"to put our own minds into the body of the animal we’re working on," DeRoos says. “Seeing live animals really inspires what I do with the dead ones.”

Mike DeRoos works on the killer whale rib cage
Mike DeRoos works on the killer whale's rib cage.

With a particular set of bones to be articulated, DeRoos and Main will consider the animal’s age, sex, and geographical origin, and look for imperfections that could serve as clues to the animal’s life. “I look at every bone of the skeleton and pick out the abnormalities, like if the animal had a broken rib or a disease in one place that has altered the bones,” he says. “That gives you an intimate, first-hand story about how the animal really lived.”

The details help shape the final narrative of the skeleton, which DeRoos and Main evoke through its posture and the setting where it will eventually be installed. For an earlier killer whale skeleton that is now exhibited at the Noyo Center for Marine Science in Fort Bragg, California, they worked from the contents of its stomach—six harbor seals—to design a posture highlighting “the ferocity, efficiency, and amazing characteristics of this hunter in the ocean,” Main says. “When people come in and experience an exhibit, they have the opportunity to really interact with a killer whale’s jaws, those big teeth. That can really be a good hook to draw people in. We decided [on] this really dynamic rolling, diving hunting posture with its jaws wide open—so when people walk into that exhibit, they walk right into the mouth of this killer whale. You can almost imagine yourself as the prey.”

Skeleton articulator Michi Main and an assistant assemble killer whale flipper bones
Michi Main (left) assembles the flipper bones on the steel support bars. Baby Kaito and assistant Nikoya Catry-Bauer help out.
Mike DeRoos

DeRoos and Main also looked at the space in the Whale Interpretive Centre where T44 would eventually reside. After talking with Borrowman about how he wanted to fit the skeleton into the museum, they decided on positioning the whale in a sharp, banking right turn, diving down as though he were chasing escaping prey. “I started imagining T44 among a group of killer whales, attacking a sea lion, ramming it with their heads, attacking it again, making tight maneuvers around the kill,” DeRoos says. “That’s a dynamic story to tell.”

Back in their workshop, DeRoos and Main faced the challenge of correctly assembling T44 as he was in life. There is no standard manual for orca anatomy, and scientists still aren't sure how many bones an orca is supposed to have. Most killer whales have about 180 bones; within that number are between 53 and 58 vertebrae, 11 to 12 pairs of ribs, and a widely varying number of flipper bones, plus the skull, jaws, and teeth. The bone totals vary among individual whales even within the same species.

That makes articulation based on previous models and skeletons a guessing game. They’ve consulted old Russian whaling texts, which contained the earliest reliable records of killer whale anatomy, for clues. They also examine 3D scans of skeletons they’ve worked on previously, which gives them a framework for conceptualizing the right number and position of bones in their current project.

Replica teeth to be placed in a killer whale skull
The 3D-printed teeth wait to be placed in T44's jaws.
Mike DeRoos

For T44, DeRoos and Main drew scaled-down sketches to make sure their vision for the skeleton was actually something a living whale could do. Using the drawings and DeRoss’s engineering skills, they fashioned the sections of strong but lightweight steel armature that would underlie the entire finished skeleton.

First, they created the steel beams to hold the heaviest pieces—the 110-pound skull and jawbones—in place. Then, they used a hydraulic pipe bender on a huge steel bar that would support the hefty spine and ribs. The big vertebrae were the literal backbone of the entire project; once the steel pipe was bent into the final position evoking a diving orca, the vertebrae were mounted on the support with steel pins. DeRoos and Main had to get these pieces in perfect position before moving on. “The key to all this is having spent time in the field with living whales,” he says. “You have to have a good plan, because you can’t go back once the bones are on.”

From there, the ribs were attached with steel cables onto another steel support, which presents a challenge. “The ribs are finicky," DeRoos says. "If they’re misaligned, it makes the whole thing look bad, because in a living animal they work together seamlessly.” He also mounted the amazing number of flipper bones—imagine the skeletons of two huge human hands, with five to seven joints in each finger—along thin steel rods. Most of the body's supports are hidden behind the larger bones, while flipper mounts blend in between the smaller pieces. He finished off the mess of cables and steel bars with permanent epoxy glues, then removed the temporary supports.

“This elegant mount has no visible external structure, and that really allows people to see what is out in nature. It helps to convey the story in a big way,” Main says.

Killer whale rib cage and vertebrae in the back of a pickup truck
T44's ribs and vertebrae are packed in the pickup for their journey to the Whale Interpretive Centre.

But then, they ran into a problem. Some of the bones were missing—likely lost while they lay in Telegraph Cover harbor, scattered by currents or accidentally cut loose by a passing boat's propeller. “The last 5 feet of tail—about 14 vertebrae—and the entire sternum, plus a couple of sternum ribs, were missing,” DeRoos says. “And we had only about two-thirds of the chevron bones, which fit underneath the tail vertebrae and protect the major blood vessel running back there. There should be about 14 and we had, like, six.”

He turned to 3D printing, comparing T44’s existing bones to those of five other killer whale skeletons in their workshop to find one that most closely matched T44’s dimensions. A slightly older male northern resident killer whale named I46, a salmon-eater from British Columbia, filled in. “We measured [I46] in three or four different ways to come up with a scaling factor for width and height. We scanned I46’s bones and applied the scaling factor to basically blow them up a bit in size to match what was missing from T44, and that’s what we had printed,” he says. “Once we get these bones mounted and painted and on the skeleton, I don’t think anyone would be able to distinguish them as replicas.”

As a finishing touch, T44 got a set of false teeth—not because he had had poor dental hygiene, but because an orca’s solid ivory teeth, each weighing a quarter-pound, can be irresistible souvenirs. “People will walk off with them or try to pull them out of the skeleton,” DeRoos says, sighing. As a solution, he cast each tooth in plastic resin, and a team of volunteers hand-painted the set, which will be bolted to the jaw. “They took each original tooth and matched the paint color, the details, and the stains using artists’ acrylics. They put a matte gloss on the tooth itself and a shiny gloss on the tips,” he says. “They’re virtually indistinguishable from the originals.”

 

Finally, in May 2018, the couple readied T44 for his new life. DeRoos and Main, their three kids, DeRoos’s parents, and several friends drove up to Telegraph Cove in a parade of pickups, the skeleton in five large articulated sections lashed onto trailers. The Whale Interpretive Centre had been prepared for their arrival; the staff had moved the fin whale and smaller orca skeletons out of the way and exhibits had been temporarily pushed to the side. The team planned to assemble the sections on the floor of the hangar-like space—a difficult task when you’re trying to connect several hundred pounds of backbone and ribs to another hundred pounds of backbone by aligning screw-hole to screw-hole. But T44 slid together without a hitch.

Killer whale skeleton mounted in a museum
Now fully assembled, T44 is mounted from the ceiling at the Whale Interpretive Centre.
Mike DeRoos

The team then rigged the completed skeleton with strong ropes, attached to a system of chain hoists, and raised it toward the ceiling, inch by inch. DeRoos checked its position; T44’s big ribcage and string of vertebrae came pretty close to the building’s interior posts. “I wasn’t sure how we’d be able to position his flippers, but we managed to fit everything,” he says. “The really fun part was when we put his lower jaws on. The big, impressive teeth were a hit with everyone.”

Now, T44 hovers overhead like the apex predator he was, menacing an imaginary sea lion in the cold, clear waters of Johnstone Strait. DeRoos pictures him diving down among the kelp, circling his frantic prey, beating it to a pulp exactly as he had when he was alive.

After nine years and thousands of hours of labor, T44 was back home.

Select photography courtesy of Taylor Roades. This story was made possible in part by the Institute for Journalism and Natural Resources.

Some Mathematicians Think the Equal Sign is On Its Way Out

Paperkites/iStock via Getty Images
Paperkites/iStock via Getty Images

A growing number of mathematicians are skeptical that the equal sign, traditionally used to show exact relationships between sets of objects, holds up to new mathematical models, WIRED reports.

To understand their arguments, it’s important to understand set theory—a theory of mathematics that’s been around since at least the 1870s [PDF]. Take the classic formula 1+1=2. Say you have four pieces of fruit—an apple, an orange, and two bananas—and you put the apple and the orange on one side of a table and the two bananas on the other. In set theory, that’s an equation: One piece of fruit plus one piece of fruit on the left side of the table equals two pieces of fruit on the right side of the table. The two sets, or collections of objects, are the same size, so they’re equal.

But here’s where it gets complicated. What if you put an apple and a banana on the left side of the table and an orange and a banana on the other side? That’s clearly different from the first scenario, but set theory writes it as the same thing: 1+1=2. What if you switched the order of the first set of objects, so instead of having an apple and an orange, you had an orange and an apple? What if you had only bananas? There are potentially infinite scenarios, but set theory is limited to expressing them all in only one way.

“The problem is, there are many ways to pair up,” Joseph Campbell, a mathematics professor at Duke University, told Quanta Magazine. “We’ve forgotten them when we say ‘equals.’”

A better alternative is the idea of equivalence, some mathematicians say [PDF]. Equality is a strict relationship, but equivalence comes in different forms. The two-bananas-on-each-side-of-the-table scenario is considered strong equivalence—all of the elements in both sets are the same. The scenario where you have an apple and an orange on one side and two bananas on the other? That’s a slightly weaker form of equivalence.

A new wave of mathematicians is turning to the idea of category theory [PDF], which is based in understanding the relationships between different objects. Category theory is better than set theory at dealing with equivalence, and it’s also more universally applicable to different branches of mathematics.

But a switch to category theory won’t come overnight, according to Quanta. Interpreting equations using equivalence rather than equality is much more complicated, and it requires relearning and rewriting everything about mathematics—even down to algebra and arithmetic.

“This complicates matters enormously, in a way that makes it seem impossible to work with this new version of mathematics we’re imagining,” mathematician David Ayala told Quanta.

Several mathematicians are at the forefront of category theory research, but the field is still relatively young. So while the equal sign isn’t passé just yet, it’s likely that an oncoming mathematical revolution will change its meaning.

[h/t Wired]

7 Facts About Blood

Moussa81/iStock via Getty Images
Moussa81/iStock via Getty Images

Everyone knows that when you get cut, you bleed—a result of the constant movement of blood through our bodies. But do you know all of the functions the circulatory system actually performs? Here are some surprising facts about human blood—and a few cringe-worthy theories that preceded the modern scientific understanding of this vital fluid.

1. Doctors still use bloodletting and leeches to treat diseases.

Ancient peoples knew the circulatory system was important to overall health. That may be one reason for bloodletting, the practice of cutting people to “cure” everything from cancer to infections to mental illness. For the better part of two millennia, it persisted as one of the most common medical procedures.

Hippocrates believed that illness was caused by an imbalance of four “humors”—blood, phlegm, black bile, and yellow bile. For centuries, doctors believed balance could be restored by removing excess blood, often by bloodletting or leeches. It didn’t always go so well. George Washington, for example, died soon after his physician treated a sore throat with bloodletting and a series of other agonizing procedures.

By the mid-19th century, bloodletting was on its way out, but it hasn’t completely disappeared. Bloodletting is an effective treatment for some rare conditions like hemochromatosis, a hereditary condition causing your body to absorb too much iron.

Leeches have also made a comeback in medicine. We now know that leech saliva contains substances with anti-inflammatory, antibiotic, and anesthetic properties. It also contains hirudin, an enzyme that prevents clotting. It lets more oxygenated blood into the wound, reducing swelling and helping to rebuild tiny blood vessels so that it can heal faster. That’s why leeches are still sometimes used in treating certain circulatory diseases, arthritis, and skin grafting, and helps reattach fingers and toes. (Contrary to popular belief, even the blood-sucking variety of leech is not all that interested in human blood.)

2. Scientists didn't understand how blood circulation worked until the 17th century.

William Harvey, an English physician, is generally credited with discovering and demonstrating the mechanics of circulation, though his work developed out of the cumulative body of research on the subject over centuries.

The prevailing theory in Harvey’s time was that the lungs, not the heart, moved blood through the body. In part by dissecting living animals and studying their still-beating hearts, Harvey was able to describe how the heart pumped blood through the body and how blood returned to the heart. He also showed how valves in veins helped control the flow of blood through the body. Harvey was ridiculed by many of his contemporaries, but his theories were ultimately vindicated.

3. Blood types were discovered in the early 20th century.

Austrian physician Karl Landsteiner discovered different blood groups in 1901, after he noticed that blood mixed from people with different types would clot. His subsequent research classified types A, B and O. (Later research identified an additional type, AB). Blood types are differentiated by the kinds of antigens—molecules that provoke an immune system reaction—that attach to red blood cells.

People with Type A blood have only A antigens attached to their red cells but have B antigens in their plasma. In those with Type B blood, the location of the antigens is reversed. Type O blood has neither A nor B antigens on red cells, but both are present in the plasma. And finally, Type AB has both A and B antigens on red cells but neither in plasma. But wait, there’s more! When a third antigen, called the Rh factor, is present, the blood type is classified as positive. When Rh factor is absent, the blood type is negative.

Scientists still don’t understand why humans have different blood types, but knowing yours is important: Some people have life-threatening reactions if they receive a blood type during a transfusion that doesn’t “mix” with their own. Before researchers developed reliable ways to detect blood types, that tended to turn out badly for people receiving an incompatible human (or animal!) blood transfusion.

4. Blood makes up about 8 percent of our total body weight.

Adult bodies contain about 5 liters (5.3 quarts) of blood. An exception is pregnant women, whose bodies can produce about 50 percent more blood to nourish a fetus.)

Plasma, the liquid portion of blood, accounts for about 3 liters. It carries red and white blood cells and platelets, which deliver oxygen to our cells, fight disease, and repair damaged vessels. These cells are joined by electrolytes, antibodies, vitamins, proteins, and other nutrients required to maintain all the other cells in the body.

5. A healthy red blood cell lasts for roughly 120 days.

Red blood cells contain an important protein called hemoglobin that delivers oxygen to all the other cells in our bodies. It also carries carbon dioxide from those cells back to the lungs.

Red blood cells are produced in bone marrow, but not everyone produces healthy ones. People with sickle cell anemia, a hereditary condition, develop malformed red blood cells that get stuck in blood vessels. These blood cells last about 10 to 20 days, which leads to a chronic shortage of red blood cells, often causing to pain, infection, and organ damage.

6. Blood might play a role in treating Alzheimer's disease.

In 2014, research led by Stanford University scientists found that injecting the plasma of young mice into older mice improved memory and learning. Their findings follow years of experiments in which scientists surgically joined the circulatory systems of old and young mice to test whether young blood could reverse signs of aging. Those results showed rejuvenating effects of a particular blood protein on the organs of older mice.

The Stanford team’s findings that young blood had positive effects on mouse memory and learning sparked intense interest in whether it could eventually lead to new treatments for Alzheimer’s disease and other age-related conditions.

7. The sight of blood can make people faint.

For 3 to 4 percent of people, squeamishness associated with blood, injury, or invasive medical procedures like injections rises to the level of a true phobia called blood injury injection phobia (BII). And most sufferers share a common reaction: fainting.

Most phobias cause an increase in heart rate and blood pressure, and often muscle tension, shakes, and sweating: part of the body’s sympathetic nervous system’s “fight or flight” response. But sufferers of BII experience an added symptom. After initially increasing, their blood pressure and heart rate will abruptly drop.

This reaction is caused by the vagus nerve, which works to keep a steady heart rate, among other things. But the vagus nerve sometimes overdoes it, pushing blood pressure and heart rate too low. (You may have experienced this phenomenon if you’ve ever felt faint while hungry, dehydrated, startled, or standing up too fast.) For people with BII, the vasovagal response can happen at the mere sight or suggestion of blood, needles, or bodily injury, making even a routine medical or dental checkup cause for dread and embarrassment.

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