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Dogs are the most physically diverse land-dwelling species on Earth. Through centuries of selective breeding, humans have poked and prodded at canine genetics to achieve an array of traits and characteristics, whether for hunting, herding, guarding, or simple appearance. 

The result is a staggering variety of shapes, sizes, facial characteristics, and coat types — and, in some cases, dog breeds that look very different from their ancestors, even after just a century or so of separation. This has created some adorable-looking creatures, but it also has given rise to certain health consequences. 

Here’s a look at some of the most dramatic before-and-after stories in canine history, from bulldogs to Saint Bernards.

English Bulldogs

The English bulldog is the poster dog for dramatic breed transformation — and not entirely in a good way. The original bulldog was bred for bull-baiting, a horrific blood sport that pitted dogs against tethered bulls. 

The bulldog was selected to be strong and agile with a flat face so it could still breathe while holding on to the bull. When bull-baiting was made illegal in 1835, bulldog breeders began selectively introducing or exaggerating certain other traits. 

While earlier bulldogs were bred for physical abilities over appearance,  the prohibition of bull-baiting pushed breeders toward more pronounced facial wrinkles, a thicker and squatter body, and a larger short-faced head for aesthetic purposes. The result was a breed that noticeably differed from its taller, longer-legged ancestor. 

Unfortunately, the desire for saggy jowls, a squattier stance, and an ever-flatter face — driven by show-ring standards and preferred aesthetics — gave rise to severe health problems in the breed, including breathing difficulties and skin issues. It’s one of the most extreme examples of form being prioritized over function in dog breeding history.

Pugs

Pugs were introduced to Europe from China in the 16th century, and within 100 years the breed had become popular thanks in part to its adoption by the royal courts of England, Holland, and France. Back then, however, pugs looked significantly different, with longer and more muscular legs, a powerful frame, and, importantly, a more obviously elongated snout than that of its modern descendants. It was only during the latter half of the 19th century that the breed began to change significantly in Europe, with breed clubs establishing formal physical “standards” and dog show judges deliberately favoring certain traits.

Due to the relentless breeding meant to achieve an ever-flatter face, today’s pugs — while adorable — typically struggle with breathing due to their deformed respiratory tracts. This condition is so severe that researchers from the Royal Veterinary College concluded in a 2022 study that the pug “can no longer be considered as a typical dog from a health perspective.” 

German Shepherds

The German shepherd of a century ago was a lean, upright, athletic working dog, built for endurance across rough terrain. But over the last hundred years, it has evolved into a larger, more barrel-chested creature. 

Many modern German shepherds also have one very significant difference when compared to their ancestors: a distinctive sloping back, with the hindquarters sitting noticeably lower than the shoulders. This trait doesn’t seem to provide any benefits over a straight back and was seemingly selected for purely aesthetic reasons, such as for dog shows. 

The trend has caused concern among vets and dog lovers alike, as the excessive downward back slope places unnecessary stress on the hips and spine. The breed is now among those most prone to developing hip dysplasia. 

Bull Terriers

The bull terrier’s most famous feature — its distinctive egg-shaped head — is largely the result of human intervention. Originally a mix of bulldog and terrier, the bull terrier of the 19th century had a clear separation between its snout and forehead. Then breeders began molding its profile into a smooth arc from nose to skull, without hollows or indentations, creating the breed’s football-shaped head and triangular eyes, a purely aesthetic choice developed to achieve a visually unique breed. 

This selective breeding has led to health issues among bull terriers, including problems with the teeth and jaws, as a direct result of reshaping their craniums. The breed also has unusually high rates of deafness — about 20% of pure white bull terriers suffer from hereditary deafness. This wasn’t caused by the skull shape, though, but rather by the selective breeding to achieve a white coat, the genes for which disrupted the pigment cells the inner ear needs to properly develop.

Saint Bernards

The Saint Bernard was originally bred during the 16th and 17th centuries as a guard dog, and then as a mountain rescue dog, by monks at the hospice of the Great St. Bernard Pass on the Italian-Swiss border. Over a period of almost two centuries, these gentle giants — well adapted to the snow and freezing temperatures of the Alps — saved some 2,000 lives. 

The dogs used their keen sense of smell to locate people buried under the snow, physically warmed hypothermic survivors by lying on them, guided lost travelers through whiteout conditions, or ran back to get help from their human companions. Despite the many ways they did provide life-saving assistance, the classic image of a Saint Bernard carrying a barrel of brandy around its neck to help freezing travelers is, unfortunately, largely a myth.

But back then, the dogs looked significantly different, being smaller in size than their modern descendants, with shorter hair and a noticeably longer tail. During the last 100 or so years, they’ve been bred to have a cuddlier appearance, with longer hair, a deeper muzzle, a slightly droopier face, and an even more massive head. 

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For humans, death is an inescapable fact of life — but in the rest of the animal kingdom, mortality isn’t always as inevitable as it is for us. While it’s true that all living things eventually die one way or another, nature has produced a handful of creatures that have a very different (and very lengthy) relationship with aging, living so long as to seem nearly immortal. 

The word “immortal,” of course, comes with a caveat here. No known animal is truly indestructible, and all creatures can fall prey to disease, predators, or simply bad luck. But a handful of creatures have essentially found a way around dying from old age alone. Here’s a look at some of the longest-living animals on Earth and how they achieve such incredible staying power. 

Immortal Jellyfish 

The appropriately named immortal jellyfish (Turritopsis dohrnii) is a tiny creature — about the size of a nail on a human’s little finger — that’s theoretically capable of living forever. When it “dies” — through environmental stress, predation, or sickness — the immortal jellyfish sinks to the ocean floor and begins to decay. This would spell the end for most other forms of life, but at that point the immortal jellyfish begins to regenerate its cells. It doesn’t become a new adult jellyfish (known as a medusa), but rather it reverts to an earlier stage of life called the polyp stage. 

The jellyfish basically reprograms its own cells, rewinding the biological clock to the very beginning of its life cycle. The “reincarnated” polyp then produces new medusae that are genetically identical to the previous adult jellyfish. The process, known as transdifferentiation, is incredibly rare — and can, in theory, repeat indefinitely.

Planarian Flatworms

Planarian flatworms are another fairly unspectacular-looking creature whose otherwise primitive nature conceals an amazing ability to regenerate. These flatworms  come in a variety of shapes and sizes and are found almost everywhere on Earth, including in freshwater, seawater, and on land. 

Planarians are packed full of special stem cells called neoblasts, which can transform into almost any other type of cell in the body. So if a planarian is cut into pieces, even tiny fragments — as small as just 1/200th of the original organism — can regrow everything it needs to survive, including a new head and a working nervous system.

Hydras

Not to be confused with the many-headed serpent from Greek mythology, Hydras are minuscule freshwater creatures related to sea anemones and jellyfish. They look like tiny tubes with a mouth and tentacles at one end — not exactly something you’d be particularly amazed by if you saw it in a pond. But Hydras are incredible little creatures, especially when it comes to their mortality. 

Hydras’ stem cells are in a continuous state of renewal, so the creature shows no signs of aging. When kept safe and in isolation (e.g., away from predators, adverse weather extremes, and disease), they can theoretically regenerate endlessly by continuously replacing their own bodily tissues. Hence the name “Hydra,” which references the mythological creature that could regenerate its own head when one was cut off. 

Turtles and Tortoises

While not biologically immortal, many species of turtles and tortoises show little evidence of age-related decline. Unlike many animals, their risk of dying isn’t related to their age and doesn’t increase year to year. 

Environment is a major factor in the lifespan of these creatures. In captivity, away from the risks of living in the wild, tortoises in particular age at a glacially slow pace. The world’s oldest known tortoise, Jonathan, is estimated to have hatched in 1832 and was still alive as of 2026. 

One of the key factors in this impressive longevity is taking things slowly: Generally speaking, longevity increases as metabolic rate drops. Recent research also suggests that tortoises and turtles may have gene variants that grant enhanced immune response, DNA repair, and cancer suppression —all of which can add up to a very long life.

Lobsters

Lobsters are also not biologically immortal, but they do occupy a fascinating middle ground in the longevity debate. Research suggests that lobsters don’t weaken, slow down, or even lose fertility as they age. They also have indeterminate growth, meaning they have no terminal size and thus continue growing throughout their lives. 

These animals show none of the typical signs of senescence (the gradual deterioration of functional characteristics in most living organisms) and can even regenerate limbs if they lose them, thanks to an enzyme called telomerase. Humans and other animals also produce telomerase, but lobsters have an infinite supply throughout their cells, which is basically an onboard cellular fountain of youth. 

But there is a catch: As they get older and continually bigger, lobsters are significantly more likely to die from exhaustion during molting — the process in which they replace their shells due to their ever-increasing size. So, rather than shuffling off this mortal coil through aging, many lobsters eventually succumb to the energy demands of being too big. 

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If you’ve ever owned a pet, you’ve probably had moments where you’ve thought your animal seemed almost human in its mannerisms and behavior. And you’re not alone: Researchers have documented behaviors across the animal kingdom that feel surprisingly similar to those of humans, from emotionally driven actions such as holding grudges to passing knowledge and skills down through generations. 

While scientists once viewed animal behavior as mostly driven by instinct, it seems we may only be starting to understand their social and emotional complexity. Here are a few examples of surprising humanlike behaviors exhibited by our fellow animals.

Elephants Call Each Other By Name

Elephants are famous for their intelligence, but their social lives may be even more sophisticated than previously thought. In fact, research suggests that they actually appear to address one another using distinct, name-like calls. 

Wild African elephants use specific low-frequency rumbles that seem to refer to particular individuals. In experiments using recorded audio, elephants responded more strongly when they heard the call associated with themselves, suggesting they can recognize when they’re being called.

What sets elephants apart from other vocal animals is how those calls function: Rather than simply imitating the recipient of the sound, the way dolphins or parrots do, the sounds appear to act as separate labels, similar to human names. This kind of communication requires the ability to learn and use new sounds in a flexible way — a rarity in the animal world.

Rats Show Each Other Compassion

Rats are often dismissed as purely instinctual and driven by survival, but they’ve actually displayed behavior that prioritizes helping others. One widely cited study found that they would help rescue a fellow rat who was trapped in a plastic tube before taking food that was simultaneously available to them. 

Another study took things a bit further and found much the same: Rats were placed in pairs with one animal forced to swim in a shallow pool while another stayed dry on a platform nearby. The dry rat could choose between opening a door to rescue the other rat or retrieving a piece of chocolate. Results showed they chose to help the other rat in distress first 50% to 80% of the time.

Interestingly, rats that had previously experienced the stressful swimming condition were even quicker to help others. While this was first believed to demonstrate a level of empathy, later research across repeated trials suggests this behavior may strengthen as rats become more familiar with the situation, becoming increasingly eager to help a trapped companion rather than simply avoid the situation. This is a pattern seen across many social species, including humans; our social bonds, as you undoubtedly know, often shape our decision-making.

Orcas Pass Down Generational Knowledge

If you’ve spent any time learning recipes in your family’s kitchen or perfecting fishing techniques on childhood trips, you’ll know those aren’t the kinds of traditions you can learn in textbooks. Not unlike the way that type of knowledge is passed down through generations in humans, orcas’ tight-knit matrilineal communities have a similar culture. 

Older whales, for example, guide younger pod members through specific hunting techniques such as coordinated wave-washing, a specific method for capturing prey in which orcas work together to create powerful waves and knock prey off ice floes. Different orca pods even develop their own distinct hunting styles, even when they live in overlapping regions and encounter the same types of food. 

And this goes beyond survival techniques: Research suggests cultures among different populations can also shape how groups socialize, play, and even how they choose mates and reproduce. Those cultural behaviors aren’t universal behaviours shared by all orcas, though; it seems that what an orca knows depends heavily on who it grows up with and not necessarily what it’s hardwired to do.

Crows Hold Grudges for Years

Crows can recognize human faces, and while that’s impressive enough on its own, it’s not quite the whole story. They also remember those faces long after a negative encounter. 

In one study, researchers wearing masks captured and released wild crows while wearing specific masks so the birds would associate particular faces with the encounter. Later, when researchers wearing those same masks walked through the area, they were scolded with caws and mobbed by dive-bombs from those same birds, sometimes years later. 

The sentiment spread, too: Even crows who were absent from the original encounter responded aggressively to the masked faces after witnessing how other crows reacted. Zoologist John Marzluff, the University of Washington professor in charge of the catch-and-release project, conducted years of follow-up observations tracking how long the birds continued reacting to people wearing the masks from the initial encounter and estimated that the angered crows stayed mad for as long as 17 years.

Neuroscientists think this is likely because crows have a region of the brain that works much like the mammalian amygdala, the part involved in processing emotions,  particularly fear and threat responses.

Chimpanzees Wage Organized Conflicts

Chimpanzees are known to live in large, humanlike social groups, and they sometimes defend them quite aggressively. Neighboring chimp communities have been known to wage coordinated raids into each other’s territory, most famously in the Gombe Stream population studied by Jane Goodall in the mid-1970s. Over time, those encounters can escalate into sustained territorial conflict, and one group can gradually expand its territory at the expense of another. 

This chaos is actually controlled competition with clear alliances, and yes, it feels all too familiar. Humans, of course, similarly draw boundaries and compete with our neighboring communities,  even if our conflicts differ in scale and complexity. 

But conflict is, of course, just one part of chimpanzee society. Humans’ closest living relatives are also incredibly physically affectionate: They form long-term social and familial bonds, are doting caregivers, and are even known to laugh, reflecting an advanced level of social intelligence.