Scientists William Russell and Rex Burch proposed in 1959 that when it comes to animal testing, there should be 'three Rs'—replace animals wherever possible; reduce their numbers; refine how they're treated.

No one is tracking the total number of animals used for research across US labs, though partial data without any rodents puts the 2024 count above 775,000 animals, including some 40,000 dogs and 100,000 primates.

US federal researchers are blocked from putting certain human cells in animals

In 2015, US policymakers put a halt to any government-funded work that would insert human stem cells into animals. The reasoning was that human cells might spread through the animal's body and perhaps to its brain, blurring the line between humans and nonhumans. The ban remains in place today even as gene-edited pig parts are being placed in humans.

Pig-to-human transplants have raised concerns about pig living conditions

Pigs are the current first choice for xenotransplantation procedures, yet such work gives some researchers and animal welfare advocates pause. Concerns include that pigs would have a poor quality of life since the animals must live in a strictly-controlled, hyper-clean environment to avoid risky pathogens.

Cross-species transplantation has been attempted in medicine for more than 300 years

Early reported xenotransplantation attempts included 17th century efforts in France to transfuse blood from animals into humans. The poor results prompted France to issue a xenotransplantation ban. In the 19th century, researchers tried animal-to-human skin grafts from species including sheep, rabbits, dogs, cats, rats, chickens, and pigeons.

Mice were able to regenerate retinal cells in the lab—a breakthrough for mammals

Using gene therapy, a team of Korean researchers has enabled retinal regeneration in mice by blocking the intercellular transfer of a single inhibitory protein. This 2025 finding creates a new potential direction for treating retinal diseases. The work, which is still in animal studies, is projected to enter early-stage clinical trials in the next few years.

Scientific advances are unlocking a wide range of alternatives to IVF

From refined artificial insemination and microsurgical sperm extraction to experimental uterine transplants, scientific innovation is rapidly advancing potential fertilization technologies. But they come along with costly trials, some ethical dilemmas, regulatory issues, and more.

Harvard drowned rats for this?

Harvard's 1950s rat study was ethically questionable, but scientifically profound. One rescue attempt made rats swim 40x longer. The finding: hope isn't poetic, it's biological.

Model organisms like yeast, mice, and flies help scientists decode the human body

Some species are used to quickly study the effects of human diseases and treatments because they are short-lived and have similar systems to those found in humans. Bacteria, like E. coli, have been used as human proxies given their rapid growth and ease of genetic manipulability.

Six of history's most unethical human experiments, from deliberate flu exposure to withholding syphilis treatment

Some of the progress made in mental health treatment, vaccines, blood transfusions, and more came about before the advent of consent and ethics committees, resulting in serious physical and psychological harm that participants in studies were not even anticipating.

Indefinite cloning of some endangered species may not sustain their longevity because cloning success rates decrease as genetic mutations accumulate.

Multiple new research paths may lead to slowing (or even reversing) aging

Aging has always been inevitable, but fasting, epigenetic reprogramming, and parabiosis seem to help people stay young. By studying centenarians, memory, and even the humble roundworm, scientists are looking for the genetic basis to live not just a long life, but a healthy one.

See different pig-to-human xenotransplantation possibilities

Xenotransplantation can include the insertion of any organ, tissue, cells or fluids from any nonhuman animal into a human. This US Food and Drug Administration graphic about pig-to-human applications shows different possibilities, including the exploration of using pig pancreatic cells for treating diabetes.

Schizophrenia is being studied with pea-sized 'mini-brains'

Brain organoid research is enabling researchers to study distinct electrical firing patterns associated with schizophrenia. These "mini-brains" that are constructed in the lab from patients' cells could lead to better diagnosis approaches and drug development.

Gut microbiome rewrites may help reduce allergies

Researchers are investigating different strategies to determine if one day they could give people a combination of gut microbes to set them up for fewer allergies. In animal research, scientists have already prevented severe allergic responses in allergy-prone mice—supplying them with gut microbes from healthy, non-allergic human babies.

Some animals, including certain tropical ants, have little or no bacterial populations in their gut, upending the idea that all animals rely on such microbes to help maintain their health and proper functioning.

Read why one man agreed to get a pig kidney in 2025 to replace his own failing organ

The 68-year-old New Hampshire man told USA Today that a motivator for the experimental surgery was his belief that he was going to die anyway, and other people suffering from kidney disease could gain valuable insights. Yet the surgery bought him time—he lived 271 days with a pig organ and later received a human kidney transplant. Clinical trials began in 2026 to test the pig xenotransplants in more people.

Scientists may have discovered why gene-edited pig kidneys are rejected in humans

In November 2025, researchers studying how a brain-dead donor’s body responded to the transplantation of a genetically engineered pig kidney, published that they’ve identified immune system reactions that may explain why these pig organs get rejected. What’s more, they were able to reverse the rejections with an already available drug combination and the kidney functioned well. They also pinpointed a way to detect a potential rejection up to five days sooner.

Researchers are investigating if nanoparticle treatments could combat allergies

In rodent work, Northwestern University’s Evan Scott (now at the University of Virginia) and his colleagues have been trying to attack allergies with specially designed nanoparticles—miniscule lab-made objects that can penetrate cells. They stud the nanoparticles with a tiny bit of the allergen specific to the allergy (i.e. cashew protein for cashew allergy) and antibodies that shut down allergic response processes.

Chinese scientists transplanted a pig lung into a human being—but it had to be removed

In August 2025, Chinese scientists transplanted a pig lung into a brain-dead person, a common research step for this type of experimental work. Researchers used CRISPR technology to alter six proteins in the pig genes to make the organ seem less foreign to the human immune system. Within a day there were indications the organ wasn’t functioning well and that the person’s body was rejecting it. Scientists ended the experiment after nine days.

Scientists have demonstrated IVF to help critically endangered rhinos

Scientists have used the technique to create embryos from eggs harvested from captive southern white rhinos and implanted into a southern white rhino. They hope to use this proof of concept to eventually use IVF to revive the population of northern white rhinos, which are extinct in the wild and have no living males left, using a precious reserve of frozen embryos and a surrogate southern white rhino mother.

Brain implants are restoring movement and communication in early human trials

Several companies developing brain-computer interfaces have begun testing on humans with promising results. These implants have helped reanimate paralyzed limbs and enable communication, though ethical concerns remain about data privacy.

Neural interfaces offer major medical potential but raise serious ethical concerns

Although brain-computer interfaces can help people recover lost functions and allow direct brain-to-computer communication in the future, surveys have shown little public support for using them to boost abilities like memory or focus in healthy people.

Early peptide research focused on isolating the substances from animal tissue

In the first half of the 20th century, peptides including insulin and adrenocorticotropic hormone were isolated from animals to provide life-saving medicines. ACTH was isolated from the pituitary glands of cows and pigs and insulin was isolated from the pancreas of dogs and cows.

Pigs are preferred for xenografts because of their size and low disease risk

Pigs are of particular interest for xenotransplants because the animals are close to human size, are easily raised in captivity, and have large litters. They’re already routined killed for food and they’re less genetically related to humans than nonhuman primates, which reduces disease transmission risks and some researchers’ ethical concerns.

The US FDA considered mitochondrial replacement therapy during 2014 hearings

An agency committee assessed if this approach could have undesirable ripple effects across multiple generations and whether a clinical trial involving this approach would be appropriate. As of 2026, the US has continued to prohibit this procedure though it is legal in other settings including the UK and Australia.

Limb regeneration research may lead to treatments for arthritis

For scientists pursuing the cure for arthritis, the holy grail of discoveries lies in how to regrow healthy cartilage inside human joints. While this feat has so far resisted our best scientific attempts, there are plenty of other human tissues—such as the liver and fingertips—that will successfully regenerate.

Artificial intelligence may improve organ donation systems—and even organ health

Mayo Clinic transplant experts suggest that artificial intelligence could potentially improve organ donation systems in several ways, including better identifying patients most at risk for organ rejection, enhancing donor-recipient matching, and helping to avoid organ transplant needs by identifying health issues earlier.

Xenotransplants are an experimental last resort for the terminally ill

David Bennett Sr., the world’s first genetically modified pig heart transplant recipient, explained his reasoning to his University of Maryland Medical Center care team in 2022 regarding why he accepted a pig organ: He was dying and ineligible for a human heart transplant so this was a last-ditch effort, he said. He died two months after receiving the heart.

Stem cell therapies

Stem cells' special attributes interest researchers developing new therapeutic tools for a variety of health problems. Much of this research is done with support from the National Institutes of Health (NIH). This page offers a snapshot of research programs funded by the NIH and the health problems those programs focus on.

Pig organ transplants are apparently kosher—you just can’t eat them

Science writer Mary Roach speaks with journalist Terry Gross about her latest book, “Replaceable You: Adventures in Human Anatomy” and discusses topics including why pig organs have become of such interest and what religious leaders have told her about pig organs and compliance with Jewish dietary law.

Can humans delay or reverse old age?

We're not sure yet. Researchers at the University of California San Francisco are studying why some conditions and behaviors, such as low-oxygen environments and exercise, benefit the aging process, hoping to reveal potential health applications. Some of this research focuses on klotho, a naturally occurring age-regulating hormone named after the Greek Fate Clotho. Animal studies on klotho brain injections found subjects had improved memory recall and age-related degeneration resistance.

NSF-funded research into matching algorithms improved the success of organ transplants

Investigations in game theory, including concepts focused on creating mutually beneficial partnerships—matching theory—led to the design of computer systems that efficiently matched kidney recipients and live donors, resulting in higher-quality matches. By 2019, these matching algorithms were used for multi-organ exchanges.

What rodent cars can tell us about human joy

Neuroscientist Kelly Lambert and her colleagues taught rats to drive in a mini car. She writes her findings from this unconventional experiment, sharing that positive and fun experiences can sculpt the brain just as powerfully as stressful ones. Click to learn more about how the apparent joy of these rodents seemed to enhance their neuroplasticity.

Synthetic biology can prevent extinction by creating create disease-resilient plants and animals

Through gene editing and the deployment of artificial cells, scientists can leverage learnings from the genetic sequencing of animals with known resistances to protect endangered species. Gene editing of certain species, such as mosquitoes, can also reduce their ability to spread diseases like malaria between humans.

A first-of-its-kind clinical trial taps livers from gene-edited pigs to clean blood

The experimental dialysis-like treatment from United Therapeutics, eGenesis, and OrganOx, is designed to help people with liver failure. The therapy, which involves attaching the modified pig liver externally, filters a patient’s blood so their own livers can temporarily rest and perhaps heal.

Efforts to create disease-sniffing capabilities for phones still can't match dogs

In this video, a scientist explains why dogs remain leaders in olfactory capabilities, outpacing technology. Scientists have attempted to create artificial "e-noses" for phones to detect early signs of disease, but so far they have not been successful.

Six pigeons were trained to detect cancer from looking at CT scans—now that work is the basis for training new AI medical tools.

Five advancements in arthritis research

It is estimated that nearly 350 million people worldwide are currently suffering from arthritis. This resource explores five of the most promising recent advancements in arthritis research as scientists work towards improved treatments and continue the search for a cure.

Research advances suggest death takes much longer than we realized

Recent research indicates that organs, including the brain, are better at handling a lack of oxygen after the heart stops beating than previously known. Such findings may open up possibilities that include someday reversing certain death processes and expanding the availability of organs available for organ donations. (Some users may experience a paywall.)

Using brain implants to restore vision

Several companies are attempting to create brain-computer interfaces that skip over retinas and optic nerves to allow visual input to go straight to the brain, potentially restoring some sight to the blind. Clinical trial findings suggest restored sight is sparse and manifests differently than a sighted person might expect, appearing as specks of "light" clusters called phosphenes to help differentiate one's surroundings.

Researchers use the brain's ability to edit memories to explore memory deletion

Scientists have successfully implanted false memories in mice after studying how the editing process works in the brain. Beyond potentially deleting memories in those with PTSD, upcoming research may allow clinicians to forecast the onset of neurodegenerative diseases.

A clinical trial is underway in 2026 to help kidney transplant recipients avoid a lifetime of immunosuppressing drugs

This later-stage clinical trial, in Chicago and Taiwan, evaluates the efficacy and safety of a new cellular therapy that may be swapped in for immunosuppressing drugs among kidney transplant recipients. The study randomizes people to either receive standard immunosuppressants or this cellular therapy and fewer immunosuppressants. It only includes kidney transplant recipients receiving organs from live donors so transplant surgery timing won't hinge on the unpredictable schedule of performing surgery and follow-up care when a donor dies.

Less than 1% of aging studies consider menopause and its effects

Nearly all studies researching the biology of aging don't consider menopause in their setup, in part because menopause is difficult to emulate in animal models. Menopause is uncommon in the animal world beyond humans and whales. This presents a problem for medicine and science because about 75% of aging-related diseases are likely influenced by menopause.

How to prevent a worst-case scenario with synbio

Author and entrepreneur Rob Reid reviews the risks of a world where more and more people have access to the technology needed to create a doomsday bug that could wipe out humanity.

Pig heart valves have been placed in humans since 1965

The first successful use of a pig heart valve in a human was reported in 1965. This 2015 video details why humans have been able to use pig animal valves for so long with good results and how that differs from what's needed for whole organ transplants.

As of February 2025, there are more than 150 clinical trials using CRISPR technology

The clinical trials are designed to determine whether experimental CRISPR-related therapies are safe and effective. The majority of trials involve treatments for blood disorders, including beta thalassemia.

The world's first commercial biological computer combines neurons with silicon

Australian start-up Cortical Labs unveiled CL1, a hybrid chip designed to help scientists study brain function in real-time. The 800,000 lab-grown neurons on the chip are kept viable for six months via a built-in life support system.

How can octopuses and MDMA help scientists understand the human brain?

Research shows that psychedelics may induce something called "critical periods" in the adult brain, which can make our brains more open to learning and changing, like they once were back in early childhood. Psychedelics similarly change how social creatures like octopuses behave, which demonstrates that these animals could help us better understand our own neurobiology.

New eye implant clinical trial recruiting in 2026

University of Southern California researchers have launched a phase 2b clinical trial of a stem cell implant designed to restore vision in people with advanced dry macular degeneration. Patients will be randomized to receive the stem cell implant or a simulated procedure and placebo implant. This type of larger, second-stage clinical trial is designed to confirm efficacy and dosing and to look for side effects. It's one of the stages that precedes the US Food & Drug Administration approval of a device.

How Western psychedelics research fell to the wayside

Psychedelics' modern era began when LSD was discovered in the 1930s. By the 1950s, clinical trials were underway. US user experimentation outside of medical settings (and high-profile violence, like the Manson murders) inspired negative attitudes toward psychedelics, leading to use restrictions that prohibited companies from patenting psychedelic compounds. This strangled psychedelics' profitability until the 1990s when the government loosened its grip and psychedelics research began seeing a resurgence.