Genetic erosion, also called genetic depletion or genomic erosion, refers to the loss of genetic diversity in a population. This can happen naturally or because of human actions. Sometimes, the term is used to describe the loss of specific genes or traits, and other times it refers to the loss of entire species.
Genetic erosion happens because each organism has a unique set of genes. If an individual dies without having offspring, the special genes it carried are lost forever. Two main causes that worsen genetic erosion are habitat loss and habitat fragmentation—often caused by farming or building projects—and low genetic diversity. Low genetic diversity is linked to inbreeding and weaker immune systems, which can quickly lead to a species becoming extinct.
By definition, endangered species experience different levels of genetic erosion. Many species rely on human-assisted breeding programs to keep their populations alive and prevent extinction over time. Smaller populations are more likely to lose genetic diversity than larger ones.
The gene pool of a species or population includes all the different genes found in every member of that group. A large gene pool means high genetic diversity, which helps populations survive difficult conditions. In contrast, low genetic diversity (as seen in inbreeding or population bottlenecks) can reduce a species’ ability to survive and increase the risk of extinction.
Causes of genetic erosion
Genetic erosion happens in many ways, often because of the loss of individuals in a population. This loss also means the unique traits carried by those individuals are lost. When many individuals are lost at once, it is called a population bottleneck. This can happen due to events like human actions or natural disasters. A bottleneck greatly reduces the number of different genes in a population and makes it harder for animals to find mates that can have babies.
Smaller populations are more likely to experience genetic erosion than larger ones. For example, if one animal in a small group dies, the traits it had are less likely to be found in other members of the group. In larger groups, the same traits are more likely to be present in other animals. Another reason genetic erosion happens is when gene flow is limited. Gene flow is the movement of genes between groups. If animals cannot move between groups, small problems with genetic diversity can become bigger and harder to fix.
These factors are seen in the Ngorongoro Crater lions, a well-known example of genetic erosion. The area has high prey density, but human activity around the crater limits where the lions can move. This stops them from leaving the area and reduces gene flow. Over the past few hundred years, the lion population faced several bottlenecks caused by hunting and disease. A major event was a disease outbreak in 1962 that reduced the population to only 15 lions. These events greatly decreased the variety of genes in the group, causing problems for the population.
Consequences to populations and individuals
The effects of losing genetic diversity can be serious and may eventually cause the extinction of a population or species. When a group of organisms has less genetic variety, it becomes harder for them to survive when faced with dangers like diseases or changes in their environment. For example, if a group is struck by a new disease, it is less likely that some members will survive or be immune if their genes are not varied. Inbreeding, which happens when closely related individuals mate, can worsen these problems. This process increases the chance of harmful traits appearing and is more common in small groups with little genetic variety. As a result, individuals may become more likely to get sick, making the whole group more at risk of a deadly outbreak. Inbreeding also raises the chances of physical or reproductive birth defects. When the likelihood of abnormal sperm increases, infertility becomes more common, and fewer babies are born. These combined issues lead to lower birth rates and weaker, less healthy offspring. Populations with weaker individuals are less able to survive environmental challenges that healthier groups could usually recover from.
Drivers in the loss of agricultural and livestock biodiversity
Genetic erosion in agriculture and livestock refers to the loss of genetic diversity, which includes the disappearance of individual genes and specific combinations of genes found in local plant and animal varieties that have adapted to their natural environments. In farming, this can involve the loss of an entire crop, a type of crop, or a specific version of a gene.
The main causes of genetic erosion in crops include replacing local plant varieties with non-local ones, clearing land for farming, overusing species, population growth, environmental damage, overgrazing, government policies, and changes in farming practices. The most significant cause is often the replacement of local plant and animal varieties with those from other regions. When commercial crops are introduced to traditional farming systems, many local varieties may quickly decline. Many researchers believe that modern agriculture often leads to less genetic and ecological variety by promoting uniformity in farming practices.
For animal genetic resources used in food and agriculture, major causes of genetic erosion include breeding different animal types without careful planning, using more animals from other regions, weak policies for managing animal genetics, ignoring certain breeds because they are not profitable, increasing the intensity of farming, effects of diseases, loss of natural grazing areas, and poor control of inbreeding.
Prevention by human intervention, modern science and safeguards
With improvements in modern biology, scientists have developed several methods and safety measures to slow the loss of genetic diversity and stop endangered species from disappearing completely. However, many of these methods are too costly to use widely, so the most effective way to protect species is to keep their natural habitats safe and let them live as naturally as possible. This is complicated because protecting a species’ genetic variety often needs keeping many separate groups of the same species in different areas. For example, to save at least 90% of the genetic diversity in northern quolls, scientists must protect at least eight separate groups of these animals across Australia.
Wildlife sanctuaries and national parks have been created to protect whole ecosystems, including all the plants and animals that naturally live there. Wildlife corridors are built to connect broken-up habitats (see Habitat fragmentation) so endangered species can move, meet, and reproduce with others of their kind. Scientists and trained staff use modern conservation techniques to manage these protected areas and the animals that live there. When habitats are too far apart or too isolated to connect through corridors, or when animals have already disappeared from an area, wild animals are moved to new locations to help rebuild their populations.
Modern zoo policies now focus more on caring for and breeding wild animals in their endangered species programs. These animals are kept in hopes of being released back into the wild. Zoos have changed their goals, spending more resources on breeding programs to help protect species in the wild. Zoos keep detailed records of breeding (called studbooks) and share animals with other zoos in the country and around the world to avoid inbreeding and increase genetic diversity as much as possible.
Expensive (and sometimes debated) methods called ex-situ conservation aim to increase genetic diversity on Earth and protect local gene pools by preventing the loss of genetic material. Modern methods like seedbanks, sperm banks, and tissue banks are now widely used and valuable. Sperm, eggs, and embryos can be frozen and stored in these banks, which are sometimes called "Modern Noah's Arks" or "Frozen Zoos." Scientists use freezing techniques to keep these materials alive forever by storing them in liquid nitrogen at very low temperatures. These preserved materials can later be used for artificial insemination, lab-grown embryos, embryo transfers, and cloning to help protect the genetic diversity of critically endangered species.
It is possible to save an endangered species by preserving parts of their bodies, such as tissues, sperm, or eggs—even after the animal has died or was found freshly dead in captivity or in the wild. A new animal can be created through cloning to help reintroduce its genes into the living population of the species. Cloning dead animals to bring them back is still being improved and is too expensive to use widely now. However, with future scientific progress, this method may become a common practice in the future.
De-extinction and bioethics: restoring biodiversity in the face of genetic erosion
De-extinction, also called resurrection biology, is the process of using science to bring back species that no longer exist or to create similar organisms, called proxy species. Scientists use methods like cloning, breeding techniques, or genetic changes (such as CRISPR) to achieve this. These methods involve using DNA from ancient remains or closely related living species. Scientists may clone preserved cells to recreate a species, change traits in living species to match extinct ones, or introduce similar species into ecosystems to restore balance. While de-extinction could help ecosystems recover and increase biodiversity, it also has risks, such as spreading diseases, mixing genes between species, and causing harm to animals. In 2016, the International Union for Conservation of Nature (IUCN) created guidelines to help manage the process of creating proxy species. The report explains that perfectly recreating an extinct species is not possible because of differences in genetics, body functions, or behavior, which is why scientists use the term "proxy species." De-extinction also raises ethical questions about animal welfare, as creating clones might lead to health problems, birth defects, or early deaths. It also brings up concerns about whether humans have a moral duty to bring back extinct species to fix past mistakes. This practice challenges the idea of human control over nature, as creating genetically altered organisms or reviving species could lead to unintended consequences. Some experts argue that the motivation behind de-extinction may be guilt or a desire to protect nature, rather than overconfidence. In conclusion, de-extinction is a complex issue that requires balancing the potential to restore ecosystems with the responsibility to avoid harming animals and respecting the limits of human influence on nature.