Extinction

Extinction is when a species comes to an end, meaning the last member of that group has died. This can happen when a species can no longer reproduce or adapt to changes in its environment. Because many species live over large areas, scientists often only realize a species has gone extinct after studying fossils or records from the past. Sometimes, a species thought to be gone will be found again, which scientists call a Lazarus taxon.

Over five billion species are believed to have gone extinct throughout Earth's history. Today, there are estimated to be around 8.7 million species of eukaryotes, with even more if prokaryotes are counted. Famous extinct animals include non-avian dinosaurs, saber-toothed cats, and mammoths. Species become extinct when they cannot survive changes in their environment or compete with other species. Most species disappear within 10 million years of appearing, but a few, known as living fossils, survive for much longer with little change.

Mass extinctions, where many species die out at once, are rare, but isolated extinctions happen often and are a natural part of evolution. Recently, scientists have noticed an ongoing mass extinction caused by human actions. Habitat destruction, such as cutting down forests and converting land for farming, is a major reason for these losses. Reports show that a large number of plant and animal species are at risk of disappearing, and many have already been lost since 1750.

Definition

A species is considered extinct when the very last member of that species dies. This means there are no individuals left that can reproduce and create new offspring. Sometimes, a species can become functionally extinct before the last member dies. This happens when only a few individuals remain and they cannot reproduce due to reasons like poor health, age, or being spread out over a large area.

In ecology, the term "extinction" can also refer to a local extinction, where a species disappears from a specific area but still exists elsewhere. For example, wolves were reintroduced to certain areas after they had disappeared from them. Scientists work hard to protect species that are in danger of disappearing completely, often by keeping them in zoos and using special breeding programs to help them survive.

Causes

Species have been going extinct since life began. Over 99.9% of all species that ever lived are now gone. On average, a species lasts between 1 and 10 million years, but this can vary a lot. Many things can cause a species to die out. Sometimes it happens quickly, like when pollution makes a habitat impossible to live in. Other times, it’s a slow process, like when a species loses competition for food over thousands of years.

Humans have played a big role in recent extinctions. Activities like overharvesting, pollution, and destroying habitats have led to many species disappearing. As human populations grow and use more resources, the pressure on other species increases. Scientists are working hard to protect endangered species and prevent more extinctions.

Mass extinctions

Earth has experienced at least five mass extinctions, times when many species disappeared quickly in geological terms. One famous example is the Permian–Triassic extinction event about 250 million years ago, likely caused by huge volcanic eruptions that filled the air with particles. Another well-known event happened 66 million years ago, ending the time of the dinosaurs and many other species.

Today, many scientists believe we are in the early stages of another mass extinction caused by human activities. They warn that without big changes, many plants and animals could disappear within the next few decades. This is happening much faster than natural extinction rates and is driven by things like pollution, habitat loss, and overconsumption.

History of scientific understanding

For much of history, people believed that the world was perfect and complete, so the idea that a species could disappear seemed impossible. This belief was strong in the 1700s with a concept called the great chain of being, where all life was linked in a perfect order. Even Thomas Jefferson did not believe that the woolly mammoth could go extinct.

However, discoveries of fossils that looked different from any living animals made scientists wonder what happened. Some, like Robert Hooke and Sir Thomas Molyneux, thought these animals might still exist somewhere unknown. It wasn’t until Georges Cuvier in 1796 that the idea of extinction became widely accepted. Cuvier studied fossils, like mammoth skulls, and argued that these animals truly were gone. He suggested that huge floods and other disasters caused many species to die out suddenly.

Later, scientists like Charles Lyell and Charles Darwin thought extinction happened slowly over time. Today, we know that both sudden disasters and gradual changes can cause species to disappear.

Human attitudes and interests

Extinction is an important topic in zoology and biology. Many groups, such as the Worldwide Fund for Nature, work to protect species from disappearing. Governments also try to save species by making laws to stop habitat loss, over-hunting, and pollution.

Scientists like Bruce Walsh say we should save species for three reasons: genetic resources, to keep ecosystems stable, and because it is ethical to do so. Sometimes, businesses hurt wildlife, but some also help with conservation.

Some diseases have been removed completely, like the smallpox virus and rinderpest virus. Scientists have also suggested removing certain disease-carrying mosquitoes to save lives. For example, biologist Olivia Judson has talked about removing some mosquito species that spread diseases like malaria. She believes this could save many lives each year.

There are also ideas about bringing back extinct animals through cloning. Scientists have tried to clone animals like the mammoth and the dodo. While these attempts have faced challenges, it shows how science is exploring ways to revival lost species.