What Causes Animals to Become Extinct?

Species slowly and gradually adapt to changing conditions in the environment through biological modifications and natural selection. As a species appears and increases in population, it always contains some injurious element that will at some point, under some pressure, cause its demise and extinction. 

This is the theory of natural selection first propounded by Charles Darwin in his publication of The Origin of the Species in 1859 and while controversial, mostly for theological reasons, it remains one of the most influential books in the history of natural sciences and his theory of natural selection is accepted by most biologists today.

New species have appeared both on land and in water, very slowly over time, one after another.  Evidence from fossils shows us too that species and groups of species gradually disappear, one after another, first from one spot and then from another, and finally from the world.

As a general matter, we needn’t be surprised or alarmed by extinction and rarity of species.  It is as natural as the creation of new species.  When a species does not adapt to changing conditions, say for example, changing temperatures or a predator’s toxin or a disease, it will die out and be replaced by a species which can survive in the changed conditions. 

Anthropogenic causes can, from one vantage point, be considered a natural pressure causing the extinction of a species.  The concern today is the accelerated rate of extinction of a great number of species due to anthropogenic causes, the rate being somewhere between a thousand-and ten-thousand-fold what it would be absent the population explosion and subsequent development activities [1].

What is an extinct species?

An extinct species is one no longer found anywhere on earth.

How do animals go extinct?

Anthropogenic causes aside, animals become extinct over time through the process of natural selection. 

It is not believed that a species has a definite time period that it will exist, as humans have a life expectancy. Instead, a species will evolve over time with minor variations from one generation to the next, subsequent generations being born with small improvements making it better suited to its environment than its parents. 

If a competing species evolves more quickly to become better suited to its environment and can outstrip its competitors in avoiding predators and wins the battle for food, then that species has a better chance for survival.

That is how the natural world works when populations are balanced. Populations are kept in check by this process of natural selection.

But humans, at the top of the chain, now dominate every aspect of the natural world and are changing the equation governing ecosystems by wholesale destroying ecosystems and severely compromising others. 

In many situations, we are upsetting the natural checks and balances in place where superior survival traits would otherwise govern relationships between species, by causing the extinction of species through habitat destruction, pollution and slaughter for commerce or trophy.

Why do some species survive while others go extinct?

Life favors the fittest to survive. This is the theory of natural selection. 

Favorable variations in a species will boost its position toward dominance in its ecosystem. Let us consider a tropical rainforest scenario where the mutual relations of the many life forms are infinitely complex and close-fitting, having developed over many years in a relatively closed system with little temperature variation or other external factors that might tend to pressure a species. Instead, the competition to survive takes place within a diversely populated environment under the forest canopy. 

Let us consider a snake that has developed a poison on its tongue that can lash out and paralyze a rodent. The rodent who has not developed an immunity to the toxin will be stunned and devoured.

The rodent who has developed an immunity may escape. A snake competing for the same food source who has not developed this special variation will be at a disadvantage. 

The latter species of snake may starve to death while the former survives. The species of rodent who has not developed the resistance likewise may be eliminated by predators and the species of rodent which has developed the resistance to the toxin will survive.

Or consider a fish who can swim through toxins from petroleum byproducts polluting its waters unaffected and compare it with a fish from a different species who is suffocated when oil congeals in its gills. As the waters become more polluted, the first species may survive while the second species does not.

Adaptation takes time and proceeds at uneven rates. 

The species able to adapt more quickly to changing conditions has an advantage. Spaces in the food web will be filled in as quickly as possible as all species are competing to survive. 

In an ecosystem that has developed over time, the natural inhabitants will have developed immunities and other abilities to resist some, but not all of the threats to its population and will continue to develop adaptation modifications as its natural enemies develop new abilities.

When a competing species begins to assert an advantage and dominate, generally the weaker species will diminish in numbers. 

Over time, smaller populations are at a disadvantage, primarily because they lack the genetic diversity of a large population. Genetic diversity allows for more possibilities of genes that are strong enough to maintain through stressors like disease and pollution. 

Smaller populations tend to become weaker and more vulnerable to stressors as the gene pool diminishes and will eventually become extinct.

Natural causes of species extinction

In many cases, we do not know exactly why a species become extinct.

We do know that if a species does not become modified and improved in corresponding degree with its competitors or in adaptation to its changing environment, it will not survive.

We don’t know how many species there are, as evidenced by current estimates, which range from 3.6 million to over 100 million [2]. And if there are just a few of some species, we may well not know of their existence or of their imminent demise. 

What specific injurious trait caused the extinction of a species in the past or a species not well-studied today will probably remain a mystery to humans.  We can only realize that it appears a principle of life that species become extinct.

Many different theories have been advanced for each: amphibians have thin, porous skin and may not be able to survive the sun’s harsh ultraviolet rays allowed in through the thinning protective ozone layer or perhaps they have absorbed more pollutants from the air, land or water than their organs can filtrate, or maybe critical food sources have likewise been poisoned or vanished. Maybe the decline leading to extinction was due to a disease or parasite.

Many believe that pesticides are responsible for the disappearance of bees and worry that all of our pollinators may be subject to the same fate.

#1 Natural disasters

We can conjecture with a bit more confidence what causes the extinction of more obvious species. If a species has only a small, local population, a natural disaster such as a fire, volcano, hurricane or tsunami can decimate the species in one fell swoop.

Some would argue against calling a fire a natural “disaster.” Periodic fires can be viewed as an element of natural succession in the growth of forests. Fires destroy trees that have grown so large their canopies prohibit understory growth. After a fire, which may also clear away microbial growth adversely affecting the health of the forest, the succession of plant life from the floor, to low understory trees, to large trees begins again.

Natural disasters will be touched upon again as an anthropogenic cause as recently, an overabundance of greenhouse gas emissions in the atmosphere caused by the copious burning of fossil fuels has led to more tempestuous weather than ever before recorded [3].  

It is treated here, and for the purposes of this argument can also include toxins in the air, water and land that are adversely affecting us because from one vantage point the our activities can be considered as natural behavior as we are mammals. 

In accordance with the principles of natural selection then, should these severe weather instances and the poisoned environment so severely threaten the species that the majority of people will not be able to adapt in time, as is likely on the current trajectory, given the great number of homo sapiens, a small viable population will probably still survive. 

From experience, we can conclude that these will be the strongest, not necessarily the most intelligent or compassionate, but the most powerful. Gentle readers can be consoled by the knowledge that you probably would not want your progeny to have to co-exist with them anyway.

#2 Changes in the weather

Extended droughts, prolonged flooding or sudden extreme changes in temperature can deplete the food source of a species causing starvation. 

If a species does not have the ability to migrate for whatever reason, the creatures may not survive the bitter elements.

#3 Disease

The introduction of a new disease or a parasite to which a species has not evolved a resistance or defense can decimate a species.

Anthropogenic causes of species extinction

#1 Habitat loss

Small land animals and birds have been declining due to habitat loss. 

There is only so much room on earth and the human population is growing exponentially. While there is some hope that species can co-exist with humans, the anecdotal evidence of the possibility is slim. There are reported sightings of mountain lions in Los Angeles, coyotes in Chicago and leopards in Mumbai [5].

As more homes are being built, more land cleared for agriculture and industry, more roads being constructed, gas pipelines laid, as cities and their infrastructure expand, animal habitats are being eliminated or fragmented. 

Many suburban areas still serve as homes for squirrels, rabbit, deer and birds, but every road has evidence of the risks for these small animals. Larger animals are generally removed or shot through fear or as trophies. 

Some smaller animals have adjusted to urban and suburban environments, but by no means all have adjusted to the elimination of their natural habitats by human development. 

The remaining members will not only face new pressures from its new habitat in the form of unfamiliar predators to which it has not adapted and uncertain food sources, and possibly heavy noise, road and human traffic and bright lights and very limited habitat options. 

If they must migrate, they will also confront different weather to that which they are acclimated.

#2 Pollution

The advent of the environmental movement is generally attributed to a seminal book by Rachel Carson in 1962 called Silent Spring, silent to the dearth of songbirds caused by their poisoning by DDT, a pesticide sprayed ubiquitously at the time. 

Agribusiness and homeowners are still applying pesticides, herbicides, fungicides and defoliants, and at an unprecedented rate. 

We have dead zones in our oceans and lakes from eutrophication [6].  Half of our topsoil has been lost over the past 150 years [7] due to industrial activities and the acid rain that deposits their byproducts far distances and one-third of arable land has been lost to desertification [8]. This means that the soil hosts no organisms.

#3 Overexploitation

Following habitat loss, overexploitation is the second major threat to many species. 

And the growing international black market trade in illegal wildlife is estimated to account for only slightly less than illegal narcotic sales.  It is presently a ten-billion dollar annual industry [9].

#4 Climate change

Climate change is listed here as an anthropogenic cause because of the dramatically accelerated rate of warming since the dramatic rise of the use of fossil fuels in industry and transportation [10].

There has been a lot of attention on a few species of animals who do not appear to be able to adapt to our changing climate. 

Everyone has seen photographs of the polar bears losing their habitat in the Arctic as they drift helplessly on chunks of ice from melting glaciers. 

The loss of habitat for one species affects many others.

What will happen if all animals become extinct?

If the human population continues growing at its present rate [11] and the species extinction rate continues on its trajectory and we do not learn to co-exist with animals, it is likely that animals, fish and birds will become extinct. 

How will this impact us? Why does the loss of species matter? 

The natural balance sustaining healthy, well-functioning ecosystems is contingent upon biological diversity.  The loss of a key player in an ecosystem compromises and can easily destroy its ability to operate effectively. 

For example, the loss of a predator will allow the population of its prey to burgeon, which in turn could easily and quickly eliminate its food source, causing that population to starve and any remaining members to be more vulnerable to disease. 

The food source may have been shared by another species, which may also then face starvation.

Loss of the stronghold of the food source, say it is a plant, may allow an invasive species to more easily move in and take hold. The invasive species, having no natural checks, can then take over the area. 

Since the invasive species by definition is not endemic to the new environment, chances are high that it will not provide the necessary habitat or food for the remaining native species and thus force them to migrate and face other pressures, like predators and lack of food, which will likely quickly destroy them.  Even if some are able to survive, smaller populations of species cannot through inbreeding sustain the genetic diversity a healthy population needs to survive and thus, the entire ecosystem falls apart.

Our ecosystems are providing services absolutely necessary to maintain a biosphere that can support human life. 

These are services we cannot replicate on a scale required to sustain our population of 7.6 billion, let alone the projected population of 10 billion by 2050.  The services range from purifying our air and water, to making and preserving healthy soil, to the cycling of nutrients, and to the seed dispersal and pollination necessary to grow food and the medicinal plants that are the basis of our pharmaceuticals. 

The dynamics of ecosystems also further sustain biological diversity.

• A wetland lacking aquatic vegetation cannot purify the water.
• A timbered forest cannot provide the photosynthesis necessary to clear the air of carbon.
• Soil depleted of organisms cannot create new soil or hold the roots of plants and prevent erosion.
• If the animals responsible for seed dispersion or the insects responsible for pollination become extinct, the plants they serve will become sterile and die off as well.

The consequences of our intervention

It is a principle of natural selection that some species will become extinct in our lifetimes and all of the species we know will become extinct over a long period of time. 

The focus here is on those presently facing a precipitous decline due to human activities like habitat destruction, pollution or overexploitation, all activities destroying populations far more rapidly than the natural biological process of species adaptation can occur.

Considering the infinite complexity of the relations of all organic beings to each other and to their conditions of existence, the simple answer to whether we are causing an irreversible fatal problem by overseeing the extinction of all animals is that we do not know. 

Though many claim a complete understanding of life, based on wildly differing internal beliefs, the fact remains that we have no empirical test for proving why life exists at all, let alone how. 

We have observed food chains and food webs in certain ecosystems and can only guess that we have an understanding of a number of the relations that sustain life. We can safely conjecture that the links missing from our food web due to extinction via natural selection do not threaten homo sapiens since we have co-evolved with the present species. 

The big question mark appears when the cause of extinction is anthropogenic. 

What if land animals, birds and fish become extinct before our eyes?  Will it matter?

We are herbivores and can change our food source, so we don’t have to eat meat, fish or poultry.  Possibly we can synthesize the missing nutrients like calcium.  In addition to food, we need to breathe and a global temperature averaging 59 degrees Fahrenheit or 15 degrees Celsius [12].  

Phytoplankton and other related marine plants provide 70% of our oxygen; our rainforests contribute most of the remaining 30% [13]. Phytoplankton needs only sunlight and gases from the atmosphere.  It is possible that other animals do not contribute significantly to this cycle.  

• But do the ecosystems that provide the filtration services need animals, birds and fish to remain balanced and functioning?  – Wetlands probably need fish.

• Will plants still grow? – If so, we can make clothing and build shelter from plant materials.

• But will plants survive? – Bats eat moths that eat corn, so if there are no bats, insects that have adapted to our arsenal of insecticides may easily decimate the agribusiness crops much of the world depends upon for food as well as nutritious food grown sustainably. 

• What would be the consequences of losing the animals who feed on fruit and nuts? 

• Would the overpopulation of fruit and nut trees be subject to a sudden epidemic of disease, a natural phenomenon designed to reduce the numbers? 

• And where would that leave humans?  Could we quickly concoct synthetic vitamins and minerals to satisfy the dietary requirements fresh fruit and nuts fulfill?   

• Do small animals provide an essential service in the cycle of soil formation? – It does not appear so at first blush, but we do not know particularly of the many, variable tiny mites and insects that travel with migrating animals or their possible dual roles in the kingdom of soil organisms working to decompose plant material into soil.

• Do birds play any role in the growth of plants or otherwise in our survival or will their loss be a romantic sorrow at most? 

• And should we be concerned that the extinction of all animals is a signal that our environment is also becoming unsuitable for humans? 

As custodians of the planet, we are playing roulette. For we don’t know the answers to these questions.

How can we prevent animal extinction?

#1 Sustainable development

Most developed countries do have legislation requiring environmental impact studies for major development activities, at least where government funds are involved. 

When an issue does arise that threatens the progress of construction, if it is not covered up, it is often minimized, even trivialized.  This is because there is a general lack of understanding of the impact of losing a habitat, say a wetland or a small fish. 

If the consequence was better understood, that is, the impact statement not viewed in the vacuum of one subdivision of land, but in the context of how the proposed development would affect the larger region and dependent populations, the argument for saving a wetland or a fish would command deeper respect.  As it stands, absent a very clear, compelling argument economic development will be favored over environmental conservation.

A better idea would be comprehensive planning at the outset.  A county, town or city should consider and set forth its goals and incorporate sustainable development procedures at each step. 

For example, a legislative district should identify the ideal sustainable habitat for humans and native creatures and plants and then design ways to achieve that. 

If mountain lions can coexist with humans in Los Angeles, surely habitats can be created for mosquito-eating bats, otters and songbirds in a small town.  

If a developer is going to be allowed to put in a strip mall, that developer can be required to leave the pond for frogs, put in a buffer of hedges to discourage turtles from venturing toward vehicular traffic and plant a stand of trees to soak storm water draining from the asphalt parking lot.

#2 Restoration ecology

Many habitats have simply been destroyed through development.  

For example, forests have been cleared and wetlands filled in and shopping malls and roads built where they once were.  This cannot be undone. 

However, damaged ecosystems such as abandoned strip mines or hazardous waste sites can be reclaimed to more closely resemble a natural habitat. 

Once an ecosystem is in place, it generally regenerates itself.  Trees and plants will drop leaves and debris to the ground.  Earth organisms and molds and fungi will decompose the litter into rich soil, capable of regenerating vegetative growth, whose roots will capture precipitation and hold the soil.  Leaves will photosynthesize, capturing excess carbon dioxide and purifying the air.

#3 Providing sanctuary

A last step measure we have been taking to save species on the brink of extinction is capturing them and taking them to a safe environment, like a zoo, where they are safe from predators and their health can be monitored. 

The goal in these situations is to find mates, breed the animals and when there are a certain minimum number, teach them how to survive in their natural habitat and reintroduce them into the wild.  Another measure is to simply keep them in a sanctuary that emulates natural conditions, absent the threats and adding food and medical attention.

Unfortunately, many animals are becoming extinct due to over fishing and overhunting.  Sometimes this is done legally and sometimes not. 

For example, the seas have been overfished because no country was able to expressly claim the open seas, so fishing in a number of areas was a free for all until the fish were depleted.

#4 Enforcing bans on wildlife trade of endangered species

Over the course of human history, many species have been hunted to extinction [14].

We know of course that animals are hunted for food.  In many areas in the United States today, hunting licenses are required and the number and type of animals allowed to be killed is limited.

Big game hunting was a very popular industry worldwide in the last century and still brings substantial revenues to some African countries [15].  And it is still considered by many cultures an achievement if a hunter is able to shoot a large animal. Often, an animal’s head is stuffed and displayed as a trophy of the hunter’s achievement.

Animals have been overhunted for their perceived value for jewelry, talismans and curative powers.  These are hunted and sold illegally on the black market for a lot of money. 

International attention on the problem of illegal wildlife trade resulted in the Convention on International Trade in Endangered Species of Wild Fauna and Flora, which banned commercial trade of endangered species among its members. 

Not only are international efforts being taken to halt the illegal wildlife trade, but in many instances, private individuals are mobilizing efforts since it is very difficult to catch a poacher.

#5 Passing and enforcing pollution laws

It is difficult to assess how many species are succumbing to pollution. 

It is a straightforward matter to find the cause when one dissects the carcass of a sea turtle or albatross who has starved to death and find that shards of plastic has torn its gut.  But we can have no idea how many animals have suffered a similar fate.  We cannot know the extent of the adverse health effects of plastic on marine life. 

We can see the carcasses of fish washed up on the shoes after an oil spill, but we cannot know how much marine life was adversely affected. 

It is seldom clear that one can draw a straight line between the disappearance of a species of birds from even a notoriously polluted heavily industrialized area to the polluted air itself. 

Developed countries regulate pollution, but political administrations influenced by big businesses that oppose regulation, often weaken existing legislation and fail to fund enforcement efforts. 

Developing countries must be compelled to pass legislation and developed countries must be watched.  Pollution regulation and enforcement are vital to maintaining a habitable planet.