Manipulating Biology: Costs, Benefits and Controversies

Background Content Knowledge

According to Anthony D. Branosky, a professor at UC Berkeley, et al, “Paleontologists characterize mass extinction as times when Earth loses more than three quarters of its species in a geologically short interval, as happened only five times in the past 540 million years or so.”³

Some scientists believe that humans are causing the sixth mass extinction, which would be the first one to occur with humans present as a species. According to science writer, Emily Monosson, there are 21,000 species at-risk for extinction across the globe.⁴ Barnosky et al describe the situation in this way, “The huge difference between where we are now, and where we could easily be within a few generations, reveals the urgency of relieving the pressures that are pushing today’s species towards extinction.”⁵

Some of the ways humans are causing the mass extinction include: land transformation/habitat fragmentation, transporting invasive species, toxic pollution, ocean acidification, overharvesting, climate change, and direct killing of species.

Land Transformation

Vitousek defines land transformation as the altering of land to produce goods and services. Farming, forestry and urbanization are the main ways the land is transformed. According to Vitousek, “39-50% of the land has been transformed.”⁶ Additional land has been fragmented which also impacts species and ecosystems. Land transformation and fragmentation not only alter ecosystems, but also the way organisms interact with their environment. Land transformation is the single greatest cause of extinction, and if it continues at the current rate, many more species will become extinct.

Oceans

The impact of humans is harder to determine in the oceans. With 60% of humans living within 100 km of the coasts, the ocean’s productive coastal areas have been significantly impacted by humans. Vitousek states, “Moreover, a recent analysis suggested that although humans use about 8% of the primary production of the oceans, that fraction grows to more than 25% for upwelling areas and to 35% for temperate continental shelf areas.”⁷

There are unintended consequences of harvesting this “primary production.” Many of the species harvested are top predators and removing them has a greater effect on the balance of the ecosystem. Also, some of the methods of fishing damage the habitat, such as a dredge that is dragged along the bottom of the ocean floor. Other consequences are that non-targeted species are unintentionally captured and species get caught in nets left behind as in Figure 1.

Figure 1: A sea turtle entangled in a fishing net. 

Creative Commons NOAA

A massive amount of plastic, with some estimates of few hundred billion pounds, float around the earth’s oceans.⁸ This garbage jeopardizes organisms when they become entrapped and when the plastic is ingested. Recently a dead pilot whale was found in Thailand with 17 pounds of plastic in its stomach!⁹

Invasive species

Approximately 335 million years ago, the continents were all connected into a single land mass called Pangea. The massive continent started to break apart about 175 million years ago. Darwin noted that even though parts of South America, Africa, and Australia shared a similar topography and climate, the plants and animals were not so similar. Darwin believed that because the species evolved separately in isolated areas, the result was differing adaptations to local condition that led to greater species biodiversity. 

Since the Industrial Revolution and the invention of the steamship, technology has been advancing rapidly. Today the globe is crisscrossed with tanker ships and airplanes; in addition to cargo and passengers this causes other species to be inadvertently moved around the globe depositing them in foreign environments. Upon arrival, sometimes they have no natural predators or parasites and they can become invasive, and possibly displace the local species. Transporting species and the resulting “biological invasion” is the second-greatest cause of extinction. Some invasions take over the native species, thus decreasing the biodiversity.¹⁰ According to Kolbert, in one day about 10,000 species are moved around the world in ballast water alone. Due to the remixing of the species in some parts of the world, non-native flora and fauna outnumber native ones.¹¹ While the remixing of species may increase the biodiversity locally, it will lead to a decrease globally.¹²

Some scientists refer to this phenomenon as New Pangea. The world is once again “connected.” While the world is not physically connected, species from one continent are able to hitch a ride to another continent. “Thus, a single tanker (or for that matter, a jet passenger) can undo millions of years of geographic separation.¹³

One specific example is the Burmese python which has invaded the Everglades in Florida. Like other invasive species it has no known predators. But, to make matters worse, it is an apex predator. It is easy to find a video online of a python battling with a large alligator, a native apex predator. There is much concern about the impact the pythons are having on the Florida ecosystem as many of the small mammals are disappearing.¹⁴

Toxic Pollutants

For hundreds of years, human activity has altered the Earth’s atmosphere. Beginning with the Industrial Revolution, “Humans have burned through enough fossil fuels – coal, oil, and natural gas to add some 365 billion metric tons of carbon to the atmosphere.”¹⁵ Kolbert goes on to describe the effect of deforestation. By cutting down forests, trees that normally put oxygen in the air are removed. The result is another 180 billion tons of carbon in the atmosphere. Today the air has four hundred ppm (parts per million) of carbon dioxide in the air which is the highest amount in the last eight hundred thousand years.¹⁶ According to science writer, Carl Zimmer, “By the end of the twenty-first century, humans had raised the level of carbon dioxide in the atmosphere to its highest level in millions of years.”¹⁷ The changes to the atmosphere have a larger impact on the Earth as they are causing climate change.

Ocean Acidification

When the gases in the atmosphere and the ocean become lopsided, the ocean will absorb more carbon. Kolbert describes the change, “In effect: Every American pumps seven pounds of carbon into the sea.”¹⁸ She goes on to state that the ocean’s pH is expected to reach 7.8 in 2100. When the pH reaches this level, organisms disappear.¹⁹ Ulf Riebesell, a professor at GEOMAR Helmholtz Centre for Ocean Research Kiel, describes how highly tolerant organisms will become more abundant, but the biodiversity will decrease.  Ocean acidification was a factor in at least two of the five mass extinctions, and possibly in a third.²⁰

Climate Change

The increased levels of CO₂ are projected to increase the Earth’s temperatures by as much as seven degrees Fahrenheit by 2050, which would eliminate the remaining glaciers.²¹ The rise in temperature and the melting of the glaciers will raise the level of oceans. The rise in temperature is similar to moving the climate bands poleward by 30 feet each day.²²

Killing Species

Humans kill species for a variety of reasons, including as food sources, for black market sale of animal products such as ivory, to remove agricultural threats, for cultural beliefs, and for sport.

The passenger pigeon is an example of a species that was both hunted for meat and was killed because it posed an agricultural threat to farmers’ crops (Figure 2). The pigeons were an easy target since their flocks were so large; the flocks were so numerous that they would turn the sky dark. These massive flocks posed a threat to farmers’ crops, so farmers shot them. According to Stewart Brand’s TED Talk on de-extinction, the population of passenger pigeons went from five billion to zero in just a few decades.²³

Figure 2: Passenger pigeon flock being hunted in Louisiana. The Illustrated Shooting and Dramatic News. (Public domain)

Elephants and rhinoceros are poached for the ivory in their horns. Even though laws exist to protect these creatures, the value of their ivory horns and tusks drives the black market.

Overharvesting

Many species are endangered or extinct due to humans overharvesting them. This is true of many marine invertebrates, fish, mammals, birds, reptiles, and amphibians. Some have been overharvested for food, medicine, skin, and body parts. Tigers, the passenger pigeon, the Carolina parakeet, and certain primates are a few examples of species that have been overharvested.²⁴ Overfishing is also a prevalent problem. Paul Crutzen, a professor at the Scripps Institution of Oceanography, University of California, San Diego, states, “Fisheries remove more than 25% of the primary production in upwelling ocean regions and 35% in the temperate continental shelf.”²⁵