Speciation and extinction are ordinary processes in the natural world. The fossil record suggests that most of the species that have ever lived on Earth have gone extinct.  About 10 million species of higher organisms now occupy the world. Averaged over long periods, about one species goes extinct each year for every one million species that are present. Thus, at nominal rates, about 10 should go extinct this year. Most, being very small and perhaps still without a name, will disappear quietly without notice.

The species disappearing are presumably balanced by new species evolving to join the Earth’s biodiversity. The evolution of new species is also a natural process, albeit at extremely slow rates. Conservation biologists have been looking for the appearance of a new species for the past 100 years or so, and I have yet to see a report of even one such event.

The long-term average rate of extinction masks periods of mass extinction in Earth’s history.  Digging through this record, paleontologists see five major periods of extinction, when lots of species disappeared in a relatively short period of time.  One of these about 65 million years ago, took the dinosaurs.

Today, the rate of species loss is about 100 to 1000 times greater than the long-term historical record.  Are we entering another epoch of mass extinction?  Are humans to blame?  Will we be haunted by the ghost of extinctions past?

Unfortunately the answer to these questions seems to be “yes.”  Currently, we are witnessing a major extinction of the Earth’s species at our own hands.  Loss of habitat is likely to be the largest cause of species extinction, as we usurp natural land for agriculture, roads, and habitation.  Upon habitat conversions, more than 75 percent of local species are usually lost, and the abundance of those remaining is reduced nearly 40 percent.

Introductions of species from far-off lands, which out-compete species at home, are also a major cause of extinction.  The native birds of Hawaii are largely extinct in the face of competition from introduced, exotic competitors and avian malaria.  We are homogenizing the diversity of the world and in the process losing a considerable amount of its richness.

Armed conflict, hunting and poaching are likely to cause the extinction of some of the remaining big animals in Africa, and projected changes in climate are estimated to drive about one-third of today’s species extinct within a few centuries.

Setting aside the Passenger Pigeon, which humans set upon with unusual vengeance, the most vulnerable species are those with relatively small population sizes and limited range.  In the United States, these are species that the Endangered Species Act was designed to save.  But rare species are also found throughout the world, where their protection is limited.  Bird-watchers and those on safari pay big money to go see them.

There are lots of reasons to preserve species.  Some species are of economic value for timber, fisheries, and ecotourism.  Others aid human health, provide and protect agricultural crops, and lower damages to human infrastructure.  The loss of the wolf as a predator of white-tailed deer in the eastern United States is now associated with the expenditure of $4 billion each year for repairs to automobiles that collide with deer.

Sometimes, we can substitute human ingenuity to perform the function of species, often at considerable incremental cost.  Loss of the predators of insects that feed on crops is the basis of a large portion of the $29 billion that is spent on pesticides each year. These pesticides often poison species, including us, that were not intended as targets.

Being a relatively new species to evolve on Earth and possessing putative sapiens skills, humans have a compelling ethos to preserve biodiversity.  As Michael Northcott points out, in the correct Hebrew translation of the Bible, God instructs humans not only to have dominion, but to be a steward of the natural world.  Certainly, we should not stand by and shrug our shoulders when we hear that humans have endangered a species, which is now likely to go extinct. The world will be a less healthy, less productive, and less interesting place when it is impoverished of nature.

Each year, people are born and people die.  That’s natural, but when we cause someone to die, it’s called murder. Murder is unethical.

Each year species appear and species disappear. That’s natural, but when humans eliminate a species, it’s called extinction—the equivalent of murder.  Extinction is unethical.

Like it or not, we are keepers of the biosphere, and our judgment day will assess how well we did.



Barnosky, A.D. and 11 others. 2011. Has the Earth’s sixth mass extinction already arrived?  Nature 471: 51-57.

Keesing, F. and 11 others. 2010.  Impacts of biodiversity on the emergence and transmission of infectious diseases.  Nature 468: 647-652.

Newbold, T. and 40 others. 2015.  Global effects of land use on local terrestrial biodiversity.  Nature 520: 45-50.

Northcott, M.  1996   The Environment and Christian Ethics.  Cambridge University Press.

Pimm, S.L., G.J. Russell, J.L. Gittleman, and T.M. Brooks.  1995. The future of biodiversity. Science 269: 347-350.

Thomas, C.D. and 18 others. 2004.  Extinction risk from climate change.  Nature 427: 145-148.

2 thoughts on “Extinction

  1. Wow, thanks Bill for this provocative article. You provide a profound perspective on extinction — extinction=murder. I feel so sad and frustrated by the impact of incessant human activity on the natural world. We seem so hell bent on taking advantage of our ability to use nature as a source of resources and as a dumping ground… this morning when I let the dog outside, I heard a song bird singing in the trees behind our home. We whistled back and forth a bit until the little critter got bored I guess.

    Thanks to Rachael Carson I had that moment. Thanks to you, I have better understand of the connection between human nature and the wilder natural world.

    1. Accurate, vitally important, and well-presented as usual.

      For better or worse, however, I must report that there will be no single literal “judgment day.” Rather, every day is judgment day. To wait for the proverbial one, which millions appear to be doing, would be a substantial mistake, and would come too late for adequate corrective action.

      Our current wrestling match with climate change denial reminds us that this marvelous excuse-making factory sitting on our shoulders continuously demonstrates its capacity to convert lemons into oranges and vice versa. In doing so, it creates or aggravates nearly every problem we have in living on Earth.

      This is why we need all the citizen science we can get. While the people we refer to as “scientists” can identify and construct functional solutions for most problems we face, there aren’t enough of them, they are greatly underrepresented in our legislative assemblies, they are not usually trained for public communication, and neither they nor the public view their pole as policy advocates. We need far better science literacy taught in our K-college schools, not just by requiring additional science courses, but by teaching broadly the theory and practice of rational problem-solving, including its practical application in the community. The goal should be holistic thinking that can be applied to all problems rather than simply skills for job preparation.

      As for the scientists, I submit that that we need to have them move out of the restrictive view of themselves as politically neutral technical experts whose roles should be restricted to research in hopes that societal decision-makers will notice and appropriately apply the findings. They need to become much more active in political controversies about which they have relevant knowledge. The risk of tarnished reputations is far outweighed by the advantages of greater contribution to public education and enhanced influence in political decision-making processes.

      Climate change, I think, presents a greater danger than did the crisis of World War II. Yet for many, the enormity of its implications is an incentive to turn one’s head and pretend it will go away. As in World War II, a massive mobilization of human resources, prominently including scientists in many fields, is called for.

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