R. Alexander Pyron's Nov. 26 Outlook essay, "Species die. Get over it," was scientifically naive and very out of date. Modern biology moved from thinking in terms of individual species in the 1950s, growing to understand that the inhabitants of Earth depend on each other in complex ecosystems on which each species, humans included, are utterly dependent.

The author noted that we are now deep into the sixth mass extinction, but failed to recognize that this is a giant, perhaps existential threat to humanity. The species we see disappearing point to a basic, human-caused sickness in ecosystems across the world, the ultimate consequences of which we cannot yet define, but the end of our unsustainable methods of agriculture is one likely outcome. The loss of a snail darter or black-footed ferret should be seen as canaries in the mine: a strong warning that we are behaving in a way that is damaging the ecosystem.

Earth has recovered from the prior mass extinctions, but the recoveries took eons, longer than the history of Homo sapiens. The explosion of new species after the extinctions was possible because the driver and the top-level predators perished also, allowing new and novel species to flourish at least for a time. The sixth extinction may be different because we, the apex predator, are the cause. We may survive the extinction and we may lack the will or wisdom to change our behavior.

Craig Miller, Alexandria

R. Alexander Pyron's essay neglected the full significance of this extinction, the sixth in the geologic record. Although extinctions are natural, this one is like none other; it is happening faster than any other, is caused by one species (us) and will leave a relatively barren, infertile landscape, crisscrossed with roads and buildings and with which evolution will struggle to proceed.

To ensure life, human and especially otherwise, we must learn to better work with nature, to better emulate natural systems, to better appreciate all that nature produces: a diverse and wondrous natural world that provides ecosystem services (e.g., soil, clean air and water) estimated to be worth $33 trillion annually .

Peter McLean, Middletown, Del.

R. Alexander Pyron's essay will give support to those who even now are trying to destroy the Endangered Species Act, drill for oil in the Arctic National Wildlife Refuge and exploit other public lands for profit. He argued that extinction is natural and inevitable, so we shouldn't worry about the mass extinctions being caused by human actions — oh, except to save the species that are useful to us or the ones that are "easily saved," such as the bald eagle and the peregrine falcon. (As one who worked on conservation efforts for those species, I can assure him he is wrong about how "easy" that was.) Who needs polar bears? And introduced pythons are just as desirable as the native species of the Everglades, right?

I'm guessing Mr. Pyron either didn't read or didn't understand the writings of America's most influential conservation writer, Aldo Leopold, who taught that "to save every cog and wheel is the first precaution of intelligent tinkering."

Mr. Pyron is arrogant to believe that we already understand what species may be useful in the future, for example as sources of new medicines. Leopold said, "There are some who can live without wild things and some who cannot." Millions of us cannot, and we will go on trying to save those useless polar bears and every other cog and wheel.

Megan Durham, Reston

The idea that we should let species go extinct even if humans are responsible, and preserve biodiversity only when it helps us, is abhorrent. It ignores the interdependence of flora and fauna, discounts what may be important to people other than the author, and contravenes lessons in the Bible to value all of creation. This seems to be a path to satisfy only certain people who may benefit from certain changes to our culture.

Jonas Weiss, Silver Spring

This paean glorifying extinction was feeble in the extreme, even to a layperson.

Immense disruptions in ecosystems threaten unknown consequences. The destruction of large predators, for example — lions, tigers, bears, wolves, leopards — would destabilize the propagation of prey animals, perhaps causing large fluctuations between disease and starvation and pulses of recovery and overpopulation. The populations of wolves and prey on Lake Superior's Isle Royale, for instance, were anything but stable, specifically because of meager species diversity.

In such an unsettled scenario, there is no predicting whether new disease agents might arise within the disrupted species, perhaps jumping to livestock as effortlessly as did tuberculosis and other diseases.

Similarly, more-or-less good-faith reliance on antibiotics has resulted in the selection and dominance of antibiotic-resistant pathogens. There is no predicting what the final chapter of this story will bring.

Indeed, the writer's emphasis on the inevitability of species extinction implies that the extinction of the human family itself — represented by a single surviving species — would be of little note in coming millennia, if not sooner. The primates are hardly a linchpin the biosphere could not spare. If orangutans can be recklessly extirpated, intentionally or not, why not humans?

Dave O'Connell, Gaithersburg