Human-Induced Mass Extinction Severely Dismantles Life’s Evolutionary Network

Human activities have led to an accelerated rate of extinction among vertebrate species, resulting not only in the disappearance of individual species but also of entire genera, critically undermining global biodiversity. Termed as “biological annihilation” by researchers, this phenomenon has far-reaching implications for human existence, ecological balance, and potential advancements in medicine, thereby necessitating immediate, large-scale interventions.

Notable examples like the passenger pigeon, the Tasmanian tiger, and the Baiji (a dolphin from the Yangtze river) represent the broader phenomenon often referred to as the sixth mass extinction. This rapid decline in animal populations is occurring hundreds of times faster than their natural extinction rates, primarily due to human-induced factors.

Recent research from Stanford University and the National Autonomous University of Mexico, published in the Proceedings of the National Academy of Sciences, suggests that the problem might be even more grave. Each of the aforementioned species was also the last existing member of its genus—a taxonomical rank higher than species.

While past discussions have concentrated on the extinction of species, this new study by Gerardo Ceballos, senior researcher at the Institute of Ecology at the National Autonomous University of Mexico, and Paul Ehrlich, Bing Professor of Population Studies, Emeritus, at Stanford University, reveals that entire genera are also disappearing. This has been described as a “dismantling of life’s evolutionary lineage.”

In Ceballos’ words, “Long-term impacts on life’s evolutionary progression are immense, and these disruptions will also have substantial implications for human society within this century.”

“Our ongoing extinction crisis erases our sole known living counterparts in the universe,” added Ehrlich, who also holds an emeritus senior fellowship at the Stanford Woods Institute for the Environment.

Catastrophic Loss on Multiple Fronts

Recent improvements in databases from the International Union for the Conservation of Nature and Birdlife International have allowed researchers to examine extinction at the level of genera. Analyzing 5,400 genera of terrestrial vertebrates that include 34,600 species, Ceballos and Ehrlich discovered that 73 genera have become extinct since the year 1500. The worst affected were birds with 44 genera extinctions, followed by mammals, amphibians, and reptiles.

The present rate of genus extinction among vertebrates surpasses historical rates by a factor of 35, based on calculations by Anthony Barnosky, professor emeritus of integrative biology at UC Berkeley. Without human intervention, only two genera would have likely become extinct over the last million years. Thus, human activities have caused a wave of extinctions that would naturally take approximately 18,000 years to occur.

Ceballos advises caution against alarmism but emphasizes the urgent necessity to communicate the magnitude of the crisis, stating, “The ethical imperative is clear; we must convey the seriousness of the situation as we are deeply concerned.”

Compounded Impact, Expanded Consequences

The extinction of genera has more far-reaching consequences than the loss of individual species. When a species becomes extinct, other species within its genus often step in to fill the ecological void, preserving the balance to some extent. But when an entire genus is lost, the void is much larger, requiring tens of millions of years of evolutionary development to recover—a timeframe humanity cannot afford to wait for, says Ceballos.

For instance, the increase in Lyme disease can be traced back to the extinction of the passenger pigeon. Once a competitor for food with white-footed mice, the primary carriers of the disease, the absence of the pigeon has led to an explosion in mouse populations and consequently, human Lyme disease cases.

This is but a single example. The loss of multiple genera could trigger a series of cascading catastrophes for human civilization. It also limits our scientific understanding, as highlighted by the extinction of the gastric brooding frog, which had potential implications for studying diseases like acid reflux.

Imperative for Coordinated Action

In the quest to mitigate further losses and their societal ramifications, Ceballos and Ehrlich call for sweeping political, economic, and social reforms. Special attention should be given to tropical regions due to their high concentration of both extinct and critically endangered genera. Enhanced public awareness and integrative conservation policies are needed, especially given the interplay between mass extinction and the escalating climate crisis.

“The escalation of human population size, increasing resource consumption, and the unequal distribution of consumption are all significant contributors to the current crisis,” the researchers stated.

Continuing on this path while expecting to preserve biodiversity is untenable, warns Ehrlich: “It’s akin to sawing off the branch on which you are seated.”

Reference: “Dismantling of Life’s Evolutionary Lineage via Mass Extinction of Animal Genera” by Gerardo Ceballos and Paul R. Ehrlich, 18 September 2023, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2306987120

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More about Biological Annihilation

• Proceedings of the National Academy of Sciences
• International Union for the Conservation of Nature
• Birdlife International
• Stanford University School of Humanities and Sciences
• National Autonomous University of Mexico’s Institute of Ecology
• Stanford Woods Institute for the Environment
• Climate Crisis and Biodiversity
• UC Berkeley Department of Integrative Biology