The history of life on Earth has been marked five times by events of mass
biodiversity extinction caused by extreme natural phenomena. Today, many
experts warn that a Sixth Mass Extinction crisis is underway, this time
entirely caused by human activities.
A comprehensive assessment of evidence of this ongoing extinction event was
published recently in the journal Biological Reviews by biologists from the
University of Hawai‘i at Mānoa and the Muséum National d’Histoire Naturelle
in Paris, France.
“Drastically increased rates of species extinctions and declining abundances
of many animal and plant populations are well documented, yet some deny that
these phenomena amount to mass extinction,” said Robert Cowie, lead author
of the study and research professor at the UH Mānoa Pacific Biosciences
Research Center in the School of Ocean and Earth Science and Technology
(SOEST). “This denial is based on a highly biased assessment of the crisis
which focuses on mammals and birds and ignores invertebrates, which of
course constitute the great majority of biodiversity.”
By extrapolating from estimates obtained for land snails and slugs, Cowie
and co-authors estimated that since the year 1500, Earth could already have
lost between 7.5 and 13% of the two million known species – a staggering
150,000 to 260,000 species.
“Including invertebrates was key to confirming that we are indeed witnessing
the onset of the Sixth Mass Extinction in Earth’s history,” said Cowie.
The situation is not the same everywhere, however. Although marine species
face significant threats, there is no evidence that the crisis is affecting
the oceans to the same extent as the land. On land, island species, such as
those of the Hawaiian Islands, are much more affected than continental
species. And the rate of extinction of plants seems lower than that of
terrestrial animals.
Unfortunately, along with science denial taking a foothold in modern society
on a range of issues, the new study points out that some people also deny
that the Sixth Extinction has begun. Additionally, others accept it as a new
and natural evolutionary trajectory, as humans are just another species
playing their natural role in Earth’s history. Some even consider that
biodiversity should be manipulated solely for the benefit of humanity – but
benefit defined by whom?
“Humans are the only species capable of manipulating the biosphere on a
large scale,” Cowie emphasized. “We are not just another species evolving in
the face of external influences. In contrast, we are the only species that
has conscious choice regarding our future and that of Earth’s biodiversity.”
To fight the crisis, various conservation initiatives have been successful
for certain charismatic animals. But these initiatives cannot target all
species, and they cannot reverse the overall trend of species extinction.
Nonetheless, it is essential to continue such efforts, to continue to
cultivate a wonder for nature, and crucially to document biodiversity before
it disappears.
“Despite the rhetoric about the gravity of the crisis, and although remedial
solutions exist and are brought to the attention of decision-makers, it is
clear that political will is lacking,” said Cowie. “Denying the crisis,
accepting it without reacting, or even encouraging it constitutes an
abrogation of humanity’s common responsibility and paves the way for Earth
to continue on its sad trajectory towards the Sixth Mass Extinction.”
Reference:
The Sixth Mass Extinction: fact, fiction or speculation? by Robert H. Cowie,
Philippe Bouchet and Benoît Fontaine, 10 January 2022, Biological Reviews.
DOI: 10.1111/brv.12816
Tags:
Planet and Environment