A controversial opinion piece on extinction and biodiversity
conservation was published Thanksgiving week in the Washington Post by an
evolutionary biologist. In the last few days, scathing assessments of the op-ed
came across my Twitter feed, but I avoided the article until today. I finally
dove in, and here are a few thoughts that emerged during the time I could
muster on a Sunday evening.
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| Diverse assemblage of flowering plants in the understory of a montane forest in the John Muir Wilderness, California, summer 2017. |
In the op-ed R. Alexander Pyron argues that “extinction is
the engine of evolution”, states that almost all species that have ever lived on
Earth have already become extinct, and notes that extinctions are inevitable for
all currently living species. He argues that despite the loss of a species “the
world will be none the poorer from it”. From this assortment of assertions (some
obviously true like the inevitability of eventual extinction of all species),
he then goes on to build a case that conservation is only prudent in-so-far as
it benefits humankind.
In taking a rather extreme view of the role of conservation,
the visceral reaction of many biologists to publication of this op-ed in a
major media outlet is understandable. But does the author miss the mark? I
think so on several major fronts:
1. The author paints an incomplete and superficial view of
evolution and the production of biodiversity. Succinctly put, extinction is not
the “engine” of evolution as the author claims. Rather, natural selection is
the mechanism of evolutionary change, and as another evolutionary biologist S.
Claramunt points out in a rebuttal, natural selection operates at the
population level, not at the species level that Pyron discusses. Natural
selection is one of the key processes of microevolution, which involves the generation
of genetic variation within a species (novel genotypes and phenotypes) and its
subsequent persistence or demise in the next generation by selection. This
initial step in microevolution – the generation of genetic variability such as
by mutation or genetic drift – is inherently a creative process, albeit a
mostly random and inefficient one. In this light, the two major steps of microevolution
(generation of variability and environmental selection) are both productive and destructive. Claramunt and Caroline Tucker address other controversial statements by Pyron here and here.
Where Pyron may be partially correct about extinction is its
role in producing biodiversity at the macroevolutionary level. As one example,
he cites the radiation of mammals and birds following the global mass
extinction that wiped out the dinosaurs. However, while extinction may be an
occasionally helpful mechanism for promoting radiations of new lineages over
geologic time, it is certainly not necessary to generate new species.
Speciation, on the other hand, is
requisite for the creation of new biodiversity, and it can proceed easily
enough in the absence of extinction through allopatric or sympatric mechanisms.
A report just this week suggests the very rapid evolution of a new finch
species in the Galapagos stemming from a hybridization event. Many species form
from others without the parent lineage going extinct, increasing biodiversity.
Moreover, when one surveys the history of life on Earth, despite messy
fluctuations over geologic history, there may be more biodiversity today than
during any geologic era of the past. For a net increase in global diversity to
occur over the long term, long-term speciation rates have been greater than
extinction rates. If anything speciation is the “engine” of evolution.
2. Though Pyron advocates for conservation if it serves a
direct human need, the extent of species he seems willing to advocate for
probably falls far short of the number really needed, even from simply a
utilitarian point of view. The problem here is obvious: any argument about
selective conservation of a smaller fraction of species fails to recognize the unknown
inter-dependency of species in all ecosystems. What of the undiscovered
connections and dependencies in the global web of life of which we are still woefully
ignorant as ecologists? What of species that hold future drug discoveries, or
that will only in the future be discovered to be critical to the persistence of
other species or even the functioning of whole ecosystems? Even if impending
extinction provokes difficult conservation decisions about which species to
save in the future, those decisions need to be informed by understanding the
ecological roles of the species and the relative loss of services that could
result from extinction. I posit that we presently know very little about the
ecological roles of the vast majority of species to be able to effectively
triage our conservation efforts.
This notion of the interdependency of life is not just the
poetry and song of nature lovers. Rigorous empirical research manipulating
biodiversity levels at smaller spatial scales over the last two decades
demonstrates that biodiversity often matters in order to sustain ecosystem
productivity, stability, or other services upon which humankind depends (Cardinale
et al. 2012, Lefcheck et al. 2015). Put simply, a grassland with two or three
species is not the same as one with several dozen species; that extra plant
biodiversity has measurable effects on the functioning of the grassland
ecosystem. The importance of biodiversity for ecological functioning extends to
genetic diversity within a species (Hughes & Stachowicz 2004), and by extrapolation
(though we cannot experiment on continental or global scales) also reasonably
extends to the whole biosphere: global diversity sustains a global suite of
diverse ecosystem functions. A prudent, precautionary approach is to conserve
as much global biodiversity as possible.
3. Finally, the op-ed fails on the ethical front. I won’t
argue from a particular religious or philosophical point of view here, but
rather simply from a humanistic one. To appreciate, conserve, and cultivate
biodiversity is an inherently human experience. We need look no further than
zoos and gardens to understand our intrinsic desire to connect with other
species. As much as Homo sapiens is a
destructive, warlike, compulsive, and competitive species, we are also inherently
caring, empathetic, altruistic, and prudent. Biodiversity enriches our human
experience, spiritually and aesthetically. And conservation of a mere fraction of
Earth’s species upon which we are most dependent for food and shelter will not
satisfy that enduring need for connection to the biosphere. Pyron’s
anthropocentric arguments about conservation were taken to an extreme in the
op-ed, and in so doing that viewpoint paradoxically harms our species by artificially
disconnecting us from our deep human need for biodiversity.
The global, bipartisan efforts we put towards conservation,
towards preservation of wilderness, towards city and national parks attest to
the value we place on the conservation of other species. We cannot escape the
deep connection (the “biophilia” of E.O. Wilson) that we have as humans to other
forms of life. Though they lived long before the term “biodiversity” was
coined, naturalists such as Humboldt, Haeckel, and Muir intuitively assessed
the interconnected nature of life through observation of the natural world
(Wulf 2015). Muir understood this dependency of all species on each other and
asked a powerful ethical question useful as an antidote to an overly
anthropocentric view of the value of biodiversity: “Why ought man to value
himself as more than an infinitely small unit of the one great unit of
creation?”
References
Cardinale et al. 2012.
Biodiversity loss and its impact on humanity. Nature 486:59-67.
Hughes AR, Stachowicz JJ. 2004. Genetic diversity
enhances the resistance of a seagrass ecosystem to disturbance. Proceedings of
the National Academy
Lefcheck et al. 2015. Biodiversity
enhances ecosystem multifunctionality across trophic levels and habitats.
Nature Communications 6:6936.
Wulf A. 2015. The Invention of Nature. Vintage Books, New York .
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