What Are We Really Saying When We Talk About "Biodiversity"?

Imagine you’re packing for a trip to a place you’ve never been before. You don’t know what the weather will be like, what food you’ll find, or what you might need. So you throw in a little bit of everything—a jacket, sandals, a book, a snack, a water bottle, maybe some weird gadget you found in a drawer. You don’t know which thing will turn out to be useful. You just know that having options is better than not having them.

Now imagine someone says: “You need to get rid of most of your stuff. But you can keep a few items.” Which ones do you choose? You don’t know what you’ll need. So you want to keep as much variety as possible—different kinds of things that might turn out to be important.

This is basically the problem that philosophers, scientists, and policymakers have been wrestling with for decades when they talk about “biodiversity.” Only instead of a suitcase, we’re talking about the entire living world. And the question isn’t just “what should we save?” but something deeper: what do we even mean by “biodiversity” in the first place?

The Word That Wasn’t There Before 1985

The word “biodiversity” is surprisingly young. It was invented around 1985. Before that, people talked about “biological diversity” or “biotic diversity” or just “variety of life.” But the invention of the word didn’t invent the problem. For at least a decade before, scientists had been noticing something alarming: species were going extinct at rates that seemed much faster than normal. And they started asking: does losing lots of different kinds of life matter? Not just because some particular animal or plant is useful, but because losing variety itself might be a problem.

This is where things get interesting—and tricky.

Two Ways Variety Matters: Insurance and Investment

In 1980, an international conservation group called the IUCN wrote something that still captures a key idea. They said that preserving the diversity of life—the range of different genes, species, and ecosystems—is both “a matter of insurance and investment to keep open future options.”

Let’s unpack that with examples a 12-year-old would recognize.

Insurance. Imagine your family has one flashlight. If the batteries die, you’re in the dark. But if you have five different kinds of flashlights—some battery-powered, some hand-crank, one that uses solar—you’re covered no matter what. The variety of flashlights is insurance against things going wrong. In nature, having many different species means that if one species gets wiped out by disease or climate change, others might be able to do its job—keeping the ecosystem running. Nobody knows which species are the “key” ones until they’re gone. That’s the insurance idea.

Investment. Now imagine you’re picking stocks (stay with me). You have no idea which company will be the next big thing. So you buy a little bit of many different companies. The variety of your investments increases the chance that some of them will pay off big. In nature, we don’t know which species might turn out to have a chemical that cures a disease, or a gene that helps crops survive drought. Keeping lots of different species is like having a huge library of solutions we haven’t discovered yet. That’s the investment idea.

So biodiversity—the variety of life—matters because it keeps our options open. It’s a kind of savings account for the future.

But Wait—What IS Biodiversity, Really?

Here’s where it gets messy. The Convention on Biological Diversity (an international treaty) defines biodiversity as “the variability among living organisms from all sources.” That’s awfully vague. It’s like saying “a sandwich is the stuff between bread.” Okay, but what kind of stuff? What kind of bread? How do we measure it?

Some people think biodiversity means the number of species in an area. That’s simple and easy to count. But others point out that this misses a lot. Two areas could have the same number of species but be very different in how diverse they really are. Imagine a soccer field with 100 dandelions and a tropical forest with 100 different kinds of trees, insects, and birds. Same number of species, but clearly the forest has more variety.

So maybe biodiversity should also consider how different the species are from each other. A community of 10 very different species might be more “diverse” than a community of 20 very similar ones. This is where things get technical fast.

The Tree of Life as a Measuring Stick

One powerful way to measure biodiversity is to use the “tree of life”—the evolutionary relationships between species. Here’s how it works.

Imagine you have three animals: a human, a chimpanzee, and a cockroach. The human and chimp are very closely related (they share most of their genes). The cockroach is way out on a different branch. If you measure biodiversity using the tree of life, those three species have a lot of diversity because the cockroach brings in so much different evolutionary history. But if your three species are a human, a chimp, and a gorilla, they’re all close together on the tree—less phylogenetic diversity.

This matters because a species that is the only surviving member of an ancient branch of life (like the tuatara lizard, which is the last of its lineage from the time of dinosaurs) carries a lot of unique evolutionary information. Losing it would mean losing more “features” than losing one of many similar species. Scientists call this “phylogenetic diversity” (PD for short), and some argue it’s the best way to measure biodiversity’s option value—the unknown future benefits we might get.

The Big Fight: What Should “Biodiversity” Mean?

Here’s the thing: philosophers and scientists don’t agree. There are basically three different camps, and they’re not really talking to each other.

The Variationists

These people say biodiversity is fundamentally about variety—counting up different units (species, genes, features) and measuring how much difference there is. They trace their ideas back to the 1970s, before the word “biodiversity” even existed. For them, biodiversity has clear value (insurance and investment) and clear normative weight—we ought to protect it because it matters for future generations. This is the oldest and simplest view.

The Conservation Biologists

These folks say: look, biodiversity is whatever conservation biologists try to conserve. It’s defined by the practice of conservation, not by some abstract scientific definition. This can lead to weird results: under this view, a sacred grove or a monarch butterfly migration route counts as “biodiversity” even though they’re not really about variety. Some conservation biologists have become “eliminativists”—they think the term is so confused that we should just stop using it. Others are “deflationists”—they think “biodiversity” has meaning only in local conservation practice, not as a global scientific concept.

The Socio-Ecological Thinkers

This newer group argues that “biodiversity” has been too biological, too focused on counting species and genes, and disconnected from what actual human communities value about nature. They want to broaden the term to include human relationships with nature, cultural values, and social justice. For them, biodiversity isn’t just about variety—it’s about everything that makes life worth living, including the ways people connect to their environment.

Why This Debate Actually Matters

You might be thinking: “Okay, academics arguing about definitions. Who cares?”

But it matters a lot. Governments use these definitions to decide where to put national parks, which species to protect, and how to spend money. The Convention on Biological Diversity makes international laws based on how “biodiversity” is understood. When scientists report that “biodiversity is declining,” what exactly are they measuring? Different definitions give different answers.

Here’s a concrete example. In 2019, a global assessment reported that one million species are at risk of extinction. Sounds terrible, right? But forty years earlier, in 1981, a report had the same headline: “The Threat to One Million Species.” The problem was recognized before the word “biodiversity” existed. And the worry then was about losing variety and future options for humanity. But in the more recent report, that message is just one of many storylines in a complicated mess of different ways of understanding “biodiversity.”

Some philosophers worry that we now face a “second biodiversity crisis”—not of species going extinct, but of the word “biodiversity” becoming so stretched and confused that it no longer means anything useful. If the term can mean anything, it might end up meaning nothing.

The Uncomfortable Truth

Nobody really knows what “biodiversity” should mean. The word was invented to capture something important—the value of the variety of life—but it’s been stretched, pulled, and redefined so many times that it’s not clear what it’s doing anymore.

Here’s what most people can agree on: variety matters. Having many different kinds of living things—species, genes, ecosystems—is valuable. It provides insurance against disasters, investment in future discoveries, and something that seems morally important to pass on to future generations. But beyond that, the arguments continue.

Maybe that’s okay. Maybe the word “biodiversity” is like a big tent that covers different concerns that sometimes conflict. Or maybe we need to be more careful about what we mean. Either way, the next time you hear someone say “we need to protect biodiversity,” you can ask: “Which kind? And why?” The answers you get might tell you a lot about what they really value.

Appendices

Key Terms

Term	What it does in this debate
Biodiversity	The name for the variety of life, but nobody agrees on exactly what it includes or how to measure it
Option value	The current benefit of having variety, because it keeps future possibilities open—like having options you haven’t used yet
Insurance value	The benefit of having variety as a buffer against disaster—if one thing fails, something else might work
Phylogenetic diversity (PD)	A way of measuring biodiversity using the evolutionary tree of life, capturing how much unique evolutionary history a set of species carries
Variety	The core idea behind biodiversity—having many different kinds of things, not just many things
Complementarity	A calculation of how much new biodiversity a particular area or species adds to what you already have

Key People

Norman Myers (British environmentalist who wrote about the extinction crisis in the 1970s, arguing that losing species means losing unknown future benefits for humanity)
E.O. Wilson (American biologist who popularized the term “biodiversity” in the 1980s and argued for the importance of discovering and cataloguing all species before they disappear)
Daniel Faith (Australian researcher who developed the phylogenetic diversity measure and argued that variety itself has current value because of its link to future generations)

Things to Think About

The gut microbe problem. Your body hosts trillions of microbes. Some are helpful, some are harmful. Should we try to preserve all the microbial variety in our guts? If not, where do we draw the line between “valuable biodiversity” and “stuff we’d rather get rid of”?
The trading problem. If we could save 100 species of beetles OR one species of elephant, which should we choose? The variety argument says the beetles (more different units). But most people would save the elephant. Does this mean variety isn’t actually what we value most?
The future generations problem. We don’t know what people 200 years from now will need or want. How much should we sacrifice today to keep options open for them? Is it fair to ask poor communities to protect biodiversity when they need resources right now?
The definition problem. If “biodiversity” can mean almost anything, is it still useful? Or would we be better off just talking specifically about “species richness” or “ecosystem health” or “evolutionary history” and ditching the vague umbrella term?

Where This Shows Up

Whenever you hear about endangered species. News reports about pandas, tigers, or coral reefs are usually making some assumption about what biodiversity is and why it matters
In debates about new medicines. About 40% of modern medicines come from natural sources. When people argue for preserving rainforests because “there might be a cure for cancer in there,” they’re using the option value argument
In discussions about farming. Modern agriculture uses very few crop varieties. The Irish Potato Famine happened because everyone planted the same kind of potato—no variety meant no insurance against disease
In your own backyard. People who plant many different kinds of plants in their gardens (instead of just grass) are creating more biodiversity. Whether that matters depends on what you think biodiversity is for