Putting Humans and Biodiversity into Context

Action(s): Donate to non-profits that educate women (I don’t know of a great international one, if you have one please share in the comments and I’ll link to it here), protect the environment, or choose to be child free.

People are often surprised to hear that I do not want to have children. They either argue with me or deny that my wants are legitimate. That I’ll somehow mature despite being in my early 30s and having developed a successful life and career. Sometimes they turn to anger and call me selfish for not wanting to reproduce. All of this while I try to defend myself discussing my concerns for the environment and the fate of the planet.

My fear is that conservationists and those of us that are child free because of environmental concerns have not done a great job of describing the scope of the environmental problem we see. News articles about the loss of biodiversity around the planet and dire warnings for the future of the earth are just too abstract to relate to.

For example, indicating that bird populations declined by 3 billion in North America in the last 25 years is interesting, but also allows you to draw the conclusion “so what, there are still BILLIONS of birds, what’s the real problem here?” We don’t eat these birds or hunt them for trophies or Chinese medicine, so there is no human pressure.

Instead of editorializing, I thought it might be interesting to approach the problem of explaining human population and our ecological role slightly differently and with graphs.

Taxonomy and Humans

Before relating the problem of humanity and biodiversity, we can review how biologists have classified life on earth. Biologists over the last 150 years have worked hard to classify all life in a logical way. They do this by using a taxonomy where they classify a group of organisms based on shared characteristics. They then group those shared characteristics into more detailed categories based on how organisms have evolved.

For example, the biggest groups of life currently defined by biologists are: Bacteria, Archaea, Protozoa, Chromista, Plantae, Fungi, and Animalia. All of those groups of life sit at the “Kingdom” level of the taxonomic tree, which has 8 levels.

And as you work your way down the tree you eventually get to each individual species that you can readily recognize, such as us – humans or homo sapiens. The below table will give you an idea of how granular each category is.

Humans vs. Other Animals

As you can see – humans are a very small branch on the entire taxonomy in biology.

As humans we have been incredibly successful at competing for the earth’s resources and increasing our population. To put this into context, it might be interesting to view the weight of humanity vs. the weight of other types of living organisms. I use weight as a proxy for the amount of life and resources an organism contains.

Humans vs. Our Closest Relatives

The closest relatives to humans living today are chimpanzees (bonobos included) and gorillas, who are related to us at the level of “Family” on the tree of life.

According to Wikipedia there are approximately 250,000 chimpanzees (avg. weight: 50kg) living in the wild today and approximately 105,000 gorillas (avg. weight: 125kg) living in the wild.

Our nearest relatives occupy just 0.0053% of the weight of the earth when compared to humans.

Humans vs. Primates

Moving up the tree of life to primates, you’ll find over 500 different species of primates alive today. From humans, to gorillas, to langurs, to gibbons, to tamarins. Over 60% of primates are now threatened with extinction and ~75% have declining populations.

This category of species is much larger, so I’ve approximated the weight of all primates by taking the estimated weight of the 10 most populous primate species and multiplying that entire weight by 3x.

According to this estimate all primates occupy just 0.024% of the weight of the earth when compared to humans.

Humans vs. Wild Mammals

Mammals are probably the most common types of animals that first jump to mind when we think of the richness of the animal kingdom. Almost all of the characteristic mega fauna that humans actively try to protect and save fall into this category. Elephants, tigers, pandas, and all the other poster animals for conservation organizations fall into this category.

There are over 5,400 different mammal species on this planet and they are extremely diverse in size and distribution. Rats for example fall into this category as well as whales. Given the diversity of life and the more than 5,400 mammals living today, you would expect wild mammals to outweigh humans, but this is not the case.

Moving away from using raw weight to compare animals, the rest of this blog post will use the results of a research paper that attempts to estimate the entire biomass of earth through measuring the estimated carbon in each living thing.

According to The Biomass Distribution of Earth the cumulative weight of humans greatly outweighs the weight of wild mammals. Their best illustration of this comes from a chart in the appendix of their paper:

This chart attempts to show the cumulative biomass of mammals living before human civilization started to take a toll on biodiversity globally and the cumulative estimated biomass of wild animals, humans, and livestock living today. The implications of this chart are terrifying to think about.

The entire estimated stock of carbon in wild animals prior to human impact on the planet is lower than only the amount of carbon in humans today before including the weight of carbon in livestock that we use to feed ourselves. The number of humans on this planet does not feel sustainable when looking at these numbers.

New Humans vs. Primates

At the top of this blog post I compared the weight of humans vs. the weight of primates. The relative magnitude was so large as to make the comparison meaningless. Given that humanity continues to grow and the global population is expected to surpass 10 billion over the next 50 years, another way to look at this is to compare the current human birth rate to the entire stock of primates on the planet.

The earth is expected to add approximately 80 million people in 2019 (deaths are taken into account). Just those 80 million people born in 2019 at their estimated adult weight will weigh 41x all primates.

Or put another way, every 9 days the planet is adding enough people (assuming adult weight) to exceed the full weight of all 500+ species of primates globally.

Conclusion

People are often surprised by my lack of interest in having children. Many claim that it is a moral imperative to pass on your genetics to a new generation and to make sure that humanity keeps thriving.

With 7.8 billion people and counting, humanity is putting a massive toll on the earth and the great biodiversity that evolved over millions of years. Scientists almost unanimously agree that the next major extinction event will be led by humans and our impact on this environment. No wonder this is the case, when you look at the weight of life we occupy relative to other mammals on this planet.

Given the ecological crisis we face, I feel that our true moral imperative is to stop growing the size of the human population.

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