The Tragedy of the Commons

In my recent post on greed, I explained how the underlying psychology that leads some people to have an intense and selfish desire to acquire wealth evolved. In doing so, I focused on how these traits favored individuals that had them in the past. One reader pointed out that this leads to resource depletion in humans (which it does), and wanted to know whether this or any other “bad outcomes” occur in other species.

The drive to leave more surviving offspring than other individuals is integral to the evolution of all traits. Reproduction is the only currency of natural selection, and all traits are tied back to this in one way or another. Survival is an important trait, but it is only important so far as living longer allows one to leave more offspring. Social behavior is important for some species, but only if it improves survival and reproduction. The same goes for intelligence, opposable thumbs, wings, or any other trait.

It’s obvious to see how the drive for reproduction can be bad for other species. For example, if an animal enhances its survival and reproduction by being a predator, the survival and reproduction of its prey will suffer — being eaten for lunch certainly qualifies as a “bad outcome.” For this post, though, I’ll focus only on how the evolutionary ambitions of a species can hurt itself.

Parasites have the same drive to reproduce that other organisms have, although the drive is based entirely on physiology instead of having a psychological component. Their lifestyle requires them to be careful (in physiological and evolutionary terms) about how fast they consume their resources (their hosts). If they reproduce too fast inside their hosts, the host will become so sick that it cannot transmit the infection effectively anymore. The virulence (pathogenicity) of a parasite is carefully tuned to suit the host. If a parasite jumps to a new host species, the virulence may be too high to be good for the parasite. This is exactly what happens with ebola.

The ebola virus sometimes infects humans, but we are not its primary host. In humans, ebola is very contagious but it kills the host very quickly — too quickly to infect enough other hosts. For this reason, ebola outbreaks in humans tend to “burn out” fairly quickly and do not infect large portions of our population. Humans are the virus’s resources, and by reproducing so quickly, the resources are depleted and the virus population dies out.

Electron micrograph of an ebola virion. Image from

In the boreal forests of North America, the Canadian lynx (Lynx canadensis) has a 9- to 11-year cycle of population increase and decrease. The Canadian lynx specializes in hunting the snowshoe hare, and they are very good at it. Lynxes that are better at catching snowshoe hare will get more resources, and are able to have more offspring. These offspring will inherit a superior ability at catching snowshoe hares, allowing them to have more offspring of their own. Hares are renowned for their rapid reproduction, but the lynx is renowned for its ability to kill hares. When the lynx population gets too big, they will kill so many of the hares that there is not enough food left to support the lynx population. The lynxes starve to death and the population crashes.


Canadian Lynx (Lynx canadensis). Image from

This is obviously not a complete list of how resource consumption can result in problems for non-human species, but it shows that it can be a real problem. Most resources are limited, and the tragedy of the commons applies to everyone, human or not.



Have a topic you want me to cover in a future post? Let me know in the comments or on twitter @CGEppig.


About Christopher Eppig, Ph.D.

I have a Ph.D. in biology and a passion for sharing my knowledge and understanding of the natural world with anyone who will listen. At a time where science is permeating public life more than ever, it is especially important that the public understand what science is, and how its findings intersect with their own lives. In addition to the more practical benefits of scientific literacy, I believe strongly that understanding the natural world enriches peoples lives. The man behind the curtain is not me — it is the real world, which we can discover through science, and it is beautiful. Let me show it to you.  Follow me on twitter @CGEppig. View all posts by Christopher Eppig, Ph.D.

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