Scientists say simplifying life on Earth will make us sick

A recent UN report on biodiversity says we’re doing a lot lately to simplify life on Earth — which is actually a bad thing. Life has evolved to be complex, rich and diverse. The current massive decline in biodiversity is expected to make the planet as a whole ecosystem a bit weaker, more fragile.

Now, scientists say loss of species diversity also raises the risk of human disease. But first, a quick look at what we mean by “biodiversity” by Mr. Christopher’s 7th period biology class:

The fact that animals and humans can exchange diseases is fairly well known, even if the word for it  — zoonosis — isn’t in common use. It’s an important area of global health. Paul Allen just gave $26 million to Washington State University in support of the study of the transfer of disease between animals and humans.

Most human diseases, in fact, begin in animals and so you might be forgiven for thinking that reducing the number of animals around us could help reduce the risk of any number of diseases. Wrong-O.

The new report in the journal Nature, based on an analysis of a dozen studies focused on the emergence of a number of zoonotic diseases like West Nile virus and Lyme disease, says it appears to be just the opposite:

The finding suggests that loss of species from an environment could have dangerous consequences for the spread and incidence of infections, including those that affect humans….”A pattern is emerging which shows that biodiversity loss increases disease transmission,” says lead author Felicia Keesing of Bard College in New York.

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Some of the current rate of loss of biodiversity is due to land use policies, habitat destruction, human population growth and the accompanying environmental destruction.

But some is also due to climate change, which has made this report of high interest to those attending the Cancun climate summit this week. Bloomberg News quotes another scientist on the study:

“Global change is accelerating, bringing with it a host of unintended consequences,” says study co author Sam Scheiner, an ecologist and disease specialist at the National Science Foundation.

It’s not clear to the researchers exactly why disease risk goes up as biodiversity goes down. But the assumption is that as the Earth’s ecological diversity is diminished certain pathogens — viruses, bacteria or other pests — find it easier to spread due to lack of biological competition and the targets of infection also become less able to resist attack. As Kate Shaw in ArsTechnica reports:

Research also shows that the types of species that persist in the face of declining biodiversity tend to be more prone to infection than the species that are lost first…. In terms of disease emergence, high biodiversity initially helps pathogens gain a foothold in an ecosystem, since there are many available host species. However, once a disease is established, the converse is true. High host density favors transmission, and this usually occurs only in areas with low biodiversity, such as agricultural areas.

Side note: Some top scientists believe Haiti’s cholera epidemic is likely due to environmental conditions even though many continue to believe the massive outbreak was started by infected UN peacekeepers who brought the infection with them. Cholera can be passed person-to-person, but it is also a zoonotic disease that can be transmitted animals-to-human — or via the environment to humans.

The UN has declared 2010 the International Year of Biodiversity and called for aggressive action to reverse the current rapid decline in the number of plant and animal species on Earth. Here’s the pitch from UN Secretary General Ban ki-Moon:

UN Secretary General Welcome Message for the 2010 International Year of Biodiversity from CBD on Vimeo.

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Editor Tom Paulson is founder and lead journalist at Humanosphere. Prior to operating this online news site, he reported on science,  medicine, health policy, aid and development for the Seattle Post-Intelligencer. Contact him at tom-at-humanosphere.org, follow him on Twitter @tompaulson and/or send a comment below.