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Trevor Hancock: Humans are the most invasive species of all

Two recent stories on species extinction — one global, the other local — caught my eye last month. Globally, the World Wide Fund for Nature released its biannual Living Planet Report.

Two recent stories on species extinction — one global, the other local — caught my eye last month.

Globally, the World Wide Fund for Nature released its biannual Living Planet Report. This report tracks the abundance of more than 14,000 populations of over 3,700 vertebrate species around the world; amphibians, reptiles, fish, birds and mammals.

Between 1970 and 2012, these populations declined by 58 per cent, up six per cent from two years previously. In fact, it is worse than that, since these are data from four years ago. On land, populations have declined by 38 per cent, and by 36 per cent in the oceans. But the decline in freshwater species is dramatically worse — 81 per cent since 1970.

In short, we are causing a sixth Great Extinction. The WWF attributes these dramatic declines to four main factors: Habitat loss, food production, climate change and over-exploitation of species. And it warns “people are at risk, too. Without action, the Earth will become much less hospitable for all of us.”

The health benefits of biodiversity were the subject of a 2015 report from the Montreal-based Secretariat of the Convention on Biological Diversity and the World Health Organization. The report concluded that “biodiversity is a key environmental determinant of human health, and the conservation and the sustainable use of biodiversity can benefit human health by maintaining ecosystem services and by maintaining options for the future.”

As the Duwamish Chief Seattle is reported to have said in about 1854: “We are part of the web of life, and whatever we do to the web of life, we do to ourselves.” What we are doing to ourselves is not pretty.

The local story that caught my eye (“Island biodoversity characterized by extremes,” Oct. 30) mentioned the threat to Garry oak ecosystems from invasive plant species. But the real story, as was noted, is that 90 per cent of the loss is due to development. So it is clearly not the invasive plants that are the problem, it’s us; we not only carry invasive species with us, we are an invasive species in our own right.

In fact, we are the most invasive species of all, according to Curtis Marean, a professor and associate director of the Institute of Human Origins at Arizona State University. In a 2015 article in Scientific American, he noted that as we moved out of Africa, about 70,000 years ago, and colonized the planet, “everywhere Homo sapiens went, massive ecological changes followed. The archaic humans they encountered went extinct, as did vast numbers of animal species.”

This was especially true of the large animals (megafauna), including here in the Americas; a recent article in the journal Ecography notes that: “Our world has lost most of the large terrestrial animals present 100,000 years ago.” The authors conclude that “human colonization was the dominant driver of megafaunal extinction across the world,” although they also note that climate change played a role.

The formal definition of invasive alien species in Canada is that they are “introduced by human action outside their natural past or present distribution” and that their “introduction or spread threatens the environment, the economy, or society, including human health.” It is troubling to consider this definition from the perspective of indigenous people in the Americas, and especially in the Pacific Northwest.

According to the First Nations Health Authority, B.C.’s indigenous population pre-contact was between 200,000 and one million people. But the Europeans brought with them a variety of diseases to which indigenous people had not been exposed, so they had no immunity, and the population collapsed in the 19th century.

“It is clear that in some cases, entire villages were significantly reduced in single disease events, with mortality rates ranging from 50 per cent to 90 per cent of the population.”

European settlers were certainly outside their natural past or present distribution, and our settlement over the past 200 years or so has certainly caused harm to the health and the society of the people who have lived here for thousands of years, as well as environmental and economic harm. So from an indigenous perspective, it seems to me, European explorers and settlers can be considered to be an invasive species. An uncomfortable thought that is worth pondering.


Dr. Trevor Hancock is a professor and senior scholar at the University of Victoria’s school of public health and social policy.