Legacy

Some years ago, while reading the book Sapiens: A Brief History of Humankind by Yuval Harrari, I was struck by the author's thoughts about the effect of human beings on other species of our planet.

Taking Australia as an example, Harrari pointed out that before humans set foot, Australia had numerous large and unusual marsupial mammals as evidenced by fossils. Yet, within a few thousand years of human arrival, twenty-three of Australia's twenty-four largest mammals had become extinct.

Harrari then discussed similar catastrophes in other continents as homo sapiens radiated outward over our planet from its origin in the Afro-Asian landmass.

The remorse of extinction hit me hard when I saw the egg of the elephant bird, the largest bird that ever lived, in a Madagascar museum. It was wiped out after humans settled on that island – only a few hundred years ago in fact. I could only imagine what a sight the bird must have been!

Recently a news item on a similar theme caught my eye, this time from The Guardian. It reported on an unusual research project in the life sciences. While the variety and number of species (biodiversity) has been a popular research topic, this project by Professor Ron Milo and colleagues of the Weizmann Institute of Science, looks at the biomass (net weight) taken up by different forms of life on earth.

Using advanced scientific techniques from satellite-based remote sensing to gene sequencing, the report concludes that humans take up .01percent of the mass of all living things on earth. In comparison, Milo's research finds that trees are 82 percent of earth's biomass, while bacteria account for 13 percent. All the other life forms – elephants, monkeys, birds, insects, fish and everything else – add to only 5 percent of the biomass of our planet.

There are several surprises in the article. Oceans cover three-quarters of the earth's surface so we naturally think that there is a huge biomass undersea. Instead, we find that the oceanic biomass is only 1percent of our planetary total.

Another surprise is about birds. Despite National Geographic and Discovery videos showing huge flocks of wild birds, it turns out that 70 percent of the birds on the planet are actually domesticated species – that is, the ubiquitous chicken – and only 30 percent are wild. The picture is even starker in the case of mammals: 60percent are livestock, 36 percent are human and only 4 percent are wild mammals.

I guess planet earth has not been a safe home if you evolved into a mammal species of non-human variety.

The overriding theme of the article is the legacy of human race and the ascendancy of human civilization on other forms of life on this planet. Despite our relatively tiny biomass, humans have proven extraordinarily adept at exploiting the natural resources that surround us. Our ruthless efficiency has left earth with only one-sixth of the wild mammals and one-fifth of oceanic life from the days when our ancestors were hunter-gatherers.

The legacy of humans on animals of our planet has been indisputably harsh, but what about on plants? Yes, we have killed off many plant species, but there is a startling theory about how a certain plant family may have domesticated us, humans, thousands of years ago in order to aid in its proliferation over our planet. That's the subject of a future column.

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