“You don’t know what you’ve got till its gone”
Although the Ebola epidemic is terrible, there is an invisible epidemic that might end up being even worse for humanity. We depend on the great web of life, but paradoxically we are constantly weakening that web.
We receive services from many different biological species and communities. Plants remove carbon dioxide and harmful chemicals, purifying the air we breathe and liberating oxygen. Various invertebrate animals cleanse both salt and fresh water. Bees pollinate a quarter of our crops. And the list goes on.
Unfortunately, we humans are causing species of animals and plants to go extinct at a terrible rate. There have been five prior eras of mass extinction—the most recent was 65 million years ago when a huge meteor plunged to Earth. The resulting explosion threw up dust that altered the climate for centuries, and ended most of then current life—including dinosaurs.
Scientists estimate that the current rate of extinction of species is about 1000 times normal. The causes of this epidemic include loss of habitat, climate change, introduction of exotic species and pollution. What do these have in common? they are all human-caused. The more people there are, and the more each of us consumes, the more species we unwittingly kill off.
The dodo is a classic example. It was a flightless bird that lived on the island of Mauritius. In the 17th century sailors stopped there to replenish food and water supplies. The dodo had no fear of humans and was an easy target—sailors could walk right up and club them for fresh meat. The last of these innocent animals was slaughtered before 1700.
Closer to home, the passenger pigeon cluttered the skies of North America in the 19th century. Their annual migrations were estimated to encompass several billion birds! They were easy prey for hunters; sometimes people brought them down simply by throwing sticks or rocks in the air. It was thought that the supply of this delicious meat would never end.
You probably already know the end of this story. The last passenger pigeon, “Martha”, died in the Cincinnati Zoo 100 years ago this month. Attempts to find a mate for Martha had been unsuccessful. Causes of the extinction were overhunting and loss of habitat, since much of the North American forest was being cut down and plowed.
We now know that, even if an amorous male had been found, the species still wouldn’t have been saved. Some species have complex social systems and require large numbers to survive. Passenger pigeons were gregarious—they needed huge flocks to breed successfully. Furthermore, from a genetic standpoint, diversity is important to prevent lethal mutations from gaining sway,
With only a small number of individuals the genetic code is likely to have enough errors that the species will inbreed and die out. We are incredibly fortunate that two other species of birds, the California condor and the whooping crane, were saved from extinction before their numbers reached the critical figure. There were just 23 whoopers alive in 1941 when protection and a captive breeding program saved the tallest of all American birds. Luckily, this small number of individuals must have had adequate genetic diversity to keep the species healthy, because now there are about 600 of these magnificent birds.
Why not splice some of Martha’s genetic material into the DNA of a related pigeon so the passenger pigeon species can be resurrected? Theoretically, “de-extinction” might be possible using modern genetics, but the concept has problems. Remember they need a huge flock to be sustainable. The major problem, however, is that de-extinction is a diversion from saving species from extermination in the first place. What we really need is the humility to share resources with other species.
To commemorate the centennial of Martha’s final flight, the Smithsonian has established the multimedia program “Once There Were Billions”. Striking statues of passenger pigeons, part of The Lost Bird Project (www.lostbirdproject.org), will be on display in Washington.
Bees are in trouble. Colony Collapse Disorder has devastated almost a third of honeybee colonies worldwide. Many native bees species are also being ravaged. What is causing this collapse? research points to climate change (some flowers bloom before the insects are ready), harmful mites and a virus. In addition, omnipresent neonicotinoid insecticides are probably killing bees.
Biological diversity is essential for human survival, yet, unthinkingly, we are rapidly destroying species in unprecedented numbers. We should safeguard the web of life, for our own species’ sake.
© Richard Grossman MD, 2014