Thursday, November 1, 2007


Take a look a this picture.That is a reconstructed moa. Moas were the tallest birds ever to have walked the Earth -- and they were kicking about New Zealand until at least 400 years ago. There are even a handful of intact moa eggs still extant, even though their shells are much thinner that those of the related ostrich.

Though the tallest birds ever (as far as we know), moas weren't the heaviest -- that honor goes to crazy 'terror birds' of South America, which probably grew to over 350 pounds and made a living hunting hapless South American mammals before the closing of the Isthmus of Panama allowed big mammalian predators to move down from South America. Still, the moas are totally incredible to behold. They are the most vivid representatives of how evolution works with what it has to fill ecological niches with the materials at hand: in the absence of mammals, birds in New Zealand diverged to an incredible degree. Moas even had predators in the form of ginormous, Tolkeinesque eagles.

So what happened? Same thing that happened to the terror birds of South America: mammals showed up. You see, birds had a leg (or wing) up over mammals when it came to these large islands: they, or their ancestors, could fly. This fact allowed birds to get to big, detached landmasses like New Zealand and ancient South America long before mammals could, and when they had enough habitat to support gigantic inhabitants, some of those birds became giant. But evolution works with what it has; it doesn't craft organisms according to some sort of ideal. That means that some of the very adaptations that allowed the moa's ancestors to make it to New Zealand in the first place, like delicate bone structure, presence of wings instead of grasping forearms, and weight-saving absence of true teeth, hampered the moa's ability to compete with mammals when they finally did show up. Of course, it didn't help that the moas were competing with the most devastatingly successful mammal ever: us.

Archaeological and cultural evidence suggests that the ancestors of New Zealand's native Maori people first came to the islands around 1000 years ago. Around 600 years later, the last of the six or so species of moa were extinct. Like the terror birds of Tertiary South America, moas were no match for invading mammals.

It's immediately obvious that this is a totally natural phenomenon: the natural history of life on Earth is really the story of new species driving old species extinct. Human-mediated extinction is really just a special case of a pervasive pattern. (It is even arguable that some of the first species modern humans drove extinct were their contemporary hominid relatives!) The problem, of course, lies with the fact that we're so much better at driving other species extinct than anything ever before -- well, except maybe for giant asteroids.

What of it? Well, natural history is also full of species that drove themselves extinct -- organisms that evolved, or invaded, and used up the available resources so quickly that they perished. Again, humans offer great case studies: Polynesians related to New Zealand's Maori people colonized almost every island in the South Pacific; and on many islands, they drove themselves locally extinct. They didn't make it. Sometimes, like on Easter Island, they almost went extinct, losing their entire culture and social organization in the process. Even the remarkable Maori, who so successfully adapted to New Zealand's challenges, found that their centuries-old social structures nearly collapsed with the sudden influx of new technology from Europe.

There's nothing that we've found in Nature's rulebook that says that successful species necessarily stay successful. In fact, in terms of persistence over evolutionary time, the species that seem to do the best are those that tread lightly: cockroaches, ants, mosses, and chitons have been around for much longer than their flashier, and more impactful, relatives.

I thought a lot about this today as a walked around downtown Auckland. Europeans haven't been here for all that long -- heck, even America seems old compared to this -- but already there are pieces that seem ancient against the backdrop of the city. Tucked under a bridge near the university district, for instance, there's an old graveyard predominantly from a brief period in the mid 1800's. Many of the headstones are already fallen over or broken, testament to the truly transient nature of our species's monuments.

Those headstones were also a reminder, as I walked through the wonderful Auckland Museum, of the unique opportunity we humans have to learn from the past. Much of the Museum is devoted to preserving and communicating the incredible cultural heritage of the Maori for future generations, and I think New Zealand's (comparatively) exemplary efforts to value and nurture its native culture represents one of our successes on that front. If we are to succeed as a species, we will need to save much, much more of our collective cultural and biological diversity to provision ourselves for an uncertain future.

And, of course, the way to do that is through our children. These two characters reminded me of that: evolution is simply the story of children doing things better than their parents. We would be well served to give our children the best opportunities possible for doing things better than we did.

Today was good. Perhaps for reasons unrelated to how the world is actually doing, I have hope.


Anonymous said...

Whoa! I've never seen a moa! : )

It's very hard to us to think of ourselves as beings that are destined for extinction. The ability to contemplate our own mortality was the forbidden fruit in the Garden of Eden, wasn't it?

A lot can happen in a few hundred years . . .

Love, Mom

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