Good morning, ladies and gentlemen. I'm going to be talking about
something far more specific than my colleagues. I'm going to be talking
about extinction. It occurs to me that, as teachers, one of the things
that you're most interested in encouraging in your students is the
capacity to think in critical terms. That just because you hear somebody
saying something and that guy's a scientist or politician or what
have you, you don't necessarily need to believe it. What you need
to do is go to the facts and see whether the facts actually lead to
the results claimed. The reason why this is so important with respect
to biodiversity is that the future of the planet is at stake, not
just our stewardship. In fact, the lives of all the millions and millions
of species that make up the biota of the planet are at stake.
In order to project properly what might happen to that biota, we need
facts. We need feelings as well. We need to know in our hearts how
important it is to keep the world together, to have a stewardship
that actually amounts to careful management. But we need to know what
to do that's right. We need to know where the facts just don't match
up to the predictions. We need to know when what we're trying to do
actually oversteps what we ought to do. These are all difficult subjects.
With respect to extinctions, in particular, the way to think about
them is, first of all, how do people use this term, what do they mean
by it, and in what way should we be critically thinking about what
extinction is and how to mitigate it?
Can I have this first slide, please? You've all seen diagrams like
this. This is a sociological effort, sociologically I would say, to
get people to think about extinction. There's a couple of things you
ought to be thinking about when looking at such a figure. As Joel
told you, most of biodiversity consists of little squirmy things with
lots of legs living in forest litter. But we don't see those here.
What we see here are charismatic vertebrates—in the form of toucans,
apparently a lot of toucans—going out at a rapid rate. Amusingly,
in the background, there is a brontophere That died out in the Miocene.
I'm not quite sure why it's here, other than to suggest a very important
thing: one way to find out about extinction is to look at past extinctions.
At least in the popular press, you see figures, figures of enormous
magnitude. Figures like the ones you see here. While you were sleeping,
lots and lots of species died. One thing that any informed adult needs
to know is where such figures come from, and whether the estimates
are reliable. And if they're not, what should we do about it? If they
are reliable, what should we do about it? If it is true that we are
losing species on the order of 27,000 per annum, then clearly we're
in a very critical state. If we're losing fewer than that, or if extinction
is the wrong word to use for what's happening, then we need to know
that as well, and we need to think about how to deal with the situation.
This is a diagram recently put together by a couple of researchers
at Texas A&M University, and it's a way of focusing thought on what
the present biodiversity crisis is like with respect to extinction,
and how we might imagine our responses and what the nature of our
should response be, and what we need to take into account as we go
forward. Well, clearly, if the extinction curve is going up exponentially—as
you see over on the far left—we ought to be in a panic mode.
That is clearly the right response if we're losing an enormous number
of species every year. If it is the case that it's more of a straight
line, kind of a linear loss with respect to time, then we most certainly
should be alarmed, because what this primarily means is that our efforts
to mitigate extinctions—the kinds of things that conservation
biologists are doing right now to control species extinction - are
probably not working if the graph continues to rise.
But there is a third outcome, and this is indicated by the graph entitled
"Remorse," which implies that Yes, there have been an inordinate number
of extinctions on our watch, and those were in many cases, the direct
result of impact by humans. But if the slope as we approach the present
is declining, then it means that we are being successfu-that we're
beating back the anthropogenic or the human-caused influences on extinction.
As an aspect of critical thinking about extinction, we need to know
which of these three is most likely to be correct, and to organize
ourselves and our ideas and what we might do in the future based on
that knowledge. This is presumably the contribution of science to
the whole debate.
This is the same kind of graph that Andy just showed you with respect
to fishes, and Joel had a similar graph in his presentation. All of
them are really the same in what they show. These are modern data.
By modern, I'm going to restrict myself to the last 500 years. And
they have this kind of form - they're opening upward. The suggestion
is, in this cumulative part of the graph, that from a situation of
fewer extinctions and maybe no extinctions, we've gone up to a huge
number in a relatively short period of time. This is what the biodiversity
crisis in a nutshell is all about: the notion that from a period of
few extinctions we've gone into a period of many more extinctions
and the only culprit on the block seems to be humans.
But the world is 4 billion years old. Ninety-nine point nine percent
of all species that have ever existed at any point in the past are
now extinct. In short, extinction happens. And since it does, it's
clearly a natural phenomenon, and we mustn't think that whatever influence
people have had on changing the curve, on driving it upward and so
forth, needs be put in the perspective of all other extinctions that
have taken place. We need, in other words, to have a historical perspective
when we look at extinction, so that we can more clearly see an outline
in relief of what people appear to be directly responsible for, or
at least to suggest the areas in which they have been directly responsible.
So what are the forms of past extinctions? If we think that anthropogenic
extinction has been the most critical cause of extinction, then one
thing we would want to ask is what the course of extinction has been
during the entire period for which anatomically modern humans have
been on the planet. (You'll hear figures that humans have existed
for 40,000 years based on fossil evidence, to something like 140,000
years based on the evidence of genes.) But somewhere within that time
frame—let's say 100,000 years—humans like us have been on
the planet, doing bad things. Now, does that translate into extinctions?
Well, one prediction we might make is that, since nobody is nastier
than modern people, the extinction curve was probably relatively low
in the past until the appearance of humans on the planet. What made
us nasty was technology. It is our capacity to modify our environment
in the way that Andy so eloquently showed that is most critical, most
damaging to the earth's ecosystems. But we might also imagine, and
as anybody who walks on the fourth floor of the Natural History Museum
knows, that there are a lot of dead things from the past, as well
as a lot of recently dead things. So is it possible that there have
been losses in the past, and if so, what has been our role? Do we
know? And does it have any relevance to the modern crisis?
Extinctions have been going on during our watch for a very long period
of time. Humans, as we think is the case, originated in Africa, and
then spread out into Europe and the southern parts of Asia very early
in their tenure. They were, to a certain extent, limited in their
range in the early part of their evolutionary history because they
didn't have the technology to get elsewhere. But about 60,000 years
ago, the record dramatically changes. We begin to find evidence of
humans in places where humans never existed before. First in places
like New Guinea, then in Australia—as I say at about 50,000 to
60,000 years ago—then, much later, about 13,000 years ago, in
North and South America, and then, subsequently, in the last big habitable
places on Earth, which would be the major island groups, such as Madagascar
and New Zealand, very close to the present, or only 1,000 or 2,000
years ago.
Now, that's all right. This is just humans doing what humans do: going
to new places, starting life anew, carrying on. But along with these
movements came a startling series of losses. Everywhere that humans
went, there were incredible collapses of fauna everywhere around them.
Some of you are from the Northeast, and you know what New Jersey is.
Can you imagine a scene like this in New Jersey, which is a scene
not unreasonable for a period as recent as 11,000 years ago? It is
the case that in a state like New Jersey you now have no megafauna.
You have no species of any size other than the white-tailed deer,
whereas 10,000 or 11,000 years ago, there were mammoths, mastodons,
saber-toothed cats, giant ground sloths, American lions, American
cheetahs, horses, giant birds, and so on and so forth. In other words,
the kind of diversity that you nowadays associate only with game reserves
in places like East and South Africa. And it's all gone.
In North America and South America today, there are only about a dozen
species among mammals, that qualify as megafauna or mammals weighing
in the range of 100 pounds or more. Whereas 10,000 or 11,000 years
ago, there were dozens and dozens and dozens of big mammals in these
ranges. They've all gone. A particular interest of mine is what has
gone on in the northern part of the world. In microcosm, the diversity
was really not very different from what we showed you for the central
part of the continent. Here we have mammoths, short-faced bears, horses
- horses originated on this continent and were common up to 11,000
years ago—and giant bison. It goes on and on. Now, whatever this
ecosystem was like, however these animals managed to support themselves,
they were there. And then something happened. What happened was they
disappeared virtually overnight, an event strongly coincident with
the first archaeological evidence of humans in the New World.
This second diagram shows you, by means of these ghost cutouts, all
that has been lost, which means all of the elephants that used to
live here, many of the carnivores, many of the other kinds of herbivores.
In halo, we have the species that managed to survive elsewhere, primarily
in Asia, but that have become or did become extinct in North America—like
horses, for example. So the contrast that you see here—and this
is one of the things that I'd like you to think about—between
our continent now and what it was only a few thousand years ago, is
that, with respect to mammals, it has been utterly transformed. And
it's been utterly transformed during our tenure.
Now, what kinds of causes could possibly be responsible? Today, we're
very used to talking about habitat destruction, exotic species introduction,
and this sort of thing as the causes of modern losses, but what about
some time depth? Would it be reasonable to think that other forces
must have been applied? And surely that's the case before humans came
on the planet. It's been frequently argued that climate change, by
itself, is a major cause of extinction, and maybe that had something
to do with the extinctions 11,000 years ago, although in detail, the
record does not support that. The kinds of changes that occurred in
the earlier part of the Quaternary, the period that we're living in
now, were more dramatic than you can imagine. The worst kinds of scenarios
for the global warming that we're experiencing right now are as nothing
compared to what we know took place, based on the existing climatic
record for the last couple of hundred thousand years: wild sweeps
of temperature change on the order of five to seven degrees Celsius
within the space of 50 years, whereas what we're experiencing now—or
at least up to the present, with regard to the modern phase of global
warming—is less than one degree Celsius in the last hundred years.
(And you know that it makes a difference, if you've been in New York
for the last couple of days or the last week.) If this is global warming,
can you imagine what it would be like at seven times that load? Well,
can we imagine, as many do, that humans were somehow directly responsible?
If they were directly responsible, we're talking about humans coming
into the continent with tool kits that were nothing like those that
we have available today. They didn't come in with guns, they didn't
come in with sophisticated ways of locating animals, they didn't come
in with SUVs. They came with bone. They came with wood. They came
with stone tools as their only real vehicle for gathering food. Their
only way of hunting would have been by that means, by that kind of
technology, as opposed to what we associate with our capacities today.
It is seriously considered, however, and there are many biologists
who would agree with this, that what likely happened in the case of
North America was that many of the losses were directly caused by
humans over-hunting—over-hunting on a scale that we can scarcely
imagine nowadays. Now, for a number of reasons which I'm not going
to go into now, although I earnestly believe that humans had something
to do with it, I believe that most of their impact was of a more indirect
sort. And that one of the things that suggests itself to me as a major
cause of extinction was not that the humans were hunting, but they
were bringing in a lot of biotic baggage. You know what humans do.
They're very messy types. They always carry a lot of stuff with them,
and they're not too clean, and they're not too worried about what
might be going along with them. This is why endangerment in many parts
of the world is caused by exotic species. It's because people bring
them in thinking nothing of the consequences, and there is at least
some theoretical reason to believe that maybe it's not these grand
events caused by humans in respect to overkill, but microbes that
could have fantastically transformed life for many of the species
that went to extinction.
Well, the reason for introducing all of this is not to convince you
of any one scenario. It is instead to say that part of what you need
to think about here is that extinction is a very complicated sort
of idea, and that in talking about it, it is necessary to connect
facts with consequences. It's easy to guess that humans were responsible
for every bad thing that's happened since Homo sapiens came
to be, but if it is wrong—in the sense that there are other factors
that are of equal or greater importance—we need to know about
that. Just as we need to know that the Earth is not a static place,
and that our interventions in the environment should not be with the
notion of keeping everything the way it is, because there is no way
of keeping everything the way it is. Even without the presence of
humans, things will change. And it's that kind of perspective that
one has to bring to the notion of what biodiversity crises are and
how they might be dealt with.
Now, I want to finish off here with some facts about modern losses
since this is, of course, what we're all really concerned with at
present. Andy gave you a very solid idea of what the probable proportionate
value of each of several kinds of factors is in causing population
damage of one sort or another, leading to endangerment and possibly
to outright extinction. And this is, of course, a very important thing
to know about. But in the interests of trying to relate facts to consequences,
what my colleague Clare Flemming and I did a few years ago was to
try and determine what would seem to be a very simple thing: how many
species of mammals have actually gone extinct in the last 500 years?
We've got all these scientists talking about it - the number of species
that have disappeared. Surely it should therefore be possible to do
a body count. We should have some kind of empirical, real values that
we can talk about as being possible indicators of what the nature
of the biodiversity crisis is like. And we found some very interesting
things. One of the things that we found is that it's not really the
continental parts of the world, with the exception of Australia, that
have taken the biggest hit with respect to mammal losses over the
last 500 years. It's not the rain forests, in other words. It's not
the kinds of places that you would think would be the most sensitive
and the easiest to overturn. This is not to say there's not a problem.
It is instead to say that the extinctions have not yet occurred in
such places. But when we look at the entire record, what we see is
that it's the world's major island groups that have really suffered
a great deal. I don't know whether you can make out this specific
pie diagram, there's going to be another one like it in a second—but
it suggests that over 70% of all the extinctions that have occurred
in the last 500 years have occurred on islands. And that's a very
important concept to think about.
Another interesting thing is that, compared to the losses among the
megafauna-big organisms like mammoths and so on—most of the losses
have been among the rodents, and, to a lesser degree, the bats over
here. I know there's a lot of $10 terms here, but the point of this
diagram is to tell you that, at least among mammals, the extinctions
of the last half millenium have been concentrated in the microfaunal
realm. And that's another important thing to think about. And as I
said, it's the islands of the world that have really suffered an enormous
amount of loss compared to the continents.
Now, why am I making a big deal of this? About 10 or 15 years ago,
people started using and thinking about the term "hot spots" - that
there are places on the planet that we need to worry about most. Diagrams
like this one were developed. This is from one of E.O. Wilson's books.
And it suggests that many of the places we really need to worry about
are continental, which I'm sure makes a lot of sense to you because
this is what we often hear, in the press in particular. It's the rain
forests of the world that are disappearing. It's continental habitats
of one sort or another that are suffering most. And in a sense, just
as Andy showed you, that is true. But what evidence do we have that
these ecosystems are the most important? Very recently, an update
of this chart appeared. And it has been changed, in the sense that,
although many of these continental places are still clearly regarded
as "hot spots," there's much more focus now on the islands. Now, why
would that be? It's because, at least with respect to most kinds of
terrestrial life, an island is an absolutely bounded system, and it's
small. If you get in trouble, there is nowhere to go. And if there
is nowhere to go, in all probability you're going to disappear. The
parallel, the metaphor to carry over to the continents, is not that
the rain forest is disappearing, in some grand sense, but instead
what's being done to it. It's being cut up, subdivided, tractored
over, so that what's been created are these virtual islands. Virtual
islands which are separated by seas of areas in which the native flora
can't live, are just like being on a real island. So the worse it
gets with respect to subdivision, the worse it's going to get with
population damage and outright extinction.
From this long view of history, what is the one thing that I want
you to carry away? The notion that's incorporated in this quote by
Colin Tudge, which I won't read to you, you can do that yourselves,
but it is the idea that we must do something because that is, in fact,
now our job. In addition to any other jobs we might have had in our
evolutionary history, we must be concerned with the preservation of
biodiversity, and it would be an evil thing to do otherwise. Thanks.
