>>ROSS MACPHEE (Curator, Division of Vertebrate
Zoology, American Museum of Natural History):
Thank you.
It’s nice to see what a crowd this is.
I did just recently publish this book.
I think you should all at least look at it,
and otherwise enjoy it, because it’s going
to answer all your questions.
What happened to the world’s megafauna?
Is the extinction a thing, and should I be
worried about it?
Did I, Ross MacPhee, ever eat a mammoth steak
on the Siberian Tundra?
The answers to which are yes, yes, no.
In a nutshell, End of the Megafauna, the book,
is about a lost world.
One not that different from ours today, but
sadly diminished; diminished in the sense
that all of the largest, fiercest, hugest,
as the subtitle goes, animals, with few exceptions,
have disappeared.
How it came to be so is what I want to talk
about tonight.
We are going to be talking about theories,
and we are going to be talking about evidence,
because that is what this institution is all
about.
What has been lost?
One of the things you are looking at right
now is a gorilla-sized lemur from the Island
of Madagascar.
This too, was a Madagascan vertebrate.
This is an elephant bird that weighed in at
about 500 to 800 pounds, so three to five
ostrich-worth in its size.
This splendid animal, woolly rhino, which
disappeared about 11,000 years ago.
And finally, this relative of the Komodo dragon,
which is the world’s largest living lizard.
This guy was 30 feet long, lived in Australia
up until about 40,000 years ago.
You’re not the only one that’s terrified,
so is this wallaby, who is about to be a meal.
We still, of course, have lots of megafauna
left.
We have elephants, ostriches, crocodiles,
all of these animals that are 100 pounds or
better, which is the body size that we use
to define megafauna.
What you are looking at now is an illustration
of mammals of two kinds.
The ones in grey are the super megafauna,
the really big guys that come in at 2,000
pounds or better.
You see that they are restricted to elephants
and rhinos that live in South Asia and Africa.
Everything else you see, which includes some
smaller animals as well, have completely disappeared.
You notice, for example, that there aren’t
any super megavores that are left in the new
world, whereas there were just a few thousand
years ago.
What does this mean?
It obviously means that there has been a lot
of losses.
What I want to bring forward to you so you
appreciate the level of loss, is that this
is a world-wide phenomenon.
It’s not just the new world, it’s not
just Europe; it’s practically every island,
habitable island, on the face of the planet,
that has lost a very substantial part of its
fauna in the last 50,000 years.
Fifty thousand years is what we now call near
time, as opposed to deep time that real paleontologists
deal with.
This is South America shortly before the extinctions
that occurred there.
Giant ground sloths, giant armadillos, other
weird beasts; the only living lineage is represented
by this canid, this dog-like animal that you
see here, which still survives on the continent.
Madagascar has lost practically everything
of size that used to live there as recently
as 1,000 years ago.
All of the big lemurs, pygmy hippos, native
crocodiles, elephant birds, giant tortoises,
they are all gone.
Everybody here, with the exception of this
snake bird, anhinga, which still lives in
Africa and Europe and elsewhere, it is the
only survivor that you are seeing in this
particular painting.
Here is the body count.
This is based on a number of assumptions,
because we don’t necessarily have good evidence
for the totality of these losses.
Within a ball park kind of frame, it is probably
fairly accurate.
Somewhere around 300 to 350 mammal species.
Many more birds, because bird extinctions
on islands, particularly in the South Pacific,
have been prodigious indeed.
Reptiles, we’re not really sure.
I’m saying 100; it could be much more, it
could be much less.
Amphibians, we have not idea whatsoever how
many have been lost in near time.
This raises the question, what the heck happened?
There are many ideas, and ideas is what we
work with.
This is our currency in science — developing
ideas, testing them, and seeing what comes
out in the wash as the ideas that are best
supported by the evidence.
In the case of near time extinctions there
are a lot of ideas, some of which we will
be able to talk about tonight, but I’m going
to group them into three units.
First of all, there is ones that are concerned
with climate, climate change, because in the
period that we are talking about 50,000 years
ago, there was an enormous amount of change
on the planet, because that was the last ice
age that we have now come out into and are
now in a warming period, a very warming period.
Then there is a number of arguments that would
suggest that people were, if not universally
responsible, at least responsible for a large
number of these losses.
We are going to take a close look at those
as well.
Then there is other ideas.
Some of these are half-baked, wacko, but the
point is they have been proposed because the
other main theories, which would be climate
change and people, have deficits; they have
problems with the argument.
That is what I want to bring out tonight,
so that when you walk away from this it’s
not, “Oh, MacPhee, he just can’t make
up his mind.”
Instead, it is that this is the way the process
of science actually works.
You accept nothing.
You look at the evidence, and after much grueling
effort you decide what you are going to support.
And you also look at ideas that are on the
fringes because from time to time those are
the ones that are correct.
Just ask Albert Einstein.
We’re going to use some of Patricia Wynne’s
cartoons to illustrate these major ideas.
This is one that would implicate people, which
my colleagues lovingly call overkill.
Using this form of identification, we are
going to go to climate change, and we are
going to call that overchill.
Then the final one we are going to look at
is about an impactor that might have hit the
planet 12,900 years ago.
What do you think we’re going to call it?
Overgrill, of course.
Thank you, thank you.
Because we don’t have a clear idea at all
what was really responsible, we’re looking
back; we don’t have a time machine, all
we’ve got are the kinds of evidence we can
collect in the form of bones, now with biomolecules
to a certain extent, dating through radiocarbon.
This is what we have to conjure with, and
put together stories that are worth testing.
Let’s begin with overchill, and let’s
talk about the facts.
In grade school we probably all learned about
ecological zonation.
Ecological zonation being, in the simplest
form, that we’ve got a tropical part of
the world around the equator, we go into the
semi-tropics, temperate regions, and then
high latitude polar.
This is what we think of as normal, because
this is what we’re used to.
But you only have to go back 20,000 years
to see a very different world indeed.
The biggest difference has to do with the
ice.
Twenty-five thousand years ago, where we are
standing right now was under ice, ice that
originated in the northern part of Canada
and spread out from there as the illustration
suggests, all across Canada into the northern
tier of the U.S. Smaller, but nevertheless
still very large ice caps, existed in Eurasia
as well.
Among many other things, just the size of
these objects made a difference.
There was so much fresh water that was locked
up in them, that sea level dropped about 120
meters, well over 300 feet.
There was so much water locked up and it was
so cold that evaporation over the world ocean
was lessened, which means there was less water
everywhere.
That had a prodigious effect on plant life.
For example, here, if you combine the white
and the blue areas, the blue area being step
of one form or another, you can see that the
whole northern part of the planet was in very,
very cold or semi-cold conditions with reduced
plant life, and so forth.
Everything else, all of this zonation, was
packed much more towards the equator; unlike
today, where you’ve got temperate regions
going well up into the northern part of our
continent.
One of the things that happened was that the
rainforest, having less precipitation, generally
cooler conditions, reduced down to refugial
areas.
If you have in your mind’s eye an idea of
how big the rainforest is in the Democratic
Republic of Congo, for example, you can see
here that it is a fraction of that.
Similarly, with Amazonia.
Amazonia was cut up into bits with grassland
intervening, which is a very hard thing to
imagine today, as the result of climate at
the time.
What it also meant was that grasslands could
expand dramatically since they are dry-adapted,
and the mid-latitude deserts.
So yes, this world looks a lot like the world
today, but in detail it wasn’t.
This was the world of the megafauna.
Here for example, in this painting what we
are seeing is a scene in Rancho La Brea.
Everything here is dead, it’s all disappeared
including sloths, camels.
Does everyone know that camels originated
in North America?
You don’t have to like camels, I’m not
asking that you like camels, but they’re
yours, they’re your own.
You should respect them.
So the climate change people don’t have
a great answer to how climate change by itself
could have produced these effects.
The particular effect that I’m talking about
in respect of North America was the collapse
of this fauna, some of which is illustrated
here, in a very short period, maybe no longer
than 400 years between, roughly speaking,
11,000 and 12,000 years ago.
The big ice age which you’d think would
have been responsible for these extinctions,
was over and done with by about 18,000.
From 18,000 forward, we were into a warming
period and thinks were not exactly like today,
but they were getting warmer.
So how can it be that the most dramatic effect
of the recent period produced no extinctions,
or very few?
Another aspect of this is that there was more
than one ice age.
In fact, there were 22, that we know of, advances
and retreats of the ice in the last 2.6 million
years, which is the Pleistocene and the Holocene.
During this period, most of the species that
I’m going to be talking about were already
in existence.
They’d already evolved.
Yet, they weathered those particular ups and
downs of climate.
They may well have suffered in respect of
range size, they may well have suffered in
respect of the kinds of food they could eat,
but they made it through until 11,000 to 12,000
years ago.
Who knows what happened?
Well, let me tell you.
This man, Paul Martin, thought he knew.
Paul Martin was a good friend of mine, was
a professor of geosciences at the University
of Arizona for many years, and he was really
the one who developed and elaborated the theory
that I am now going to talk about — overkill.
This is how he approached the question.
He developed a series of three features, which
I am going to briefly go over, that seem to
be true of this entire period of near time.
These are structural features of what was
going on, and in each case there is verification
from various bodies of evidence suggesting
that Paul was correct in isolating them as
critical features.
The first one there is no real disagreement
about.
Where the extinctions occurred, there were
a lot of losses.
By no disagreement, I mean people supporting
climate change or other theories also agree
with this.
And that large mammals were affected disproportionately.
This is very important.
They were not globally synchronous.
You’d think if there was one serious effect
that was global in extent, it would have affected
all of these species that disappeared at more
or less the same time.
Yes, there could have been survival in some
places, greater losses in other places, but
you’d expect to see a general envelope of
synchronicity.
That is what we don’t see, and we know that
from carbon 14 dating, which was Paul’s
biggest contribution, by pointing out that
you could date, to a very large degree, when
these extinctions occurred.
Another thing that’s very important is that
when people spread across the planet from
Africa, which occurred over a couple of hundred
thousand years, it seems that whenever they
got to a new place where they hadn’t been
previously resident, the next thing that happened
was a faunal collapse of serious magnitude
on most of the continents, and absolutely
devastating on islands.
What you have to picture is that as people
spread across the planet, every time they
showed up in a new place, something bad happened.
We call this first biological contact — the
idea that when people came to a new place
and encountered the biota that lived there
at the time, it was new on both sides.
Let’s look at what we’re calling the diaspora
here.
This is a very simplified version, of course,
of what happened as homo sapiens spread across
the planet.
Point number one — we originated in Africa;
homo sapiens is African by origin.
That is our lineage.
The dating now is that we were already present
at least 350,000 years ago in Northern Africa
and at some time shortly subsequent to that,
we got into Eurasia.
Thereafter, it’s a question of spreading
wherever we could possibly go.
By 65,000 years ago, so the current evidence
is, we were probably in Australia.
We were in northernmost Siberia by 45,000
years ago.
These are minimum estimates.
We got to the new world somewhere after the
close of the Last Glacial Maximum.
This is a very controversial area, but let’s
just say 16,000 to 18,000 years ago people
were in the new world for the first time.
Finally, people spread throughout and into
the last habitable places on earth, which
would be the temperate and equatorial islands,
wherever they lay, with the South Pacific
being the last of them.
There were people, for the first time probably,
in New Zealand about 800,000 years ago.
Let’s couple the diaspora with the extinctions.
The first major losses, and by major I mean
lots of species within an apparently short
period of time, so in that sense at least
temporally connected.
This was in Australia about 40,000 years ago
as best as we can estimate at the moment.
Remember, people seem to have got there about
65,000 years ago, so there is a gap, but nevertheless
the losses occurred subsequent to the first
human appearance, at least for the Pleistocene.
Animals were lost around 11,000 to 12,000
years ago in all the places where the yellow
explosions are.
So across the northern tier of Asia, down
into all of North America and all of South
America for that matter.
Then it’s the islands in the Mediterranean
around 10,000 years ago.
The islands forming the West Indies, perhaps
6,000 years ago.
Madagascar, about 1,000 years ago.
And then all of these last places on earth
where people could make a living, the South
Pacific, with the very last of them occurring
perhaps only a couple of hundred years before
Captain Cook ended up in New Zealand.
It is this coupling of the first appearance
of humans and the subsequent faunal collapse
that gives particular strength to the overkill
argument.
It seems we got there, we did something hideous,
which is not like us at all, right?
And the animals died in droves.
So, there are puzzles connected with this.
Here is mystery number one — you saw the
pattern of loss.
Northern Eurasia, continents of the new world,
all of these islands, so on and so forth.
But there were some places where coupled losses,
lots of them in a short time period, didn’t
occur.
Those are Africa and South Asia.
What do you do with this?
This is a major puzzle because, as I said,
humans originated in Africa, so we go back
and the mammals that we dealt with through
this long history were all there at the time.
How could it be that there weren’t all of
these losses in those places, yet there were
everywhere else?
Well, Paul turned this into a positive for
his argument by pointing out that since people
arose there and lived there for a very long
period of time, they were known to the prey
species.
There was sort of arms race that went on.
As we got better at making tools, they got
better at avoiding predators.
So, over time, the balance was that yes, hunting
was possible, but this destruction on unbelievable
scales like you saw in North and South America,
did not happen.
He made the same argument for the south.
End result, no faunal Armageddon in Africa
and South Asia, but destruction everywhere
else.
Okay, so we’ll accept that.
Another problem — in North America there
were about 70 species that disappeared between
11,000 and 12,000 years ago according to the
paleontology.
Not all of those were large, more than 100
pounds, but probably around three-quarters
were.
So you’re talking about a large number of
large animals.
You’d think that if there was a mass slaughter,
that we’d have good evidence of it, that
there would be all kinds of kill sights, windrows
of bones, and evidence of butchery, and all
of this kind of thing if people were killing
on this kind of scale.
In fact, we don’t see that.
What we see instead is the very occasional
evidence of hunting.
I’m talking just hunting, not overhunting.
So the question comes, where are the bodies?
If people were responsible at this level,
shouldn’t we expect to see more?
Paul’s argument, not a very strong rejoinder
I must say, was that we can’t really expect
that because this is far back in the past,
10,000 years or more.
And the absence of evidence, you’ve all
heard this, absence of evidence is not evidence
of absence.
You know, try that out with your significant
other when you come home late one night.
See where that gets you.
It doesn’t cut the mustard.
It’s an explanation that we don’t know
what to do with, or it’s a set of facts
that we don’t know what to do with.
You’d expect that under any of these circumstances,
that there should be lots of bodies, but there
isn’t.
That’s a conundrum.
Now, let’s think about this.
You are recently arrived in North America.
You’ve got across the Bering land bridge,
you’re seeing all of these big mammals that
nobody has ever hunted.
They look at you and they see this awkward
looking, featherless biped, doesn’t seem
to know what he’s all about.
There’s no big canines, there is no horns
or other ornamentation, just running around
with pointy sticks.
What’s that all about?
The idea here, which is borrowed from ecology,
is that you can have the phenomenon called
behavioral naiveté — that unless you have
been, for example, predated upon very heavily,
you as an animal are not going to recognize
a predator, particularly a novel, weird looking
predator like a hominin.
So you are just going to ignore it.
But meanwhile, those humans are seeing all
the meat on the hoof and thinking, “All
right, party time.”
Paul’s argument was that when these first
inhabitants came over, if they weren’t already
big game hunters, they quickly became such
because what did they want?
They want what humans want in all circumstances,
which is to control all resources and to make
as many copies of themselves as possible.
The idea was that there was a massive population
expansion right at this period when humans
were first moving into the Americas.
Now you had food security, you had all of
these guys that you could easily hunt, and
then of course, the extinctions went to completion
because there was so much overhunting.
The end result was these losses.
Let’s go to overgrill.
Overgrill — I don’t think I have to tell
you a lot about this particular scenario.
Sixty-six million years ago, an impactor from
outer space hit, as we now know, somewhere
off the Yucatan Peninsula, and whammo…end
of story.
Whatever happened…nuclear winter, global
wildfire, you name it.
It took out around 75%, so we estimate, of
species then living.
They weren’t all dinosaurs.
It went all the way down to planktonic forams
living in the ocean surface.
The parallel argument for us is that there
was an impactor.
The people who developed this argument coyly
suggested that it came down at about 12,900
years ago and wherever it hit it did the same
sort of thing, but probably on a reduced scale,
as compared to the Chicxulub impactor 66 million
years ago.
How do we know this?
There is evidence.
Like shocked quartz grains, which are all
about the strength of the impact.
Something peculiar to these Pleistocene examples
of this particular impactor is something called
black mats which are found in the southwestern
part of this country, which the supporters
of overgrill suggest are exemplary of a very
widespread fire initiated by the impactor.
I think it is distinctly possible that there
was an impactor at this time.
The fundamental question for us, however,
is did it do the job?
Did it do any of the jobs in respect of the
losses that we are talking about?
You won’t be surprised when I say that we
don’t know very much about exactly what
happened.
But to give you one note of optimism, thanks
to lots of thinking and effort, we do have
a good idea why large mammals were hit in
particular.
This is really easy to relate with, because
we are large mammals; at least I am.
Here is how it works — large mammals have
very similar life histories, as we call them,
for certain features.
One is that gestational periods are long.
We’re nine months, but if you go to the
living elephants, it is anywhere from 22 to
24 months.
Typically, there is also, relative to smaller
species, a longer maturation.
Again to point to elephants, it’s something
like 10 or 11 years before they are sexually
mature in the case of African elephants; 12
to 14 in the case of Asian elephants.
Yes, we live long lives.
That’s another part of being big.
That’s one of our, I guess, positives in
life history.
These other features are ones that mean that
if our populations get hit very hard in certain
parts of the life cycle, certain parts of
the demography, then it takes a long time
to come back.
For all of these arguments, what we really
should have in mind as to why it was bad to
be big is not the details of what specific
trigger mechanism took them out, but because
they suffer or they have as their native aspect
that there are these risks you take as a result
of being big, that smaller animals don’t.
One other thing to mention is that most births
for larger animals are singletons.
Twins rarely, anything larger than that is
unusual.
You can imagine if you get hit very hard,
what it is going to take to recover from that.
Whether it was climate change, overkill, an
impactor, it doesn’t matter.
I want to leave you with another kind of idea,
which is since we don’t know the whole story
and since there are these arguments against
any of the theories that I have developed
here, maybe the most serviceable idea is that
it was some combination of the likeliest events,
which is what this particular figure is trying
to show.
I kind of like this because at this point
in our understanding of these megafauna extinctions,
there is no point in being a very strong advocate
of any one of these solutions.
They all might have played a role.
The point is, and the reason why this is still
a great natural history puzzle well worth
spending our time on, is because it has certain
implications.
This is the implication that I want to leave
you with.
Why should we be particularly worried about
the surviving megafauna on the planet?
It’s because they have these same life history
characters that I was just talking about.
Here you’re looking at the last male northern
white rhino that died out earlier this year.
Fortunately in this case, I suppose fortunately
is the right word, semen was collected from
him and in future there is going to be an
effort to see whether you will get viable
hybrids, as you probably will, with southern
white rhinos.
You can see the handwriting on the wall.
As we continue to despoil the planet, taking
resources wherever we want to take them, doing
what we please, then inevitably animals like
this are the ones that are going to suffer
most.
The end of the megafauna that I’m talking
about is not necessarily the end of the end,
and I want you to bear that in mind.
Thank you.
