The Last Panda

The Last Panda

University of Chicago Press

Chapter One

Is the giant panda a bear? Are the red and giant pandas closely related?
These two questions have been debated for over a century. Anatomists,
behaviorists, paleontologists, and molecular biologists have led the
fascinating inquiry into the evolutionary relationships of these species
with ingenuity and persistence, yet they continue to derive different
conclusions on the basis of different evidence, and they still pursue the
elusive answers. Their quest well illustrates the logic and method of
scientific inquiry, the search for a resolution that satisfies the
intellect. I have no emotional investment in the outcome, such research
being peripheral to my interests, but I find the unraveling of the riddle
intriguing.

Red pandas and giant pandas are inextricably linked. They share not only a
name but also many physical similarities. Skull, teeth, and forepaws in
each are similar, evolved to process bamboo. They even grip bamboo in much
the same manner, except that the red panda lacks the functional sixth
digit or pseudothumb souseful to the giant panda for manipulating stems.
No one questions that the two pandas resemble each other. But are they
actually related? This has been a subject of scientific controversy since
Pere David discovered the giant panda in 1869. He gave it the generic name
Ursus on the assumption that the animal was a bear. The following year,
Alphonse Milne-Edwards looked at the same skeletal material and decided
that the giant panda was not a bear but allied to the raccoons. Since then
the two pandas have been bounced around in an ever more esoteric and
technical manner from one taxonomic home to another.

The issue is basically simple. Some biologists looked at the two pandas
and decided they were not closely related, that their physical
similarities had evolved because of the same food habits and life-style.
They placed the red panda into the raccoon family, the Procyonidae, and
the giant panda into the bear family, the Ursidae. Other biologists looked
at the same evidence and came away convinced that the two were relatives,
belonging to the same branch of the evolutionary tree. They placed the
pandas either into a separate family or tucked them in with the raccoons.
Each school of thought could point to specific features to reinforce its
claims. The bear school, for example, stressed the giant panda's bearlike
body proportions, but the raccoon school countered that the giant panda's
skeleton was unusually heavy-boned, giving "the impression of being the
skeleton of a 'fake' bear," as Ramona and Desmond Morris wrote. The giant
panda certainly looks like a bear, but is it a bear pure and simple? Or is
it a raccoonlike animal that resembles a bear because it has grown large,
with a heavy body that requires special modifications such as stout legs
to support it?

In some ways, the long-running issue is trivial, an illustration of a
scientific discomfort with uncertainty and a penchant for putting
everything tidily in place. If the giant panda is a bear, it is a highly
aberrant one. If the giant panda is a raccoon, it can look around at a
peculiar hodgepodge of family members: the long-nosed coati, the
prehensile-tailed kinkajou, the conservative ringtail, a living fossil
little changed from its Oligocene ancestor thirty million years ago, and
the nimble-fingered raccoon.

However, the controversy also poses a fundamental scientific problem-what
features are important and significant when classifying an animal?
Classification was difficult enough when only physical characteristics
were considered, but with the advent of molecular biology more, and often
conflicting, lines of evidence had to be evaluated. Surprisingly, the
puzzle of the panda's origin has seeped into public awareness, and the
problem is viewed with some of the same fascination as the disappearance
of dinosaurs. When giving a lecture, I am often asked at the end whether
the giant panda is a bear or raccoon. To keep my reply brief, I usually
answer, "The panda is a panda."

This view places me in a distinct minority at a time when the bear
proponents are the most vocal. Take a scientific review on the subject
published in 1986 in the journal Nature. The author, clearly impatient
with the whole controversy, noted that some still view the two pandas as
"each other's closest relatives. It would seem that this suggestion is
clearly refuted by the near-unanimous and highly diverse evidence ...,"
and he hoped that the "overwhelming evidence for the bear relationship of
the giant panda would end the argument.... Only some of the behaviour
students were not yet persuaded." When "overwhelming" evidence is invoked,
beware. Is the article a polemic promoting a dogma rather than a careful
examination of the facts? In science, an issue that has been truly
resolved is absorbed and disseminated quietly without need to make the
"near-unanimous" unanimous, to prod heretics into becoming true believers.

Am I reluctant to become a bear proponent because of mental inertia, am I
unable to divest myself of an outdated notion, or is there reasonable
doubt about the majority view? I am admittedly delighted that in spite of
its being dissected, observed, measured, and subjected to a host of
advanced molecular techniques, the giant panda still cannot be neatly
categorized. Just as I hope that there is a yeti but that it will never be
found, so I would like the panda to retain this minor mystery. Still,
there is intellectual pleasure in trying to solve such a puzzle.

Molecular studies have in recent years provided important insights into
the classification of pandas. Since protein molecules are an integral part
of DNA, they closely reflect the hereditary and therefore the evolutionary
history of an animal. Proteins are composed of different amino acids. The
number of differences between the amino acids of any two proteins should,
it was reasoned, be proportional to the time elapsed since they diverged
from a common ancestor. With molecular evolution supposedly freed from
environmental influences, it might be regular enough to be used as a
molecular clock, one that provides precise information about the amount of
genetic change that has occurred over the past few million years. In one
such study, published in 1976, Vincent Sarich used immunological
techniques to compare two blood proteins from giant pandas, red pandas,
bears, and raccoons. In this method the proteins are injected into
rabbits, producing antibodies, which then react strongly against the
proteins for which they were prepared and progressively more weakly
against proteins in species more distantly related. He concluded that "the
association of the Giant Panda and other bears is clear and unequivocal....
The one rather unexpected result there is the fact that the Lesser
Panda, Ailurus, does not group with the other procyonids," that it seems
to have started a separate lineage before the giant panda and bears.

In 1985, Stephen O'Brien and his coworkers published an article in Nature
entitled: "A molecular solution to the riddle of the giant panda's
phylogeny." Using gel electrophoresis, a technique by which proteins can
be sorted by electric charge and size, proteins from pandas, bears, and
members of the raccoon family were compared. To check their results, the
investigators conducted DNA hybridization tests. This method compares the
DNA of each species, the actual hereditary material, rather than just the
proteins. Radioactively tagged DNA from one species is hybridized with the
DNA of another and the stability of the union measured. The study
concluded that "the lesser panda diverged from New World procyonids at
approximately the same time as their departure from ursids, while
ancestors of the giant panda split from the ursid lineage much later, just
before the radiation which led to modern bears." This split is said to
have occurred as long as 15 to 25 million years ago. In other words, the
giant panda is a bear, the red panda a raccoon. Yet within a year after
this study, another investigation into a blood protein showed that the two
pandas are more alike than are either giant pandas and bears or red pandas
and raccoons. Which blood protein should be used as a taxonomic character:
albumin, which makes the giant panda a bear, or hemoglobin, which does
not? The molecular clock may at times not be as precise as suggested.
Different proteins in an organism may mutate at different rates, and
natural selection may affect some proteins, such as hemoglobin, more than
others.

David Goldman, Rathna Giri, and Stephen O'Brien returned to the fray in
1989 with a molecular study of all seven bear species, the giant pandas,
the red pandas, and the raccoon. Published in the journal Evolution, the
study was "based on the extent of electrophoretic variation of 289
radiolabeled fibroblast proteins resolved by two-dimensional gel
electrophoresis and among 44 isozyme loci resolved by one-dimensional
electrophoresis." I am too ignorant of molecular biology to understand
such studies, much less to comment critically on techniques and analyses.
The results generally confirmed Stephen O'Brien's 1985 report. The
progenitors of raccoons and bears split during the Oligocene, and within
10 million years the red panda lineage diverged from the raccoon lineage.
In the Miocene, there were three major radiations among the bears, the
earliest line leading to the giant panda, the second to the South American
spectacled bear, and the last to the six other bear species. If the
authors expected to settle the panda debate with this study, it must have
been a forlorn hope. Indeed, given the history of molecular studies, the
next one would most likely contradict their findings. And so it did.

In 1991, Zhang Yaping and Shi Liming published in Nature the results of a
detailed analysis of mitochondrial DNA from the two pandas, Asiatic black
bear, and sun bear. Their conclusion: the giant panda is more closely
related to the red panda than to the bears. And they noted that, "there
are 1,000-10,000 copies of mitochondrial DNA in every cell; the selection
pressure on this DNA is very low. So the similarities between the two
pandas ... may not be the result of convergent evolution."

The contradictory results from molecular studies teach an important
scientific lesson. Slick and ultramodern techniques may not always be
enough to elucidate the incomprehensible. Morphology, paleontology, and
natural history continue to have an important role in unraveling the
evolution of the two pandas.

Fossils often provide insights into the past of a species, but there are
giant gaps in the fossil record, especially of pandas. The raccoon family,
an early branch of the dog family, the Canidae, evolved in North America
and spread across Asia to Europe where, during the Miocene, 20 million
years ago, the raccoonlike Sivanasua was found. The bears, also a branch
of the Canidae, appeared in the early Miocene in the form of Ursavus, a
bearlike creature as large as a medium-sized dog. The first definite
panda, Parailurus, a small animal resembling the red panda, occurred in
the early Pliocene about 12 million years ago in southern Europe and North
America; it persisted into Europe's last ice age, where it was quite
common in temperate forests. Some researchers think that a small, bearlike
animal of the Ursavus lineage named Agriarctos, dating from the
mid-Miocene, was the ancestor of the giant panda. Support for this
supposition came in 1989 when Qiu Zhanxiang and his colleagues described a
new fossil from the late Miocene in Yunnan with teeth that resemble those
of the giant panda but also share characters with the ancestral forms of
bears. The animal, given the name Ailurarctos lufengesis, was less than
half the size of today's giant panda.

The giant panda itself appeared suddenly during the late Pliocene or early
Pleistocene, perhaps no more than two to three million years ago. Panda
fossils have been found in Burma, Vietnam, and particularly in eastern
China, as far north as Beijing, where they appear so often with the
Pleistocene elephant Stegadon that the two species are used to designate a
distinct fossil fauna. The pandas of the early Pleistocene were about half
the size of today's giant panda and are considered a separate species,
Ailuropoda microta.

New species originate mainly when a small segment of an ancestral
population becomes isolated, and the animals change form and behavior
through natural selection until a population with new characteristics is
well established. This process may be so rapid that no recognizable
intermediate forms or missing links are found in the fossil record.
Animals can apparently evolve quickly, through major chromosomal
rearrangements, as well as more slowly through mutations of single genes.
Then, having settled in, the new species may remain unaltered, except for
slight modifications, for millions of years. The giant panda is known only
in its existing form, apparently not an ancient relic, as is often
claimed, but a relative newcomer. Its previous incarnations still remain
uncertain.

Can the behavior of the giant panda provide clues to the animal's
evolutionary relationships? This approach has problems. Species living in
similar habitats may evolve similar societies and similar physical
appearances, which in turn may result in similar behavior without there
being a close relationship. When comparing species, one first has to
decide which aspects of behavior have been strongly influenced by
ecological conditions. For instance, the amount, quality, and distribution
of food effects an animal's movements, activity cycles, and social
structure. Consequently two separate populations, even of the same
species, may behave differently. However, certain kinds of behavior such
as scent marking and vocalizing can function well under a wide variety of
conditions, and therefore they may be less influenced by ecological
pressures.

The giant panda produces a surprising mix of sounds, some of which it
shares with bears, some with the red panda, and some with both. For
instance, the giant panda's chomping, in which the animal clacks its teeth
and smacks its lips when anxious, is found in bears and, in a modified
form, also in red panda and even coati. The giant panda's plaintive honk,
which denotes light distress, is similar to the grunts made by bears and
several procyonids, but in these animals the calling has a different
function, that of a contact call between mother and young. More exclusive
is the moan, a highly variable call ranging from hoots and whiney groans
to long-drawn-out moans. Only giant panda and bear share this warning
signal. Particularly noteworthy is the giant panda's goat-like bleat, a
friendly call that provides animals with reassurance on meeting.

Continues...

---

Excerpted from The Last Panda
by George B. Schaller
Copyright © 2003
by University of Chicago.
Excerpted by permission.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.

---