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Orangutan genetics races and reproduction. Review of the orang utan. Its biology and conservation edited by Leobert E. M. de Boer. The Hague Dr. W. Junk Publishers 1982 353 pp. $76

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American Journal of Primatology 9:151-155 (1985)
Orangutan Genetics, Races, and Reproduction
Review of The Orang Utan. Its Biology and Conservation, edited by Leobert E.M. de Boer.
The Hague, Dr. W. Junk Publishers, 1982,353 pp. $76.00
Although the volume The Orang Utan Its Biology and Conservation makes a
formidable contribution to the study of the “person of the forest” (Malay translation
for the word “orangutan”), almost one third of the contributed articles deal with
orangutan cytogenetics. This, however, is not its weakness nor necessarily surprising as the book’s editor, L.E.M. de Boer, authored or coauthored all six papers on
cytogenetic topics as they relate to orangutans. It might, however, disappoint those
expecting to find the volume biased toward behavioral studies on wild and rehabilitant orangutans. But be assured, the increasingly sophisticated fields of cytogenetics
and molecular biology are providing the serious primatologist with a wealth of
information that has bearing on the conservation of endangered species both in the
wild and in captive populations. As is made clear in one chapter on genetics and
conservation of the orangutan, “Genetic studies are pre-eminently suitable to detect
the existence of intraspecific difference.” The chromosomal and cytogenetic methods
and results (detailed in chapters 4-7) used in the evaluation of the tremendous
amount of polymorphism in the orangutan (the most of any hominoid) have until
recently been typically used in comparing the orangutan with other primates (especially humans and the other great apes) to determine evolutionary affinities. But
knowing how to distinguish a Sumatran from a Bornean orangutan unambiguously
(as cytogenetic and chromosomal tests permit) is a “prerequisite of a good conservation policy for wild populations and to proper management of captive stocks.”
Characterizing orangutan population genetics (eg, determining the gene frequency of polymorphic loci or the presence of rare lethal alleles) can aid in conservation and zoo management decisions. The information and techniques described in
the various chapters should benefit responsible managers of captive orangutans who
want to insure a genetically healthy population of animals (eg, captive populations
whose genetic structure is similar to wild populations, free of excessive inbreeding,
and characterized as to hereditary diseases). The papers on orangutan cytogenetics
are, therefore, relevant not only to individuals who have a theoretical interest in
population genetics, but also to the practical and responsible managers of relatively
small orangutan populations where problems of genetic variability can exist.
The other chapters in the volume, which developed out of the 1979 “Workshop
on the Conservation of the Orang Utan,” are equally informative and valuable to
readers interested in orangutan conservation and reproductive biology. In the first
chapter Van Koenigswald presents a n enjoyable and fascinating review of orangutan
zoogeography and evolution. In contrast to characterizing populations of orangutans
according to genetic loci, the article reviews a few classic studies used to differentiate
0 1985 Alan R. Liss, Inc.
152 I Shapiro
orangutan races. For example, the author recounts the study by Selenka 118981who,
in the tradition of contemporary phrenologists, distinguished some eight Bornean
races (Simia satyrus ssp.) and two Sumatran races (Simia sumatranus ssp.) of
orangutan based upon brain capacities and cheek flanges. The comment on races of
male orangutans without “flanges” or cheekpads (p 3) indicates that classic observations from the old naturalist tradition should occasionally be questioned. Such
“flangeless” males represent the subadult age group of orangutans (Kingsley, chapter 11)and not another race. More significantly, the author details the evolutionary
and zoogeographical history of orangutans from the paleontological (primarily dental) evidence that has slowly accumulated over the last two centuries from many
areas of Southeast Asia.
In the second chapter M. Jones presents a compilation of material concerning
captive orangutan histories since their first appearance in Western Europe in 1776.
As Jones mentions in the chapter, over 1,400 orangutans have been exported from
Borneo and Sumatra during the last two centuries. A vast amount of information
has been summarized from the literature and unpublished archives with the international studbook serving a s a reference. A number of tables provide summary data
on the importation of wild orangutans, the breeding success of wild-born and/or
captive orangutans, and the longevity of orangutans in captivity. The chapter is
thus valuable to individuals interested in origins and present state of captive
orangutan populations worldwide.
Several chapters are specifically aimed a t the managers of zoological collections
that maintain orangutans. D. Jones provides a n objective, clinical “cookbook” on
orangutan maintenance, nutrition, reproduction and rearing, and handling techniques that have been successful in keeping captive orangutans alive. There is a
detailed section on medical concerns which should be of value to zoo veterinarians
and others who are interested in the health and well-being of the orangutan.
The intentionally clinical texture of this article contrasts with the chapter by
Maple on the management of captive orangutan behavior. The psychological wellbeing of captive orangutans is of equal concern to Maple, and a n understanding of
this is revealed from detailed behavioral studies of captive orangutans. The results
of these studies are discussed in terms of the orangutan social potential in the play
and parenting context. The author advises that infants be kept with their mothers
and presents methods successfully used to reintroduce hand-reared infants to their
mothers. Finally, a mention is given to the orangutan’s climbing and manipulative
proclivities, and Maple suggests how exhibits should be constructed or modified to
encourage movement and foraging activity.
The degree of orangutan social potential is further explored in a n article by
Edwards. Interactive and solitary behaviors and use of space were studied in two
captive groups (adult and juvenile) of orangutans. The findings of obvious social
behavior, age-related differences in activities, differential allocation of cage space,
and discrete relationships in captive orangutans does empirically indicate their
social potential in a captive setting. The findings, however, would not be surprising
to ethologists that have observed wild and captive orangutans. Although the adult
males are predominantly solitary, wild orangutans are better described a s “semisocial” [Galdikas, personal communication] and not asocial. In a captive setting,
enhancement of social expression and interactions would be expected. The conclusion that observations of wild orangutan social interaction may not always be
obvious due to “limitations presented while doing research” shows a failure to
appreciate the degree of ecological constraint faced by the red ape. Also, after many
thousands of observation hours, it is obvious to observers that wild orangutan social
behavior can be observed. Proximate social interaction just doesn’t occur as frequently among certain age-sex classes of wild orangutans (male-male) as it does with
TheOrangUtan I 153
the African apes; however, distal social interactions using the vocal-auditory modalities illustrate how the social potential is most frequently expressed [see Schurmann,
Rijksen this volume].
Several articles cover aspects of orangutan reproduction. The chapter by van
der Werf‘f ten Bosch details reproductive physiology and behavior during the life
cycle of the orangutan. Much of it is from zoo literature although the author does
not neglect to cite observations made by behaviorists in the field. Many of the
behavioral observations concerning various phases of the orangutan reproductive
cycle are based on a limited number of citings and, therefore, may not reflect what
is “normal.” For example, the author writes (p 202) that following the birth of her
infant, the rehabilitant orangutan, Joan, ate the afterbirth. Some rehabilitants do
not eat the afterbirth [Galdikas, personal communication]. It is, therefore, difficult
to characterize some aspects of the reproductive behavior of orangutans when so few
observations have been made. An unusual but interesting account of caged male
assistance during the birthing process is given. Again, this is not typical orangutan
behavior as a male would probably never witness the birth of his offspring in the
wild. The sections on rearing, somatic growth, and mating behavior round out this
The chapter by Kingsley examines the relationship between hormonal production, breeding success, and secondary sexual characteristics in captive male orangutans. Over a period of almost a year and a half, growth rates of secondary sexual
characteristics and hormone levels in various age groups of 20 males (juveniles and
adolescents, nonflanged adults, adults with growing flanges, and flanged adults)
were measured and statistically compared. A number of interesting conclusions
were suggested by the data. For example, in exploring whether the presence of a
flanged male suppressed the development of flanges in a nonflanged male, Kingsley
reports that the onset of flange development preceded separation from the older
male and then concludes that the relationship appears to inhibit flange growth in
the adult male. Supplemental data are used to bolster the case. Although the
hormonal data did not reveal a relationship between the hormones examined and
breeding success by males, the paper does illustrate that sensitive laboratory techniques can be used to better understand the dynamics of sexual development and
fertility in a n endangered species.
Although the next chapter focuses on orangutans, Nadler examines three related aspects of reproductive biology in great apes: cyclicity, periovulatory restriction, and hormonal regulation of sexual behavior. Data are presented that modify
Yerkes’ early assertions that 1)female mating initiative and degree of periovulatory
restriction of mating is controlled by hormones, while 2) performance of mating
outside the periovulatory period reflects a degree of behavioral emancipation from
hormonal control. After studying the chimpanzee, Yerkes believed this emancipation
was the result of the ape’s advanced taxonomic status and higher intellect. In his
comparative study, Nadler shows that male mating initiative, not taxonomic status,
regulates mating in captive great apes. With captive adult orangutans, male initiative is very strong, but Nadler points out it isn’t clear how these laboratory results
relate to “species-typical” behavior since in the wild, “rape” has been observed to
be a subadult male pattern, not a n adult male pattern. Several possibilities are
explored but it appears that captive adult orangutans display a different distribution
of mating during the female’s cycle because of the male’s strong initiative, male
dominance, and the inability of the female to avoid the male’s advances. By providing the female with the ability to avoid the male, Nadler shows that female initiative
in captive orangutans can be expressed and is greatest during midcycle. During this
time, the adult male is essentially passive, and this pattern more closely reflects
what has been observed in the wild.
154 I Shapiro
Schurmann’s chapter on mating behavior in wild orangutans confirms the role
of female mating initiative in Sumatran orangutans as far as adolescent females are
concerned. Galdikas [ 19811 earlier reported similar findings. Although admitting
that “rapes” do occur, Schurmann contends that the majority of the sexual interactions leading to copulation occur cooperatively and in consort relationships. In a
case history of two individuals, data are presented that show obvious cyclicity in
consorting and mating behavior. Since female orangutans show no visible sign of
estrus, female proceptivity during midcycle and her clear preference for adult males
may be necessary for her to choose a mate and may thus account for the marked
sexual dimorphism in this species.
In the final three chapters of this volume, the authors examine the orangutan
in the context of conservation. Galdikas explores the role of the orangutan as a
major seed dispersal agent in the complex tropical rain forest ecosystem. The frugivorous orangutan is seen as a n important modifier of the tropical rain forest both by
its physical manipulation of trees and tree parts and, in the context of this article,
by processing and dispersing numerous species of seeds. Seed dispersal by orangutans in Tanjung Puting, Central Indonesian Borneo, has been observed a t least in
four forms: 1)seed consumption and dispersion via feces, 2) fruit and seed chewing
and spitting, 3) carrying fruits a distance before consuming andlor spitting out the
seeds, and 4) dropping defective and/or unripe fruits. This last form of orangutan
seed dispersal is indirect as the gathering and dropping action provides a number of
terrestrial mammals more immediate access to the fruit. Observation and fecal
analysis indicate that orangutans can disperse seeds from the majority of the fruits
they consume. Galdikas shows that many of those seeds are of plants that have
considerable value to humans a s well as to orangutans. The value of the orangutan
is thereby increased: it is not only our endangered simian cousin, but a n important
seed disperser in a potentially valuable genetic reservoir, that is, the forest it
The last two chapters deal with more traditional considerations of conservation.
The chapter by Aveling is a n account of the state of orangutan conservation efforts
in Sumatra, specifically in the areas of law enforcement, habitat protection, and
conservation education. The prognosis for orangutan survival is uncertain owing to
the threat of huntingltrading and habitat destruction. A number of other uncertainties are also considered: estimates of orangutan populations, ability in enforcing
conservation policy and law, and the role of orangutan rehabilitation centers. Aveling gives a review of the efforts that have been made by Indonesian and foreign
conservation agencies. Although the author believes there are enough orangutan
rehabilitation stations throughout Sumatra and Borneo, the stations can have a n
effective role in orangutan conservation, primarily through conservation education.
Accomplishments in the area of conservation education and orangutan rehabilitation a t the Ketambe and Bohorok rehabilitation stations are detailed.
In the final chapter, Rijksen attempts to clarify some of the confusion and
“mystery” surrounding the orangutan: its name, distribution, population density
and size, social organization, reproductive strategy, and prospects for survival. For
example, after tracing the name for the genera, Pongo, back to the Congolese name
for the gorilla, “mpungu,” Rijksen suggests that the old name, Simia satyrus (Linneaus 1766), be restored as appropriate nomenclature for the orangutan. A discussion on various estimates of orangutan population is presented in context with
conservation concerns. The description of orangutan social organization and reproductive strategy is necessarily brief but accurate for the most part. Occasionally the
author’s interpretations become overly colorful, as in the statement. “For a female
in heat the long call of her particular male($ serves as a beacon of love” (p 323).
The Orang Utan / 155
Although some of the information in this chapter has been covered earlier in the
volume, Rijksen uses the information to consider measures he feels will ensure the
ape’s survival. For example, a suggestion is presented concerning the calculation of
the minimal size of a protected area necessary to insure the survival of orangutan
populations. Regarding orangutan rehabilitation centers, the author, like Aveling,
views them as a valuable component of law enforcement and conservation efforts;
however, Rijksen considers tourism in the context of orangutan rehabilitation inadvisable due to the potential of disease transfer and rehabilitation setbacks. The
suggestion is made that rehabilitant orangutans be transferred to protected areas of
Borneo and Sumatra where orangutans are not presently found so as not to contaminate existing wild populations.
Although the book provides a n excellent array of topics concerning orangutan
biology and conservation, it does not cover every aspect of this growing field. For
example, i t does not contain any articles that express the excitement that has been
generated in recent years in primate developmental biology, psychobiology, and
sociobiology. A volume like this, however, must limit itself, and in that respect it
succeeds by concentrating on several important disciplines which illustrate the attempts that have been made over the past decade to facilitate the survival of the
orangutan in both captivity and in the wild. Finally, the editor could have organized
the articles more carefully by placing them into appropriate sections such as cytogenetics, reproductive biology, and conservation, etc. This, however, is a minor point
for the reader will find the volume to be a n informative and useful reference.
Gary L. Shapiro
Department of Zoology
University of Oklahoma
Norman, OK
Galdikas, B.M.F. Orangutan reproduction in
C.E. Graham, ed. New York, Academic
Press, 1981.
Selenka, E. Menschenaffen:
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