Zoos and Zoological Parks consideration is rates of fertility and infant and adult mortality; these estimates are used to project the number of breeding pairs that will be required in order to end up with the desired number of births that will balance deaths and also generate the recommended population growth or shrinkage ‘‘Genetic representation’’ of individual animals is the primary variable considered in deciding the animal-by-animal breeding priorities, except that aging, genetically underrepresented animals with only a few breeding years left may be given special breeding priority Genetic algorithms, largely developed by the Chicago Zoological Society’s Robert Lacy, use pedigree-based genetic simulations to assess the genetics of each animal and potential pairing in the population Managers attempt to simultaneously maximize three parameters when recommending breeding matches: (1) good matches will improve the genetic diversity of the population (i.e., by increasing underrepresented lineages), (2) good matches will attempt to balance the genetic value of male and female, and (3) good matches will avoid inbreeding with close relatives Balancing the genetic value, which is done by looking at a parameter called mean kinship, or the effective number of close kin, is important because it breeds big families with other big ones and little families with other little ones New ways of visualizing mean kinship are now being used in PMx so that mismatching of animals with different mean kinship values becomes less important This is especially useful in managing polygynous species where other difficulties can emerge if genetic management trumps social management Although the science of conservation breeding has advanced considerably, practical considerations also must enter into planning Wild animal keeping in practice is a complex art, and it would be foolish to ignore details such as the distance of a proposed transfer and behavioral and physiological observations For example, there is no point in recommending a pairing of two gorillas that are incompatible Similarly, if an animal has not bred after many attempts at several zoos, there may be a physiological problem, or perhaps managers have not yet tried the right trick Group-breeding species are a special challenge to zoo population biologists, as they are for zoo animal records keepers The methods outlined above work less optimally for populations in which a significant proportion of the pedigree is unknown, and also when managers cannot control which individuals mate with which, as is generally the case with groupbreeding animals An approach that is sometimes used is to completely ignore the pedigree and manage the species as a subdivided population, with occasional transfers of animals between demes or subpopulations But the pedigree-free approach often throws out large amounts of information about a population and results in overly conservative management that will require larger populations than might otherwise be needed Similarly, species whose life history is more sizedependent than age-dependent are not well served by current methods, and may be better managed using stage-based population management As zoos move beyond management of animals with relatively simple breeding biology, such as tigers, and tackle species with more complex life histories, new population approaches will be needed Similarly, as the ‘‘brave new world’’ of reproductive technology develops, frozen zoos will need to become integrated into population planning 477 Frozen Zoos and Other High-Tech Solutions An alluring prospect is that someday we may be able to preserve biodiversity in bottles on a warehouse shelf Another enticing prospect is the use of reproductive technology to propagate animals that have not reproduced naturally New technologies are making these prospects possible in some cases ‘‘Assisted reproduction’’ is a catchall phrase for a variety of veterinary or endocrine interventions used to promote breeding (Gibbons et al., 1995) Artificial insemination, using fresh or frozen sperm, has been in use for many years in the domestic livestock industry and also for some zoo animals The techniques can be readily adapted to zoo animals if there is a closely related domestic model in which the technique has been developed; for example, rare species of cows can benefit from research with domestic cows Zoos have also employed other techniques, such as in vitro fertilization with harvested eggs, or embryo transfer both within and between species The idea of growing a rare species in the womb of a common one is appealing, and has been achieved in some instances ‘‘Frozen zoos’’ are being developed by several zoos In these superchilled repositories, sperm, eggs, and embryos are committed to long-term storage Now that cloning is also a real possibility, frozen zoos of living cell lines are also being developed (Ryder and Bernirschke, 1997) Saving biodiversity in freezers is tantalizing, but there are many limitations to this approach and hurdles to be overcome Assisted reproductive techniques are difficult and costly to adapt to animals that not have a closely related model, and also for those with complex reproductive physiology, for example, animals with induced ovulation By and large, the techniques for animals with shelled eggs have been limited to artificial insemination We cannot, as of yet, grow embryos in a test tube, so those derived from a frozen zoo must be grown in a real womb (or egg) This means a real population of surrogates will be needed to mother the frozen zoo, although in some cases these surrogate mothers can be of a different species Surrogate mothers may produce animals with species-inappropriate behaviors and possibly even a hybrid phenotype Frozen zoos will not preserve learned animal behaviors (culture), and they will not eliminate the need to keep real populations Frozen zoos, cloning techniques, and the like, as San Diego’s Oliver Ryder predicts, will probably become powerful adjuncts to the management of populations So far, genetic and demographic models for managing zoo populations have not factored in frozen resources, but some day they probably will This will allow managers to keep smaller numbers of living animals In addition, relative to the transfer of whole animals, the transfer of sperm, eggs, and embryos between wild and captive populations can be done with far less risk of cotransferring disease-causing pathogens Thus, these techniques may be highly useful in importing new gene lines into small populations, both wild and captive Supporting Diversity in Nature The Ark Paradigm Enamored, perhaps, with their newfound ability to breed and manage exotic animals, zoos and their commentators were for