Zoo History: Mapping the Family Tree

"A little more than kin and less than kind."

- William Shakespeare Hamlet, Act I, Scene II

For most of their history, zoos and aquariums were able to replenish their exhibits from the seemingly inexhaustible stores of the wild.  In the decades following the end of World War II, however, the doors to the wild began to slam shut, one by one.  Newly independent nations of Africa and Asia began imposing limits of the export of their wildlife.  New national laws and international treaties regulated the trade of species.  Public opinion began to turn against the idea of capturing wild born animals for zoo displays.  And, finally, it began to become apparent that the wild maybe wasn't as inexhaustible as it once seemed.

For zoo curators and collection managers, the choice was stark.  Either stop displaying certain species... or learn to breed your own.

Many of the more positive trends in zoo husbandry began to develop as a result of this trend.  In order to breed species, zoos began to move towards large exhibits that allowed for the expression of more natural behaviors.  Collections moved from single-specimen "stamp collections" (one white rhino, one black rhino, one Indian rhino, one Sumatran rhino...) to species-specific social groups.  Then came the realization that mental health was just as important as physical health, resulting in the adoption of more behavioral enrichment.

The work began to pay-off.  Animals began to breed.  Sometimes the babies thrived.  Other times... not so much.

In the late 1970s and early 1980s, National Zoo biologists Katherine Rawls and John Ballou began a study of the survival rates of mammals in zoos.  They started with ungulates, but also looked at small mammals, primates, and other taxa.  In each case, they made the same discovery.  The more closely the parents were related - the more inbred a young animal was - the less likely its chances of future survival.  Inbreeding led to reduced fertility and greater infant mortality.

Like many genetic developments, this seems old news now, but was pretty serious stuff back in the day.  After all, while direct incest - mother to son, brother and sister - was frowned upon in human society, a lot of royal families, such as those of Europe in the 1700s and 1800s, were basically a bunch of family trees with seriously intertwined branches.  Even among the middle class, marrying cousins was normal; heck, Charles Darwin married his.  And Cleopatra was the product of who knows how many generations on inbreeding.  And that's just people!  Look at our domestic animals, such as purebred dogs if you want to see some murky genetic issues.

The solution in this case was pretty straightforward.  Stop inbreeding.  That became the tricky part, however.  Zoo populations tend to be small ones, especially when you are dealing with very endangered species which have seen a tremendous loss in their numbers.  The Arabian Oryx World Herd, for example, started with NINE animals.  Plus, how do you keep track of how related all of these animals are?

Out of the work that Rawls and Ballou published came changes that reshaped the zoo world.  The international zoo community worked to create a registry of all the animals (as many as possible, anyway) in their collections.  The International Species Information System, or ISIS (for reasons I can't begin to imagine, they recently changed their name, opting for Species360 instead) keeps track of what animals are in what collections around the globe.  On a more specific scale, Rawls and Ballou saw their work lead to the development and adoption of the studbook program.

I saw this sign at the San Diego Zoo, and thought that it summed the concept up pretty nicely.

A studbook is essentially a biography of a population.  It keeps track of what animals, both current and historic, are born and die, where they lived, who their parents and offspring are, and how they fit into the population as a whole.  Studbook keepers (the biographers of the populations, if you will), help maintain the genetic health of the population by making sure it retains as much diversity as possible by deciding who breeds with who.

The Rawls and Ballou papers never achieved much fame or glory.  I doubt that's what they were looking for, but they deserve it nonetheless, having helped crack open one of the greatest threats to maintaining animals under human care for several generations.  Their research and insights into the dangers of inbreeding also have important consequences for the study of wild populations, especially those trapped in small and increasingly isolated patches of protected habitat.  When the first of their papers were published, biologists were worried about zoos being the "small" populations.  Today, for several species in zoos, the zoo population is getting bigger.  The wild ones, however, are getting smaller and smaller.