Are rare breeds important for the conservation of genetic diversity?

Today is the International Day of Biological Diversity. As it happens, Eat This Podcast today published an episode that raises a question I have seldom seen given any serious discussion. Are rare breeds important for the conservation of genetic diversity?

Like all headline questions, the answer is probably “No”. Let me explain.

A very common justification for preserving rare breeds is that they are reservoirs of valuable genetic diversity. Just this week, for example, the Interim Executive Director of The Livestock Conservancy said:

[H]eritage breeds serve as primary reservoirs of the genetic diversity found within most domesticated species of animals. Up to 50 percent of a breed’s biodiversity is found nowhere else within the species.

She added,

[W]hen a breed goes extinct, those genetics are lost and can never be recovered. Many heritage breeds retain traits like natural immunity, drought tolerance, easy birthing, flavor, mothering instincts, and foraging abilities that are important both today and tomorrow.

The people who look after heritage breeds, despite their being less productive, “serve as a volunteer army in the fight to save irreplaceable genetics”.

Contrast that with the approach of Koen Vanmechelen, a Belgian artist and one of the two guests on Eat This Podcast. In 1999, he crossed a Belgian Mechelse Koekoek rooster with a French Poulet de Bresse hen, and from the resulting clutch of highly diverse chicks hatched the Cosmopolitan Chicken Project (CCP). Each year, Vanmechelen added yet another breed to the population, bringing in chickens from all around the world. When they eventually surveyed the genetic diversity of CCP birds, they discovered that they were three to four times more genetically diverse than any of the pure-bred breeds.

The Global Goes Local

This diversity is proving extremely useful for just the kind of breeding effort for which The Livestock Conservancy and others tell us we need to preserve heritage breeds: helping livestock to adapt to changing environments. Reversing the Cosmopolitan Chicken Project, Vanmechelen and scientific collaborators created the Planetary Community Chicken, crossing CCP birds with locally-adapted village chickens in Africa and elsewhere to produce birds that are more disease resistant, more resilient and that grow faster and larger.

Could the same have been done with pure-bred chicken lines? Who cares? It wasn’t. And the PCC project improved local birds very rapidly by injecting large amounts of genetic diversity into the population.

Do we, then, need to preserve heritage breeds as reservoirs of genetic diversity? I’m not sure we do. Maybe a massive cross-breeding operation to build a highly diverse population would be enough. It might also help to do away with the greatest drawback of heritage breeds, that because the population is effectively so small, there is a great risk that some of those valuable traits will be lost as a result of random forces. Instead of lots of rinky-dink collections that might be worrying about effective population size and how best to manage stud books to preserve maximum diversity, lets have a few large populations with the animals free to decide with whom they wish to mate and natural selection preserving genetic diversity.

That would be a lot less expensive.

Of course, we might lose the visual, gustatory and behavioural diversity that currently makes breeds interesting to behold and, probably, worth conserving for aesthetic and hedonistic reasons. But at least that would become the best reason to conserve them, rather than a pretty nebulous appeal to genetic conservation.