Posts Tagged Outbreeding
Zoos spend a lot of time trying to find the right match between males and females, not to pair those individuals that like each other, but to maximise genetic diversity in what is often a very small population. This is important to minimise the effects of any deleterious genes on the population as a whole. Many physical characteristics, behavioural traits and diseases are genetically determined. There is a condition in humans called sickle cell anaemia. Affected people have abnormal red blood cells. To develop the disease the person needs to have received a sickle cell gene from both their father and their mother. If the father carries the gene and has children with one of his relatives, chances are that relative will also carry the gene and so any children will be much more likely to receive both genes and develop the disease. If he had children with someone else those children may carry one of the genes but probably not both and will live and be well. Interestingly people with one sickle cell gene have increased resistance to malaria compared with people that have no sickle cell genes, which is probably why the gene has not disappeared from the human population.
Similar problems can occur in zoo animals once the genetic pool is too small. This can happen naturally in the wild if species pass through severe population bottlenecks, as occurred with cheetahs, or live on islands where there is minimal influx of new genes, such as the Chatham Island robin. This reduced genetic diversity is why the Tasmanian devil is in so much trouble with its facial tumour. Because they are all so genetically similar if one devil is susceptible to the tumour then they all are. If individuals were more genetically diverse there would be more chance of encountering resistant individuals.
How perverse then is our desire for purebred dogs, cats, cattle, horses, etc. These animals have been created by doing exactly those things that zoos desperately try to avoid: brother/sister matings, father/daughter matings, etc. because misguided breeders are trying desperately to select for certain specific traits they deem important. The trouble is when one trait is selected other traits tend to fall by the wayside. Dairy cattle are selectively bred to produce huge volumes of milk to maximise profits. What they are not selected for is an ability to deliver calves naturally resulting in more and more veterinary interventions. Belgian Blue cattle are selected for an ability to lay down mountains of muscle, so much so that they cannot give birth naturally any more. Every birth needs a caesarean.
This lunacy has reached its pinnacle when it comes to dog breeds. Every breed of dog has its own specific inherited genetic abnormalities caused by this inbreeding. Bulldogs can’t breathe because they have been selected for pushed in faces. Shar Peis develop horrible skin diseases because they have been bred to have insanely wrinkly skin. A large number of Dalmatians are deaf and develop kidney stones. Many Dobermans suffer from a bleeding disorder called von Willebrand’s disease. Up to 25% of Bedlington terriers develop chronic hepatitis because they cannot metabolise copper. The list goes on to the point where it is almost impossible to buy a dog that does not have some form of genetic defect (For a complete list of inherited dog diseases check out http://www.upei.ca/~cidd/intro.htm). Your best chance of getting something reasonably healthy is to stick as closely as possible to the original wolf model. After all this was developed over centuries of natural selection for hardiness, ease of breeding and no genetic problems. If you are a wolf that can’t breathe, gets a skin condition or bleeds to death if someone bites you then you are not going to last long enough to pass that trait on to your offspring.
Unfortunately all these ridiculous dog shows, like Crufts, just perpetuate this sort of nonsense. It seems ironic that, this time, zoos are actually trying to do the right thing by encouraging outbreeding and maximising genetic diversity. It’s a pity that our domestic animal breeders refuse to do the same thing.
Dr. F. Bunny