The problem with line breeding (inbreeding)

First, let's clear one thing up. Line breeding is inbreeding. Period. People can use whatever fancy words they'd like to make line-breeding sound like something different than what it is, but genetically speaking, it's inbreeding. Calling it something different doesn't change what it does genetically. It's a red herring when people try to go on about how they don't inbreed, they line breed. While there is a time and a place for it (rare breeds, new breeds, etc) I'd strongly encourage anyone interested to do some research into population genetics in general. The reason I often see quoted for line breeding is "to solidify type" or some other human-selected trait. The problem is that genes don't exist in a vacuum. They're on a chromosome and chromosomes contain several genes. We have not completely mapped out the canine genome. When you select breeding dogs via linebreeding to solidify a certain trait, let's say perfect ears for the sake of argument, you end up doubling up on certain chromosomes and eliminating others. The chromosome you eliminated may have contained the genetics that help prevent cancer for example. You don't know what you're "throwing away" when you double up on one chromosome. People get so focused on what they're trying to "get", that they forget what they're *losing* that may be lurking under the surface in those recessive genetics. You might be getting better type while losing health and not even realize it for several generations and by then the damage is done. When we eliminate a gene from our line, we eliminate everything else that lived on that chromosome. One thing we know is that high COI comes with an entire host of problems. To me, there is simply no good justification for line breeding in any breed with a decent sized gene pool. It isn't worth the risk. You can find a dog with the traits you're wanting to solidify wthout breeding closely and raising your COI. These things affect not just your program but the breed as a whole and can lead to problems down the road, which is why we have breeds with average COIs up in the 20%+ mark which is associated with a ton of health risks. My opinion is to protect COI at any cost. There is no man-made priority (looks, sport ability, etc) that is worth harming genetic health. If our dogs aren't healthy, we have nothing. The number 1 reason I see people use to justify line breeding is "type". Type is irrelevant to health and certainly doesn't justify creating high COIs. Now, there was a time in history when line breeding was very normal but we need to remember an uncomfortable fact or two. Predominately that during those periods of time, hard culling was considered socially acceptable when the "line breeding" didn't work out. The founder of my own breed has stated that during its creation her vet flatly told her to "heavily line breed, keep the best and cull the rest". Species where line breeding is still highly acceptable are generally meat animals who only need certain phenotypic traits and who aren't expected to live past market age which is generally around late adolescence depending on the species. You can line breed there because you don't *care* about health or longevity or temperament. You care about muscle and size and nothing else matters. Dogs are companion animals. We can't use livestock strategies for them. Line breeding creates homozygousity and consistency which are NOT good for the long term health of any breed/species. Diversity is always optimal for health. Trying to create a breed that is identical is actually a very bad idea for anything from a scientific perspective and there is tons of science to back this up. Old school breeders will fight this tooth and nail but they want a reason to justify what they do. The science is clear.