Why are dogs so dif­fer­ent?

EQUUS - - Eq Truetale -

Many do­mes­tic an­i­mal species have been se­lec­tively bred for thou­sands of years now, yet dogs seem unique in the num­ber of dif­fer­ent shapes and sizes they ap­pear in. How do dogs man­age to take so many dif­fer­ent forms? Is there some­thing un­usual about the ca­nine genome that al­lows this? Could other do­mes­tic species, if bred over time for a wider ar­ray of pur­poses, also the­o­ret­i­cally as­sume such widely di­ver­gent forms?

This is a good ques­tion. I'm now sure we have a good an­swer, but there are a num­ber of the­o­ries. First, it's fairly easy to un­der­stand how ar­ti­fi­cial se­lec­tion helps us de­velop the same species into dif­fer­ent breeds based on the traits we de­sire most. If one group of peo­ple needs help chas­ing down rab­bits, say, they will keep breed­ing their fastest pups to each other un­til af­ter mul­ti­ple gen­er­a­tions they have cre­ated a dog that is much leaner and faster than his cousins. Mean­while, other groups of peo­ple are choos­ing dogs based on their own needs, such as to hunt larger prey, herd sheep, pull carts or guard home­steads. The same goes for other do­mes­tic species, when peo­ple choose breed­ing an­i­mals based on the traits they value: the pro­duc­tion of richer milk vs. more meat vs. a finer wool, for ex­am­ple.

A num­ber of fac­tors may have in­flu­enced our abil­ity to pro­duce more changes in dogs over the mil­len­nia:

DOGS have a shorter gen­er­a­tion in­ter­val than horses or other live stock Dogs were do­mes­ti­cated roughly 10,000 years ear­lier than horses were, and we have bred many more gen­er­a­tions of dogs than we have horses. An­other boost comes from the fact that dogs come in lit­ters rather than the horse’s much slower rate of one baby a year. Each in­di­vid­ual pup born presents a new op­por­tu­nity for ge­netic change that may be se­lected for fur­ther prop­a­ga­tion.

Dogs are om­ni­vores Their var­ied diet al­lows them to con­tinue to eat af­ter stack­ing up mul­ti­ple changes in the head and teeth. Horses, in con­trast, need to main­tain good teeth in de­cent align­ment be­cause grass is one of the tough­est things to eat. Any sig­nif­i­cant changes to a horse’s head are likely to lead to a de­cline in func­tion that will not be se­lected for prop­a­ga­tion to fu­ture gen­er­a­tions.

Dogs are used for a wider­va­ri­ety of pur­poses This tends to drive se­lec­tion in dif­fer­ent di­rec­tions as own­ers choose the best among the can­di­dates for these uses. Horses have al­ways been bred for just two ba­sic jobs, pulling and rid­ing. These pur­poses re­quire a cer­tain base­line ath­letic abil­ity. That, com­bined with the diet and teeth needed to sup­port it, has added a de­gree of con­ser­vatism into the changes that are at­trac­tive to own­ers. With horses, the orig­i­nal pack­age is pretty close to what was needed and de­sired all along, so se­lec­tion rarely dis­rupts this in rad­i­cal ways. In con­trast, the orig­i­nal form of the dog is rarely the fi­nal tar­get, so se­lec­tion tends to opt for change over time.

In any pop­u­la­tion, an in­di­vid­ual will oc­ca­sion­ally be born with a sig­nif­i­cant ge­netic mu­ta­tion. I knew a horse at a lo­cal barn, years ago, who had a spine that was dra­mat­i­cally shorter than nor­mal. This led to dis­com­fort for both horse and rider, and it was

need to worry about? What signs should I watch out for? How of­ten should an older dog be tested for age-re­lated dis­eases?

What an ob­ser­vant pair you and your neigh­bor make! Our farm dogs are lucky to have a bit more freedom than many house pets, but the down­side is that we might miss some early warn­ing signs of chronic disease---like sub­tle changes in thirst and uri­na­tion---that are eas­ier to no­tice in dogs with a more ur­ban life­style.

Risk fac­tors for di­a­betes mel­li­tus in­clude obe­sity, age, ge­net­ics, some med­i­ca­tions and episodes of pan­cre­ati­tis. Still, re­gard­less of how many risk fac­tors your dog might have, your ques­tions are ex­cel­lent. Signs of di­a­betes that are of­ten seen by own­ers do in­clude in­creased thirst and uri­na­tion, but you may also no­tice lethargy, weak­ness of the rear limbs (which is es­pe­cially no­tice­able when the dog is jump­ing), and in­creased ap­petite that is of­ten ac­com­pa­nied by weight loss (rather than the weight gain you might ex­pect).

But di­a­betes is not the only disease that can cause in­creased thirst and uri­na­tion. Your vet­eri­nar­ian might also look for kid­ney disease, Ad­di­son’s disease (hy­poa­d­reno­cor­ti­cism), Cush­ing’s disease (hy­per­a­dreno­cor­ti­cism), thy­roid disease and other prob­lems.

How of­ten you need to screen an older dog for di­a­betes and other agere­lated dis­eases will vary, depend­ing on his over­all health and other risk fac­tors. In gen­eral, though, I rec­om­mend twice an­nual phys­i­cal ex­am­i­na­tions for older dogs and cats. At these visits you can dis­cuss your dog’s health risks with your vet­eri­nar­ian, and to­gether you can de­cide how of­ten to do some blood­work to screen for age-re­lated dis­eases.

I hope that you and your dog have many healthy years ahead! Keen ob­ser­va­tion at home, com­bined with reg­u­lar visits with your small an­i­mal vet­eri­nar­ian, will help to en­sure that fu­ture.

Newspapers in English

Newspapers from USA

© PressReader. All rights reserved.