Nature or Nurture?

by C.A. Sharp

First published in Double Helix Network News, Fall 2003, Rev. April 2013

Mary receives two phone calls, both from puppy buyers of a few years before.  The first is an exhibitor and fellow breeder calling to let her know the dog she sold him has just gone Best of Breed at a prestigious show.  Mary expresses her delight and congratulates the proud owner.  No sooner has she set down the phone than the second owner calls.  The woman’s young bitch is extremely ill.  Mary commiserates, asks about the dog’s veterinary care and offers advice.  She makes a note to call the owner back in a few days to see how things are going.  The bad news didn’t diminish her pleasure with the first dog’s win, but she knew she needed to consider what the second one’s illness meant for her breeding program.

Triumph and tragedy are part of breeding dogs.  Mary has received two pieces of news that may provide insight on the genetics of her line, but the question is:  How much?  Is the show winner an example of her astute breeding choices or his owner’s presentation skills and campaign strategy?  Could the sick dog be a victim of unfortunate circumstance or is the fact that she is ill a sign of genetic problems in Mary’s line?

The truth is, while some things are solely the result of environmental factors and others are inherited, many are a combination of both.  Genes to not function in a vacuum, they continually interact with the environment.  It’s Nature and Nurture, together, not a battle of opposing and distinct entities. As a breeder, you must deal with both in every decision you make.   Maintaining a good environment for your dogs is vital not only to their health and well-being, but to success in the show ring, performance arena, or home. But the ultimate legacy of your efforts is the genetic combinations you pass on to future generations of breeders through the dogs you produce.  To do this well, you must sort out how much is Nature and now much Nurture so your decisions will be good ones.

Often what we observe in our dogs will be an amalgam of Nature and Nurture.  Winners of major events would not be posing for trophy pictures without better than average training and handling.  In the case of coated show breeds, quality grooming is also a must.  The business cards of trainers, handlers, and groomers do not come encoded in DNA.  However, the dog must have inherited potential to be a serious competitor or even the best human support team will not be able to achieve more than so-so results.

Even before conception, environment begins to shape what the individual will become.  The genes a newly conceived puppy inherits from its parents carry the blueprint for its ultimate potential.  That potential will be for things you want to see and also for some that you don’t.  What happens to a pup before birth, during its early months and on through adulthood can amend the basic design created by sire and dam.  There is even a possibility that the parents’ environment may have left epigenetic changes – chemical tags that alter gene function – which can be passed to offspring, though this is still open to scientific debate.

Breeders know it is important to keep brood bitches healthy and comfortable.   The bitch’s nutritional level, her mental and physical health and medications or toxins she might be exposed to during pregnancy can all impact the health of her litter, not only during gestation but throughout their lives.  Much of the research on the effect of prenatal environment on the action of genes has taken place in mice.  There is a strain called “viable yellow agouti,” developed to study obesity.  In a research project at Duke University, a group of female mice were fed an extra dose of particular vitamins.  Their offspring, which should all have been obese and yellow, were instead svelte and brown.  The special vitamin cocktail given to the mothers effectively silenced the action of the gene that would normally have made the mouse pups look like their mothers.

No matter how careful you are things will sometimes go wrong.  If a pregnant bitch becomes ill or suffers a serious accident, talk to your veterinarian about whether there may be any impact on the puppies.  If so, know what you need to watch for and whether there is anything you can do to mitigate potential damage.  At the same time, you must avoid the temptation to dismiss things that subsequently go awry as due to their mother’s mishap.  If you do this without facts to back it up, you may be ignoring something genetic.

The interaction between nature and nurture is integral to a many conditions.  Hip dysplasia (HD,) for example, is, by some measures, 70% heritable.  This does not mean that 30% of dysplastic dogs are so due to environment while the rest are genetic.  Heritability is the portion of an observed trait that results from the individual’s genotype.  HD is always inherited, however the exact condition of a dog’ hips can be swayed one way or the other by its environment.

The environmental factors at play in HD are nutrition and exercise.  Puppies that are kept lean are less likely to develop HD than puppies that are kept fat.  Given all the media attention on the long-term dangers of obesity in children, it shouldn’t come as a surprise that being overweight is also bad for puppies.  Excess weight puts unnecessary stress on growing bones and joints.  If there is an inherent weakness there, the weight will make it worse.  For similar reasons, young animals require a proper exercise regimen.  Both young puppies and growing dogs need daily exercise.  For young puppies high-impact activities need to be avoided; older pups and young adults should engage in varied physical activities.  Dogs which do not receive this type of exercise are more prone to negative effects on their hip joints.  You cannot cure or prevent HD through any diet or exercise alone, however you can mitigate its effects.

Autoimmune diseases are another example of a nature/nurture combination.  In this case, the diseases are genetically predisposed.  This means that to have the disease the individual must have the genes, but not every individual with the genes will get sick.  To develop disease, the dog must experience an environmental trigger.  That trigger might be an accident, an illness, or some other stress factor. It could be something so subtle you will never figure out what it was.

Despite the environmental involvement, autoimmune diseases and HD are inherited and breeders must treat them as such.  Assuming that the environmental factors render the genetic aspect less important is playing a dangerous game with the health of the dogs you produce and their descendants.

That behavioral traits can be inherited is no surprise to any dog breeder.  We would not have the grand variety of breeds we see today if breeders long ago hadn’t selected animals that possessed the mental ability to perform a needed function along with the physical characteristics that enabled them to carry it out.   There are behaviors you would expect to see in a Saluki but not in a Cocker Spaniel, and vice versa.  Even between closely related breeds there can be distinctions.

Border collies typically exhibit strong “eye” when working livestock.  They also lower their bodies to creep toward the herd or flock and “wear” repeatedly back and forth behind it once the stock are moving.   The presence of some of these behaviors in working-line Australian Shepherds, where they are atypical, especially in combination, has fueled rancorous debate about the heritage of those individuals since the 1990s.

Temperament problems can also be inherited.  Sound shyness, exemplified by fear of gunshots, fireworks or thunder, is very common in some breeds and virtually absent in others.  This behavior can also be acquired if something happens to the dog that causes a strong negative association with that kind of loud noise.

A great deal of behavior is learned.  The dam is a puppy’s first teacher, followed by people and other dogs it lives with in its first few months.  Its environment continues to shape it throughout its life.  A dog reared by a large family in a country home would become a completely different individual as an adult if it spent its life with an elderly lady in a city apartment.

Mate preference is another basic behavior that results from both genes and environment.  Studies in numerous bird species have shown that baby birds that are not raised by members of their own species may not choose proper mates as adults.  Hand-raised parrots often pair bond with people, rejecting overtures from other parrots.  This makes them better pets, but poor breeding prospects.  Captive California condor chicks are “raised” by condor puppets so they will recognize their own species as adults.  The genes of parrots and condors tell them to seek their own kind, but the environment in which they are raised determines their perceptions of “us” and “them.”

Several mammal studies on species ranging from mice to humans have indicated that females are more attracted to less-related males, behavior that helps limit inbreeding.  To our benefit as dog breeders—and sometimes our despair—dogs are extremely easy going about whom they will mate with.  This open acceptance of mates has probably been part of breeders’ selection criteria for millennia.  Very early on, dogs that wouldn’t breed in a domestic situation would have been less closely associated with humans and therefore less likely to contribute to a domestic population.  When people started making specific mate choices for dogs, picky individuals would have been too much bother to use.  But even now, after millennia of domestic breeding, you may encounter animals that refuse to breed with close kin or with others with whom they have lived all their lives and therefore may perceive to be “family.”

Behavior is such an intricate blend of inheritance and environment that we probably will not ever parse it all out.  The best you can do as a breeder is make careful note of what traits are fairly consistent in the families of dogs you work with.  This is especially so with individual dogs of the same or very similar breeding that live in different environments.  Traits that are strongly inherited will show up in close kin even in very different homes.  Having identified behaviors that are likely to be highly heritable, you can take steps to maintain them or be rid of them depending on your needs and preferences.

Intelligence is another area where the nature/nurture line gets fuzzy.  Smart dogs are more likely to produce smart puppies.  However, the health of the mother and conditions in the womb or during birth may prevent a puppy from reaching its genetic potential.  Poor early nutrition and non-stimulating environments during a puppy first weeks or months can stunt its mental growth.  Fortunately, a lot of this is under the breeder’s direct control.

One of the biggest problems posed by the whole nature/nurture debate in dog breeding is the tendency to ascribe the things we like to genetics while we put things we don’t like off as the result of environment—something that “just happened.”

While you may have little or no influence on a dog’s environment once you have sold it, it is dangerous to assume that anything that goes wrong beyond that point must be bad luck or the fault of the new owner.  This is just as short sighted as pointing fingers at the parent you don’t own as the sole source of problem genes.

Like Mary, whose puppies brought her good news and bad, you need to get a firm handle on which factors to control in your dogs’ environment and which must be manipulated through genetic selection.  Doing so will help you achieve your breeding goals while minimizing the risk that things may go wrong.