Does size matter? For dog owners, the answer is usually yes. Looking after a little dog that stands ankle-high is quite a different prospect than adopting one that can look a small pony in the eye.

In the past, nobody was really sure how to predict height. Some thought it was entirely genetic, that height is determined purely by the size of the parents. Others said it depended entirely on environment, like whether the puppies have enough to eat at various life stages. Still others argued it was a blend of the two.

For the people who thought it was all in the diet, it led to some weird ideas about controlling how tall a pup will grow by feeding it specific things.

Luckily, figuring out heritability – exactly what is due to genes and what is due to environment – is an active field of scientific research and it has yielded some good information.

Humans and height heritability

When it comes to humans, geneticists have worked out that when it comes to difference between individuals in terms of height, about 60-80% is due to genetic factors, and the remaining 20-40% is environmental.

However, as several different genes and environmental factors are involved, height heritability varies, depending on the group you’re talking about.

Yes, there is no one answer to how much genetics and environment are responsible for height in people – it depends entirely on the group you’re discussing.

How does that work?

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A study of Finnish twins put height heritability at 78% for the men and 75% for the women for their group. However, another study of local families, by Hunan Normal University, China, put height heritability at 65% for the people in their group. Photo: 123rf.com

A study in 2000 of 8,798 pairs of Finnish twins at the University of Helsinki, Finland, put height heritability at 78% for the men and 75% for the women for their group. However, a 2004 study of 385 local families in Hunan Normal University, China, put height heritability at 65% for the people in their group.

Scientists are now thinking that genetics may perhaps be a bigger factor in determining height in Caucasian male populations than in other ethnic populations.

Wild, right?

Dogs and height heritability

When it comes to dogs, scientists are focusing on studying pedigrees whose breeding and ancestry is carefully documented. This is because so many pedigrees suffer horribly from inbreeding, that heritability studies are looking into how genetics and specific canine diseases are linked.

But luckily for us, many also take a quick look at how height figures in these matters. And the results are fascinating.

In 2001, a study of 2,929 purebred Boxer dogs from 414 litters at Aarhus University, Denmark, estimated height heritability at 53% for their group. In the same year, a study of 2,334 German shepherds and 2,028 Labrador retrievers at the University of Illinois, the United States, led to height heritability estimated as 35% for the German Shepherds and 46% for the Labs.

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When it comes to estimating how tall your pup will grow, genetic factors matter a lot but not quite as much as they do in humans. Filepic

To me, that suggests that when it comes to estimating how tall your pup will grow, genetic factors matter a lot but not quite as much as they do in humans. It would also vary from breed to breed across countries. So if you looked at Illinois-bred German Shepherds, looking at the mum and dad wouldn’t be as useful as looking at the parents of a Danish Boxer.

Does that matter? My guess is that when it comes to pedigrees, then probably not so much, purely because of the scale we’re talking about. Let’s face it, there’s only an inch or two of difference in a short German Shepherd and a tall one.

Also, when we think of the kind of dog we want, we tend to talk in terms of big differences. Breed books, for example, are sorted into toy, small, medium, large and giant dog sizes.

However, when it comes to mixed breed pups, there is less to go on. Common sense suggests that looking at mum and dad is going to give you at least part of the story: if they’re both tall dogs, their pups are bound to inherit their height potential.

The difficulty would be to figure out exactly who the father is, as even the shyest female dog may have several suitors when she’s in heat. Also, a litter of pups may have more than one father.

Yes, you read that right.


A dog’s love life is complicated

Female dogs release multiple eggs during ovulation, and each egg matures at its own rate. When she is in heat, all male dogs are attracted to her. Very often, she is mounted by several dogs over the days she’s in heat.

Now, boy dog sperm cells can reach the eggs in under 60 seconds, but they also stay around, perfectly viable for up to seven days. During these days, several of the female dog’s eggs may mature.

In other words, a female dog can become pregnant several days after she has mated.

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At six to eight months old, a puppy’s end size is more or less predictable. Filepic

Although dogs may know their pups, people have more trouble figuring it out. This is why Kennel Clubs used to be unable to deal with multi-sired litters. However, now that DNA profiling is available, some will allow breeders to register pups – if they can prove the parentage.

So the bottom line appears to be this: if you are buying a pedigree, you can predict more or less how tall your pet will grow. But when you’re adopting a mixed breed pup, it can be rather hard to tell who’s going to grow up into a big dog and who will be bijou-sized.

For the best guess, go to the shelter nearest you, and ask the people there to introduce you to a young dog that’s six to eight months or older. At this age, they’re still pups but they are grown up enough for you to guess their end size.

It means less chance of seeing your tiny pup growing up to rival a carthorse.