Cats, Sex, and Natural Selection

“Survival of the fittest.” We all want to believe that this grim-sounding phrase means something more than just strong winners and weak losers.

And it does. Without “soft” characteristics like kindness and empathy, for example, humanity would have gone extinct long ago no matter how smart and/or strong some of us were.

In evolutionary terms, fitness means living long enough to pass your genes along to the next generation. Which brings us to domestic cats–animals with a peculiar combination of ferocity and vulnerability.

Most importantly, in terms of evolution, they are sex maniacs. Domestic cats reproduce fast, giving artifical and natural selection a lot to work with. Even scientists are impressed.

Animals usually show some form of sexual selection. Not domestic cats.

All that noise and fighting when a female comes into heat? No one really knows what it’s all about, because the she-cat is just as likely to choose the loser of the battle as the winner.

This promiscuity means that domestic cats are in something called a Hardy-Weinberg equilibrium. In plain English, they breed so randomly that it’s relatively easy to study their population genetics.

It also means that cats are very fit, in evolutionary terms.

Domestic cats become sexually mature around seven months to one year old. Queens average two litters a year, with one to ten kittens per litter.

Here is a queen and her kitten (you’ve probably seen this already):

Each kitten may have a different father. Domestic cats do not get “yo mama” jokes.

All this genetic shuffling down through the millennia has given cats quite a “bank” of gene pool variability for selection to work on. And just like money in a financial bank, having lots of variability helps you do well in this unpredictable, changing world.

Variability often comes from mutations, but a kitten has DNA from both of its parents, so there’s already some variation present as life begins.

Having multiple fathers for a litter boosts the gene “bank” balance that much higher.

A little more variability may come in during embryo development since the DNA doesn’t always reproduce itself exactly. This duplication error is a mutation.

While some mutations are lethal before or after birth, others are so mild that they don’t even change the gene’s position on the chromosome. The mutated gene still does its thing–making hair grow, for instance.

Still, it’s not precisely the same gene, so there may be some different effects. Perhaps the fur will grow much longer than usual.

Now long hair is not going to help a domestic cat living near sea level at the Equator; in fact, the mutation would make that kitty unfit for its hot environment. It probably wouldn’t live long enough to reproduce.

But in the chilly high country of Persia and Turkey, where experts suspect long-haired domestic cats originated, an insulating fur coat would be an advantage.


deborasanfedele, Pixabay. Public domain.

In this example, “survival of the fittest” simply means that there are going to be more long-haired cats in Persia and more short-hairs along the Equator.

But what if climate change changes the conditions? A warm-up in the mountains, if it became the new normal, would be bad news for the region’s Persian and Angora cat populations.

But if the opposite happened – another ice age – cats on the Equator might turn into long-hairs.

Yes, natural selection can have creative effects, as well as destructive ones.

Those warm-weather shorthairs might be carrying the long hair gene simply because this mutation is recessive. It can be there and not show up all the time.


“This long-hair gene – is it serious?” (Drhesslen. CC BY-SA 3.0)

Natural selection would work against any carriers at the Equator who were born with long hair during a global warm spell. But the mutation wouldn’t disappear completely– some cats carrying this recessive gene would have short hair.

Then, during colder times, natural selection would work the opposite way, letting long-hairs now live long enough to pass that mutation along. Very soon, given how quickly they reproduce, domestic cats on the Equator would be sporting lush fur coats.

In science speak, all this would happen because cats are in Hardy-Weinberg equilibrium; therefore, the frequency of the long-hair gene would change and this population of equatorial kitties would evolve.

I’m no expert, but my general impression from reading is that this is all much more complicated in groups that don’t breed randomly like cats.

Of course, in real life the evolution of cats is also much more complicated.

For instance, a single gene might control more than one characteristic (pleiotropy). On the other hand, a group of genes–not just one, like the long-hair gene–may control a characteristic (a/k/a a polygenic trait).

  • Pleiotropic: Deafness in white cats
  • Polygenic: Some cat fur colors

To make things even harder for zoologists, there are also different kinds of natural selection – extremes may be favored in certain circumstances, while more moderate adaptations may work at other times.

And then there’s artificial selection–us. Even in this simple example, we’ve had to ignore the fact that very busy trade routes once passed through Turkey and Persia. People liked the look of long-haired domestic cats enough to carry them eventually across the vast continent of Eurasia, from Paris and London to Beijing and beyond.

Nowadays, even if global warming turned the mountains of Turkey and Iran into a Hawaiian-style paradise, Persian cats and Angoras would not go extinct because they are present throughout the world.

And thanks to AC/heating, long-haired cats now thrive in equatorial lands while bald cats are very popular in Russia despite its harsh and long winters.


“What’s a winter?” (artbot, Pixabay. Public domain)

These are only a few of the many effects humanity has had on the domestic cat during our long history together.

But before we could play any role at all, the cat had to be there.

And with a high balance at the feline variability bank, not to mention a very high birth rate, cats were present, with an amazing variety of appearances thanks to natural selection.

Perhaps this process even led to domestication in the first place. Although a “domestication gene” hasn’t been found yet, researchers are looking for it.

Does knowing all this make it any easier for a cat owner to get through the caterwauling and other drama of their pet’s breeding season?

Perhaps not, but it’s definitely reassuring to realize that “survival of the fittest” in the real world has given us the multi-faceted beauty of the domestic cat.

Featured image: Alvimann at


Fitch, W. M., and Ayala, F. J. 1995. Preface. Tempo and Mode in Evolution: Genetics and Paleontology 50 Years After Simpson. Washington: National Academy Press.

Lemmon, A. R. n.d. EvoTutor: Natural Selection: Modes of Selection. Accessed March 2018.-

Lobo, I. 2008. Pleiotropy: One Gene Can Affect Multiple Traits. Nature Education. 1(1):10. Last accessed March 5, 2018.

O’Neill, D. n.d. Modern Theories of Evolution: An introduction to the concepts and theories that led to our current understanding of evolution.

Ottoni, C.; Van Neer, W.; De Cupere, B.; Daligault, J.; and others. 2017. The palaeogenetics of cat dispersal in the ancient world. Nature Ecology & Evolution. 1:0139.

Simpson, G. G. 1944. Tempo and Mode in Evolution. New York: Columbia University Press.

Sunquist, M. and Sunquist, F. 2002. Wild cats of the world. Chicago and London: University of Chicago Press.

Todd, N. B. 1977. Cats and Commerce. Scientific American. 237:100-107.

University of California Museum of Paleontology. 2018. Understanding Evolution. n.d. Last accessed March 4, 2018.

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