Coolidge Effect

Frank Beach

When an ethologist, Frank Beach, needed to name an effect he had noticed whereby male animals show a renewed interest in sex when presented with a new and receptive partner he chose to use the anecdote of the 30th President of America, Calvin Coolidge, as he toured a farm with his wife Grace.

The President and his wife visited a government chicken farm in Kentucky and separately were taken to inspect the workings of the farm. In a large barn a rooster was busy servicing many fowl. Mrs Coolidge asked the stock man if a single rooster was capable of mating many times a day. Yes Ma’am. She asked the attendant to make sure he told the President when he came by. When the President arrived in the same barn the rooster was still mating. The manager said to the President – your wife wanted you to note the capabilities of a single rooster, Sir. The President, known to be a man of few words then asked the stock man – Same hen? To which the attendant replied, No Sir, always a different hen.

Make sure you tell that to Mrs Coolidge, said the President.


This is how the phenomenon, witnessed in mammalian males whereby there is an increased appetite for sex with a new partner, came to be called the Coolidge effect. It is the reason why a single bull can service many cows. It is the reason why a single ram can do the same with a flock of ewes. Maybe it is the reason men are aroused by affairs and strip tease. Maybe it is the reason why marriages fail or become loveless. Is it why men use the service of brothels more than women seek the service of male prostitutes? And is it why fluffers are required in the pornography industry? After all we are all just animals in the end. We like to think we are more than hormones and brain chemistry.

Frank Beach was a great scholar with a keen sense of humour. He also believed in seeking knowledge and continually learning. Beneath a list of things “to do” he wrote, “Of course, I shall never accomplish all the goals just listed, but that is unimportant. What counts is to have aims, to be able to work hard toward them and to experience the satisfaction of at least believing that progress is being made. I do not want to cross the finish line of this race – not ever – but I do hope I will be able to keep running at my own pace until I drop out still moving in full stride. It’s been one hell of a good race.”

Compare this effect with that called the Bruce effect after its discoverer, zoologist Hilda Bruce, in the late 1950’s. She discovered that mice could block their pregnancy if they were placed with an unfamiliar male after mating. This effect is seen only in some rodent species but is thought to have arisen because male rodents tend to kill offspring unrelated to them. Evolution has ensured that mice are capable of miscarrying and then mating with the new male rather than wasting time and energy gestating young that are likely to be killed after they are born.

Don’t you love science?