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Elephant gestation: why 22 months?

Elephants are known for having one of the longest gestation periods in the entire animal kingdom. An elephant pregnancy lasts about 22 months – almost two entire years. However, until recently, no one was completely sure of the reason why.

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By Griffy Vigneron (The Cascade) – Email

Print Edition: March 27, 2013

If you thought nine months of pregnancy was bad, be thankful you’re not an elephant.

Elephants are known for having one of the longest gestation periods in the entire animal kingdom. An elephant pregnancy lasts about 22 months – almost two entire years. However, until recently, no one was completely sure of the reason why.

A recent study has found that the cause results from an excess of a hormone-secreting gland known as the corpus luteum. Elephants have been found to have up to 42 corpus luteums for one fetus, whereas humans only require one.

In humans, the corpus luteum is a structure left behind after the egg exits the ovary during ovulation in the middle of the menstrual cycle. After the egg remains unfertilized, the corpus luteum degrades before the next menstrual cycle begins. Since humans aren’t really built to hold more than one embryo at a time, generally only one egg will be released at a time – in turn producing only one corpus luteum at a time.

The corpus luteum is known for its hormonal involvement in extending pregnancy. If the egg becomes fertilized in the womb, the corpus luteum will not break down. Instead it continues to produce progesterone, a hormone that effectively stops the menstrual cycle

This also stops more eggs from being produced, which is why progesterone is often used in hormonal birth control methods. It tricks the body into thinking it’s pregnant, so it won’t release any more eggs to be fertilized.

But why do elephants have more than one corpus luteum?

Elephants only carry one offspring at a time, so there doesn’t seem to be a specific need for more than one. They can’t be releasing more eggs while being already pregnant, so why the need for extra corpus luteums?

Regardless of why elephants have them, it’s the excess of progesterone from the extra corpus luteums that is now thought to extend the length of the elephant gestation period.

Why is this beneficial?

Mammals with lengthier gestation periods allow a lot more time for the development of the fetus. In smaller mammals with shorter gestation periods, protected development of offspring in the womb allows mainly for structural development. Once the baby is born it might spend more of its time depending on these structures for survival.

A longer gestation period allows for extra development, especially of features like the brain. It’s often speculated that elephants highly emotional and intelligent. They are social creatures, much like humans or apes. They need to be able to navigate the complexities of group living and understanding. Long gestation periods prepare elephants developmentally. It readies them for the complex world they are about to enter.

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