Kangaroos are quite strange on the exterior: They’re the world’s biggest marsupials, they hop to navigate, and they utilize their tails as a 5th limbThey’re likewise quite uncommon on the within: Female kangaroos have 2 vaginal areas– or 3, if they’ve offered birth. Why could that be?

The most likely description is that it’s an adjustment to Australia’s unforgiving environment. Several vaginal areas– and uteruses, of which they likewise have 2– make it possible for female kangaroos, and all marsupials, to have numerous offspring at various phases of advancement at any offered time. That assists increase the opportunities of one making it through to the adult years.

“ They can have a joey that’s still dependent on them, but it’s out of the pouch,” Dr. Marcie Logsdonan associate teacher in the College of Veterinary Medicine at Washington State University, informed Live Science. “They can have a joey that’s in the pouch, and they can have one that’s kind of in reserve up there, waiting to start development.”

A newborn kangaroo is underdeveloped and requires to invest a long period of time in its mom’s pouch nursing and growing before it’s prepared for the outdoors world.

“The first 10 months, they go from being these pink, scraggly skeletons into little fuzzy cute babies that you see in the pictures,” Kelly Forrestera doctoral trainee at the University of Alberta who has actually co-authored research studies on kangaroo recreation, informed Live Science. “And then the last eight months, you call them ‘young at foot,’ where they’re coming in and out of the pouch and they’re learning to hop around, but they’re still pretty gangly and they can’t thermoregulate … so 18 months of their life is spent highly reliant on mom.”

Related: Why exist a lot of marsupials in Australia?

All that nursing in the pouch needs a substantial quantity of energy for the mom kangaroo. “Lactation is very, very expensive,” Logsdon stated. “Lactation is more expensive than pregnancy, oftentimes.”

When kangaroos experience dry spell conditionsthey frequently can’t get sufficient food to continue lactating, which joey in their pouch passes away. To pass their genes to the next generation, they require to produce another joey as rapidly as possible.

Fortunately, pregnancy and lactation do not stop a kangaroo’s estrous, or reproductive cycle. At any time throughout estrous, a male kangaroo’s sperm can take a trip up among the 2 lateral vaginal areas and fertilize an egg, which implants in whichever of the 2 uteruses isn’t being utilized at the minute. (Although lots of other marsupials have a two-pronged penis to assist send out sperm through both vaginal areas, kangaroos have just one.)

If there’s currently a joey in the pouch, there’s an issue: That joey will require that pouch for 18 months, however an egg goes from conception to birth in about 30 days, according to Forrester. The kangaroo’s body puts the egg’s advancement on time out.

“If they’re waiting for optimal conditions or maybe for their young to come out, that fertilized egg will just sit, waiting,” Forrester stated.

Once it’s completely established and all set to be born, the jellybean-size joey emerges through a brand-new opening. “The central [vagina] doesn’t fully connect to the opening into the outside until a female marsupial becomes pregnant for the first time,” Logsdon stated. “Then it connects and it opens up, and that’s their road out.”

The kangaroo’s odd anatomy might likewise be a factor for their offspring’s little size. Through a peculiarity of development, a female kangaroo’s 2 urinary systems travel through the areas in between the 3 vaginal areas

“If the babies got a lot larger, then there would be an issue because of that strange anatomy,” Logsdon stated. “It’s not a very conducive environment to have large things passing in and out if you’re going to have your urinary tract worked up in that too.”

Animal test: Test yourself on these enjoyable animal trivia concerns

Ashley Hamer is a contributing author for Live Science who has actually blogged about whatever from area and quantum physics to health and psychology. She’s the host of the podcast Taboo Science and the previous host of Curiosity Daily from Discovery. She has actually likewise composed for the YouTube channels SciShow and It’s Okay to Be Smart. With a master’s degree in jazz saxophone from the University of North Texas, Ashley has a non-traditional background that provides her science composing a distinct viewpoint and an outsider’s perspective.