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Kangaroos are pretty queer on the exterior : They ’re the world ’s largest pouched mammal , they hop to get around , and they use theirtails as a 5th tree branch . But they ’re also pretty unusual on the inside : Female kangaroos have two vagina — or three , if they ’ve given nascence . Why could that be ?
The most likely explanation is that it ’s an adaptation to Australia ’s unforgiving environment . Multiple vaginas — and womb , of which they also have two — enable female kangaroo , and all marsupials , to have multiple offspring at different stage of development at any given time . That help increase the chances of one surviving to adulthood .
When they’re giving birth, kangaroos have a total of three vaginas.
" They can have a joey that ’s still dependent on them , but it ’s out of the pouch,“Dr . Marcie Logsdon , an associate professor in the College of Veterinary Medicine at Washington State University , told 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 out development . "
A newborn kangaroo is underdeveloped and need to spend a foresightful sentence in its mother ’s pouch breast feeding and growing before it ’s ready for the outside world .
" The first 10 month , they go from being these pinkish , scraggly skeletal system into little hazy precious infant that you see in the pictures,“Kelly Forrester , a doctoral educatee at the University of Alberta who has co - authored study on kangaroo reproduction , told Live Science . " And then the last eight month , you call them ' immature at metrical unit , ' where they ’re come in and out of the pouch and they ’re learning to hop-skip around , but they ’re still middling gangly and they ca n’t thermoregulate … so 18 calendar month of their life is spent extremely reliant on mummy . "
When they’re giving birth, kangaroos have a total of three vaginas.
Related : Why are there so many pouched mammal in Australia ?
All that nursing in the pouch want a vast amount of energy for the mother kangaroo . " Lactation is very , very expensive , " Logsdon said . " suckling is more expensive than maternity , oftentimes . "
When kangaroos experience drought weather , they often ca n’t get enough food to continue lactating , and that joey in their pocket dies . To pass their gene to the next generation , they need to produce another joey as promptly as possible .
Kangaroo joeys are about the size of a jellybean when they’re born.
fortunately , gestation and lactation do n’t stop a kangaroo ’s estrous , or reproductive cycle . At any sentence during estrous , a male kangaroo ’s sperm cell can travel up one of the two sidelong vaginas and fertilize an ballock , which implants in whichever of the two uterus is n’t being used at the second . ( Although many other marsupials have a two - pronged penis to aid send sperm cell through both vaginas , kangaroo have only one . )
But if there ’s already a joey in the pouch , there ’s a problem : That joey will need that pouch for 18 months , but an egg goes from conception to birthing in about 30 day , accord to Forrester . So the kangaroo ’s trunk puts the egg ’s development on pause .
" If they ’re wait for optimal conditions or maybe for their untried to fare out , that fertilized eggs will just posture , look , " Forrester said .
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Once it ’s fully developed and ready to be bear , the jellybean - sizing joey emerge through a new possible action . " The central [ vagina ] does n’t fully connect to the opening into the outside until a female marsupial becomes fraught for the first time , " Logsdon order . " Then it link up and it opens up , and that ’s their route out . "
The kangaroo ’s unusual figure may also be a reason for their offspring ’s pocket-size size of it . Through a crotchet of evolution , a female kangaroo ’s two urinary piece of ground pass through the space between the three vaginas .
" If the baby engender a lot larger , then there would be an publication because of that foreign bod , " Logsdon said . " It ’s not a very contributive environment to have large things passing in and out if you ’re going to have your urinary tract work up in that too . "
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