This hypothetical marsupial species raises young in a manner loosely similar to seahorses. Only the males have pouches: after gestation the female deposits the fetus into his pouch to compete development. Is this adaptation competitive?

EDIT: Here are some revisions to address problems brought up by answers:

  • Nutrition: The male's pouch has nipples and lactates.
  • Evolution: I would assume that they developed along a loosely similar path to seahorses when developing into mammals. As reptiles that fertilized internally and then laid eggs, they developed a strategy of attaching the eggs to the male, then as time went on the male developed a brood pouch and nipples like a marsupial while the eggs degenerated and the burden of gestation was foisted on the male.

  • Advantage: The intended advantage is that the female foists the burden of pregnancy on to the male, allowing her to devote energy to producing more offspring at lower cost. Polyandry would probably be common.

  • Avoiding parasites: If necessary, perhaps the female lays a soft shelled egg in the male's pouch to prevent parasites from attaching to the fetus. The shell later dissolves to allow the fetus to attach to a nipple.


Picture a bamboo forest. Most years are quite routine. Your hypo-marsupials scavenge for (non-bamboo) seeds and other foods. In turn, they are eaten by whatever predators they have (owls, hawks, weasels, wolves, large cats, etc).

Every 50 years the bamboo forest blooms as the previous generation prepares to die off and drop its seeds. Many, many tons of food are literally dropped in the hypo-marsupials laps.

During this time of overwhelmingly plentiful food, a female marsupial that can pass on the development and growth of the younglings while she recovers from the initial pregnancy and preps for the next litter will give her bloodline a distinct advantage in out-competing and out-numbering rivals.

During this time, the predators will be well fed, but will have almost no impact on the massive amount of hypo-marsupials that will swarm the area.

Eventually, the seeds are gone (either eaten or sprouted) leaving to massive outward migrating swarms and population crashes as there is nowhere near enough food to support even a fraction of the massively expanded population.

The more progeny a hypo-marsupial has, the more likely that some will survive the massive die-off to go back to the routine year-to-year survival until the next wave of bamboo seeds.

  • $\begingroup$ This only explains the benefit to the female, but not the male. Why would the male willingly accept extra responsibility for caring for young when he could instead focus on 'sowing his oats' and impregnating multiple females? There is also the threat of cuckoldry, of being tricked into carrying another male's children, which would decrease a male's incentive to accept duties of carrying for the young. $\endgroup$ – dsollen Jan 29 '19 at 15:28
  • $\begingroup$ Perhaps the hypo-marsupials first developed monogamous pairing. Moving the offspring out of the female's pouch allows her to recover and set-up for the next batch. Holding the offspring in his pouch for further development could give them higher odds of survivial. $\endgroup$ – Michael Richardson Feb 15 '19 at 23:06

In seahorses the eggs that develop in a males pouch have yolks like other egg laying species. The male has to provide no nutrients for the embryos to develop, just a place for the eggs to be safe.

Marsupial mammals young need milk for the fetus to develop, in order for a male to carry the young it would have to evolve mammary glands that function to secrete milk.

Here I am presuming that by marsupial you are not just using it as a term for a pouch bearing animal, but the proper definition.

  • $\begingroup$ Yes, this is what I meant to imply. In the absence of an egg, the male lactates to provide nutrition to the developing fetus. $\endgroup$ – Anonymous Feb 27 '17 at 16:41

I don't see a clear competitive advantage.

In such a specie the female has to be fertilized by the male, and then has to transfer the fetus from her body to the male's one, adding additional risks related to the manipulation. Having no shell to protect it, the fertilezed egg would be highly subject to parasitic infections.

The only valid reason for doing this would be a large sexual dismorphism, with the male much bigger than the female, and thus more suited for protecting the fetus. On the other hand, a much bigger body requires already a bigger amount of food, and if we add the energy needed by the growing fetus it further increases.

Harvesting more food carries additional risks (injuries, being attacked by predators, etc.). If such a specie would exist, I am pretty sure over few generations the male would turn to a female (producing the egg and hosting the fetus) and female to a male (simply producing sperms to fertilize the egg)

  • $\begingroup$ Couldn't the female lay a soft shelled egg in the male's pouch, which dissolves to allow the fetus to attach to a nipple? $\endgroup$ – Anonymous Feb 27 '17 at 16:44
  • $\begingroup$ @Anonymous, OP specifies a marsupial. Marsupials do not lay eggs. $\endgroup$ – L.Dutch - Reinstate Monica Feb 28 '17 at 7:19

No, this will fail

The female has breasts, the male does not. For a marsupial, the newborn, tiny creature goes into the pouch and grows on breast-milk.

Since the male does not have breast-milk, there isn't much of a chance of the infant marsupial surviving.

  • $\begingroup$ I had assumed this was implied. I am sorry for the confusion and have edited the question body. $\endgroup$ – Anonymous Feb 27 '17 at 16:40


It is believed this strange trait evolved to allow seahorses to reproduce at an astonishly rapid rate, because so few seahorse babies actualy survive.

It functions like this:

Instead of having to manufacture new eggs and gestate at the same time, the female seahorse unloads all her eggs onto a male who fertilizes them and carries the resulting embryo for her.

This way she can concentrate all her energies on creating more eggs and perhaps even have them finished by the time the male gives birth allowing a seamless cycle of continuous reproduction (as in the male gives birth and then immediately afterwards begins incubating more babies).

This strategy of "make as many as possible because atleast some will survive" is not usuable in the environments Earth marsupials live in.

Even the mammals who do display this stategy to a degree (mice, rabbits, etc) do not do so at a level so extreme.

In conclusion, unless you change something about your creature or it's environment this is utterly implausible.

  • 2
    $\begingroup$ That is the intended advantage: the female foists the burden of pregnancy on to the male, allowing her to devote energy to producing more offspring at lower cost. Polyandry would probably be common. What change would need to be made to the environment, do you think? $\endgroup$ – Anonymous Feb 27 '17 at 16:47
  • 2
    $\begingroup$ Not utterly impossible. Not even improbable. One species of rat routinely has a population spike and crash every 50 years, because of the massive amount of seeds that bamboo drop on that cycle. A "marsupial-rat" female that could pass the babies off to the male be further developed earlier in the pregnancy while she recovers and preps for the next litter would give her bloodline a distinct advantage in out-competing others during the times of overwhelmingly plentiful food. $\endgroup$ – Michael Richardson Feb 27 '17 at 17:02

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