why animals like dogs and cats can give birth to multiple offspring at a time whereas humans can only give birth to (most of the time) one child only at a time?
In: Biology
Basically Biology has come up with two reproductive strategies.
R selection, where organisms breed regularly, have large litters and grow quickly, a good number might die but so long a some make it to adulthood its a win
or K-selection. Where organisms breed slowly have limited numbers of offspring at any 1 time, grow slowly and the offspring’s survival is ensured by high levels of parental investment. Each individual is more likely to survive to adulthood but f they don’t it a far greater loss to the parents in terms of investment in passing on their genes
Both work, and what type given organism evolved depends on a number of outside factors, size, stability of environment, resource availability etc but the bottom line is apes K select, small carnivorans more often than not R select
Human infants are significantly more developed than newborn animals that make “litters” of young. This is because our monkey ancestors spent a lot of time in trees and the infant needed the ability to strongly grasp our mother while they moved around. An infant can grasp strong enough to hold up it’s own weight very quickly. While a new born puppy or kitten has to be taken care of for weeks by the mother. They have to spend nearly all their time an energy taking care of their young.
That’s not a problem for predators like dogs and cats. Nothing is probably actively hunting their ancestors. It’s not a problem for prey animals that just don’t take good care of their young because they breed so often, like rabbits. But for other animals, we need a more developed child. Horses are born and stand rather quickly because their survival means they need to stay with the moving herd of animals. Horses survival strategy is run so fast you can’t catch us. So a foal is on its legs and running within a day of birth or it becomes a target for predators.
The very short version is: We make proportionally bigger babies.
Look at a new born puppy or kitten and they’re *tiny*.
If a human could make babies that were that small, they’d be the size of your hand and part of your forearm at most.
In fact, we do occasionally birth babies that proportionally small, typically prematurely, and they have to be placed in incubators to survive.
Human babies are in fact still technically born prematurely compared to most animals, which is why they take a year or three to learn to walk, while if a baby horse isn’t walking on the same day, there’s something dreadfully wrong and it’s time to call the vet.
Humans however have large brains, and therefore large heads, which still have to get out of the mother somehow.
We birth as late as we can get away with and still be able to fit our massive heads through the mother’s birth-canal, but we’re still not really fully developed enough to be walking or crawling or able to self-feed on the same day.
So we make proportionally massive babies, and because of that the resources required to make that baby put a real strain on the mother. Imagine an extra 6lb of body-mass consuming as much of your resources, particularly protein and minerals as it can get away with. It’s literally draining resources out of the mother and it takes a lot to keep up that supply.
The most we’re normally equipped for is two or three babies, one at a time is enough to be challenging.
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