So the kangaroo (and possums) are at the extreme end of the ‘precocial / altricial’ continuum - i.e. born less or more developed. The opposite end is the hamster, who, upon birth, is just a small adult hamster. Horses are altricial, because they have to stand up and go soon after birth.
Humans are eccentric here. The other apes tend to be more altricial, giving birth to babies who are carried and nurse, but who are soon up and about on their own. Humans, bless us, have been evolutionarily busy growing our crania, and given the geometry of the female human pelvis, need to get out of town before it’s too late. So we are born more precocial than other apes, and have to be nurse and potties and fed for a few years before we can participate. Plus, we have to learn all that language stuff. It’s complicated.
So the kangaroo (and possums) are at the extreme end of the ‘precocial / altricial’ continuum - i.e. born less or more developed. The opposite end is the hamster, who, upon birth, is just a small adult hamster. Horses are altricial, because they have to stand up and go soon after birth.
Humans are eccentric here. The other apes tend to be more altricial, giving birth to babies who are carried and nurse, but who are soon up and about on their own. Humans, bless us, have been evolutionarily busy growing our crania, and given the geometry of the female human pelvis, need to get out of town before it’s too late. So we are born more precocial than other apes, and have to be nurse and potties and fed for a few years before we can participate. Plus, we have to learn all that language stuff. It’s complicated.
Sorry, I had precocial and altricial reversed. It’s the kangaroos who are altricial and horses are precocial.