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Have you ever noticed that some animal babies, like baby deer, can walk around basically right after they're born, but other animal babies, like kittens, can't even open their eyes? There’s a reason for that, and it comes down to two different reproductive strategies with their own advantages and disadvantages.

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Most kinds of babies are pretty cute. But when you compare, say, a kitten a day after birth with a baby deer, there are some clear differences.

The kitten can't open its eyes, while the deer can walk. Why did nature give us some animals babies that are almost totally helpless, while other animals have babies that walk, hop, or run just hours after birth? There are advantages and disadvantages to both reproductive strategies.

Take hares and rabbits, for example. They're similar animals, but baby rabbits are altricial -- meaning they're born helpless, and require a ton of parental care. Their eyes are closed, they lack fur, and they can't regulate their own body temperature.

Hares, on the other hand, are precocial, meaning they're born more developed. Their newborns have fur, and their eyes are open. These terms are typically applied to mammals and birds, where we can observe clear differences in the relative helplessness of their babies -- like the kitten and the deer.

Both groups are known for parental care, as well. In altricial species, in particular, parental care is a huge commitment. They spend a large amount of time investing in their offspring, compared to parents of precocial species -- things like preparing nests or caring for their babies.

And animals that are more helpless at birth are extra vulnerable when they encounter a predator. But the parent also spends less time incubating the offspring before they're born and hatched, and as a result, altricial animals may be able to produce larger, more frequent litters. But while the parental investment required of these animals is enormous, it may also be relatively short-lived.

Altricial birds, for example, require a lot of care in the beginning, but they mature more rapidly and become independent more quickly than precocial birds. Many precocial animals take longer to develop before birth, and parents usually give birth to only one or a few babies. That's fewer offspring available to pass on the parents' genes, compared to altricial species -- at least if those bigger litters survive.

And some precocial babies, like certain species of bird, still receive food from their parents, even though they're capable of leaving the nest on their own. Meaning they still need some parental care. But, there are also advantages to being precocial.

Because precocial babies are well-developed, they require less parental care overall. Their parents still invest in them, since it takes more energy to incubate more developed babies. But once they're born, the kids are more independent.

When confronted by a predator, a precocial baby has a better chance of survival than an altricial baby. Some precocial babies, like the blue wildebeest, can even outrun predators within a day of birth. So each strategy has its advantages, and not all birds and mammals fit neatly into one group or the other.

Like humans, for example: our offspring incubate for a long time, but they're still super helpless. The precocial or altricial question is a spectrum, with babies born at varying stages of development, and parents providing varying degrees of care. How helpless a baby is, and how much care its parents provide depends a lot on the species' own individual adaptations given its environment and circumstances.

And that can influence how developed the babies of each species will be. What works for the rabbit may not necessarily work for the hare, and vice versa. If you love baby animals of all kinds, altricial or precocial, you might like to immortalize them in photographs.

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The first 500 SciShow subscribers to use the link in the description will get a 2-month free trial. So you can take all those courses for a test drive and see which of them are right for you! ♪♪♪.