I see the phrase "live young" used when describing mammals. For example, in Wikipedia:

Most mammals are viviparous, giving birth to live young.

What does the phrase "live young" signify here? I guess it might mean "a young [animal] that is alive", but if this is the case isn't it at best redundant?

I mean of course an animal gives birth to a live thing (people don't say "give birth to eggs" or "give birth to rocks", right?). And of course when it's born it's young by definition - one can't be old when they're just born. So what does "live young" signify here?

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    See: stillborn. – lurker Jan 13 '16 at 4:22
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    Look up viviparous and see if that doesn't answer your question. – GoDucks Jan 13 '16 at 4:26
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    Eggs are alive but, as you say, neither young nor born. The word live in "live young" and "live birth" is just a bad choice that is probably here to stay. Too bad that an accepted term can be so inaccurate in biology, of all fields, which is all about the word "live" itself. – lauir Jan 13 '16 at 5:48
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    @GoDucks: I understand what it means, I'm just asking why "live young" is part of such sentence at all. – user69715 Jan 13 '16 at 6:15
  • That part, Most mammals are viviparous, giving birth to live young which is confusing you is nothing but extra information. Remove it and won't change a single thing. – Usernew Jan 13 '16 at 6:55

It's redundant for the purposes of emphasis and clarity. After all, I suppose you could shorten the sentence to:

Most mammals are viviparous, giving birth.

and then let the reader infer that "giving birth" implies "to a young, living offspring." However, that doesn't really help the reader understand the meaning of the rather uncommon word viviparous. The main point of viviparous is that the animals give birth to live offspring (as opposed to, say, laying eggs), a fact that is made more readily apparant when we lengthen the sentence:

Most mammals are viviparous, giving birth to live young.

Now, instead of the reader thinking, "Wait, doesn't every animal give birth?" the reader is more prone to say, "Oh, I see – as opposed to laying eggs, or splitting."

There's times when redundant language is helpful, and one place is in an educational text. This is one case where I don't think striking the "redundant" text would constitute an improvement.


[Birth to] live young is a phrase that means the opposite of "hatched from an egg".

Oviparous would mean born from an egg that is laid by the mother, rather than developing in a womb.

Of course the embryos in eggs are alive, but a meaning of live is also "moving around visibly."


Well, this is a very old phrase that's just been repeated for years and years without any critical thought, and so you're going to have to look back a couple hundred years at the old definitions of these words.

First interesting thing: "birth" and "berth" were originally alternate spellings of the same word. They're related to bear in the "carry" sense. One's packages and offspring are both born. So if you consider this sense, anything that's carried is born. Eggs are therefore just as born as live young are.

Next up: "live" is more in the activity sense than the literal "having life." Like, pulling the pin on a grenade makes it a live grenade, and if you don't get away from it, you won't be very lively soon yourself.

And "young" is a case of the very common phenomenon in this era of just using an adjective as a noun, much like how we love to use nouns as verbs in our era. (except back then, no one was screaming that it was ungrammatical.) So it's synonymous with "young ones" and one's "young ones" is their offspring. So they used young instead of offspring to denote one's progeny. (I can keep going with more and more exotic words for the same thing, but I won't.)

  • Using young nominally is not a phenomenon restricted to the modern era. books.google.com/… – Tᴚoɯɐuo Jan 13 '16 at 13:00
  • I didn't mean to imply it was. I meant only that it isn't as common today. Many languages are perfectly happy with using adjectives as nouns, but for today's English, most of those cases are grandfathered in or somewhat dialectical. Verbing nouns, on the other hand, is a very productive phenomenon today, and doesn't seem to have been so productive before. – modulusshift Jan 15 '16 at 6:15

Giving birth to live young is a possible characteristic of being mammal, but does not define being mammalian. This detail is often either unknown or overlooked when speaking about mammals.

Being a mammal is defined by the production of nutritional milk for their young. Thus the term mammary glands which provides the milk. Cats, dogs, horses are all commonly thought of as being mammals, however, whales, dolphins, and porpoises are part of a group known as marine mammals

In your quote

Most mammals are viviparous, giving birth to live young.

the operative word is most (see below). The phrases

giving birth to live young

giving birth to live offspring
giving live-birth
produce living young
which are live-bearing

can be used interchangeably without loss of understanding.

Giving birth can lead to a live birth or a stillbirth and by law both need to be registered for humans.

An additional distinction needs to be made between being born live and being born from an egg.
Egg laying mammals are called monotremes and egg laying this is due to evolutionary considerations, but they still produce the characteristic nutritional milk for their young.

  • "Stillborn" is a red herring here. Any reproductive scheme can have young that do not survive the first major phase (don't hatch, die in the womb, or whatever). – Nathan Tuggy Jan 13 '16 at 19:44
  • Why is stillborn a red herring? I was using it as an illustration for birth, if a baby does not survive, it does not mean it wasn't born, thus the distinction, I think the OP was assuming that birth assumed live. Birth can be defined as merely the emergence from a mother's womb. – Peter Jan 13 '16 at 19:50
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    It's a red herring because it has nothing to do with the normal mode that defines biological descriptions like "viviparous". You can correctly describe "oviparous" as "lays eggs that hatch"; you don't need to also mention that some eggs are eaten, break by accident, are somehow infertile, don't have the correct conditions maintained long enough, or whatever else. All that is irrelevant. "Live birth" is not opposed to still birth here, but to laying eggs or to hatching eggs internally (and, as J.R. suggests, to splitting). – Nathan Tuggy Jan 13 '16 at 19:55

Although "giving birth to live young" sounds redundant, I'd argue that it isn't. There are alternative scenarios that could be presented by changing any of the three keywords to different circumstances.

This other animal gives birth to fully mature offspring.

This other animal's young are born dormant until coming alive after a short period of time.

This other animal lays eggs, rather than giving birth.

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