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Stages of life cycle of mammals

  1. Jul 9, 2013 #1
    Dear experts, please help me with this debate between my buddy and I.

    I'm on the side that most mammals, like cats, dogs, humans and monkeys have 2 stage life cycle. Young --> adult and back.

    My buddy says it should be 3 stage egg--> young--> adult and back.

    We are both rather weak on this topic. Please help. Thanks!
  2. jcsd
  3. Jul 9, 2013 #2


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    Staff: Mentor

    Hopefully some biologists will chime in with more insight, but on some level this is a moot.

    You can define "stage" any way you want, and you will have as many stages as the definition will allow. You can have stages of life defined in biological terms - then between egg and young you can add morula, blastocyst, gastrula and some other and count them all. You can have stages defined in social terms - like childhood and adulthood - and you can count them again. You can also look at the stages of learning, of sexual life - each approach will give you different numbers.

    Basically - you have to define what you mean first, and then you can start the discussion. Without a definition that you both agree on you are wasting time (doesn't mean you can't have a good time wasting time, that's a stage of life as well).
  4. Jul 9, 2013 #3


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    Staff Emeritus
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    Quick post from my phone: borek is correct that in mammals it's pretty hard to draw any distinctive lines between stages of life. Unlike animals which undergo metamorphosis we don't change in radical spurts (I.e form cocoons). If you take the first 20 years of life a human obviously goes through a lot of development but its far more gradual. As for embryological development there are many, many stages defined by key events but that too is a gradual process.
  5. Jul 9, 2013 #4
    Forgive my ignorance, but what is "back"?

    I agree with Borek and Ryan, trying to tease out a life cycle for mammals isn't as clear cut as, say, doing the same for a butterfly, especially since there are thorny issues such as "neoteny" and "juvenalism" you have to sort through particularly when it comes to the primates. These issues are still very controversial in contemporary primatology, so you and your buddy are in good company.
  6. Jul 24, 2013 #5
    Human construct vs. metaphysics

    Pre-script - Txs to Borek for the seed of this post's idea.

    Hey, Discovering the truth about life cycles is interesting - but don't argue about what you call different stages, compare the facts, look at underlying truths in histology, endocrinology, embryology, population biology, etc. Remember that the stages we teach as current theory need to have human constructs in order to communicate. So we have terms for stages and we assign them based on recognizable current facts in morphology, embryology, evolution, etc.

    If you're a current student, don't waste your time debating human constructs with fellow students - ask your prof. how she sees it and then regugitate that on the test. Outside of schoolwork and testing you can ask the important questions. Txs, Jack "Philosophy, Who Needs It?
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