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Evolution of live birth: Provided we ignore the placenta

Here’s an article on the supposed evolution of live birth:

… even the live-bearers have not got rid of the shell entirely. Baby skinks that are born live come out encased in a membrane – all that is left of the eggshell. With a bit of help from their mothers, most of them break out of the membrane within 36 hours.

How did live birth evolve? One group of the egg-laying skinks retain their eggs inside their bodies for longer than the others, and it seems that the live-bearers evolved from these “intermediate” skinks.

Reptiles are more likely to develop live birth if they live in cold climates, where it is a good idea to protect their offspring in their bodies, rather than exposing them to the rigours of the environment too soon. Sarah Smith of Stony Brook University, New York, points out that this explains why it is the skinks who live in the chilly highlands that give birth to live young.

Journal reference: Journal of Morphology, DOI: 10.1002/jmor.10877

I don’t get how this shows that live birth is evolving.

Animals that produce their young in eggs have way different systems from those that produce them via placentas, as do mammals.

With eggs, live birth is just a technicality.

Some snakes lay eggs, and others give live birth.

In other words, the eggs hatch indoors instead of outdoors.

Maybe some snakes or skinks are in between, but so?

To me, a more significant interest is the reptiles that protect their eggs or young, like crocodiles, alligators and cobras. that suggests that the theory of the unfeeling reptilian brain is not true.

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2 Responses to Evolution of live birth: Provided we ignore the placenta

  1. I don’t get how this shows that live birth is evolving.

    Animals that produce their young in eggs have way different systems from those that produce them via placentas, as do mammals.

    With eggs, live birth is just a technicality.

    Chalk one up for the nested hierarchy of life.

  2. I don’t agree there is a difference between egg laying or live birthing.
    yes snakes and these skinks birth in different ways but still are the same creatures.
    This biblical creationist insists that marsupials are just placental creatures with minor adaptation for certain reasons. so this explains the seeming marsupial anomaly’s in Australia or old South America.
    They are simply the same creatures from the same kinds off the biblical arl.
    So a marsupial bear, lion, wolf, mole, mouse, tapir etc are just the same creatures as their namesakes elsewhere on the planet.
    The classification system has been wrong and interfering with true biology divisions .
    This is a common theme in these areas .

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