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highwaystar101 on 11 September 2010
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Slimebeast said:
highwaystar101 said:

Those that are better at producing the hormones in cold weather are more likely to produce offspring which share that ability, seems like a perfect example of natural selection to me.

Also, I don't think this is a step towards mammalian birth, I think this maybe something new, you've just assumed that position of me.

But yet again you've avoided my question. My question is concerning the fact that these animals can pass on their traits, and the strong survive to do so. That is exactly what this is. All you've got to do is prove to me that either the most fit don't survive or that genetic traits are not passed on from one generation to the next. Yet you've avoided this question twice now!

Your postulation that this is not evolution rests on the notion that the fit members of a population do not have the ability to pass on their genes. Please, show this to me; the burden of proof is one you. In fact I think every biology department of every top university in the world would be interested in this.

You don't get it. These snakes already have a system fully functional for both environments, cold as well as warm. You just assume they should get an advantage by becoming better at producing hormones. But the hormone production is already there, fully functional, regulated and adaptive - when it's hot eggs are hatched when it's cold eggs are retained! In that article there is nothing to suggest your scenario of further adaptation is needed.

That is not an example of evolution. You have the burden of proof to show that the northerners are genetically changed regarding regulation of live birth due to the cold environment. 

But as for your question, yes I believe in natural selection.

I don't get it? I get it fine, it's you who is (I think on purpose) failing to understand.

No system is ever fully formed, there is always the need for improvement when the environment requires it. Do you think humans just sprouted a fully formed opposable thumb one day? Or do you think it would have evolved from another "fully formed" organ when the thumb offered a new evolutionary advantage? 

In the case of the lizards the environment has changed, which has favoured those who can reproduce with this ability for at least this generation. If this trait is required from generation to generation then an advanced form of this will become the norm for that species. This "fully formed" mechanism will change. If this mechanism is required over an extended period of time an advanced form of this will eventually it will become the common place method of birth.

In the paper they effectively say that if this form of birth is retained over a period of many generations then it will lead to an evolution in reduced egg shell thickness which fits with the hypothetical model. This will be an evolution as a result of natural selection.

The eggs of most viviparous lizards are surrounded by some form of tertiary egg envelope during early stages of embryonic development, but the thickness of this structure is less than that of oviparous species (Blackburn, 1993a, 1998). Reduction in eggshell thickness is believed to be a necessary correlate to the evolution of viviparity because thick eggshells would impede respiratory gas exchange during prolonged uterine egg retention (Packard et al., 1977; but see Mathies and Andrews, 2000). If the evolution of viviparity is preceded by gradual increases in the length of intrauterine gestation, gradual reductions in eggshell thickness should also occur (Packard et al., 1977; Guillette, 1993; Qualls, 1996). This hypothesis is supported by interpopulational comparisons within three species of lizards that demonstrate an inverse correlation between length of uterine egg retention and eggshell thickness (Heulin, 1990; Heulin et al., 1992,2002; Mathies and Andrews, 1995; Qualls, 1996).

(source)

The scientists at work here clearly think that the lizards are genetically changing as a result of this. Thy more than suggest that further adaptation is necessary. You can take this as the proof if you like, but I know that regardless of how much proof I show you, you will never accept it.

You claim to accept natural selection, yet you have shown many times that you reject it, almost as an automated response. The weak don't reproduce, the fit do, the successful traits are passed on to the next generation, this is natural selection at work. Natural selection leads to an evolution.