On 8/28/2013 12:35 AM, Thomas de Groot wrote:
> On 27-8-2013 23:09, Patrick Elliott wrote:
>> On 8/27/2013 10:20 AM, Orchid Win7 v1 wrote:
>>> I was thinking more like if there was one member of the frog family
>>> which has five legs instead of the usual four, or something. THAT would
>>> be weird...
>> Yeah, well.. That isn't likely to happen, six maybe, since you have the
>> whole bi-lateral symmetry thing going on, but then, you would find that,
>> much like "missing" ones, the extras are either a) caused by
>> environmental toxins (common issue with frogs in fact), or b) a copying
>> on the genes needed to produce the limbs. Whether or not, without other
>> regulatory changes, you can get "functional" ones is another matter.
>
> During evolution, Nature does it the other way round. During the
> Devonian when lobe-finned bony fishes appeared and evolved into
> amphibians, Nature experimented with different possibilities. There were
> animals with 7 or more numbers of digits on their legs. Eventually, only
> the animals with 5 digits made it. All the others became extinct.
>
> Search for Acanthostega, Ventastega and Tiktaalik.
>
> Thomas
>
Think I covered that. You are talking about "digits", not "limbs". And, 
yeah, you can change the number of digits trivially, due to, as I said, 
them being coded so that you get, starting with the "thumb" as 0: build 
1, then 2, then 3, then 4, then... either stop and build 0, or keep 
adding on digits, until the "kill point", when the process stops making 
new digits, and goes back to finish with what, for us, is the "fifth", 
i.e., the thumb. The same code that allowed for 7 or more back then, 
still works the same now. It just hits the "stop" point in the cycle 
sooner. But, you can see from, for example, some cats, a case where you 
get 6 toes. Same thing, it start with 1, then goes up to 5, before going 
back to make '0', i.e., the analogous "thumb".

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