On 8/27/2013 10:20 AM, Orchid Win7 v1 wrote:
> On 27/08/2013 12:07 AM, clipka wrote:
>> Am 26.08.2013 23:16, schrieb Orchid Win7 v1:
>>> On 26/08/2013 03:49 PM, Warp wrote:
>>>> For example, all terrestrial tetrapods (which includes us) have the
>>>> same basic limb bone structure: One bone (upper arm) -> two bones
>>>> (lower
>>>> arm) -> a bunch of small bones (wrist) -> a group of long thin bones
>>>> (palm/fingers).
>>>
>>> In a way, that's pretty amazing. But in a way, it would be far more
>>> amazing if all these animals did *not* have the same bone structure -
>>> that would imply a sudden change in skeletal design, which is quite
>>> unlikely.
>>
>> You mean, like the disconnection of the collarbone from the sternum in
>> felids, or the disconnection of the pelvis and complete disappearance of
>> hind limbs in cetaceans?
>
> 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.

Now.. toes/fingers are a different oddity. Their genetics function like 
this: Start growing the index finger, then add another, and another, 
until you hit a stop number, *then* grow a thumb. This means you can get 
one less, or one more, finger, or even several more, if the timing got 
way off (and it will end up next to the "pinky" when it forms), but its 
not going to be common, since you would have to nuke "all" of the 
fingers for the process to be interrupted. The thumb on the other hand 
is a separate process, but dependent on the first set being formed, so 
you could, in principle, have it be knocked out all by itself, by, in 
effect, having the genes just "skip over" the code for it. But, it isn't 
formed in the same stage in the process as the rest of the fingers.

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