On 1/11/2011 5:53 AM, Paul Fuller wrote:
> Replying to Invisible but some comments on what Darren kicked off about
> fingers.
>
> On 8/01/2011 5:05 AM, Darren New wrote:
>  >
>  > I remember reading somewhere that there's a gene that controls how many
>  > fingers you have *and* something about the reproductive system, so any
>  > mutation in that gene tends to keep you from reproducing for entirely
>  > unrelated reasons. Hence the reason why everything from fish to bats to
>  > birds to people have five finger bones.
>  >
>
> On 11/01/2011 8:54 PM, Invisible wrote:
>>
>> I suspect what it boils down so is that there's no specific reason why
>> some number other than 5 would be an advantage, so it hasn't changed.
>> (This of course doesn't rule out random "neutral" changes I suppose...)
>>
>
> Given the enormous range of limb variations it is surprising that the
> number 5 is so common. Sure some of the digits might be fused or reduced
> to almost nothing.
>
> However I don't think it is true that *all* tetrapods have 5 digits.
>
> Snakes are tetrapods. While some snakes have vestigial hind legs, I
> don't know that they actually have digits. Most snakes have no remaining
> legs to speak of - maybe a bump where the legs might have been but no
> identifiable limbs and certainly no digits.
>
> Similar with whale hind limbs I think. Some species have vestigial
> pelvis and hind limbs. Usually within their bodies. Occasionally some
> individuals have some protrusion. Maybe digits are present during
> development of the foetus but as far as I know there are not actual
> digits by the time they are born. Could be wrong on that but in any case
> they are well on the path to losing them altogether.
>
> The limb changes here might start out as 'the limb genes are still there
> but the gene(s) controlling their size, placement, function etc cause
> them to get smaller, relocated or stop working'. Given enough time
> though, genes that generate something that is irrelevant tend to
> accumulate changes and either become 'broken' or can be co-opted for
> something else.
>
> Then going the other way there are animals with more than 5 digits on
> one or more limbs. Some people for instance - see 'polydactylism'. Some
> of the pictures out there are fake but it is a real condition. Most
> common is 6 fingers or toes instead of 5. It may be a quite harmless
> single gene mutation or part of a more severe complex. As far as I know
> the milder form doesn't render the individual prematurely dead or
> infertile.
>
> There is a breed or at least a population of 'polydactyl cats' that have
> more than the usual number of toes on their front legs, back legs or
> both. They even apparently can be more dextrous than normal so that
> might confer an advantage in some ways but there may be some
> disadvantages as well. Again, I don't think that the genetic change that
> causes this is fatal. It certainly does not prevent development from egg
> to adult because these cats are real.
>
Its a single point mutation in a stop Cordon, which causes the 
"paw/hand/foot" to go Index, second, third, pinkie, extra (woops), Stop, 
now make the thumb. Since its specific to those digits, in this case, it 
doesn't effect anything else.

Oh, and in the case of snakes, during very early development, as I 
understand it, they do form limbs, but then those are reabsorbed, before 
they form fully, the "code" turning off, and other code scavenging the 
remains for other purposes.

-- 
void main () {
   If Schrödingers_cat is alive or version > 98 {
     if version = "Vista" {
       call slow_by_half();
       call DRM_everything();
     }
     call functional_code();
   }
   else
     call crash_windows();
}

<A HREF='http://www.daz3d.com/index.php?refid=16130551'>Get 3D Models, 
3D Content, and 3D Software at DAZ3D!</A>

Post a reply to this message