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The polydactyly gene is dominant over the common gene for finger number. Will humans ever have six fingers?

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  • $\begingroup$ Is it really dominant? From the pictures at linked web page, it does not seem to be any beneficial, and extra useless digit is removed. If it were dominant and beneficial I would expect it to be more widespread, but it is rare. $\endgroup$ – Peter M. - stands for Monica Jan 9 '15 at 16:26
  • $\begingroup$ @PeterMasiar The Wikipedia page says "autosomal dominant transmission is suspected" for at least one type. So yes, it's dominant. Being beneficial is dependent on the environment, not the dominance of the gene. $\endgroup$ – Samuel Jan 9 '15 at 17:44
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    $\begingroup$ I feel like this question would be more appropriate on the biology stack exchange, or do they not take what if questions? How is this world building? $\endgroup$ – James Jan 9 '15 at 19:06
  • $\begingroup$ @Samuel - autosomal dominant means only that you have to get the gene from one parent. It does not mean that if you have a parent that has it, you will automatically get it. It's also a mutation, not an adaptation. And, given that we had several million years in which it could occur and be passed on and still only occurs rarely, I would say that no, it won't. $\endgroup$ – JohnP Jan 9 '15 at 21:34
  • $\begingroup$ @JohnP Yes, obviously. Its inheritance is 50% if one parent has it and 75% if both have it. It is still around though, despite millions of years. If it ever becomes an advantage, then it will be defined as an adaptation and could become much more common. $\endgroup$ – Samuel Jan 9 '15 at 22:13
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Will humans ever have six fingers?

I'm assuming you mean all/most humans here.

Unlikely. Being dominant means it will show up when present. It also makes it easier to spot. If 6 fingered people became 'desirable' and reproduced more then it's possible. But more likely it has the opposite affect and it reduces their opportunities because it is a 'strange' physical 'defect' that often will make them less desirable (less successful in producing heirs to carry the gene).

My understanding is that in general humans are slowly losing the pinky finger and in a few hundred generations we will have 3 fingers and a thumb.

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    $\begingroup$ You should give credit to Darwin :) $\endgroup$ – Vincent Jan 9 '15 at 16:45
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    $\begingroup$ @Vincent I thought that was a given! :) $\endgroup$ – bowlturner Jan 9 '15 at 16:47
  • $\begingroup$ Your understanding is slightly off. Pinkies won't disappear because of the opposable thumb, pinky finger is what gives you the majority of strength in your grip. Pinky is the worst finger to lose if you have a choice (First finger, non writing hand is the most desirable. Don't ask). We are, however, most likely going to lose our pinky toes, as balance passes more through the middle of the foot than the edges. $\endgroup$ – JohnP Jan 9 '15 at 22:22
  • $\begingroup$ @JohnP I thought the third finger of the non-dominant hand is best to lose. It's already partially slaved to the middle finger. What's your source? $\endgroup$ – Samuel Jan 9 '15 at 22:31
  • $\begingroup$ @Samuel - Anatomy classes way back when. Fingers work best when together, losing that finger leaves a gap, and also weakens the connected muscle/tendon complex. Also corroborated by broscience on the web. $\endgroup$ – JohnP Jan 9 '15 at 22:34

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