# Does this Mutation of the Hand Occur? **URL:** \ **Category:** Factual Questions\ **Created:** [May 4, 2006, 7:44pm UTC](https://boards.straightdope.com/t/does-this-mutation-of-the-hand-occur/355439 "2006-05-04T19:44:29Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Hooleehootoo](https://avatars.discourse-cdn.com/v4/letter/h/eada6e/32.png) [@Hooleehootoo](https://boards.straightdope.com/u/Hooleehootoo)\ **Post date:** [May 4, 2006, 7:44pm UTC](https://boards.straightdope.com/t/does-this-mutation-of-the-hand-occur/355439/1 "2006-05-04T19:44:29Z")
I know my thumb is shorter than my fingers, but I did not know until a few minutes ago that the thumb is missing the Intermediate phalange bone that all the other digits have. Does a mutation ever occur where the thumb has an intermediate phalange? How do we know that the tip of the thumb is a distal phalange, and not an intermediate phalange missing a distal part (the shape of the tip of the thumb, I’ll bet)? Any mutations where other digits are missing an intermediate as the thumb? ---
**Author:** ![WhyNot](https://avatars.discourse-cdn.com/v4/letter/w/c77e96/32.png) [@WhyNot](https://boards.straightdope.com/u/WhyNot)\ **Post date:** [May 4, 2006, 8:16pm UTC](https://boards.straightdope.com/t/does-this-mutation-of-the-hand-occur/355439/2 "2006-05-04T20:16:42Z")
> [@Hooleehootoo](#): > > How do we know that the tip of the thumb is a distal phalange, and not an intermediate phalange missing a distal part (the shape of the tip of the thumb, I’ll bet)? Because distal means “(furthest) away from the main trunk of the body” and intermediate means “in the middle.” If there’s no middle, all you have is distal (and proximal, of course). As for the rest of your questions, I’ve seen finger deformities where there was no intermediate phalange, but I don’t know what it’s called. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [May 4, 2006, 8:22pm UTC](https://boards.straightdope.com/t/does-this-mutation-of-the-hand-occur/355439/3 "2006-05-04T20:22:59Z")
AFAIK, terrestrial vertebrates in general have had no more than 2 phalanges on the innermost digit for hundreds of millions of years. The mutation may occur, I suppose, but it would be pretty bizarre. The phalangeal formula for early land vertrbrates, from inner to outer, is 2,3,4,5,4 (still observable in lizards, etc). This was reduced in mammals to the formula we have, that is 2,3,3,3,3. This is a very very old arrangement. ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [May 4, 2006, 9:11pm UTC](https://boards.straightdope.com/t/does-this-mutation-of-the-hand-occur/355439/4 "2006-05-04T21:11:20Z")
> [@Colibri](#): > > The phalangeal formula for early land vertrbrates, from inner to outer, is 2,3,4,5,4 (still observable in lizards, etc). This was reduced in mammals to the formula we have, that is 2,3,3,3,3. This is a very very old arrangement. Tell me more, tell me more! All mammals? What about birds-- what’s their fromula? ---
**Author:** ![Darwins\_Finch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darwins_finch/32/20304_2.png) [@Darwins\_Finch](https://boards.straightdope.com/u/Darwins_Finch)\ **Post date:** [May 4, 2006, 9:58pm UTC](https://boards.straightdope.com/t/does-this-mutation-of-the-hand-occur/355439/5 "2006-05-04T21:58:40Z")
> [@John Mace](#): > > What about birds-- what’s their fromula? Depending on who’s doing the counting, it’s either 0,2,2,1,0 or 2,2,1,0,0 (the controversy being whether a bird’s manus consists of digits I, II and III or digits II, III and IV; the latter is the more genrally accepted version). And, obviously, the phalangeal formula of 2,3,3,3,3 does not apply to _all_ mammals. Consider, for example, the ungulates, which have taken the extreme evolutionary pathway of doing away with all but one digit. ---
**Author:** ![Darwins\_Finch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darwins_finch/32/20304_2.png) [@Darwins\_Finch](https://boards.straightdope.com/u/Darwins_Finch)\ **Post date:** [May 4, 2006, 10:00pm UTC](https://boards.straightdope.com/t/does-this-mutation-of-the-hand-occur/355439/6 "2006-05-04T22:00:31Z")
> [@Darwin's Finch](#): > > Depending on who’s doing the counting, it’s either 0,2,2,1,0 or 2,2,1,0,0 (the controversy being whether a bird’s manus consists of digits I, II and III or digits II, III and IV; the latter is the more genrally accepted version). I should clarify this: the phalangeal formula 0,2,2,1,0 corresponds to the II, III, IV digit formula. ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [May 4, 2006, 10:09pm UTC](https://boards.straightdope.com/t/does-this-mutation-of-the-hand-occur/355439/7 "2006-05-04T22:09:58Z")
> [@Darwin's Finch](#): > > And, obviously, the phalangeal formula of 2,3,3,3,3 does not apply to _all_ mammals. Consider, for example, the ungulates, which have taken the extreme evolutionary pathway of doing away with all but one digit. Is that true of all ungulates? I thought some were two-toed. And did the other toes completely disapear or just atrophy? ---
**Author:** ![Darwins\_Finch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darwins_finch/32/20304_2.png) [@Darwins\_Finch](https://boards.straightdope.com/u/Darwins_Finch)\ **Post date:** [May 4, 2006, 10:22pm UTC](https://boards.straightdope.com/t/does-this-mutation-of-the-hand-occur/355439/8 "2006-05-04T22:22:53Z")
> [@John Mace](#): > > Is that true of all ungulates? I thought some were two-toed. And did the other toes completely disapear or just atrophy? I’m getting sloppy in my old age. Horses have taken the extreme route, retaining only the third digit (other digits may occasionally appear as splints, but these seldom, if ever, develop beyond metacarpals/metatarsals). Other ungulates may retain 2, 3 or even 4 digits (Artiodactyls retain only digits III and IV, for example), with the others much reduced or absent altogether. The first digit of the forelimb is lost in all ungulates, however (tubulidentates, e.g., the armadillo, have 4 digits on their forelimbs, and 5 on their hindlimbs). Among those various digit arrangements, though, the phalangeal formula for a given digit is generally maintained; horse retain but the third digit, and it retains three phalanges, for example. ---
**Author:** ![Fear\_Itself](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fear_itself/32/19637_2.png) [@Fear\_Itself](https://boards.straightdope.com/u/Fear_Itself)\ **Post date:** [May 4, 2006, 10:31pm UTC](https://boards.straightdope.com/t/does-this-mutation-of-the-hand-occur/355439/9 "2006-05-04T22:31:22Z")
I use to work for a guy who had four phalanges on the ring finger of his right hand. Right at the last knuckle, his finger split into two fingertips. Very creepy. He would always stick his hand out to shake hands, and note how the other person reacted. ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [May 4, 2006, 10:39pm UTC](https://boards.straightdope.com/t/does-this-mutation-of-the-hand-occur/355439/10 "2006-05-04T22:39:45Z")
> [@Darwin's Finch](#): > > tubulidentates, e.g., the armadillo You meant aardvark, right? ---
**Author:** ![Darwins\_Finch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darwins_finch/32/20304_2.png) [@Darwins\_Finch](https://boards.straightdope.com/u/Darwins_Finch)\ **Post date:** [May 4, 2006, 11:03pm UTC](https://boards.straightdope.com/t/does-this-mutation-of-the-hand-occur/355439/11 "2006-05-04T23:03:09Z")
Yes, that. Like I said…sloppy. I give up before I put my foot further into my mouth… ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [May 4, 2006, 11:08pm UTC](https://boards.straightdope.com/t/does-this-mutation-of-the-hand-occur/355439/12 "2006-05-04T23:08:34Z")
> [@Darwin's Finch](#): > > Yes, that. Like I said…sloppy. I give up before I put my foot further into my mouth… All five toes, or just one? 🙂 ---
**Author:** ![Broomstick](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/broomstick/32/246_2.png) [@Broomstick](https://boards.straightdope.com/u/Broomstick)\ **Post date:** [May 5, 2006, 12:05am UTC](https://boards.straightdope.com/t/does-this-mutation-of-the-hand-occur/355439/13 "2006-05-05T00:05:47Z")
> [@Darwin's Finch](#): > > Depending on who’s doing the counting, it’s either 0,2,2,1,0 or 2,2,1,0,0 (the controversy being whether a bird’s manus consists of digits I, II and III or digits II, III and IV; the latter is the more genrally accepted version) (consults family cockatiels. Also photos of family lovebirds and jenday conure) Um… what about birds like parrots, which have four digits per foot? ---
**Author:** ![Darwins\_Finch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darwins_finch/32/20304_2.png) [@Darwins\_Finch](https://boards.straightdope.com/u/Darwins_Finch)\ **Post date:** [May 5, 2006, 12:42am UTC](https://boards.straightdope.com/t/does-this-mutation-of-the-hand-occur/355439/14 "2006-05-05T00:42:52Z")
> [@Broomstick](#): > > (consults family cockatiels. Also photos of family lovebirds and jenday conure) > > Um… what about birds like parrots, which have four digits per foot? More sloppiness on my part: that formula is for bird-hands. Most birds have four toes (some chicken breeds have five, while some other groups, like the ostrich, only have two) with the pharyngeal formula 2,3,4,5 (that’s also the pattern seen in _Archaeopteryx_, indicating it’s likely the ancestral condition). ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [May 5, 2006, 2:48am UTC](https://boards.straightdope.com/t/does-this-mutation-of-the-hand-occur/355439/15 "2006-05-05T02:48:06Z")
> [@Darwin's Finch](#): > > And, obviously, the phalangeal formula of 2,3,3,3,3 does not apply to _all_ mammals. Of course, I was referring to the basal formula. Also it might be mentioned that snakes have a much reduced formula compared to other “reptiles”: 0,0,0,0,0. 😉 > [@Darwin's Finch](#): > > Depending on who’s doing the counting, it’s either 0,2,2,1,0 or 2,2,1,0,0 (the controversy being whether a bird’s manus consists of digits I, II and III or digits II, III and IV; the latter is the more genrally accepted version). The latter is possibly the strongest line of evidence advanced by the dwindling ranks of the birds-are-not-dinosaurs camp, since theropod dinosaurs clearly are I,II,III. The evidence for birds being II,III,IV is from embryology; the other is based on paleontology. However, a reconciliation of the two views has been proposed: [1,2,3 = 2,3,4: A solution to the problem of the homology of the digits in the avian hand](http://www.pubmedcentral.gov/articlerender.fcgi?artid=21825) > [@](#): > > Assigning homology to the three fingers in the hand of living birds is a problem that has challenged morphologists since well before the Theory of Descent was first proposed (e.g., refs. 3 and 4; see reviews in refs. 2 and 5–7). The morphology of well preserved and fully formed hands of an early maniraptoran theropod dinosaur from the late Jurassic, Archaeopteryx lithographica (Avialae; Fig. 1), led many to accept the identity of the three fingers as being digits I, II, and III (Fig. 2b). Some embryologists, however, countered this hypothesis, instead producing empirical evidence in early hand morphogenesis suggesting that the three avian digits are actually II, III and IV. Strikingly, this debate has endured to the present day (1). > > In this paper, we first review paleontological and embryological evidence that support and contradict, respectively, the I, II, III hypothesis and then proceed to review data regarding the phylogenetic position of birds. Based on this review, we conclude that the conflict between paleontological and embryological data is real; it can be resolved neither by rejecting one kind of data nor by assuming that birds are not theropod dinosaurs. We argue that early theropod dinosaurs faced a conflict between the functional constraints favoring the retention of digits I, II, and III and the developmental constraints that favored the loss of the condensation that normally develops into the first finger. We propose that, after the secondary loss of digit DIV, a frame shift in digit identity occurred that forced condensation CII into the developmental pathway of digit DI, condensation CIII into digit DII, etc. > [@Darwin's Finch](#): > > pharyngeal formula Sloppy, indeed. **DF** , have you been drinking? 😃 ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [May 5, 2006, 3:10am UTC](https://boards.straightdope.com/t/does-this-mutation-of-the-hand-occur/355439/16 "2006-05-05T03:10:56Z")
> [@Broomstick](#): > > (consults family cockatiels. Also photos of family lovebirds and jenday conure) > > Um… what about birds like parrots, which have four digits per foot? As \*\*Darwin’s Finch \*\* suggests, birds have lost one of the toes of the hind foot, that is, the fifth toe. The remaining toes, I,II,III, and IV, have the basic reptilian formula of 2,3,4,5. Note that in birds that retain four toes, digit 1, the hallux (thumb/big toe) usually faces backwards. It has only 2 phalanges. The common arrangement of 3 toes forward and one back is called anisodactyl. Parrots, like woodpeckers, cuckoos, and a few other birds, have two toes facing forward and two back. The outermost toe has become reversed, so that the two forward toes are II and III, and the two back are I and IV, with their corresponding phalangeal formulas. The trogons, a group of tropical birds, are the only ones with the reverse arrangement, called heterodactyl, in which the innermost toe has become reversed, so they have III and IV in front, and I and II back. ---
**Author:** ![Fear\_Itself](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fear_itself/32/19637_2.png) [@Fear\_Itself](https://boards.straightdope.com/u/Fear_Itself)\ **Post date:** [May 5, 2006, 3:24am UTC](https://boards.straightdope.com/t/does-this-mutation-of-the-hand-occur/355439/17 "2006-05-05T03:24:41Z")
> [@Colibri](#): > > As \*\*Darwin’s Finch \*\* suggests, birds have lost one of the toes of the hind foot… HInd foot? Is there some kind of bizarre four-legged bird of which I was previous unaware, but will now haunt my nightmares? ---
**Author:** ![Wendell\_Wagner](https://avatars.discourse-cdn.com/v4/letter/w/8491ac/32.png) [@Wendell\_Wagner](https://boards.straightdope.com/u/Wendell_Wagner)\ **Post date:** [May 5, 2006, 3:31am UTC](https://boards.straightdope.com/t/does-this-mutation-of-the-hand-occur/355439/18 "2006-05-05T03:31:47Z")
Hooleehootoo writes: \> Does a mutation ever occur where the thumb has an intermediate phalange? This isn’t quite the same thing, but C. S. Lewis discusses at one point the fact he, his brother, and his father were all missing a joint in their thumbs. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [May 5, 2006, 4:29am UTC](https://boards.straightdope.com/t/does-this-mutation-of-the-hand-occur/355439/19 "2006-05-05T04:29:05Z")
> [@Fear Itself](#): > > HInd foot? Is there some kind of bizarre four-legged bird of which I was previous unaware, but will now haunt my nightmares? As a matter of fact, the Terror Bird [_Titanis walleri_](http://www.phonono.com/titanis_titel.jpg) was enough to give anyone nightmares, even without the clawed forefeet. It stood somewhere between 7 and 9 feet tall, and roamed Florida in the Pleistocene. A few more jolly restorations: [![](http://www.wildlife-art.co.uk/new_site/graphics/prehistory/titanis.jpg) ](http://www.wildlife-art.co.uk/new_site/graphics/prehistory/titanis.jpg) [http://nicholnl.wcp.muohio.edu/DingosBreakfastClub/BioMech/ImagesAtlas/Titanis\_Horse.jpg](http://nicholnl.wcp.muohio.edu/DingosBreakfastClub/BioMech/ImagesAtlas/Titanis_Horse.jpg) [http://www.geocities.co.jp/NatureLand/5218/thitanisu.JPG](http://www.geocities.co.jp/NatureLand/5218/thitanisu.JPG) And a skeleton: [http://www.dinosaursociety.com/images/titanis.jpg](http://www.dinosaursociety.com/images/titanis.jpg) ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [May 5, 2006, 8:24am UTC](https://boards.straightdope.com/t/does-this-mutation-of-the-hand-occur/355439/20 "2006-05-05T08:24:59Z")
Back to my earlier question about mammals… I wasn’t so much interested in ungulants who might have lost some digits, but whether all mammals had the pattern outlined by **Colibri** – if we look at primitive mammals like a platypus, does it have the typical mammlian pattern? [Next page](https://boards.straightdope.com/t/does-this-mutation-of-the-hand-occur/355439.md?page=2)