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| Page from Darwin's notebooks around July 1837 showing his first sketch of an evolutionary tree. |
"An organ serving for two purposes, may become rudimentary or utterly aborted for one, even the more important purpose, and remain perfectly efficient for the other. ...
[A]n organ may become rudimentary for its proper purpose, and be used for a distinct object."[1][2]
Charles Darwin On the Origin of Species
[A]n organ may become rudimentary for its proper purpose, and be used for a distinct object."[1][2]
Charles Darwin On the Origin of Species
I remember this being one of my favorite topics in University, not only because it is so very interesting, but also because my professor was French and my ears loved his pronunciation of homologous and vestigial. And going back further to high school, I recall a certain science teacher saying how those with a genetic predisposition to balding were actually more evolved than their full-headed counterparts. And being sans wisdom teeth, I like to think the same about myself.
Yes, it seems from nipples to tails, I have been reading a lot lately about the genetic threads that link us to our hairy, tree climbing, cellulose munching ancestors. And like all pasts, these threads too can come back to, well, perhaps not haunt us, but at the very least to remind us of where we come from. Vestigiality, the stuff of tails, wisdom teeth, and appendix. The seemingly superfluous stuff that may not jive with notions of survival driven evolution. And you may ask yourself, why on earth do we hang on to these bits and bobs when they appear to serve no purpose? Well, I rather like how Étienne Geoffroy Saint-Hilaire put it back in 1798:
“Whereas useless in this circumstance, these rudiments… have not been eliminated, because nature never works by rapid jumps, and She always leaves vestiges of an organ, even though it is completely superfluous, if that organ plays an important role in the species of the same family." [1][3]
I think this is a nice way of looking at it because, after all, it has been through the study of functional versions of these structures in other organisms that we have come to broaden our understanding of the roles they play in our bodies, and thus, of our own evolution. For instance, it was not that long ago that the appendix was commonly thought to be a useless organ. But as it turns out, the appendix is not without purpose, just not the same purpose as it had thousands of years ago.
VESTIGIALITY
- "In the context of human evolution, human vestigiality involves those traits (such as organs or behaviors) occurring in humans that have lost all or most of their original function through evolution. Although structures called vestigial often appear to be without function, a vestigial structure may retain lesser functions or develop minor new ones."[6]
PSEUDOGENES often result from the accumulation of multiple mutations within a gene whose product is not required for the survival of the organism. This is not to say they are no longer functional, as they may have a regulatory role, just that they have lost their former protein coding function.[1][28]
One example of this is a gene that is functional in most other mammals and which produces an enzyme that can make vitamin C (ascorbic acid). A documented mutation deactivated the gene in an ancestor of modern of monkeys and apes, and it now remains in their genomes, including the human genome, as a vestigial sequence or pseudogene.[1][5]
It has been suggested that uric acid may have taken over some of the functions of ascorbic acid in higher primates.[31][32]
Wisdom teeth are vestigial third molars that would have been beneficial to our ancestors, you know, because they didn't have utensils back then. But what they did have were larger jaws and more teeth. And with a diet high in vegetation, these molars would have helped to grind plant tissue, which would in turn have compensated for their inability to efficiently digest the cellulose.[14][16][23]
It has been suggested that uric acid may have taken over some of the functions of ascorbic acid in higher primates.[31][32]
Wisdom teeth are vestigial third molars that would have been beneficial to our ancestors, you know, because they didn't have utensils back then. But what they did have were larger jaws and more teeth. And with a diet high in vegetation, these molars would have helped to grind plant tissue, which would in turn have compensated for their inability to efficiently digest the cellulose.[14][16][23]
Why do some people not have wisdom teeth? Research into hypodontia, the congenital failure to develop one or several permanent teeth, suggests it is related to mutations in the PAX9 and MSX1 families of genes.[17][18]
The APPENDIX, like wisdom teeth, is also thought to have had a role in digestion when our ancestor’s diets were high in cellulose rich vegetation. It has over time shrunk significantly due to our changing diets and is now believed to be a 'safe-house' of good bacteria, useful in defense and recovery from intestinal infections, like cholera and c. difficile.[19]
The TAILBONE (coccyx), is the remnant of a lost tail. All mammals have a tail at some point in their development; in humans, it is present for a period of 4 weeks, during stages 14 to 22 of human embryogenesis.[6][8]
The TAILBONE (coccyx), is the remnant of a lost tail. All mammals have a tail at some point in their development; in humans, it is present for a period of 4 weeks, during stages 14 to 22 of human embryogenesis.[6][8]
The tailbone, located at the end of the spine, has lost its original function in assisting balance and mobility, though it still serves as a functional anchor for certain pelvic muscles.[1][6]
In rare cases, a congenital defect results in a short tail-like structure being present at birth.[1][30]
But that tail isn't a vestigial organ, it's an atavism, or a trait from an ancestor that appears sporadically. Though it is connected to the vestigial tail bone.[20]
The SEMILUNAR FOLD in the corner of the human eye is homologous to the third eyelid seen in some other mammals and other vertebrates.[10][22]
In rare cases, a congenital defect results in a short tail-like structure being present at birth.[1][30]
But that tail isn't a vestigial organ, it's an atavism, or a trait from an ancestor that appears sporadically. Though it is connected to the vestigial tail bone.[20]
In most primate species a semilunar fold is present, though the fully developed translucent or transparent third eyelid (drawn across the eye for moisture and protection), has only been found in lemurs and lorisoidea primates.[15][21][24]
The EARS of humans have far less developed muscles than those of most monkeys.
 |
The muscles connected to the ears of a human do not develop
enough to have the same mobility allowed to monkeys. Arrows show the vestigial structure called Darwin's tubercle found in about 10% of the population. [6] |
Still, the non-functional musculature of human ears is large enough to be identifiable.[6][7]
However, what humans can do is turn their head on a horizontal plane, which is an ability lacking in most monkeys.[6][9]
The OCCIPITOFRONTALIS MUSCLE (muscles covering parts of the skull), has lost its original function to keep the head from falling, but it is still useful for other purposes, like facial expression.[1][4][29]
In apes, the head is not balanced on the vertebral column, therefore strong muscles are need to pull back on the skull.[29]
Extra NIPPLES or BREASTS sometimes appear along the mammary lines of humans, as a remnant from mammalian ancestors who possessed more than two nipples or breasts. But this would be more an example of atavism than vestigiality. However, it could be argued that male nipples are vestigial as, although they may no longer function in their original role, they can play a lesser one in male arousal.
(As an aside) In his book The Odd Body , Dr. Stephen Juan, offers:
GOOSE BUMPS in humans under stress is a vestigial reflex.[6][10]
In apes, the head is not balanced on the vertebral column, therefore strong muscles are need to pull back on the skull.[29]
Extra NIPPLES or BREASTS sometimes appear along the mammary lines of humans, as a remnant from mammalian ancestors who possessed more than two nipples or breasts. But this would be more an example of atavism than vestigiality. However, it could be argued that male nipples are vestigial as, although they may no longer function in their original role, they can play a lesser one in male arousal.
(As an aside) In his book The Odd Body , Dr. Stephen Juan, offers:
"In theory, we all could have fully functioning breasts capable of giving milk. But male breasts, including the nipples do not get enough of the female hormone oestrogen so they never achieve the ability to lactate." Gynaecomastia, or the enlargement of breasts in men, "occurs when there is excess oestrogen."[25]
A possible function was to raise the body's hair, making the ancestor appear larger to scare off predators.[26]
Though body hair no longer serves as our primary protection from the elements, it still provides a form of insulation. When we get goose bumps in the cold for instance, the cold air is trapped between the raised hairs, reducing direct contact with skin.[26]
Though body hair no longer serves as our primary protection from the elements, it still provides a form of insulation. When we get goose bumps in the cold for instance, the cold air is trapped between the raised hairs, reducing direct contact with skin.[26]
And, according to Dr. Juan, “Hair also reduces friction problems in body movement. This is perhaps one of the reasons why we have hair in our armpits and between our legs.”[25]
Unlike our moms, ancestral primates would have had sufficient body hair to which an infant could cling.[6] And living under constant threat from predators, this grasping reflex would have been crucial to enabling mom and baby to flee in a hurry.
A FINAL ASIDE ...
[2] Darwin, Charles (1859). On the Origin of Species by Means of Natural Selection. John Murray: London.
[3] St. Hilaire, Geoffroy (1798). "Observations sur l'aile de l'Autruche, par le citoyen Geoffroy", La Decade Egyptienne, Journal Litteraire et D'Economie Politique 1 (pp. 46–51).
[4] Saladin, Kenneth S. (2003). 3rd, ed. Anatomy & Physiology: The Unity of Form and Function. McGraw-Hill. pp. 286–287.
[5] Nishikimi M, Fukuyama R, Minoshima S, Shimizu N, Yagi K (May 6, 1994). "Cloning and chromosomal mapping of the human nonfunctional gene for L-gulono-gamma-lactone oxidase, the enzyme for L-ascorbic acid biosynthesis missing in man". J. Biol. Chem. 269 (18): 13685–8. PMID 8175804.
[6] http://en.wikipedia.org/wiki/Human_vestigiality
[7]Darwin, Charles (1871). The Descent of Man, and Selection in Relation to Sex. John Murray: London.
[8]Saraga-Babić, M; Lehtonen, E; Svajger, A; Wartiovaara, J (1994). "Morphological and immunohistochemical characteristics of axial structures in the transitory human tail". Annals of Anatomy 176 (3): 277–86. doi:10.1016/S0940-9602(11)80496-6. PMID 8059973.
[9] Mr. St. George Mivart, Elementary Anatomy, 1873, p. 396
[10] Darwin, Charles. (1872) The Expression of the Emotions in Man and Animals John Murray, London.
[11] Peter Gray (2007). Psychology (fifth ed.). Worth Publishers. p. 66. ISBN 0-7167-0617-2.
[12] Jerry Coyne (2009). Why Evolution is True. Penguin Group. pp. 85–86. ISBN 9780670020539.
[13] Anthony Stevens (1982). Archetype: A Natural History of the Self. Routledge & Kegan Paul. p. 87. ISBN 0-7100-0980-1.
[14] http://en.wikipedia.org/wiki/Wisdom_tooth
[15] Johnson, Dr. George B. "Evidence for Evolution". (Page 12) Txtwriter Inc. 8 Jun 2006
The PALMAR GRASP REFLEX may be an example of a vestigial behavior in human infants.
When placing a finger or object to the palm of an infant, it will securely grasp it.[11] The grasp is evident in the feet as well.[12][13]
When placing a finger or object to the palm of an infant, it will securely grasp it.[11] The grasp is evident in the feet as well.[12][13]
Unlike our moms, ancestral primates would have had sufficient body hair to which an infant could cling.[6] And living under constant threat from predators, this grasping reflex would have been crucial to enabling mom and baby to flee in a hurry.
A FINAL ASIDE ...
"Until, up to six or ten thousand years ago, all humans had brown eyes. One genetic mutation is responsible for blue eyes, which occurred in one single ancestor. Thus scientists surmised that people with blue eyes all share the same common ancestor."[27]
[2] Darwin, Charles (1859). On the Origin of Species by Means of Natural Selection. John Murray: London.
[3] St. Hilaire, Geoffroy (1798). "Observations sur l'aile de l'Autruche, par le citoyen Geoffroy", La Decade Egyptienne, Journal Litteraire et D'Economie Politique 1 (pp. 46–51).
[4] Saladin, Kenneth S. (2003). 3rd, ed. Anatomy & Physiology: The Unity of Form and Function. McGraw-Hill. pp. 286–287.
[5] Nishikimi M, Fukuyama R, Minoshima S, Shimizu N, Yagi K (May 6, 1994). "Cloning and chromosomal mapping of the human nonfunctional gene for L-gulono-gamma-lactone oxidase, the enzyme for L-ascorbic acid biosynthesis missing in man". J. Biol. Chem. 269 (18): 13685–8. PMID 8175804.
[6] http://en.wikipedia.org/wiki/Human_vestigiality
[7]Darwin, Charles (1871). The Descent of Man, and Selection in Relation to Sex. John Murray: London.
[8]Saraga-Babić, M; Lehtonen, E; Svajger, A; Wartiovaara, J (1994). "Morphological and immunohistochemical characteristics of axial structures in the transitory human tail". Annals of Anatomy 176 (3): 277–86. doi:10.1016/S0940-9602(11)80496-6. PMID 8059973.
[9] Mr. St. George Mivart, Elementary Anatomy, 1873, p. 396
[10] Darwin, Charles. (1872) The Expression of the Emotions in Man and Animals John Murray, London.
[11] Peter Gray (2007). Psychology (fifth ed.). Worth Publishers. p. 66. ISBN 0-7167-0617-2.
[12] Jerry Coyne (2009). Why Evolution is True. Penguin Group. pp. 85–86. ISBN 9780670020539.
[13] Anthony Stevens (1982). Archetype: A Natural History of the Self. Routledge & Kegan Paul. p. 87. ISBN 0-7100-0980-1.
[14] http://en.wikipedia.org/wiki/Wisdom_tooth
[15] Johnson, Dr. George B. "Evidence for Evolution". (Page 12) Txtwriter Inc. 8 Jun 2006
[16] Edmonds, Molly. "Are people without wisdom teeth more highly evolved?" 11 August 2008. HowStuffWorks.com. <http://science.howstuffworks.com/life/evolution/no-wisdom-teeth.htm> 18 September 2014.
[17] http://www.eurekaselect.com/56293/article/suggestive-associations-between-polymorphisms-pax9-msx1-genes-and-third-molar-agenesis
[18] http://www.answers.com/Q/Why_are_your_wisdom_teeth_vestigial
[19] http://en.wikipedia.org/wiki/Vermiform_appendix
[20] Edmonds, Molly. "How Vestigial Organs Work" 11 August 2008. HowStuffWorks.com. <http://health.howstuffworks.com/human-body/parts/vestigial-organ.htm> 18 September 2014.
[21] http://en.wikipedia.org/wiki/Nictitating_membrane
[22] The Eye: Basic Sciences in Practice by John V. Forrester, p. 82
[23]Osman Hill, W. C. (1953). Primates Comparative Anatomy and Taxonomy I—Strepsirhini. Edinburgh Univ Pubs Science & Maths, No 3. Edinburgh University Press. p. 13. OCLC 500576914.
[24]Ankel-Simons, F. (2007). Primate Anatomy (3rd ed.). Academic Press. p. 471. ISBN 0-12-372576-3.
[25] Juan, Dr. Stephen; (2004) The Odd Body. HarperCollins Publishing: pages 199-200 & 192-193.
[26] http://en.wikipedia.org/wiki/Goose_bumps
[17] http://www.eurekaselect.com/56293/article/suggestive-associations-between-polymorphisms-pax9-msx1-genes-and-third-molar-agenesis
[18] http://www.answers.com/Q/Why_are_your_wisdom_teeth_vestigial
[19] http://en.wikipedia.org/wiki/Vermiform_appendix
[20] Edmonds, Molly. "How Vestigial Organs Work" 11 August 2008. HowStuffWorks.com. <http://health.howstuffworks.com/human-body/parts/vestigial-organ.htm> 18 September 2014.
[21] http://en.wikipedia.org/wiki/Nictitating_membrane
[22] The Eye: Basic Sciences in Practice by John V. Forrester, p. 82
[23]Osman Hill, W. C. (1953). Primates Comparative Anatomy and Taxonomy I—Strepsirhini. Edinburgh Univ Pubs Science & Maths, No 3. Edinburgh University Press. p. 13. OCLC 500576914.
[24]Ankel-Simons, F. (2007). Primate Anatomy (3rd ed.). Academic Press. p. 471. ISBN 0-12-372576-3.
[25] Juan, Dr. Stephen; (2004) The Odd Body. HarperCollins Publishing: pages 199-200 & 192-193.
[26] http://en.wikipedia.org/wiki/Goose_bumps
[27] http://www.medicaldaily.com/our-human-ancestors-had-tails-and-other-things-our-bodies-used-have-302988#.VBn-KUAsqEY.google_plusone_share
[28] http://en.wikipedia.org/wiki/Pseudogene
[28] http://en.wikipedia.org/wiki/Pseudogene
[29] http://en.wikipedia.org/wiki/Occipitofrontalis_muscle
[30]Saladin, Kenneth S. (2003). Anatomy & Physiology: The Unity of Form and Function (3rd ed.). McGraw-Hill. pp. 286–287.
[31] http://en.wikipedia.org/wiki/Vitamin_C#cite_ref-pmid5477017_31-0
[32] Proctor P (November 1970). "Similar functions of uric acid and ascorbate in man?". Nature 228 (5274): 868. Bibcode:1970Natur.228..868P. doi:10.1038/228868a0. PMID 5477017.
[30]Saladin, Kenneth S. (2003). Anatomy & Physiology: The Unity of Form and Function (3rd ed.). McGraw-Hill. pp. 286–287.
[31] http://en.wikipedia.org/wiki/Vitamin_C#cite_ref-pmid5477017_31-0
[32] Proctor P (November 1970). "Similar functions of uric acid and ascorbate in man?". Nature 228 (5274): 868. Bibcode:1970Natur.228..868P. doi:10.1038/228868a0. PMID 5477017.
OTHERS SOURCES
http://www.newscientist.com/article/dn13927-five-things-humans-no-longer-need.html#.VBpkgBRzbIU
http://www.medicaldaily.com/our-human-ancestors-had-tails-and-other-things-our-bodies-used-have-302988#.VBn-KUAsqEY.google_plusone_share
http://en.wikipedia.org/wiki/Primitive_reflexes
IMAGE CREDITS
"Darwin tree" by Charles Darwin - http://www.english.uga.edu/nhilton/4890/darwin/DarwinTree.html. Licensed under Public domain via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Darwin_tree.png#mediaviewer/File:Darwin_tree.png
"Appendix function diagram". Via Wikipedia - http://en.wikipedia.org/wiki/File:Appendix_function_diagram.svg#mediaviewer/File:Appendix_function_diagram.svg
"Gray892". Licensed under Public domain via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Gray892.png#mediaviewer/File:Gray892.png
"Darwin-s-tubercle". Licensed under Creative Commons Attribution-Share Alike 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Darwin-s-tubercle.jpg#mediaviewer/File:Darwin-s-tubercle.jpg
"Gray378". Licensed under Public domain via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Gray378.png#mediaviewer/File:Gray378.png
"Gaensehaut". Licensed under Creative Commons Attribution-Share Alike 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Gaensehaut.jpg#mediaviewer/File:Gaensehaut.jpg "Grasp". Via Wikipedia - http://en.wikipedia.org/wiki/File:Grasp.jpg#mediaviewer/File:Grasp.jpg
http://www.medicaldaily.com/our-human-ancestors-had-tails-and-other-things-our-bodies-used-have-302988#.VBn-KUAsqEY.google_plusone_share
http://en.wikipedia.org/wiki/Primitive_reflexes
IMAGE CREDITS
"Darwin tree" by Charles Darwin - http://www.english.uga.edu/nhilton/4890/darwin/DarwinTree.html. Licensed under Public domain via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Darwin_tree.png#mediaviewer/File:Darwin_tree.png
"Appendix function diagram". Via Wikipedia - http://en.wikipedia.org/wiki/File:Appendix_function_diagram.svg#mediaviewer/File:Appendix_function_diagram.svg
"Gray892". Licensed under Public domain via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Gray892.png#mediaviewer/File:Gray892.png
"Darwin-s-tubercle". Licensed under Creative Commons Attribution-Share Alike 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Darwin-s-tubercle.jpg#mediaviewer/File:Darwin-s-tubercle.jpg
"Gray378". Licensed under Public domain via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Gray378.png#mediaviewer/File:Gray378.png
"Gaensehaut". Licensed under Creative Commons Attribution-Share Alike 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Gaensehaut.jpg#mediaviewer/File:Gaensehaut.jpg "Grasp". Via Wikipedia - http://en.wikipedia.org/wiki/File:Grasp.jpg#mediaviewer/File:Grasp.jpg
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