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The opposable thumb. Human genetic engineering at its finest…. WHAT IS AN OPPOSABLE THUMB?. An opposable thumb refers to a thumb that is capable of being moved freely and independently from the rest of the fingers.

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The opposable thumb

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The opposable thumb l.jpg

The opposable thumb

Human genetic engineering at its finest…


What is an opposable thumb l.jpg

WHAT IS AN OPPOSABLE THUMB?

  • An opposable thumb refers to a thumb that is capable of being moved freely and independently from the rest of the fingers.

  • The movement of opposition is a rotary movement in which the thumb, swinging about its own axis, comes to face the lower surface of the tips of the fingers. Thus the opposable thumb is the basis of precision.

  • The opposable thumb is unique in its ability to swing toward the palm and oppose the other four fingers to provide a tighter and more precise grip on objects. Thus an opposable thumb helps in grasping things more easily, picking up small objects, and eating with one hand.


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THE IMPORTANCE OF THE THUMB

  • The presence of the opposable thumb has created mainly two prehensile actions: these are called the precision grip and the power grip; which provided the basis for all prehensile activities.

  • Descriptions of these grips highlight that the ‘precision grip’ is a throwing grip, and the ‘power grip’ is a clubbing grip.

  • These physical adaptations produced more fit organisms that were able to survive and reproduce.


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IS THE OPPOSABLE THUMB SPECIFIC TO HUMANS?

  • The opposable thumb is not only characteristic of humans, but also chimpanzees, gorillas, orangutans, Old World monkeys, as well as some other animals such as opossums and giant pandas.

  • Opposable thumbs help monkeys and apes climb trees as well as gather and eat their food.

  • However, the opposable thumb in these organisms is small, weak and relatively immobile.

  • Only apes and primates have hands capable of grasping objects.


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WHAT IS THE GENETIC BASIS OF IT’S DEVELOPMENT?

  • Researchers noted the contribution made by the gene enhancer (which functions in turning on genes in the appropriate cells that is uniquely human-specific), HACNS1, to the evolution of the opposable thumb.

  • This gene enhancer has also contributed to modifications in the ankle or foot that allowed bipedalism to occur.

  • Thus these gene enhancers have produced the traits which are hallmarks of our species: opposable thumbs, manual dexterity, and ankle or foot adaptations to walking on two legs.


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I GIVE EVOLUTION TWO THUMBS UP!


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WHAT IS THE GENETIC BASIS OF IT’S DEVELOPMENT? (continued)

  • Evolutionary changes in the DNA sequence of enhancers are thought to have triggered changes in human development which makes us different from chimpanzees and other apes.

  • Other observable differences between chimpanzees and humans such as brain size, hair density, tooth patterns, pelvic structure and hand and foot modifications, could be due to the way developmental genes are turned on.


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NATURAL SELECTION AT WORK?

  • The opposable thumb is a clear example of natural selection in progress as this modification to a species, which is beneficial to the species, allows it to survive.

  • The five considerations of natural selection include: a) all species are engaged in a struggle to survive in their environment, b) environmental conditions change over time, c) species change through continual modifications, d) modifications that are best suited for the environment are preserved, and e) evolutionary change is result of the natural selection of successful modifications.


References l.jpg

REFERENCES

  • Damonte, K. (2004). Thumbs are handy digits. Retrieved April 4,

    2009, from http://www3.nsta.org/main/news/stories/science_and_children.php?news_story_ID=49036

  • Miller, K.R. & Levine, J.S. (2006). Biology. Boston, MA: Pearson

    Education Inc.

  • Setform Limited (2008). Evolution of human opposable thumb.

    Retrieved April 4, 2009, from

    http://www.scientistlive.com/European-Science-

    News/Genetics/Evolution_of_human_opposable_thumb/21015/

  • Young, R.W. (2003). Evolution of the human hand: the role of throwing

    and clubbing. Journal of Anatomy. Retrieved April 4, 2009, from

    http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1571064


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