Transcript The opposable THUMB

Human genetic engineering at its finest…
 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.
 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.
 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.
 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.
 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.
 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.
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-ScienceNews/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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