Evolution in Humans and the
Thoughts of Major Evolutionary
Scientists
Sarim Baig
Evidence for Human Evolution
• Homology
• Vestigial Organs
• Appendix, Tailbone, and others
• Paleoanthropology
• Similarities between humans and others in the “Homo”
genus, as well as earlier species.
Homology
• Mammalian Forelimbs
• Most often cited example of homology
• Humans differ greatly from other mammals such as bats and
whales yet have almost the exact same bone structures in
the forelimbs.
• Single bone attached to two bones which are then attached
to multiple bones.
• Each of these structures was slightly modified in order for
the organism to adapt to its surroundings.
• Same bone structure allows species to fly, swim, run, etc.
Homologous Structures
Vestigiality
• Structures whose physiological roles in the organism
have either been diminished or have disappeared
altogether.
• Human tailbone:
• Other organisms use the tailbone as a means for balance,
communication, and even movement.
• Other organisms such as dogs have a much larger and more
pronounced tailbone than humans.
• Human tailbone is a small “hook” at the end of the vertebral
column and has no function in movement and/or balance.
Human Appendix
• The human appendix is a “worm-like” structure found
in the digestive system at the end of the “caecum”.
• Gradually shrinks in humans as we age.
• The appendix can be removed surgically without any
major side effects.
• Other mammalian organisms such as rabbits also
have an appendix, yet their appendix has a defined
function.
The function of the appendix
• Appendix and caecum play a vital role in the
digestion of cellulose in herbivorous animals.
• In humans, enzymes that are used to digest cellulose
are found in low quantities in the caecum and are
mostly absent in the appendix.
• In rabbits, the appendix plays a major role in its
immune system
• Half of its lymphoid tissue found in appendix
• Majority of human lymphoid tissue is found in the small and
large intestines.
Vestigial Organs: Appendix
Figure: Rabbit Appendix (Left), Fetal Human (Middle), Adult Human (Right)
Other Vestigial Structures in Humans
• Wisdom Teeth?
• Many individuals never have their wisdom teeth come in.
• Many are often impacted and need to be removed.
• Generally not used for biting and/or chewing.
• Genes for Vitamin C- Ascorbate
• The human genome has the majority of the genes needed to
produce vitamin C internally, yet humans are incapable of
doing this.
• Evolved this trait because early humans consumed a lot of
vitamin C in their everyday diet.
Paleoanthropology
• Study of early hominids and how their biological and
cultural characteristics are related to modern-day humans.
• Majority of the evidence in this field came from studying
the fossil record.
• Earliest definitive hominids were of the Australopithecus
group, which lived around 4 million years ago.
• Two major trends are seen in the history of hominids.
• Evolution of bipedalism
• Greater intellectual capacity
Bipedalism
• The ability to walk on two legs is
directly related to the length of the
arms relative to the legs.
• Species with longer arms and shorter
legs are much more likely to be
quadropeds.
• Species with shorter arms and longer
legs are more likely to be bipedals.
• Humerus to Femur ratio
• Chimps: ~ 1 : 1
• A. afarensis (Lucy): ~ 0.85 : 1
• Humans: ~ 0.72 : 1
Intellectual Ability
• The overall intellectual ability of mammalian species
has been attributed by some to be directly related to
the size of the organism’s brain.
• Brain sizes in hominids have gradually increased
over time.
• Led to the development of tools in later hominids and
other innovations (Fire, agriculture).
Intellectual Ability Continued
• A. afarensis: ~ 400 cc
• Lived 4 m.y.a
• Approximately the same size as chimps and other apes.
• A. boisei: ~ 530 cc
• Lived 2 m.y.a
• Homo erectus: ~ 900 cc
• Lived up until 300,000 years ago
• Homo neanderthalensis: ~ 1500 cc
• Lived up until 30,000 years ago
• Homo sapiens: ~ 1350 cc
Trends in Hominid Brain Size
Chimpanzee
Australopithecus afarensis
Australopithecus boisei
Homo erectus
Homo neanderthalensis
Homo sapiens
Differences between Early Hominids and
Late Hominids
Charles Darwin
• Witnessed the controversy that followed the
publication of his paper and Wallace’s in 1858.
• Reluctant to mention anything about evolution in
humans in the Origin of Species (1859).
• Waited twelve years before making any publication
dealing with the issue of human evolution.
• Published The Descent of Man after a number of
other scientists had already brought the topic into the
public eye.
The Descent of Man (1871)
• Cites homologous structures,
vestigial organs, and comparative
embryology as evidence that
humans evolved from earlier
species.
• “…that man is descended from
some lowly organized form, will, I
regret to think, be highly
distasteful to many. But there can
hardly be a doubt that we are
descended from barbarians.”
Alfred Russel Wallace
• Human evolution was a result of two forces, natural
selection and the work of a spiritual being.
• Natural selection could not alone account for the
“vast superiority of man over its nearest allies.”
• “The brain in savage and prehistoric man was in
advance of his needs”
Thomas Henry Huxley (1825-1895)
• “Darwin’s Bulldog”
• First to publish on evolution in humans
after reading Darwin’s Origin of
Species
• Evidence on Man’s Place in Nature
(1863)
• Much of Huxley’s work dealt with the
similarities between humans and
apes.
Huxley-Wilberforce Debate (1860)
• Oxford University
• Archbishop Wilberforce:
known as a skilled debator
• Huxley: a relative unknown
in the scientific community.
• Expected to be a defeat of
Huxley and of Darwin’s
ideas.
Results of Debate and Its Impact
• By most accounts, Huxley soundly defeated
Wilberforce in the debate.
• Wilberforce is said to have asked Huxley which side
of his family descended from apes.
• Huxley response was that he would rather be
descended from apes than from a man afraid to face
the truth.
• Huxley’s victory made believers out of many
individuals in the public who had previously attacked
evolution.
References
http://herc.berkeley.edu/middle_awash/what_is_paleoanth.php. Accessed
Nov. 18, 2008.
http://www.evoled.org/lessons/human.htm#overview. Accessed Nov. 18,
2008.
http://cogweb.ucla.edu/ep/Paleoanthropology.html. Accessed Oct. 27,
2008.
http://www.nasw.org/users/karin/globe1.html. Accessed Nov. 22, 2008.
http://www.talkorigins.org/faqs/vestiges/appendix.html. Accessed Oct. 27,
2008.
http://www.fordham.edu/halsall/mod/1871darwin.html. Accessed Oct. 31,
2008.
References Continued
Wallace, Alfred Russel. Man and Natural Selection (S173: 1870). The
Alfred Russel Wallace Page. Accessed Oct. 31, 2008.
Wallace, Alfred Russel. Darwin’s ‘The Descent of Man and Selection in
Relation to Sex’ (S186:1871) The Alfred Russel Wallace Page.
Accessed Oct. 31, 2008.
http://www.ucmp.berkeley.edu/history/thuxley.html. Accessed Oct. 31,
2008.
http://cas.bellarmine.edu/tietjen/Ec&Ev_Distance_learning/Evidence/evid
ence_main.htm. Accessed Nov. 26, 2008.
http://www.holyconservancy.org/images/history/1860ad/thomas-hhuxley.gif. Accessed Nov. 26, 2008.