Chapters 16 and 17:
Evolution – part I
Evolution – the process by which species
change over time
•People in the 1800’s did not believe in
evolution
•Thought the Earth was a few thousand
years old and did not change
•Thought all life was created by a divine
creator in the span of 1 week – very
religious!!
•Thought that life did not evolve
Charles Darwin
•1831, set sail on HMS Beagle
•Ship’s naturalist -observer/collector of
plants, animals, & fossils
•Left from England, sailed around South
America, across Pacific, around Africa,
and back to England
•Most famous for observations made at
Galapagos Islands
•Darwin was influenced by:
•Charles Lyell – geologist
•Suggested the Earth was several
million years old
•Suggested that Earth changed over
time due to geologic forces (volcanoes,
earthquakes, wind, erosion, etc.)
•Darwin reasoned that if Earth changed,
those who lived on it would have to
adapt/change to survive.
•Thomas Malthus – an economist
•Wrote an essay on overpopulation of
humans – food supply not increasing as
rapidly as population growth.
•Number of people could not keep growing
this way and growth would be limited by
factors such as disease, war, and famine.
•Darwin reasoned that the same limits could
apply to organisms in nature.
•Jean-Baptiste de Lamarck
•French scientist in 1809
•Noticed organisms are usually well-adapted to
their environments
•Suggested that organisms acquired traits during
their lifetime to adapt to their environment and
passed those acquired traits onto their offspring.
•WRONG – only traits found on genes can be
passed onto offspring!! (Remember – it wasn’t
until the 1860’s that Mendel suggested how
inheritance works)
•Example – webbed feet from stretching digits,
long neck by stretching
•Darwin also took interest in the practice
of breeding, particularly exotic pigeons
•Studied breeding of dogs, orchids, and
food crops as well
•Breeders selected individuals with
desired traits to breed the next generation
– artificial selection
•This can contribute to changes in the
genetic make-up of a population
•Darwin published his findings in 1859 in a book
entitled The Origin of Species by Means of
Natural Selection.
•He was motivated to publish his book in 1859
because Alfred Wallace had independently come
up with the same conclusions and was ready to
publish his findings.
•Darwin is credited with the theory of natural
selection due to the volume of evidence to
support his theory.
• Populations become modified through
natural selection
• Natural selection - the process by which
individuals that are better adapted to their
environment survive and reproduce more
successfully than less well-adapted
individuals do
• Fitness – reproductive success
•Natural selection involves the following:
•Overproduction – more offspring are
produced than can possibly survive
•Variation – differences within a
population
•Selection – having a particular trait may
make an individual more likely to
survive
•Adaptation – those “selected” traits
improve survival and become more
common in a population
• Patterns of natural selection:
• Stabilizing selection – average form of a
trait is favored; extreme forms of a trait
are eliminated.
• Directional selection – one extreme form
of a trait is favored.
• Disruptive selection – both extremes of a
trait are favored over an average form of
a trait.
Stabilizing selection
Directional selection
Disruptive selection
Adaptations vs. Variations
•Variations – differences that exist within a
population that may have no effect on
fitness
•Ex: length of your thumb
•Adaptations – a variation that all members
of a population have inherited because that
trait improves fitness
•Ex: an opposable thumb
•Examples of adaptations:
•Physical features of an organism
•Ex: long tongue to get food, sharp teeth
•Actions an organism takes
•Ex: migration, tracking prey, storing nuts,
growing towards light
•Chemicals produced/biochemical processes
•Ex: venom, ink of octopus, protein in web,
respiration rate, digestive enzyme, blood
clotting