Transcript evolution by natural selection

Theories of Evolution
• Type I
– Cheetahs can reach top speeds of up to 60 mph;
however, they were not always this fast. Explain
how/why cheetahs may have evolved to be such
fast animals.
Lamarck
Jean Baptiste Lamarck (1744 – 1829)
• One of the first to propose a theory of evolution.
– First to state that organisms change over time, meaning
newer generations of organisms are modified versions of
older generations of organisms.
• Theory is based on observed changes in the fossil
record for the same species
• Believed that organisms could pass down acquired
traits which are traits not determined by genes;
traits gained by experience or behavior
Ex: Cheetahs exercised and increased leg strength, then
passed it on to their offspring.
Teleology
• Comes from the root “telos” meaning end.
• Teleology – idea that evolution is purposeful
or has a pre-determined result.
• Belief that everything happens for a reason.
• Ex: Cheetahs were meant to become top
predators, so they had to become faster to
catch their prey.
Creationism/Intelligent Design
Belief in a “creator” or “higher power”.
• Creationism
– Belief in the literal meaning of the Bible and other religious
documents.
– Do not believe that species change significantly over time.
• Intelligent Design
– Belief that creator began the process of life.
– Recognize that species change over time, but do not
believe that new species are created.
Ex: Cheetahs were created by “God” to be fast runners.
Darwin
• Charles Darwin – attended medical school and studied for the clergy
• Hired as a naturalist for an expedition in 1831 – sailed on the H.M.S.
Beagle – traveled through South America and South Pacific
• Read books on geology.
– Geologic changes take place over millions of years. Organisms must adapt to
these changes.
• Collected specimens and recorded data from various locations.
– Noted differences between similar species living in different locations. Why
were they different?
• Developed a theory called evolution by natural selection.
– Now most widely accepted evolutionary theory in scientific community.
Darwin’s Theory
• Based on Descent with Modification – newer species are modified
descendents of older species.
– Different from Lamarck’s idea of descent with modification
– Believed that all species descended from a few original types of
organisms.
• Idea supported by Darwin’s observations from his specimens and travels
– Similar species showed different characteristics in different locations.
– Ex: Galapagos finches – compared birds on different islands
• Beaks shaped differently when different food sources present
– Large, wide beak for cracking seeds.
– Small, thin beak for catching insects.
Darwin’s Theory continued…
• Darwin proposed the theory of Evolution by natural
selection
– Proposed hypothesis for how evolution happens.
• He observed that environment can limit the size of
populations.
– Most populations do not grow unchecked.
• 2 ways to limit population growth.
– Increased death rate
– Decreased reproduction rate
Natural Selection
Main points of Darwin’s theory
1. All populations contain some variation – Not all individuals
are the same within a group.
2. Some organisms are more “fit” for their environment.
Fitness – the ability of an organism to survive and reproduce in its environment
3.
4.
5.
More fit organisms will have greater reproductive success.
(Have more offspring!!)
As a result, genes for these traits will be passed on more
often.
After time, the population as a whole may change.
Adapt – a species changing genetically over time to become better suited
for the environment
EX: Cheetahs who were fast were more fit for the environment
and more likely to survive and reproduce.
Important to Remember
• Evolution acts on
populations, NOT
individuals!
– Individuals do not change
spontaneously.
– Changes may be seen in the
population as a whole over
millions of years.
• Evolution is NOT
purposeful!
– Traits that are favorable in
some environments may not
be favorable in others.
– Change in the environment
may cause change in
populations.