Download 1 Theories of Evolution

Theories of Evolution
• Jean Baptiste Lamarck (1744 – 1829)
– One of the first to propose a theory of evolution.
– Observed changes in the fossil record.
He observed from that data that species changed over
time.
– Believed that organisms could pass down acquired traits.
• Acquired traits – traits not determined by genes; traits
gained by experience or behavior
– ie. Cheetahs exercised and increased leg strength, then
passed that leg strengh on to their offspring.
– First to state that organisms change over time; newer
organisms are modified versions of older organisms.
Teleology
• Derived 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.
• ie. 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.
ie. Cheetahs were created by God to be fast runners.
Charles
Darwin
• He was hired as a naturalist for an expedition in 1831 on the
H.M.S. Beagle.
• Read books on geology and noted that changes take place over
millions of years, therefore, organisms must adapt to these
changes.
• He collected specimens and recorded data from various
locations (ie. Galapagos Islands). He noted differences between
similar species living in different locations. Why were they
different?
• Developed a theory called evolution by natural selection.
This is now the most widely accepted evolutionary theory in
scientific community.
Darwin’s Theory
• “Descent with Modification” – meaning that newer species are
modified descendents of older species.
• Idea supported by Darwin’s observations
– Similar species showed different characteristics in different
locations/islands.
– ie. 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.
Natural Selection
• Evolution by natural selection
– Proposed hypothesis for how evolution happens.
• Noticed that environmental factors (ie. food, territory, mates,
predators) can limit the size of populations.
– Most populations do not grow unchecked.
• Two 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. More fit organisms will have greater reproductive success.
As a result, genes for these traits will be passed on more
often.
4. After time, the population as a whole may change.
Adapt – to change genetically over time to become better
suited for the environment
ie. 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.