Early Theories of Evolution
EVOLUTION: change in a population
(DNA) over time
• no scientific explanations of
evolution were given until the 18th
Century
• the growth of natural history led to
increased knowledge of fossils &
living organisms
1. Lamarck’s Hypothesis of Evolution
(Theory of Use and Disuse):
• 1809
• was one of the first to develop
a theory of evolution
J.B. Lamarck
Three Main Ideas:
i. organisms strive to improve themselves,
to become more advanced
ii. the most used structures develop, while
the less used ones waste away. Known as
the principle of Use and Disuse
iii. once a modification has occurred it is
passed on to the offspring
- disproved by Weisemann
• cut off the tails of mice, allowed them to
reproduce and then cut off the offspring’s tails
• he continued this for 20 generations and they
continued to produce offspring with tails
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2. Charles Darwin’s Theory of
Natural Selection(aka: Survival
of the Fittest)
• 1844(but took him 20 years to publish
his ideas)
• 5 main points:
i) there is variation within populations
ii) Some variations are favourable. A
favourable variation is one that
improves the organism’s ability to
function and reproduce
iii) More young are produced in each
generation than can survive
iv) Those with the favourable
variations, survive, reproduce and pass
on the favourable trait to their
offspring.
v) Over enormous spans of time, small
changes accumulate and populations
change.
Requirements:
1. Variation in a trait
within a population.
(some had longer necks
than rest of population)
2. those with longer necks
get better/more food, have
more babies
(have an advantage in
the struggle for existence)
3. More individuals are born each
generation than can survive
“struggle for existence”
4. those with longer necks are
more likely to survive, and pass
this trait on to their offspring
(variation is heritable)
5. gradually, over many generations, necks
became longer and longer
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Homework
Results:
• Compare how Lamarck and
Over time,
average neck
length increases
Darwin would explain the frog’s
tongue for capturing food. Use
one paragraph to explain
Lamarck’s theory and another
paragraph to explain Darwin’s
theory.
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