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Theories of Evolution
Objectives
Define biological evolution
Explain Lamarck’s theory of evolution
Explain Darwin’s two theories of
evolution
Introduction
Evolution is an orderly succession of
changes
Biological evolution is the change of
populations of organisms over
generations
Lamarck’s Explanation
Proposed by Jean Baptiste de Lamarck (17441829)
First unifying hypothesis of species
modification
Similar species descended from a common
ancestor
Species changed by acquired traits that were
passed on to offspring
Acquired trait is one that is not determined by genes
Acquired traits were a result of the organism's
experience or behavior
Modern Evolutionary Thought
Charles Darwin (1809-1882) and Alfred
Wallace (1823-1913) independently proposed
the hypothesis that species were modified by
natural selection
Natural selection – organisms best suited to
their environment reproduce more successfully
than other organisms
Over generations, the proportion of organisms
with favorable traits increases in a population
Charles Darwin
Went on a 5-year voyage
(1831-1836) on the
H.M.S. Beagle to South
America and the South
Pacific
Was the ship’s naturalist
Job was to collect
specimens and keep
careful records of his
observations
Voyage of the Beagle
While on the Beagle, Darwin read a
geology book entitled Principles of
Geology by Charles Lyell
Book discussed the age of the Earth and the
principles of uniformitarianism
Uniformitarianism – the geological structure
of the Earth resulted from cycles of
observable processes
Darwin concluded that organisms had to
adapt to geological changes over time
Voyage of the Beagle
One of the most
important stops that
influenced Darwin’s
theories was the
Galapagos Islands
The Galapagos Islands are
geologically young (5
million years old)
Each island has a different
climate, so each island had
different vegetation and
animals
Darwin’s Data
Darwin spent several years in England
analyzing his data
Collected 13 similar but separate species
of finches
Each finch species has a distinctive bill
adapted for a particular food source
Darwin considered that all of the island’s
finches had a common ancestor and
descended from a single species
Darwin’s Data
Darwin also collected tortoises
Tortoises varied in shell shape and neck
length
Shell shape and neck lengths could be used
to identify which island the tortoise came
from
Origin of Species
Darwin proposed his
hypothesis of
evolution by natural
selection in 1858
Worked on his
hypothesis for 21
years
Published his book
The Origin of Species
in 1859
Darwin’s Theories
Descent with Modification
Newer forms appearing in the fossil record
are actually modified descendants of older
species
All species descended from one or a few
original types of life
Darwin’s Theories
Modification by Natural Selection
How evolution works
“Survival of the fittest”
Adapt – to change genetically over generations to
become more suited to the environment
A favorable trait gives the individual that has it an
adaptive advantage
Fitness – a single organism’s genetic contribution to the
next generation
• An individual with high fitness is well adapted to its
environment and reproduces more successfully than
an individual with low fitness
Notes Review
Define biological evolution.
Biological evolution is the change of
populations of organisms over generations
Notes Review
Explain Lamarck’s theory of evolution.
Similar species descended from a common
ancestor
Species changed by acquired traits that were
passed on to offspring
Acquired traits are not determined by genes
but by an organism’s experiences or
behaviors
Notes Review
Explain Darwin’s two theories of
evolution.
Descent with Modification
• Newer forms appearing in the fossil record are
actually modified descendants of older species
• All species descended from one or a few original
types of life
Modification by Natural Selection
• The more fit an organism is to its environment
the more likely it is to survive and pass on its
traits to the next generation