Evolution
the change in heritable characteristics of biological populations over successive
generations. These characteristics are the expressions of genes, which are passed on
from parent to offspring during reproduction.
What is evolution?
Evolution is the gradual change or development of something. It can be
used in various senses in social or economic structures and general use.
What is biological evolution?
The change in the gene pool of a population during the course of time by
such processes as mutation, natural selection and genetic drift. The descent
with modification.
This definition covers micro-evolution (evolution with species) and macro-
evolution (the decent of different species from a common ancestor over
many generations)
Development of the Theory of Evolution
Before 1700:
• Species unrelated & remained unchanged (created by a divine
power.)
• Earth is young (6000 years old)
1700 to 1800:
• Species related & change ver time
• Earth is millions of years old
Erasmus Darwin (Charles’s Grandfather)
(1731 – 1802)
• Life on Earth descended from common ancestor.
• Species must have evolved over time.
• Offered no mechanism for ‘evolution’.
Jean Baptiste Lamarck
(1744-1829)
,Two “Laws”
1. Law of Use or disuse:
Causes used structures to enlarge and
disused structures to shrink. (A giraffes neck
would grow in height if there were trees
that were high up and shrink if they were
lower down)
2. “Law” of inheritance of an acquired traits
Acquired traits can be inherited by offspring
in the following generation.
Jean Baptiste Lamarck’s ideas/laws were not accepted why?
He imagined that when an organism tries to use an organ for some purpose
REPEATEDLY that organ will grow and its offspring would start with an already
enlarged organ. For example: A giraffe would stretch for high leaves
throughout its life and this would result in its offspring being born with a longer
neck and legs.
There is no way that an event going on during an organism’s
life can cause directed changes in its genes. Charles Darwin
(1823-1913)
• English naturalist
• College dropout
• Traveled around the world- 5 year expedition on
HMS Beagle
The data he collected made him aware of:
• Diversity amongst organisms
• Variation amongst the same species.
• Distribution of species.
The first convincing case for evolution, The Origin of Species, was published
by Charles Darwin in 1859.
In this book, Darwin argued that new species developed from ancestral ones
by natural selection.
Darwin developed his theory of “survival of the fittest” by building on earlier
ideas and supporting his views with a large body of evidence he collected
while voyaging extensively on the ship the ‘HMS Beagle’.
, Alfred Russel Wallace
(1823-1913)
Alfred Russel Wallace, a young specimen collector working
in the East Indies, developed a theory of natural selection
independently of Darwin. He suggested that ancestor
became isolated from each other by water.
However, Darwin supported the theory more extensively and receives most of
the credit for it.
Evidence of Evolution
• Fossil records
• Biogeography
• DNA (genetics) and molecular biology
• Homologies and comparative anatomy
• Embryology
• Vestigial organs
1. Fossil records
Fossils are the remains of plants and animals that have been preserved in
sedimentary rocks. Fossils are generally rare. For every animal that dies, its
chances of becoming fossilized are estimated to be less than one in a million.
, Fossils found all over the earth are a significant source of evidence for
evolution. This is known as paleontological evidence and shows both micro-
evolution and macro-evolution.
Paleontology = study of prehistoric life
What can be seen in the fossil record?
Fossil records indicate that evolution has taken place as they show:
- Increase in complexity: simplest organisms appeared first
- Increase in diversity
- More extinct species as one move back in time
- Existence of intermediate forms between groups (transitional fossils)
- Overall increase in size, from a starting point of tiny unicellular
organisms
How does the fossil evidence show that evolution has occurred?
The fossil records provide detailed information and evidence of systematic
change through time – of descent with modification. Different fossils are
found in the different rock layers with the oldest fossils in the oldest layers.
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