Download Natural Selection Powerpoint - Year 10 Life Science

Chapter 3 – Natural selection
and Evolution
Changes over generations
“Fossils and evolution”
 What is Evolution?
 A genetic change in the characteristics of a
species over many generations, resulting in
the forming of a new species.
Example of evolution
 The fossil structure of the horse has
changed over several generations; it
began as a horse – like animal the size
of a dog an animal thought to live 52
million years ago
 Since the first discovery, there have
been 17 different horse like species
found and dated
 There seems to be gradual changes in
many parts of the skeletons of all the
different fossil horses
 Some obvious changes are body shape,
size, length of legs and decrease in
toes.
Structure and relationship
 Genetics has shown us that species with the same basic
structure have many genes the same or similar.
 Organisms with some identical genes are therefore
considered to be related. (as they have inherited those genes,
through meiosis)
 However, some organisms might have similar structures, but
are NOT related.
 Homologous Vs Analogous Structures.
https://www.youtube.com/watch?v=VKEM4oFTU6Q
Homologous Structure
Homologous structures are features of organisms that have a
similar structure and provide evidence of an evolutionary
relationship
 Similar structure, different function
 E.g. wing of bird, wing of bat, leg of lizard, flipper of whale, arm
of human all have same basic structure
 Pentadactyl limb
However, in each organism is has been modified to suit a different
way of life.
Analogous Structures
Analogous characteristics are those that look similar but are
genetically very different. (no evolutionary relationship)
 Similar Structure. Not Related.
 These structures may have come about, due to the
environment in which they live in.
 Eg. sharks and dolphins seem similar in appearance however
genetically these animals are completely different.
 Both need flippers, to be able to swim in the water.
 A butterfly and a Bird are completely different species, but both
have the similar structure of ‘wings’ to enable them to fly
Artificial Selection
Artificial selection is the process by which humans choose to
breed particular organisms with desirable features.
 Eg. domesticated dogs,
different breeds of dogs are
all one species and different
breeds produced by Artificial
selection.
 Plants that are resistant to
particular pests.
Selective breeding
 Selective breeding is used in two main ways:
 Cross – breeding: combining the offspring with one desirable
feature with another offspring with a different desirable feature.
 Inbreeding: Is the process of allowing related individuals to
mate. (more successful in plants)
Textbook Review (p76)
 Questions:
 4, 5, 9 & 12
Questions
4 a Genetic change in the characteristics of a species over
many generations, resulting in a new species.
b The time between the birth of an individual and when they
produce their own offspring.
c Structures that are controlled by some of the same
inherited genes.
5 Fossils show the structure of past organisms; this can be
compared with current living species. Many look similar and
yet show some differences that suggest they changed over
time.
Questions
9 Dolphins and sharks both have a dorsal fin, and streamlined
body shape. However, dolphins have lungs and shark have gills,
so they are not very closely related.
12 The bat arm (wing) has most of the same bones as a mouse
arm, and they are therefore homologous. But the long fingers of
the bat support the membrane for the wing and are adapted for
flying, whereas a mouse arm is for walking—two entirely
different functions.
Natural Selection
In 1858, Charles Darwin proposed a process by which species change over
many generations.
 He had no knowledge of genetics because it had not been discovered at
the time
Darwin’s view of life : descendants of ancestral forms adapted to different
environments over a long period of time.
 The mechanism for adaptation is called ‘natural selection’, and is based on
a number of principles:
 Variation
 Competition/Survival of the fittest phenotype
 Favourable alleles increase
 Ability to reproduce increases
Darwin
Natural Selection cont…
Natural selection is the process where an environmental factor acts on
a population and results in some organisms having more offspring than
others.
 The factor that acts on the organism is called the selective agent.
The selective agent may be a predator, disease, natural disaster or
physical factor such as temperature.
 The individual that are favoured by the selective agent survive and
pass on their features to the next generation.
 The outcome of natural selection being that the species becomes
better adapted to their environment and survives longer.
Evolutionary Process by Darwin
Variation: Individuals vary from one another in many characteristics (even
siblings differ). Some variations are better suited then others to the conditions
of the time.
Competition: There is competition among the offspring for resources (food,
habitat etc.).
Survival of the fittest phenotype: The individuals with the most favorable
combinations of characteristics will be most likely to survive and pass their
genes on to the next generation.
Favorable combinations increase: Each new generation will contain more
offspring from individuals with favorable characters than those with
unfavorable ones.
https://www.youtube.com/watch?v=s
VVldxxbWig
Example of natural selection:
“The Peppered Moth”
The peppered moth existed in two forms white with black spots and all black.
 In city areas almost all peppered moths were black
 In country (rural) area all peppered moths were white
 The selective agents were birds (predation)
 The findings:
 In the city areas the trees were blackened by pollution any white moths resting on
the trees would be spotted and eaten, therefore the black moths survived longer.
The black moths produced black offspring, therefore the city population became
mainly black. The black peppered moth adapted to the city environment.
 In country (rural) areas, the air was cleaner and the trees were lighter. This made
the white peppered moths harder to see , the black moths were all eaten and so the
population became nearly all white as only white moths were breeding in these
areas. Now the white moths were better adapted to these areas.
Peppered Moth
Which picture is from which area?
- City?
- Country?
Peppered Moth
In England in 1850 the dark form of the moth
was virtually unknown. The map below
shows the distribution of the moth in
England in 1950.
1. What basic change occurred to the habitat
of the moth during the years following 1850?
2. How did this change affect the light form
of the moth?
3. Explain why (using the steps of natural
selection) the number of dark moths
increased dramatically from 1850 to 1950.
Use this to help you describe the steps of Natural
Selection with ‘Peppered Moths’ during the industrial
revolution. List each step and refer to example.
Sequence of events in natural selection
 1) Variation exists in a population (often due to mutation)
 2) A selection pressure occurs (specify what it is)
 3) Those with a favourable phenotype (specify what it is) will
be selected for, unfavourable phenotypes (specify what it is)
are selected against.
 4) Those with the favourable phenotype are more likely to
survive long enough to reproduce and passing on these
favourable genes to their offspring , so the next generation
will be genetically more like them and better adapted to the
environment. (what was the favourable phenotype)
Text Book Review (p83):
 Questions:
 1-3
Group Task - Poster
 Create a poster showing the different steps of evolution
through natural selection. Using YOUR OWN example
 Eg:
 Organisms:
 2 different phenotypes
 Environment:
 What are the conditions these organisms need to live in?
 Eg. The moths lived in a very polluted area in the city
 Selection Pressure:
 One that benefits one organism over another
Speciation and Evolution
The theory of evolution by
natural selection proposes
that all species are related.
Some species more closely
related than others, but
ultimately all life should be
able to be traced back to one
original species.
 A change in species is
usually due to some form
of isolation from an
original population
Speciation
It is impossible to tell whether two organisms are the same
species just based on their anatomy.
 There are now tests to determine a species, this is called
speciation.
 Speciation is the process by which one species splits into two
or more separate species.
 The process of speciation occurs in three steps:
 Variation
 Isolation
 Selection
Three Steps of Speciation
 Variation: there must be variation in the population.
 Isolation: This means that different groups must be prevented from
interbreeding, this stops any differences from one population
reaching the other population
 How might this happen?
 Selection: Natural selection affects the genotype and causes
changes (mutations) that prevent the groups breeding even if they
got back together.
RATS, RATS, RATS
Evidence for evolution
 The theory of evolution through natural selection is strongly
supported by a great deal of evidence.




Fossils
Comparative anatomy
DNA and protein structure
Embryology
What types of evidence?
Fossils
 Early fossils indicate organisms were fairly simple compared to
later fossils, which are more complex.
 Infers alleles and genes have developed from existing genes
(mutations)
 Can use the location of the fossil to help determine how old the
organism is. (stratification) – not absolute
 Shows increased diversity (due to speciation?)
Comparative Anatomy
 Compares the structures of organisms of both living species
and fossils.
 If they look the same – they may be from the same family
 Eg. Homology (strong evidence vertebrates evolved from one
ancestor.
 Pentadactyl Limb
DNA & Protein Structure
(Comparative)
 All living things have the same basic DNA structure
 4 bases (G, T, A, C)
 Proteins made from same amino acids
 If we compare the DNA of one organism (a particular
section/gene) with the DNA of another one, we can see where
there are key differences.
 Eg. Chimpanzee and Humans have 96% of genes identical to each
other.
 DNA can be compared using a special process which heats and
cools down the DNA strand to see if they will stick together in
their complementary bases. If they come apart in sections
(there is no match). Eg. C-G, T-A.
Embryology
 The study of the
development, structure and
function of embyro’s.
 Comparison of vertebrate
embryos show similarities in
the stages of their
development.
Human Evolution
 The name of our species “homo sapiens” means the “wise
man.”
 According to fossils we have been around for about
200,000 years.
 Fossils indicate other human-like species have existed too.
Primates, Hominids and Hominins
 Primates include lemurs, monkeys,
apes, gibbons and humans.
 To be classified in this species the
organism must have “grasping hands,
nails rather than claws and forward
facing eyes”
 Hominids include apes, chimps and
humans. (no tail)
 Hominins are humans and their
common ancestors. There are key
differences which show how different
Humans now are from their original
primate ancestors.
How structures have changed….
 Humans are now a ‘sub-tribe’ as they have the ability to walk on 2 legs
(known as bipedalism)
 Their ability to walk upright, is due to the evolution of key structural
components:
 Skull
 Size
 Jaw shortens
 location of foramen magnum




Vertebral Column (S Shaped)
Pelvis (wider)
Femur (angled inwards)
Feet (flat)
Out of Africa
 The theory that a common ancestor of all modern humans
evolved in EAST AFRICA.
 A Sub-group then left Africa and ended up colonising the
whole Earth.