Evolution by Natural Selection

Question 1

What is a Hypothesis?

Answer 1

Hypotheses: a possible explanation for an observation

Question 2

What is a Theory?

Answer 2

Theory: an explanation for something that has been
observed in nature which can be supported by facts,
generalizations, tested hypotheses, models and laws.

Question 3

What is the theory of evolution / theory of “descent with

modification”?

Answer 3

Theory of evolution: all things that we see today arose

from things that existed in the past but they look different because things change over long periods of time.

Question 4

What is biological evolution?

Answer 4

changes in living things over long periods of time.

Question 5

Definition of species

Answer 5

group of similar organisms that are able to

interbreed and produce fertile offspring.

Question 6

Definition of population

Answer 6

the sum of organisms of the same species

occupying the same habitat at the same time and having the ability to interbreed.

Question 7

Definition of variation

Answer 7

small differences that exist between individuals of

the same species or population.

Question 8

What is a mutation?

Answer 8

change the structure of a gene → altered

genotype → altered phenotype

Question 9

Sources of variation - small differences that exist between individuals of the same species or population.

Answer 9

1. Mutations: change the structure of a gene → altered
   genotype → altered phenotype
2. Variation due to meiosis:
   - Crossing over: during P1, the homologous chromosomes swap a segment of DNA.
   - Random arrangement of chromosomes: during M1 and M2. Chromosomes arrange randomly at the equator of the cell.
3. Random fertilization of gametes: egg and sperm cells produced by meiosis are all different so random
   fertilization results in different combinations of genetic
   material in offspring.

Question 10

Types of variation: continuous variation

Answer 10

There are a range of different phenotypes for a particular characteristics. E.g. height

• Brought about by many genes working together (polygenic inheritance)
• Environment can affect the appearance of characteristics.
• When plotted on a bar graph – you see a bell-shaped, normal distribution curve is produced.

Question 11

Types of variation: discontinuous variation

Answer 11

There is no range of different phenotypes for a particular characteristic.

• The characteristic is either present or not. E.g. blood groups (you can either be one blood group or another, there is no in-between phenotype).
• Usually controlled by alleles of a single gene.
• Environment has little effect on this type of variation.

Question 12

Who created the theory Lamarckism?

Answer 12

Jean-Baptiste Lamarck

Question 13

What are the 2 main ideas/laws of Lamarck – theory of transformation:

Answer 13

1. Law of use and disuse: organs are modified or adapted according to how frequently they are used. If they are used more frequently, they become larger and if an organ is disused, it became smaller
   until it totally disappeared.
2. Law of inheritance of modified or acquired characteristics: the modifications brought about by the use or disuse were able to be transmitted to their offspring.

Question 14

Rejection of Lamarck’s theories

Answer 14

• Organisms can’t choose to evolve, changes take place randomly.
• There is little evidence to support the idea that changes brought about by adaptation to the environment are inherited from parent to offspring.

Question 15

Who created the theory of evolution by natural selection, Darwinism?

Answer 15

Charles Darwin

Question 16

What observations and assumptions is Darwinism based on?

Answer 16

1. Variation: there is variation in appearance and abilities of organisms within every species.
2. Offspring: species produce a large number of offspring but they don’t all survive.
3. Competition: organisms compete for limited resources.
4. Genetics: Organisms pass their genes on to their offspring.
5. Natural Selection: Organisms with the most beneficial traits are more likely to survive and reproduce.

Question 17

Why is Darwin’s theory referred to as phyletic

gradualism/gradualism sometimes?

Answer 17

because evolution occurs gradually and uniformly over long periods of time.

Question 18

What is punctuated equilibrium?

Answer 18

organisms don’t undergo any changes for a long period of time (stasis). Then, suddenly, the species undergo a rapid change over a short period of geological time → a new species.

Question 19

Could rapid change occur over short periods of time?

Answer 19

YES – when natural selection is strong, rapid

and substantial evolutionary changes can occur.

Question 20

What is natural selection?

Answer 20

the process whereby organisms better adapted to their environment tend to survive and produce more offspring.

Question 21

Why would species experience long periods of stasis

without changing?

Answer 21

Stasis is possible when environment does not
change or when changes in the environment oscillate
back and forth. When species shift their geographical
ranges, stasis is also possible.

Question 22

Definition of Speciation?

Answer 22

formation of a new species

Question 23

Types of Speciation

Answer 23

1. Allopatric speciation

2. Sympatric speciation

Question 24

1. Allopatric speciation (speciation by geographical isolation)

Answer 24

⚫ When a population becomes separated into 2
sub-populations by a geographic barrier (isolation such
as a mountain or river). Each sub-population develops
into a new species.
⚫ The 2 populations become genotypically and
phenotypically different from each other. These
differences may prevent interbreeding even if they mix.
⚫ One or both populations may become a new species.

Question 25

Describe how allopatric speciation occurs
when a population becomes separated by a
geographical barrier.

Answer 25

⚫ The population will split up into two groups
⚫ and each group adapts to the new environmental factors/develops separately
⚫ each group undergoes natural selection independently
⚫ Develops differently
⚫ each group may become genotypically
⚫ and phenotypically different
⚫ which might prevent them from interbreeding /become reproductively isolated leading to the formation of a new species.

Question 26

Mechanisms of sympatric speciation (reproductive isolation)

Answer 26

⚫ Habitat isolation: if 2 closely related species live in
different habitats, there is a reduced chance that they will meet and reproduce.
⚫ Temporal isolation: if 2 species breed at different times (seasons) of the year.
⚫ Species-specific courtship behaviour: some animals have specific courtship behaviours that do not attract individuals of other species.
⚫ Prevention of fertilizations: different species may have different copulation organs.
⚫ Adaptation to different pollinating agents: some plants can have different structures that will attract different pollinators therefore preventing cross-pollination.
⚫ Hybrid infertility: some closely related species may mate and produce viable offspring but the offspring will be infertile.

Question 27

5 pieces of evidence of evolution:

Answer 27

1. Paleontology
2. Evidence from comparative anatomy/modification by descent
3. Evidence from biogeography
4. Evidence from molecular biology and genetics
5. Evidence from comparative embryology
   (on slides for in depth)

Question 28

Artificial selection/selective breeding.

Answer 28

The breeding of plants and animals for desirable

characteristics.

Question 29

Difference between natural selection and artificial selection?

Answer 29

Similar to natural selection, but in NS, the characteristics selected are those that are best suited for the environmental conditions, in artificial selection, humans determine the selected traits.

Question 30

How does variation occur due to meiosis?

Answer 30

• Crossing over: during P1, the homologous chromosomes swap a segment of DNA.
• Random arrangement of chromosomes: during M1 and M2. Chromosomes arrange randomly at the equator of the cell.

Question 31

How does variation occur due to Random fertilization of gametes?

Answer 31

The egg and sperm cells produced by meiosis are all different so random
fertilization results in different combinations of genetic
material in offspring.

Question 32

What are the types of variation:

Answer 32

continuous and discontinuous

Question 33

Why do we study variation?

Answer 33

If there is variation within a species, a particular
phenotype for a characteristic may allow an organism to be better adapted to the prevailing environmental
conditions than an alternative phenotype.

Question 34

Differences between Lamarck’s and Darwin’s theory

Answer 34

table on slide

Question 35

What is period of stasis?

Answer 35

Fossils show long periods of time where

species did not change. e.g. Coelacanth is regarded as a species in stasis.

Question 36

What is Habitat isolation:

Answer 36

if 2 closely related species live in different habitats, there is a reduced chance that they will meet and reproduce.

Question 37

What is Temporal isolation:

Answer 37

if 2 species breed at different times

(seasons) of the year.

Question 38

What is Species-specific courtship behaviour:

Answer 38

some animals have specific courtship behaviours that do not attract individuals of other species.

Question 39

What is the Prevention of fertilisation:

Answer 39

different species may have different copulation organs.

Question 40

What is hybrid infertility:

Answer 40

some closely related species may mate
and produce viable offspring but the offspring will be
infertile.