5.1 - Evidance for evolution

Question 1

Essential idea:

Answer 1

There is overwhelming evidence for the evolution of life on Earth

Question 2

Evolution:

Answer 2

The cumulative change in the heritable characteristics of a population

Question 3

Cumulative change:

Answer 3

many small changes over many generations

Question 4

Heritable characteristics:

Answer 4

gene controlled factors passed on from parent to offspring

Question 5

Population:

Answer 5

a group of organisms of the same species living in the same area at the same time

Question 6

Evidence for evolution:

Answer 6

fossil record, selective breeding, homologous structures

Question 7

The Fossil Record

Answer 7

As layers of sedimentary rock are put down, the inorganic components of plants, animals and prokaryotes are preserved
The deeper they are, the older they are

A fossil is the preserved remains or traces of any organism from the remote past
Fossil evidence may be one of two types:
Direct (body fossils) such as bones, teeth, shells, leaves, etc.
Indirect (trace fossils) such as footprints, tooth marks, tracks, burrows, etc.

The fossil record is the sum of all discovered and undiscovered fossils and their relative placement in rock.
The fossil record provides the dimension of time to the study of evolution – the layer of rock in which a fossil is found can be dated and therefore used to deduce the age of the fossil.

Question 8

There are gaps in the fossil record due to:

Answer 8

Special circumstances are required for fossilization to occur
Only hard parts of an organism are preserved
Fossils can be damaged so that only fragments remain to be discovered

The fossil record clearly shows changes (in characteristics) of organisms
Fossils show a chronological (time) sequence in which characteristics appear and develop in complexity
Fossils have been discovered of many types of organism that no longer exist, e.g. trilobites and dinosaurs.
In most cases no fossils can be found
of organisms that do exist today.
This suggests that the ancestral species evolved into the modern species

Question 9

Transitional fossils

Answer 9

Transitional fossils show the links between groups or species by exhibits traits common to both the ancestral group/species and its derived descendant group/species.
Archaeopteryx is a famous example transitional fossils – it gives evidence for the evolution of birds from dinosaurs.
Dinosaur features include:
jaws with sharp teeth
three fingers with claws
long bony tail
Bird features:
feathers

Question 10

5.1.U3 Selective breeding of domesticated animals shows that artificial selection can cause evolution.

Answer 10

Selective breeding (also called artificial selection) is the process by which humans breed animals and plants for particular traits that are suitable for human uses
Examples:
Breeding dogs for herding, e.g. sheepdogs or racing, e.g. greyhounds
Cows are bred for milk yield or meat
Crops have been bred for increased yield and/or disease resistance
Crops have been bred for size, taste and aesthetics
e.g corn

Question 11

5.1.U3 Selective breeding of domesticated animals shows that artificial selection can cause evolution.

Answer 11

Domestic breeds show great variation compared to wild populations subject to only natural variation.
Populations show variation in traits
Individuals which do not show the desired traits are not allowed to breed.
Individuals which show the most desirable traits are chosen to breed together.
The next generation will have an increased frequency of the desired trait.
The process is repeated for many generations until the entire population shows the desired trait
Artificial selection can result in evolution occurring over a relatively short period of time in comparison to geological time

Question 12

5.1.U4 Evolution of homologous structures by adaptive radiation explains similarities in structure when there are differences in function.

Answer 12

Comparative anatomy of groups of animals or plants shows certain structural features are basically similar. Structures or anatomical features having similar basic structure as in other species said to be homologous.

Homologous structures are those that are similar in shape in different types of organisms
The structural similarities imply a common ancestry
homologous structures used in different ways in different species
This illustrates adaptive radiation since the basic structure adapted to different niches
The more exclusive the shared homologies the closer two organisms are related.

Question 13

5.1.A2 Comparison of the pentadactyl limb of mammals, birds, amphibians and reptiles with different methods of locomotion.

Answer 13

The pentadactyl limb in vertebrates is an example of a homologous structure
It is adapted to different mode of locomotion in particular environment.
dolphin fin for swimming
bat wing for flying
monkey hand for grasping
horse hoof for galloping

Question 14

5.1.U5 Populations of a species can gradually diverge into separate species by evolution.

Answer 14

If populations, e.g. fruit flies, become separated (e.g. a population is blown by a storm to a distant island). Then it is very likely the population will experience different ecological conditions.
Over many generations the shape of the flies, food preference, mating rituals etc. will likely diverge as the result of natural selection.
If the island fruit flies migrate back to the mainland they will not easily mate with the mainland flies as:
Mating rituals are different
Because of genetic differences the resulting offspring are infertile
Because genes cannot flow between the populations the island fruit flies are said to have evolved into separate species (this process is called speciation).

There are many examples of speciation.
Darwin famously used the example of the finches on the Galapagos islands.
Speciation often occurs after a population of a species extends its range by migrating to an island
Endemic species – populations of organisms that only exist in one geographic location

Question 15

5.1.U6 Continuous variation across the geographical range of related populations matches the concept of gradual divergence.

Answer 15

The Red Grouse and the Willow Ptarmigan were at one time classified as two separate species. The current scientific consensus is that they are both members of the same species (Lagopus lagopus)
It is a common problem in classification to determine when two populations of one species have sufficiently diverged to become two separate species.
Populations will gradually diverge over time and it is natural to see continuous variation across a geographical range.
The greater the geographical separation and the longer the populations have been separated the greater the divergence.

Question 16

5.1.A1 Development of melanistic insects in polluted areas.

Answer 16

Variation: Peppered moths (Biston betularia) moths are found in two forms:
carbonaria and insularia
The dark form (carbonaria) is normally very rare.
Normal environment: In unpolluted areas tree branches are covered in pale coloured
lichens camouflage for the paler form (insularia).
The moths fly at night to try to find a mate, but, during the day they rest on the branches of trees.
Selective pressure: Predation from birds (and other animals) whilst resting
Environmental change: sulphur dioxide pollution kills the lichens and soot (from coal burning) blackens the tree branches.
Result: the dark moths are well camouflaged from birds against dark tree branches are many survive to reproduce, but light coloured moths are easily found and predated by birds, few survive to reproduce.
Evolution: over a number of generations the dark (carbonaria) form of the peppered moth has increased with frequency - the heritable characteristics of the population have changed.