5.1 Evidence for evolution Flashcards
What is evolution?
Evolution occurs when heritable characteristics of a species change by natural selection.
What is the evidence for evolution?
FOSSILS
- In the 20th century, reliable methods of radio isotope dating revealed the ages of the rock strata and of the fossils in them.
- The sequence in which the fossils appear matches the sequence in which they would be expected to evolve.
- The sequence also fits with the ecology of the groups with plant fossils appearing before animals.
- Many sequences of fossils are known which link together existing organisms with their likely ancestors.
EVIDENCE FROM SELECTIVE BREEDING
- Selective breeding of domesticated animals shows that artificial selection can cause evolution.
- Humans have deliberately bred and used particular animal species for thousands of years. If modern breeds of livestock are compared to the wild species that they most resemble. This shows that the change has been achieved simply by repeating selecting for and breeding the individuals most suited to human uses.
EVIDENCE FROM HOMOLOGOUS STRUCTURES
- Homologous structures are structures that may look superficially different and perform a different function but they have the same evolutionary origin and they have become different because they perform different functions.
- They do not prove that organisms have evolved or had common ancestry and do not reveal anything about the mechanism of evolution but they are difficult to explain without evolution.
- Particularly interesting are the functions that Darwin called “rudimentary organs” - reduced structures that serve no function, like the appendix found in humans. These structures are easily explained by evolution as structures that no longer have a function and so are being gradually lost.
FROM PATTERNS OF VARIATION
- Continuous variation across the geographical range of related populations matches the concept of gradual divergence.
- If populations gradually diverge over time to become separate species then at any one moment we would expect to be able to find examples of all stages of divergence and we can. This provides evidence for the evolution of species, because they are similar, we can trace that they moved and then they changed to adapt to conditions.
What is the evidence for evolution from fossils?
FOSSILS
- In the 20th century, reliable methods of radio isotope dating revealed the ages of the rock strata and of the fossils in them.
- The sequence in which the fossils appear matches the sequence in which they would be expected to evolve.
- The sequence also fits with the ecology of the groups with plant fossils appearing before animals.
- Many sequences of fossils are known which link together existing organisms with their likely ancestors.
What are analogous structures?
These are structures that look very similar but when we study them closely we realise they are very different. An evolutionary explanation is that they become similar because they perform the same of similar function. This is called convergent evolution.
What is convergent evolution?
In evolutionary biology, convergent evolution is the process whereby organisms not closely related (not monophyletic), independently evolve similar traits as a result of having to adapt to similar environments or ecological niches.
What is the evidence for evolution from selective breeding?
- Selective breeding of domesticated animals shows that artificial selection can cause evolution.
- Humans have deliberately bred and used particular animal species for thousands of years. If modern breeds of livestock are compared to the wild species that they most resemble. This shows that the change has been achieved simply by repeating selecting for and breeding the individuals most suited to human uses.
Selective breeding is the process used by breeders to develop a plant or animal over time with desired characteristics.
Selective breeding has produced thousands of different crops, pets and farm animals that did not exist in nature.
Selective breeding provides evidence for natural selection because it shows that ‘selection’ can indeed lead to “cumulative change in the heritable characteristics of a population”.
Selective breeding is called ‘artificial selection’ by biologists because it works by the same genetic process as ‘natural selection’. The only difference is that in artificial selection it is not nature but humans influencing the evolution of a particular species.
What are homologous structures?
Homologous structures are structures that may look superficially different and perform a different function but they have the same evolutionary origin and they have become different because they perform different functions.
What is the evidence for evolution from homologous structures?
- Homologous structures are structures that may look superficially different and perform a different function but they have the same evolutionary origin and they have become different because they perform different functions.
- They do not prove that organisms have evolved or had common ancestry and do not reveal anything about the mechanism of evolution but they are difficult to explain without evolution.
- Particularly interesting are the functions that Darwin called “rudimentary organs” - reduced structures that serve no function, like the appendix found in humans. These structures are easily explained by evolution as structures that no longer have a function and so are being gradually lost.
Structures derived from the same body part of a common ancestor are called homologous structures. One example of a homologous structure is the pentadactyl limb, which is an appendage comprised of five bones.
The pentadactyl limb is shared by virtually all vertebrate species (other than fish). Pentadactylism is not the ideal bone arrangement for each species; it’s just something that they are stuck with.
Do all vertebrates have a pentadactyl limb because they were created that way? Or is the pentadactyl limb evidence that all the vertebrates descended from a common ancestor?
According to evolutionists, it is inconceivable that an intelligent creator would apply the pentadactyl design to animals as different as birds, horses, and whales because the functions of their limbs are so starkly different. Such similarity does make sense, however, if the different species evolved from a common ancestor, and modified their limbs over time.
Compare the structure of the pentadactyl limb?
Mammals, birds, amphibians and reptiles all share a similar arrangement of bones in their appendages based on a five-digit limb
Despite possessing similar bone arrangements, animal limbs may be highly dissimilar according to the mode of locomotion:
Human hands are adapted for tool manipulation (power vs precision grip)
Bird and bat wings are adapted for flying
Horse hooves are adapted for galloping
Whale and dolphin fins are adapted for swimming
What is speciation?
Populations of a species can gradually diverge into separate species by evolution. If two populations of a species become separated so that they do not interbreed and natural selection then acts on them differently they will evolve in different ways. The characteristics of the two populations will gradually diverge. If the populations then merge again but do not breed they have clearly formed two different species. This process is called speciation.
Speciation often occurs after a population of a species extends its range by migrating to an island.
What are melanistic animals?
Dark varieties of typically light coloured insects are called melanistic. The most common is the peppered moth. It has been widely used as an example of natural selection as the melanistic variety become commoner in polluted industrial areas where it is better camouflaged than the pale peppered variety.
What is industrial melanism?
Dark varieties of typically light coloured insects are called melanistic. The most common is the peppered moth. It has been widely used as an example of natural selection as the melanistic variety become commoner in polluted industrial areas where it is better camouflaged than the pale peppered variety.
Adult moths fly at night to find a mate and reproduce.
During the day they roost on the branches of trees.
Birds and other animals that hunt in the day eat the moths if they find them.
Unpolluted areas have tree branches covered in pale coloured lichens and the peppered moths are well camouflaged.
Sulfur dioxide pollution kills lichens and soot from coal burning blackens tree branches in polluted areas.
Melanic moths are well camouflaged against the dark tree branches in polluted areas. So over time the melanic peppered moth has placed the pale peppered moths. This is an example of evolution by natural selection.
