5.1 Evidence for evolution Flashcards
What is evolution?
-The cumulative change in the heritable characteristics of a population
How are heritable factors transferred between generations?
-Heritable characteristics are encoded for by genes and may be transferred between generations as alleles
-Hence, biological evolution describes cumulative changes that occur within a population between one generation and the next
When does something provide evidence for evolution?
When it demonstrates a change in characteristics from an ancestral form.
How do fossil records provide evidence for evolution?
By revealing the features of an ancestor for comparison against living descendants
What is a fossil and how does it form?
-A fossil is the preserved remains or traces of any organism from the remote past
-Preserved remains (body fossils) provide direct evidence of ancestral forms and include bones, teeth, shells, leaves, etc.
-Traces provide indirect evidence of ancestral forms and include footprints, tooth marks, burrows and faeces (coprolite)
What is the fossil record and what does it show?
-The totality of fossils, both discovered and undiscovered, is referred to as the fossil record
-The fossil record shows that over time changes have occurred in the features of living organisms (evolution)
How can fossils be dated?
-Fossils can be dated by determining the age of the rock layer (strata) in which the fossil is found
-Sedimentary rock layers develop in chronological order, such that lower layers are older and newer strata form on top
-Each stratum represents a variable length of time that is classified according to a geological time scale (eons, eras, periods)
What is the law of fossil succession?
-Different kinds of organisms are found in rocks of particular ages in a consistent order, indicating a sequence of development
-Prokaryotes appear in the fossil record before eukaryotes
-Ferns appear in the fossil record before flowering plants
-Invertebrates appear in the fossil record before vertebrate species
-This chronological sequence of complexity by which characteristics appear to develop is known as the law of fossil succession
-This ordered succession of fossils suggests that newer species likely evolved as a result of changes to ancestral species
Explain why the fossil record is incomplete
-While fossils may provide clues as to evolutionary relationships, it is important to realize that the fossil record is incomplete
-Fossilisation requires an unusual set of specific circumstances in order to occur, meaning very few organisms become fossils
-Only the hard parts of an organism are typically preserved, meaning usually only fragments of remains are discovered
-With limited fossil data, it can be difficult to discern the evolutionary patterns that result from ancestral forms (‘missing links’)
What is the significance of transitional fossils?
-Transitional fossils demonstrate the intermediary forms that occurred over the evolutionary pathway taken by a single genus
-They establish the links between species by exhibiting traits common to both an ancestor and its predicted descendants
-An example of a transitional fossil is archaeopteryx, which links the evolution of dinosaurs (jaws, claws) to birds (feathers)
-As new fossils are discovered, new evolutionary patterns are emerging and old assumptions are challenged
Picture of a transitional fossil- the archaeopteryx
Give an example of how fossils provide evidence
-This can be established by comparing hominin skeletons
-Australopithecus is an early hominin ancestor that first appears in the fossil record approximately 4 million years ago
-Comparing these fossils to the bone structure of modern man (Homo sapiens) demonstrates key evolutionary changes
-These evolutionary trends (from Australopithecus to Homo sapiens) include:
Diagram comparing hominin fossils
What is selective breeding?
A form of artificial selection, whereby man intervenes in the breeding of species to produce desired traits in offspring.
How does selective breeding provide evidence for evolution?
-By breeding members of a species with a desired trait, the trait’s frequency becomes more common in successive generations
-Selective breeding provides evidence of evolution as targeted breeds can show significant variation in a (relatively) short period
Give an example of selective breeding
-Dog breeds show an enormous amount of variety due to the targeted selection of particular traits by man
-Hunting dogs (e.g. beagles) were typically bred to be smaller in stature so as to enter fox holes
-Herding dogs (e.g. sheep dogs) were bred for heightened intelligence in order to follow herding commands
-Racing dogs (e.g. greyhounds) were specifically bred to be sleek and fast
-Toy dogs (e.g. chihuahuas) were selectively bred for their diminutive size
Diagram showing selective breeding of plants and dogs
Give other examples of selective breeding
-Breeding egg-laying hens to lay lots of eggs
-Breeding racehorses for speed
-Breeding dogs for herding, hunting, or simply for specific physical features
-Breeding cattle for increased meat or milk production
-Breeding of crops to be disease- or cold-weather-resistant in order to increase production
-Breeding of plants to produce larger and sweeter fruits.
___ occurs on a small scale within a species.
Microevolution
What does the comparative anatomy of groups of organisms show?
-Certain structural features that are similar, implying common ancestry
-Anatomical features that are similar in basic structure despite being used in different ways are called homologous structures
-The more similar the homologous structures between two species are, the more closely related they are likely to be
What do homologous structures illustrate?
Adaptive radiation, whereby several new species rapidly diversify from an ancestral source, with each new species adapted to utilise a specific unoccupied niche
Describe the pentadactyl limb in a variety of different animals
-A classical example of homologous structures is the pentadactyl limb in a variety of different animals
-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
Diagram showing the pentadactyl limb in different animals
Genetic variation within a population of a given species will typically be ___
Continuous
What type of curve will genetic variation in a population of a given species follow?
A normal distribution curve as the rate of change is gradual and cumulative
What will happen if two populations of a species become geographically separated?
-They will likely experience different ecological conditions
-Over time, the two populations will adapt to the different environmental conditions and gradually diverge from one another
What factors affect the degree of divergence between populations that have become separated?
-It will depend on the extent of geographical separation and the amount of time since separation occurred
-Populations located in close proximity that separated recently will show less variation (less divergence)
-Distant populations that separated a longer period of time ago will show more variation (more divergence)
The degree of divergence between geographically separated populations will gradually increase the ___
Longer they are separated
Explain how time increases the degree of divergence between geographically separated populations
-As the genetic divergence between the related populations increase, their genetic compatibility consequently decreases
-Eventually, the two populations will diverge to an extent where they can no longer interbreed if returned to a shared environment
What is speciation?
-When two populations can no longer interbreed and produce fertile, viable offspring they are considered to be separate species
-The evolutionary process by which two related populations diverge into separate species is called speciation
Diagram showing speciation via divergent evolution
What is industrial melanism?
The change in the melanin-producing allele frequency from light to dark due to environmental changes brought on by industrial pollution.
What is transient polymorphism?
The gradual change in the allele frequency of a population due to the slow replacement of one gene of another.
What is balanced polymorphism?
A balance between both forms of the allele variations within a population.
Explain how the presence or lack of pollution affects the frequency of peppered moths in an environment
-Peppered moths (Biston betularia) exist in two distinct polymorphic forms – a light coloration and a darker melanic variant
-In an unpolluted environment, the trees are covered by a pale-colored lichen, which provides camouflage for the lighter moth
-In a polluted environment, sulfur dioxide kills the lichen while soot blackens the bark, providing camouflage for the dark moth
Pictures of peppered moth variants in an unpolluted and polluted environment
Explain how the frequency of the two different forms of the peppered moth is dependent on the environment and evolves as conditions change
-Before the industrial revolution, the environment was largely unpolluted and the lighter moth had a survival advantage
-Following the industrial revolution, the environment became heavily polluted, conferring a survival advantage to the darker moth
-Recent environmental policies in Europe are reducing pollution levels, altering the frequency of the two populations once again
Diagram showing the evolution of the peppered moth in a polluted environment
The following question refers to the figure below which shows a sedimentary rock with strata labeled i to iv (i is the most recent, and iv is the oldest layer or stratum).
If fossils from species A are located in stratum iv and it has descendants in all other strata, in which stratum would you expect to find the descendants that were the first to evolve from species X?
iii
The strata are numbered from newest (i) to oldest (iv). It takes a significant period of time for a new stratum to form, which is enough time for species X to evolve into new species. Therefore, stratum iii is likely to contain fossils of descendents that first evolved from species X (call the new species Y). Stratum ii is likely to have descendents that have evolved from species Y to create a new species Z. However, these are further away evolutionarily from X than are Y and were not the first species to evolve from X.
Fossils that show links between ancestral groups are known as ______
Transitional
Bats and cats both have forelimbs adapted for moving.
Whales (mammals) and sharks (fish) have fins adapted for swimming.
What term best describes the relationship of the bones in the forelimbs of bats and cats, and what term best describes the fins of whales and sharks?
Homologous; analogous
The forelimbs of bats and cats are forms of the pentadactyl limb and are good examples of a homologous structure. Fins in whales and sharks do not share an ancestor and this is a good example of an analogous structure.
