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