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