5.1 Evidence for evolution Flashcards
When does evolution occur?
When heritable characteristics of a species change
What is the difference between acquired characteristics and heritable chracteristics?
Acquired characteristics develop during the lifetime of an individual
Heritable characteristics are passed from parent to offspring
What is the mechanism of evolution?
Natural selection
What are the 3 types of evidence for evolution?
- Fossil record
- Selective breeding
- Homologous structures
How were geoogical eras named?
The sequence in which layers or strata of rock were deposited was worked out and the geological eras were named
What did the strata of rock tell us?
The fossils found in the various layers were different - there was a sequence of fossils.
What reliable method confirmed that various layers of rock were different.
Radioisotope dating revealed the ages of the rock strata and of the fossils in them.
What is strata? What does it represent?
Layer of rock
Each strata represents a variable length of time that is classified according to a geological time scale (eons, eras, periods)
What does the sequence in which fossils appear matches matches?
The sequence in which they would be expected to evolve
What are some selection pressures (5)?
Disease, altitude, drought, predator, climate change
What are the 4 stages of fossilization?
- Death and decay - soft body parts are decomposed or scavenged, leaving only the heard body remains
- Decomposition - The hard remains are rapidly covered with silt and sand, and over time more layers continue to build
- Permineralisation - Pressure from the covering layers of dirt/rock cause the hard organic material to be replaced by minerals
- Erosion/exposure - Movement of earth plates may displace the fossil and return it to the surface for discovery
What are the conditions for fossils to form?
- Pressure - promote permineralisation
- Anoxic conditions - prevent decompositions by decomposers
- Hard body parts - soft body parts wont fossilise
- Body parts have to be preserved - protected against predators, damage etc
- Time
What is a fossil record and what does it show?
Fossil record: The totality of fossils, both discovered and undiscovered
- The fossil record shows that over time changes have occurred in the features of living organisms (evolution)
What is the law of fossil succession?
This chronological sequence of complexity by which characteristics appear to develop is known as the law of fossil succession
Why is the fossil record so incomplete
- Very difficult for fossils to form because they require specific conditions
- May lie undiscovered
- May be disrupted e.g. predators, earthquakes, earth’s movement (movement of rock layers raise some parts but not some other parts) volcano etc.
What is selective breeding/artificial selection?
repeatedly selecting for and breeding the individuals most suited to human uses.
Humans decide which traits are favourable as opposed to nature
How does selective breeding/artificial selection provide evidence for evolution?
Provides evidence of evolution as targeted breading can show significant variation in a (relatively) short period
* Also shows that it is effective
What does selection show but not prove?
Shows that selection can cause evolution but it does not prove that evolution of species has actually occurred natrually, or that the mechanism for evolution is natural selection
What are homologous structures and analogous structures?
Homologous: A structure that appears superficially different (and may perform different functions) in different organisms, but has the same underlying structure
Analogous: Features adapted to perform the same function but have a different structure
What does analogous and homologous structures provide evidence for?
Analogous structures provide evidence for convergent evolution
Homologous structures provide evidence for adaptive radiation
What is convergent evolution and adaptive radiation?
Convergent evolution: Different origins and have become similar because they perform the same or a similar function
Adaptive radiation: Same origin, and they have become different because they perform different functions
What are vestigial organs?
Reduced structures that serve no function
How are vestigial organs explained by evolution?
These structures are easily explained by evolution as structures that no longer have a function and so are being gradually lost
What does it mean when a two populations of the same species have undergone speciation?
They become so genetically different that they can no longer interbreed and produce fertile offspring. They have undergone speciation and formed two new species.
