5.1 Flashcards
What is evolution
The cumulative change of heritable characteristics of a population over time
What is a fossil
A fossil is the remains of or impression of a prehistoric organism that has been embedded in rock & preserved in petrified form
Explain how fossils may form
- a dead organism falls to the bottom of a sea or lake and doesn’t decay (due to lack of oxygen)
- the remains become buried under layers of sediment & become replaced by minerals
- the gardener remains become compressed in layers of sedimentary rock
- land movement & erosions may bring the fossilised remains to the surface millions of years later
outline the evidence for evolution provided by fossils
- fossils of many types of organisms that no longer exist have been discovered, yet these organisms share features with existing organisms. this suggests that they may have common ancestors with existing organisms & shows how they have change over time (evolution)
- rocks can be dated to deduce the age of fossils within them. the sequence in which organisms appear in the fossil record shows increase in complexity over time
- many sequences of fossils are known which link together existing organisms with their likely ancestors
What is artificial selection
process by which plants and animals used by humans have been derived from wild organisms by breeding for desirable traits
how is selective breeding carried out
- the desired traits is identified in male and female organism
- they are bred together to produce the next generation
- the male and female offspring with the best of the desired trait are bred together
- this is repeated over many generations
outline the evidence for evolution by artificial selection
- artificial selection provides evidence that evolution happens by accumulations of small changes over time
- it provides evidence that these changes are inherited by the next generation
- although it’s quicker than natural selection it still require many generations (time consuming)
BUT: driving force for artificial selection is human choice, not the natural environment
what are homologous structure and give an example
- structures in different species which have a similar fundamental structure (and develop in a similar way) due to a common ancestor
- however, they may not necessarily have the same function
eg. pentadactyl limbs of vertebrates
what are analogous structures and give an example
- structures in different species which have the same function
- but they have a different underlying structure because they have evolved separately from different ancestors
eg. wings of bats and butterflies
what is adaptive radiation
- is when a population with the same common ancestor spreads to different environments with different selection pressures & they therefore adapt to their environments in different ways
—> produces homologous structures
comparison of the pentadactyl limb and reptiles with different methods of locomotion
cat leg:
- used for walking and running
- long bones (tibia & fibula) helps transfer force to ground when running fast
—> allows for long strides
dolphin flipper:
- used for swimming
- elongated phalanges to increase SA
- short and thick radius and ulna to withstand force of water
bat wing:
- used for flying
- thin bones (& long phalanges)
- decreases weight of bones this lighter for flying
what happens when two populations become separated and how does this happen
- two populations cannot interbreed due to geographical isolation
eg:
- tectonic plate movement & continental drift
- reduction in water level separating sea/lake
- formation of mountain ridge
-melting of a glacier
what happens when two previously geographically isolated populations merge
- the environmental conditions of the two separate locations may be different
- so the separated populations evolve in different ways to become adapted to different conditions
- their characteristics will gradually diverge
- this may mean that if the two populations come back together they cannot interbreed
—> SPECIATION HAS OCCURED
if populations gradually diverge over time to become different species then what would we expect to find
continuous variation across geographical range of related populations matches the concept of gradual divergence
- examples of the different stages of divergence should be present across a geographical range
eg. Galapagos finches
how does continuous variation between populations provide evidence for evolutions?
- disproved the belief that species were created as distinct types of organisms
- shows that there is constant change in the characteristic of species
- provides evidence for the evolution of new species
