5.1 Evidence for Evolution Flashcards
Evolution is
the cumulative change in the heritable characteristics of a population over time
Cumulative change
small changes upon small changes over many generations
Heritable characteristics:
gene-controlled factors that are passed down from parents to offspring
Population:
not an individual
Evolution occurs by the mechanism of
natural selection
The fossil record is
the sum of all discovered and undiscovered fossils and their relative placement in rock
As scientists began studying layers (strata) of rocks
it became clear the layers closest to the top are most recent, and layers closer to the bottom are most ancient.
dating of rock layers and fossils was determined in the 20th century with
radioisotope dating - the fossil record provides the dimension of time to the study of evolution
fossil records as evidence for evolution
Sequence in which fossils matches sequence in which they would be expected to evolve
- Bacteria and simple algae first, then fungi, worms, etc.
Sequence fits with the ecology of organisms
- Plant fossils present before animals, plants on land before animals on land, plants suitable for pollination before insect pollinators
Fossils present that show the transition of ancient species into their present day descendants
Fossils show a chronological (time) sequence in which characteristics appear and develop in complexity
There are gaps in the fossil record due to:
Unideal conditions for fossilization
Only hard parts of organism are preserved
Damage of fossils leaving only fragments
Transitional fossils
show the links between groups or species by exhibits traits common to both the ancestral group/species and its derived descendant group/species.
Archaeopteryx
is a famous example transitional fossils – it gives evidence for the evolution of birds from dinosaurs.
Bird features:
feathers
Dinosaur features include:
jaws with sharp teeth
three fingers with claws
long bony tail
Selective breeding (also called artificial selection) is
the process by which humans breed animals and plants for particular traits
The effectiveness of artificial selection is shown by the considerable changes that have occurred in domesticated animals over
short periods of time
Domestic breeds show great variation compared to wild populations subject to only natural variation.
Examples:
Breeding dogs for herding, e.g. sheepdogs or racing, e.g. greyhounds
Cows are bred for milk yield or meat
Crops have been bred for increased yield and/or disease resistance
Selective breeding (also called artificial selection) is
the process by which humans breed animals and plants for particular traits
Domestic breeds show great variation
compared to wild populations populations subject to only natural variation.
Analogous structures are similar in function
but differ in structure
Analogous structures DO NOT show common ancestry
convergent evolution
Darwin believed that these similarities are a result of different organisms adapting to similar environments
Comparative anatomy
of groups of animals or plants shows certain structural features are basically similar.
Homologous structures
are similar in structure but different in function.
Homologous structures ARE EVIDENCE of a common ancestor.
Darwin believed that these structures resulted from similar organisms adapting to different environments/needs –
adaptive radiation
Homologous structures are difficult to explain without evolution –
more likely that structures evolved once vs. many times in the history of organisms
Vestigial structures
are remnants of organs or structures that had a function in an early ancestor
Darwin referred to these as “rudimentary organs” – they are easily explain by evolution as structures that no longer have a function and so are being gradually lost.
The pentadactyl limb in vertebrates is an example of a
homologous structure
It is adapted to different mode of locomotion in particular environment. Ex:
dolphin fin for swimming
bat wing for flying
monkey hand for grasping
horse hoof for galloping
Populations of a species can gradually diverge into separate species by evolution.
- If populations, e.g. fruit flies, become separated (e.g. a population is blown by a storm to a distant island). Then it is very likely the population will experience different ecological conditions.
- Over many generations the characteristics of the two populations (shape of the flies, food preference, mating rituals etc.) will likely diverge as the result of natural selection.
- The two populations may meet again but they may not easily mate
Mating rituals are different
Because of genetic differences the resulting offspring are infertile - Because genes flow between the populations is reduced, the island fruit flies are said to have evolved into separate species (this process is called speciation).
Speciation often occurs after a population..
extends its range through migrating to an island
This explains the large number of endemic species on islands
Endemic species
species that is only found in a certain geographic area
The greater the geographical separation and the longer the populations have been separated the
greater the divergence
Variation:
Peppered moths (Biston betularia) moths are found in two forms
White (typical)
Black (malanistic)
Industrial melanism
development of melanistic insects in polluted areas
