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EVOLUTION
Relationships Among Organisms
Similarities Among Organisms
All organisms on Earth are related
Some relationships are easier to see than others – though most organisms have some similarity in body structure
Similarities Among Organisms
Common Descent
Living things have slowly changed over time Each living species descended from other
species over time Principle of common descent – all living
things share common ancestors
Common Descent
Anatomists discovered that when comparing adult animals with four limbs, similarities exist among the bones of the various types of arms and legs
These are called homologous structures – have the same structure, but differ in function
Means they come from common origin
Common Descent
There are also embryological similarities
Discovered vestigial organs – structures that seem to serve little or no purpose
Similarities Among Organisms
Each species has a “tool kit” containing visible and invisible tools that perform essential survival functions
Tool kits are the result of millions of years of evolution by natural selection
It is easier to modify existing tool kits than to create entirely new ones
The Role of Chance
Random change in population is called genetic drift
Can be caused by migration, random mating differences
These are changes that have nothing to do with natural selection
The Birth of New Species
Speciation is the formation of new species. New population must change enough that
breeding cannot occur with original population
Genetic changes can be from mutations or natural selection, but must lead to reproductive isolation
The Birth of New Species
Usually, speciation in plants and animals occurs when two groups of individuals become geographically isolated
Darwin’s finches p. 251
The Pace of Evolution
Gradualism is the view that evolution occurs slowly and steadily over long periods of time
Punctuated equilibrium is the view that there are long periods of stability interrupted by episodes of rapid change.
The Pace of Evolution
Adaptive Radiation
When a new species evolves in a relatively short period of time, or when an organism or a group of organisms colonizes a new area where other species compete for life’s necessities
Results in a new tool kit Leads to homologous structures
Adaptive Radiation
Sometimes called divergent evolution
Convergent Evolution
Unrelated species may independently evolve superficial similarities because of adaptations to similar environments.
Example: bats and birds both fly Leads to analogous structures – similar in
appearance and function but develop from anatomically different parts
Homologous vs. Analogous
Homologous structures – similar structure, different function
Ex. arm of a human, wing of a bird
Analogous structures – similar function, different structure
Ex. bat wing, bird wing
Distant Relationships
Looking at homologous structures, fossils, embryological similarities can show evolutionary relationships
What about single celled organisms?
Molecular similarities
Molecular Unity
Many genes are shared by a wide range of organisms
The same 20 amino acids make all proteins All cells need ribosomes – almost identical
genes The more closely two organisms are related,
the more closely their genes resemble each other
Muscle Proteins – in Yeast!
Myosin is a protein found in muscle cells in animals – and yeast cells
Yeasts do not move, so why do they need myosin?
They use it to move products around within the cell