3 conditions of natural selection (modern evidence for Darwin's hypothesis)
1. Variation must exist in the population
2. Variation must lead to differences in reproductive success
3. Variation must be genetically transmitted to the next generation
Artificial selection is a form of _______ selection that leads to evolutionary change
have no apparent function, but resemble structures their ancestors possessed. e.g. hip bones in
whales, human ear wiggling muscles
Similar forms having evolved in different, isolated areas because of similar selective pressures
in similar environments. e.g. Australian marsupials resemble placental mammals on other
Arguments against Darwin's theories (and reasons why they are in wrong)
-Evolution is not solidly demonstrated (it is a theory just like the theory of gravity)
-There are no fossil intermediates (many have been found since Darwin's time)
-The intelligent design argument (too complex for a random process, natural selection is not
random but it is not directed)
-Evolution violates the Second Law of Thermodynamics (Earth is not a closed system and energy
is constantly added from the sun)
-Proteins are too improbable
-Natural selection does not imply evolution
-The irreducible complexity argument
Sympatric species occur together in an area. Distinctive, phenotypically different, utilize different parts of the
habitat, behave separately
Ernst Mayr defined species as
groups of actually or potentially interbreeding natural populations which are reproductively
isolated from other such groups
Within a single species, individuals in populations that occur in different areas may be distinct
from one another.
Prezygotic isolating mechanisms
Geographic isolation, ecological isolation, behavioral isolation, temporal isolation, mechanical
isolation, prevention of gamete fusion.
Postzygotic isolating mechanisms
hybrid inviability or infertility
One ancestral species becomes divided into two descendant species
random changes may cause reproductive isolation. In small populations, Founder effects,
Speciation is a 2-part process
1. Initially identical populations must diverge.
2. Reproductive isolation must evolve to maintain these differences. Allopatric speciation
Geographically separated populations appear much more likely to have evolved substantial
differences leading to speciation.
One species splits into two at a single locality, without the two new species ever having been
geographically separated. One type occurs commonly as a result of polyploidy (individuals that
have more than two sets of chromosomes)
all the chromosomes arise from a single species, error in cell division produces tetraploids,
cannot produce fertile offspring with normal diploids
Two species hybridize, resulting offspring have one copy of the chromosomes of each species.
Infertile, but can reproduce asexually. Can become fertile if chromosomes spontaneously
Occurs in an environment with few other species and many resources. New trait evolves within
a species allowing it to use resources that were previously inaccessible. Island archipelago
The model that assumes that evolution proceeds with accumulation of small changes
Long periods of stasis followed by rapid change. Stabilizing and oscillating selection is
responsible for stasis. ends of a continuum
Gradualism and punctuated equilibrium are two _________
the study of the diversification of living forms, both past and present, and the relationships
among living things through time. Relationships are visualized as evolutionary trees (synonyms:
cladograms, phylogenetic trees, phylogenies)
"Descent with modification"
Darwin - all species evolved from a single common ancestor, history of life as a branching tree
Hypothesis about patterns of relationships among species.
includes the most recent common ancestor of the group and all of its descendants (clade)
includes the most recent common ancestor of the group, but NOT all of its descendants.
does not include the most recent common ancestor of all members of the group
A type of isolating mechanism that leads to reproductive isola