THE ORIGIN OF SPECIES
I.
What is a species?
a. TAXONOMY  the branch of biology concerned with naming
and classifying the diverse forms of life
b. BIOLOGICAL SPECIES CONCEPT  defines a species as a
population or group of populations whose members have the
potential to interbreed and produce fertile offspring
c. RING SPECIES  a species whose distribution forms a ring as
it extends its range around some geographic barrier
d. Other species concepts
i. MORPHOLOGICAL SPECIES CONCEPT 
classification is based mainly on observable and
measurable phenotypic traits
ii. GENEALOGICAL SPECIES CONCEPT  defines a
species as a set of organisms with a unique genetic
history
iii. ECOLOGICAL SPECIES CONCEPT  identifies
species in terms of ecological niches
II.
Reproductive barriers keep species separate
a. REPRODUCTIVE BARRIER  a biological feature of the
organisms themselves to prevent populations belonging to
closely related species from interbreeding even when ranges
overlap
REPRODUCTIVE BARRIERS BETWEEN SPECIES
Prezygotic Barriers: Prevent Mating or Fertilization
Temporal
Mating or flowering occurs at different seasons or times
Isolation
of day
Habitat Isolation Populations live in different habitats and do not meet
Behavioral
There is little or no sexual attraction between males and
Isolation
females
Mechanical
Structural differences in genitalia or flowers prevent
Isolation
copulation or pollen transfer
Gametic Isolation Male and/or female gametes die before waiting or fail to
unite
Postzygotic Barriers: Prevent the Development of Fertile Adults
Hybrid
Hybrid zygotes fail to develop or to reach sexual
Inviability
maturity
Hybrid Sterility Hybrids fail to produce functional gametes
Hybrid
Offspring of hybrids are weak or infertile
Breakdown
III.
Geographic isolation can lead to speciation
a. ALLOPATRIC SPECIATION  the initial block of gene flow
seems to have been a geographic barrier that isolated a
population
IV.
Islands are living laboratories of speciation
a. ADAPTIVE RADIATION  the emergence of numerous
species from a common ancestor introduced to new and diverse
environments
V.
New species can also arise within the same geographic area as the
parent species
a. SYMPATRIC SPECIATION  reproductive isolation
develops and new species arise without geographic separation
i. May arise from POLYPLOIDY
1. Too many chromosomes
VI.
Polyploid plants clothe and feed us
a. Wheat is a polyploidy species that is highly utilized by people
VII. Reproductive barriers may evolve as populations diverge
a. When populations are isolated, the reproductive barriers will
become more developed
VIII. The temp of speciation can appear steady or jumpy
a. GRADUALIST MODEL  populations evolve differences
gradually (slowly) as they become adapted to their local
environment, new species evolve gradually from ancestral
species
b. PUNCUATED EQUILIBRIUM  evolution occurs in spurts
(short, quick, large)
IX.
Peter and Rosemary Grant study the evolution of Darwin’s finches
a. First group to actually test Darwin’s theories