The Origin Of Species
Ch. 24
Lesson 7.4
What is the “mystery of mysteries?”
• According to Darwin, speciation – the origin of
new species on earth
• Microevolution refers to changes in one gene
pool (within a species)
• Macroevolution – evolutionary change above
the species level
What IS a species?
• Biological Species Concept – a species is a
population or group of populations whose
members have the potential to interbreed in
nature and produce viable, fertile offspring,
but are unable to produce viable, fertile
offspring with members of other populations
• Reproductive Isolation – existence of
biological factors (barriers) that impeded
members of two species from producing
viable, fertile hybrids.
How Speciation Occurs
• Allopatric Speciation – gene flow is
interrupted when a population is divided into
geographically isolated subpopulations
• Sympatric Speciation – speciation taking place
in geographically overlapping population
– Caused by chromosomal changes and nonrandom
mating that reduces gene flow
Adaptive Radiation
• Evolution of many diversely adapted species
from a common ancestor upon introduction to
various new environments
– Occurs when a few organisms make their way to
new, often distant areas or when environmental
changes cause numerous extensions, opening up
ecological niches for the survivors.
Tempo of Speciation
• Punctuated Equilibrium – apparent stasis in
speciation, punctuated by periods of change
Why is speciation important?
• Macroevolutionary changes can accumulate
through many speciation events