MACROEVOLUTION
AND THE ORIGIN OF
SPECIES
Origin of Species
• A species is a group of organisms that can breed and produce fertile
offspring together in nature.
• For a new species to arise, some members of a species must become
reproductively isolated from the rest of the species. This means they can no
longer interbreed with other members of the species. How does this
happen? Usually they become geographically isolated first.
• The macroevolution of a species happens as a result of speciation.
• Speciation is the branching off of individuals from the species they originally
were. Over time, as natural selection occurs, individuals may build up
adaptations that are no longer compatible with others in their species. This
is most often due to geographic isolation or reproductive isolation from
other individuals within the species.
• Once the DNA is different enough, or they are no longer able to interbreed,
they are now a different species that has branched off from the main
species.
• How quickly does this process happen? If evolution for most species takes a
very long time, it would be logical to think the same would happen for
speciation. However, there are two major accepted different hypotheses on
the pace of evolution due to speciation. Arguments for both hypotheses are
sound and there has been no evidence found so far to disprove either one.
Types of Speciation
Geographic Isolation
Reproductive Isolation
Allopatric Speciation
• separated by an actual
physical barrier that gets
between members of a
population
Peripatric Speciation
• extreme case of geographic
isolation where only a few
individuals are isolated,
perhaps by some sort of
disaster that kills off all but
a few of the isolated
population
Parapatric Speciation
• populations are not
isolated by a physical
barrier and are "beside"
each other; nothing
stopping the individuals in
the entire population from
mixing and mating, that
does not happen
Sympatic Speciation
• individuals in the
population are not
separated at all and all live
in the "same place".
Patterns of Macroevolution
Convergent Evolution
• The word converge means "to come together". This pattern of macroevolution
happens with distinctly different species become more similar in structure and
function. Usually, this type of macroevolution is seen in different species that live in
similar environments. The species are still different from one another, but they often
fill the same niche in their local area.
Divergent Evolution
• Nearly the opposite of convergent evolution is divergent evolution. The
term diverge means "to split apart". Also called adaptive radiation, this pattern is the
typical example of speciation. One lineage breaks into two or more separate lines that
each give rise to even more species over time. Divergent evolution is caused by
changes in the environment or migration to new areas. It happens particularly quickly
if there are few species already living in the new area. New species will emerge to fill
the available niches.
Coevolution
• All living things are affected by the other living organisms around them that share their
environment. Many have close, symbiotic relationships. The species in these
relationships tend to cause each other to evolve. If one of the species changes, then
the other will also change in response so the relationship can continue.
Timing of Macroevolution
Gradualism
Punctuated Equilibrium
• gradual accumulation of
adaptations over a long
period of time
• proposes that there
were many adaptations
that slowly added up
over a steady, long
period of time
• change happens very
rapidly with long periods
of stability and no
change in between
• short period of quick,
successive changes occur
to cause speciation and
the new species evolves
suddenly because of a
chance in their
environment
Extinction
• When every individual in a population has died off, an
extinction has occurred. This, obviously, ends the species and
no more speciation is able to happen for that lineage. When
some species die out, others tend to flourish and take over the
niche the now extinct species once filled.
• Many different species have gone extinct throughout history.
Most famously, the dinosaurs went extinct. The extinction of
the dinosaurs allowed mammals, like humans, to come into
existence and thrive. However, descendants of the dinosaurs
still live on today. Birds are a type of animal that branched off
from the dinosaur lineage.
Lesson Summary
• New species arise in the process of speciation. Allopatric
speciation occurs when some members of a species become
geographically separated. They then evolve genetic
differences. If the differences prevent them from
interbreeding with the original species, a new species has
evolved. Sympatric speciation occurs without geographic
separation.
• Coevolution occurs when species evolve together. This often
happens in species that have symbiotic relationships. Examples
include flowering plants and their pollinators.
• Darwin thought that evolution occurs gradually. This model of
evolution is called gradualism. The fossil record better supports
the model of punctuated equilibrium. In this model, long
periods of little change are interrupted by bursts of rapid
change.