IMPACT OF NATURAL
SELECTION
Evolution

IMPACT OF NATURAL SELECTION
Convergence
Regression
Radiation
Extinction
Natural
Selection

CONVERGENCE
Convergence evolution occurs when
species occupy similar ecological niches
and adapt similar ways in response to
similar selective pressure.
Traits that arise to convergent evolution
are referred as analogous structure.

1
• Species often look extremely similar, however they are not
closely related to free of life.
2
• Individual environment are offensively similar and they need
indistinguishable variations to achieve success and reproduce.
3
• Organisms with favorable distinctions can survive, while other
go away from the environment.
4
• Most cases occur in different geographical areas of world,
similar climate.

Convergent evolution between Placental Mammals & Marsupials.
 Marsupial and
placental mammals
have evolved
separately to occupy
equivalent niches on
different continents;
they are ecological
equivalents.

RADIATION
In fact, many classical examples of adaptive radiation involves Island
or lakes, notable examples include Darwin finches of Galapagos,
honeycreeper birds and silvers word plants of Hawaii, and cichlid fish
of lakes Malawai and Victoria in Africa.
An adaptive radiation occurs when single or large group of ancestral
species rapidly diversifies into large number of descendant species.
Number of descendants with great variety of adaptions to different niches.

Most common example of adaptive radiation is Darwin's Finches, discovered
during Darwin's Voyage to the Galapagos archipelago.
Speciation is the development of one of multiple new species in the
evolutionary process, where the original species produces mutated forms which
successfully survive in other environments due to these mutations.
EXAMPLE
These 14 species belong to 4 genera:
Geospiza
Camarhynchus
Certhidea
Pinaroloxias

EXAMPLE
In case of Darwin finches adaptation occurred relatively rapidly. Blown
over to various islands with various flora and fauna, beak morphology
might ensure either the survival or death of the bird.
For example, Wabler finches and ground finches have evolved from
common ancestor. Wabler finches have long, thin beak perfectly for
eating insects. Ground finches have thick, blunt beaks ideal for
breaking over the husks of nuts and seeds.

REGRESSION
Regression evolution refers to the loss of useless characters over time.
It is critical evolutionary process in all organisms.
For example, human would be as hairy and tailed as other primates if
regressive evolution did not prune unused ancestral traits.
Natural selection may favor regression.

EXAMPLE
It is a process of partial or complete reduction of organs that have lost
their adaptive significance.
For example, replacement of the notochord by a cartilaginous skeleton
and later by a bony skeleton in the process of vertebrate evolution,
replacement of gills by lungs when vertebrate emerged onto dry land.

EXTINCTION
Natural selection is a process through which the traits that are helpful in
the survival of an organism are passed on to the next generation while
those that can hinder survival are eliminated.
The extinction of species ( and larger groups) is closes tied to the
process of natural selection and is thus major component of progressive
evolution.
In some passages of the Origin, Darwin seems to have seen extinction
as part of natural selection, in other, as an inevitable outcome.

CONT….
oDinosaurs become extinct sixty five million yeas ago.
oThe end of species or group of species
oNatural selection causes extinction
Most common cause for extinction:
1. Species compete for limited resources
2. Environment resources ... individual can't survive