macroevolution

1. Factors of large evolutionary
changes(Macroevolution)

2. Macroevolution
• Macroevolutionary studies focus on change
that occurs at or above the level of species, in
contrast with microevolution, which refers to
smaller evolutionary changes (typically
described as changes in allele frequencies)
within a species or population.

3. Adaptive radiations
• The term adaptive radiation was coined by
H.F. Osborn (1902).
• It is the evolution of a number of descendants
with a great variety of adaptations to different
niches from a single ancestor.

4. • The phenomenon of adaptive radiation is the
diversification of a dominant evolutionary
group into a large number of subsidiary types
adapted to more restrictive modes of life
(different adaptive zones) within the range of
the larger group

5. • According to George Gaylord Simpson (1940,
1953), adaptive radiation is the rapid
proliferation of new taxa (species) from a
single ancestral group.
• Certain authors of evolution biology such as
Savage (1969),Stanley (1979) and Volpe (1985)
have used an entirely new term
macroevolution for the Osborn’s law of
adaptive radiation.

6. Examples of Adaptive Radiation
• Adaptive radiation in Darwin’s finches.
A classical example of speciation involving the
interplay of complex forces (such as isolation,
competition, adaptation, etc.) leading to
adaptive radiation at the species level is
provided by Darwin’s finches.

7. • These birds belong to largest family of birds,
the Fringillidae and live in Galapagos Islands in
the Pacific ocean.
• The study of these small dark birds in their
native habitat gave Darwin his first insight into
evolutionary processes.

8. • The present-day assemblages of Darwin’s finches
descended from small sparrow-like birds that
once inhabited the mainland of South America.
• The ancestors of Darwin’s finches were early
migrants to the Galapagos Islands and probably
the first land birds to reach the islands. These
early colonists have given rise to 14 distinct
species, each well adapted to a specific niche.
• Thirteen of these species occur in the Galapagos,
one is found in the small isolated Cocos Island,
northeast of Galapagos.

9. • Not all 13 species are found on each island.
These 14 species belong to 4 genera:
• 1.Geospiza
• 2. Camarhynchus
• 3. Certhidea and
• 4. Pinaroloxias.

10. • The most conspicuous difference among the
species are in the sizes and shapes of the
beak, which are correlated with marked
differences in feeding habits.

11. • The ancestral finch was a ground-dwelling,
seed-eating finch. After the burst of speciation
in the Galapagos, a total of 14 species exist:
ground-dwelling seed-eaters; some living on
cactuses and eating seeds; some living in trees
and eating seeds; and species of tree-dwelling
insect-eaters.

13. Orthogenesis
• Orthogenesis is the assumption that
evolutionary changes or variations are
produced in straight lines.
• The observed tendency of a part or organ to
change progressively in size is called
orthogenesis or evolution in a straight line.
• The theory of orthogenesis was proposed by
Eimer in 1897.

14. Evidences of orthogenesis
• Analogous or parallel variations are of
frequent observation.
• They are the modification of similar characters
which appear in different branches of the
same large group or in unrelated group.
• For example the total reduction of side toes
among artiodactyl in several unrelated genera
such as giraffe,camel and prong-
buck(Antilocarpa)

15. • Another example existed between the
pseudohorses of South America and true
horses of nothern hemisphere,both lines
showing a three-toed and finally a one-toed
modification.
• There are several structures which evolved
beyond the point of usefulness,such as tusks
of Jefferson mammoth and antlers of Irish
deer.

16. Allometry
• Allometry is an important method for
describing morphological evolution.
• It is the relation between the size of an
organism and the size of any of its parts.

17. • Within a taxon, most animals share a common
body plan that comprises a certain number of
body parts arranged in a particular way. For
example, all insects share a head, thorax,
abdomen, one pair of antennae, two pairs of
wings and three pairs of legs. Yet out of this
simple body plan has arisen the enormous
diversity of insect forms that we see around
us. Most of this diversity is a result of changes
in the relative size of the different body parts.