7. EVOLUTION
EVIDENCES FOR EVOLUTION
1. Paleontological evidences
Paleontology
is the
study of fossils.
Fossils
are remnants of life forms found in rocks (earth crust). They are written documents of evolution.
Significance of fossils:
a. To
study phylogeny (evolutionary history or race history). E.g. Horse
evolution.
b. To
study the connecting link between two groups of organisms. E.g. Archaeopteryx.
c. To
study about extinct animals. E.g. Dinosaurs.
d. To
study about geological period by analysing fossils in different sedimentary
rock layers. The study showed that life forms varied over time and
certain life forms are restricted to certain geological time spans.
2. Morphological &
Anatomical evidences
Comparative anatomy and
morphology shows that different forms of animals have some common structural
features. This can be explained as follows:
a.
Homologous organs
- Homologous organs
are the organs having fundamentally
similar
structure and origin but different functions. This phenomenon is called Homology.
- E.g.
Human hand, Whale’s flippers, Bat’s wing
& Cheetah’s foot. These forelimbs have different functions but
similar anatomical structures such as bones (e.g. humerus, radius, ulna,
carpals, metacarpals & phalanges).
- Homology
is also seen in heart, brain etc.
- Homology in plants:
E.g. Thorns of Bougainvillea and
tendrils of Cucurbita.
- The
origin of homologous organs is due to Divergent evolution. It is the
evolution by which related species
become less similar to survive and
adapt in different environmental condition.
- Homology
indicates common ancestry.
b. Analogous
organs
These are the organs
having similar function but different structure & origin. This phenomenon
is called Analogy. E.g.
§ Wings of insects
(formed of a thin flap of chitin) and wings
of birds (modified forelimbs).
§ Eyes of Octopus
(retina from skin) and mammals (retina
from embryonic brain).
§ Flipper of Penguins
and Dolphins.
§ Sweet potato
(modified root) & Potato (modified
stem).
§ Trachea of insects
(from ectoderm) and lungs of vertebrates
(from endoderm).
Origin
of analogous organs is due to Convergent evolution. It is the
evolution by which unrelated species
become more similar to survive and
adapt in similar environmental condition.
3. Adaptive radiation (Biogeographical evidences)
Adaptive radiation
(evolution by adaptation) is the evolution of different species from an
ancestor in a geographical area starting from a point. It is a type of
divergent evolution. E.g.
o
Darwin’s finches in Galapagos Islands.
o Australian
marsupials (Marsupial radiation).
o Placental
mammals in Australia.
When
more than one adaptive radiation is appeared in an isolated geographical area,
it results in convergent evolution.
E.g.
Australian Marsupials and Placental mammals.
4. Biochemical evidences
- Organisms
show similarities in proteins, genes, other biomolecules & metabolism. It
indicates common ancestry.
5. Embryological evidences
-
Proposed
by Ernst Haeckel.
-
He
observed that all vertebrate embryos have some common features that are absent
in adult.
-
E.g.
all vertebrate embryos (including human) develop vestigial gill slits just
behind the head. But it is functional
only in fish and not found in other adult vertebrates.
-
However,
Karl Ernst von Baer rejected this proposal. He noted that embryos never
pass through the adult stages of other animals.
6. Evidences for evolution by natural selection
Natural selection is the process in which organisms with
better favourable & heritable variation are survived and reproduced.
Some
evidences are given below:
§ Industrial
melanism: In England, before industrialization (1850s), there were more
white-winged moths (Biston betularia)
on trees than dark winged or melanised moths (Biston carbonaria). After
industrialization (1920), more dark-winged moths and less white winged
moths were developed.
Reason:
Before industrialization: There
was white lichens covered the trees. In that background, white winged moths
survived but dark winged moths were picked out by predators.
After industrialization: The
tree trunks became dark due to industrial smoke and soot. No growth of lichens.
So white winged moths did not survive because the predators identified them
easily. Dark winged moth survived because of suitable dark background.
§ Development
of resistant varieties in organisms against herbicides, pesticides, antibiotics
or drugs
etc.
These are the examples for natural selection by anthropogenic
action (evolution due to human activities).
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