Evidences of Evolution
Evolution: Evolution is described as a process by which a species after a several generations, gives rise to offspring
possessing features different from the earlier ones.
- is the way a different animal or species came to be, and how they are linked to a different of species that all share a
common ancestor.
Sources of Evidence for Evolution
1. Fossil records:
Fossils are remains of organisms that existed in the past geological ages. They are traces of organisms
preserved by natural process or catastrophic events in rocks, peat or ice. Most fossil are commonly found in
sedimentary rocks. They were from the hard parts of the organism like woody stem, bones and teeth.
Paleontologists - is a person who studies fossils and mention that body fossils and trace fossils are two groups
of fossils.
Body fossils - are remains of an animal or plant like bones, shells and leaves. Petrified wood, woolly mammoths
caught in ice and insects trapped in amber are some examples.
Trace fossils (impression) - records the behavior and movement of animals. These include footprints, burrows,
trails, fossilized nests and coprolites (fossilized feces).
Imprints are shallow external molds left by animal or plant tissues with little or no organic materials present.
Compression are formed most commonly in environments where fine sediment is deposited, such as in river
deltas, lagoons, along rivers, and in ponds.
How do paleontologist determine the age of a fossil?
Paleontologist makes initial estimates of the age through the position in the sedimentary rocks. Fossils
found in the bottom layer are much older than those found in the upper layer of rocks.
Relative dating is a method used to determine the age of the rocks by comparing them with the rocks in the
other layer. The younger sedimentary rock layer is assumed to be found on top and the older rock is found at
the bottom layer. The fossils of invertebrates found at the bottom part of the rock layer suggest that
invertebrates are probably one of the first and oldest organisms that lived on earth.
Another method is through the use of radioisotopes dating, carbon-14 dating and molecular techniques.
Radiometric dating is a method used to determine the age of rocks using the decay of radioactive isotopes
present in rocks. All organisms have decaying carbon-14 in it. Plants and animals that are still alive constantly
replace the supply of carbon in their body and the amount of carbon -14 in their body stays the same. When an
organism dies, carbon-14 starts to decay.
Carbon dating is used to tell the age of organic materials. Art collectors use carbon dating to determine if a
piece of art work is genuine or not.
2. Comparative anatomy:
Homologous Structures are different species which have similar internal framework, position, and embryonic
development that may perform different functions in the species living in the different environment, or it may have
the same origin but different functions. Examples are the forelimbs of dog, bird, lizard and whale, which are
structurally the same, but functionally different. Front limbs of man, cat, horse, bat, whales, and other mammals are
made up of same kinds of bones; they just vary only in size and in function.
Structures of unrelated species may evolve to look alike, because the structures are adapted to similar function.
These are called analogous structures. They have similar functions but different origin. Examples are wings of birds,
bats, and insects that have the same function but different in origin.
Divergent evolution is the presence of homologous structures is a strong indicator that the organisms evolved from
common ancestors. Divergent evolution is the splitting of an ancestral population into two
or more subpopulations that are geographically isolated from one another.
Convergence evolution is an increase in similarities among species derived from different ancestors resulting to
similar adaptation of similar environment. In convergent evolution, analogous structures
of unrelated organisms from different ancestors develop similar function such as butterfly
wings and bird wings.
3. Embryonic Development and Biological Molecules
An embryo is an early stage of development in organisms. Embryonic development includes stages such as
blastula, gastrula, and organogenesis. The embryo of fishes, salamanders, lizards, birds, cats, and humans are similar
during the first stages of their embryonic development and have several homologous structures that are not present
when the organisms are adults. Studies show that species that are closely related exhibit similar embryonic
development even when in the adult stage, the organisms are quite different.
Figure 4. Represents the similarities in embryonic development in 5 organisms suggesting that they have evolved from a common ancestor.
The molecular evidence of evolution reveals relatedness and similarities among gene, protein, chromosomal
and genome level. As species evolved, one change after another becomes part of their genetic instruction. Changes
in gene’s nucleotide sequence build up overtime.
There are two views on molecular evidence.
First is, if evolution has taken place, species that descended from a recent common ancestor should have fewer
amino acid differences between their proteins than species that share a common ancestor in the more distant past.
Second is that, the more similar the organisms’ hemoglobin proteins are, the more recent the organisms’ common
ancestor. Humans and gorillas that are believed to have shared common ancestor have few amino acid sequence
differences as compared to human and mice which are believed to have shared a common ancestor in the more
distant past have more amino acid sequence differences.
