ZOOHCC - 602: Evolutionary Biology (Theory) Unit:-2
Evidences of Evolution:
The theory of evolution is supported by numerous lines of evidence,
including the fossil record, comparative anatomy, comparative embryology,
molecular biology, biogeography, and experimental evolution.
The study of fossils is called paleontology. Paleontology is a
multidisciplinary field that combines aspects of biology, geology,
chemistry, and physics to understand the history of life on Earth.
Paleontologists study fossils to learn about the diversity of life that
existed in the past, how organisms evolved over time, and how they
interacted with their environment. They use a variety of techniques to study
fossils, including:
The fossil record provides a history of life on Earth and demonstrates how
organisms have changed over time. It can also display intermediate stages of
evolution, such as the evolution of birds from dinosaurs.
Comparative anatomy can reveal similarities and differences among
organisms, suggesting evolutionary relationships. For example, humans, bats,
and whales share similar bone structures in their forelimbs, indicating a
common ancestor.
Comparative embryology shows similarities in the embryonic development of
different organisms, which can also suggest evolutionary relationships. For
instance, all vertebrate embryos have gill slits, even though only some
develop into gills.
Molecular biology compares the DNA and protein sequences of different
organisms, revealing similarities that suggest a close evolutionary
relationship. For instance, humans and chimpanzees share over 98% of their
DNA.
Biogeography observes the distribution of species across the globe,
revealing patterns of evolution. For example, the marsupials in Australia
differ significantly from those in South America, indicating separate
evolutionary paths after the two continents separated.
Experimental evolution allows scientists to observe evolution in action by
conducting experiments in the lab. For example, breeding bacteria or fruit
flies under different conditions can reveal changes in their traits over
time.
Fossil record:-
The fossil record is an essential piece of evidence that supports the
theory of evolution. Fossils are the remains or traces of organisms that
have been preserved in rocks for millions of years. By analyzing these
fossils, scientists can learn about the history of life on Earth and how
various species have changed over time.
The fossil record demonstrates that life on Earth has transformed over
time, with new species emerging and old species disappearing. It also
provides evidence for transitional forms, which are organisms that exhibit
intermediate stages of evolution between different groups of organisms. For
instance, the discovery of Archaeopteryx, a fossil with features of both
birds and dinosaurs, is proof of the evolution of birds from
dinosaurs.
The fossil record reveals the age of different rock layers and the
organisms that lived during those periods, creating a timeline of the
history of life on Earth. By comparing the fossils found in different layers
of rock, scientists can reconstruct the evolutionary relationships between
different groups of organisms.
The fossil record is not complete, as not all organisms become fossils, and
not all fossils are discovered. Additionally, the fossil record provides
only a glimpse of the past, and it can be challenging to understand the
behavior and ecology of extinct organisms from their fossils alone.
Nevertheless, the fossil record is a valuable tool for comprehending the
evolution of life on Earth.
Types of fossils
There are several types of fossils that can be used to learn about the
history of life on Earth, including:
Body fossils: These are the remains of an organism's body, such as bones,
shells, and teeth, that have been preserved in rocks.
Trace fossils: These are evidence of an organism's activity, such as
footprints, burrows, and coprolites (fossilized feces).
Casts and molds: These are impressions left by an organism in sediment that
have been filled with minerals to create a replica of the organism (cast) or
a hollow space where the organism once was (mold).
Petrified fossils: These are fossils where the organic material has been
replaced with minerals, such as silica or calcite.
Amber fossils: These are organisms that have been trapped and preserved in
amber, a hardened form of tree resin.
Frozen fossils: These are organisms that have been preserved in ice, such
as mammoths found in the permafrost of Siberia.
Explanation with example:-
Body fossils: Dinosaur bones are a well-known example of body fossils.
These are the remains of the actual organism, preserved in rock over
millions of years.
Trace fossils: Dinosaur footprints are a type of trace fossil. These
impressions provide evidence of an organism's activity, such as its size,
gait, and behavior.
Casts and molds: A fossilized seashell is an example of a cast and mold
fossil. The original shell has decayed away, leaving behind a hollow space
(mold) in the rock. This mold is then filled with minerals, creating a
replica of the shell (cast).
Petrified fossils: Petrified wood is an example of a petrified fossil. The
organic material of the wood has been replaced with minerals, such as
silica, over time, resulting in a fossil that looks like stone.
Amber fossils: Insects trapped in amber are an example of amber fossils.
The sticky resin of a tree traps the organism, which is then preserved over
time as the resin hardens into amber.
Frozen fossils: Woolly mammoths preserved in ice are an example of frozen
fossils. These organisms have been frozen in time, with their tissues and
organs remaining intact due to the extreme cold.
What is Transitional forms in fossil:-
Transitional forms in the fossil record refer to fossils that exhibit
characteristics of both ancestral and derived groups, suggesting an
intermediate stage in the evolution of a particular organism or group. The
importance of transitional forms lies in their role as evidence for
evolutionary processes and the understanding of relationships between
different organisms. One of the most famous transitional forms is
Archaeopteryx, which displays features of both birds and dinosaurs.
Identifying transitional forms can be challenging, but advancements in
technology and new discoveries have helped scientists uncover more of them
over time. In summary, transitional forms provide valuable insights into the
evolutionary history of life on Earth and help to fill gaps between
different groups of organisms in the fossil record.
Example:-
Archaeopteryx: As mentioned earlier, Archaeopteryx is a famous transitional
form that shows characteristics of both dinosaurs and birds. It had feathers
and wings like birds but also had teeth, a long tail, and a reptilian
skeletal structure like dinosaurs.
Tiktaalik: Tiktaalik is a fish-like animal that lived around 375 million
years ago and is considered a transitional form between fish and tetrapods
(four-limbed vertebrates). It had gills and fins like fish but also had a
neck, wrist-like joints, and ribs similar to tetrapods.
Ambulocetus: Ambulocetus is an extinct mammal that lived around 50 million
years ago and is considered a transitional form between land mammals and
whales. It had a body shape similar to that of a crocodile but also had
adaptations for swimming, such as webbed feet and a tail fluke.
Geological time scale
The geological time scale is a system used by geologists and
paleontologists to describe the history of Earth and the events that have
occurred over its 4.6 billion-year existence. It is divided into eons, eras,
periods, epochs, and ages, with each unit representing a significant period
of time.
The geological time scale is based on the relative ages of rock formations
and fossils found in those rocks. Fossils are used to identify the time
period in which they existed, and they can be used to correlate the ages of
rock formations across different regions of the world.
The time scale is divided into three major eons: the Archean, Proterozoic,
and Phanerozoic. The Phanerozoic eon is further divided into three eras: the
Paleozoic, Mesozoic, and Cenozoic. Each era is divided into periods, and
each period is further subdivided into epochs and ages.
The geological time scale is a useful tool for understanding the evolution
of life on Earth and the events that have shaped the planet. It allows
scientists to study the relationships between different organisms and to
track changes in the environment over time. By analyzing the fossil record,
scientists can piece together the story of Earth's history and gain a better
understanding of the processes that have shaped life on our planet.