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.
