Biology Chapter 1: Evolution

Evolution

• Hundreds of lakhs of species exist on earth, with some known, some unknown, and some extinct.
• Fossil remains provide evidence of extinct species, such as dinosaurs, which were present on earth from 2000 to 600 lakh years ago.
• Dinosaurs were of various types, including carnivores, herbivores, bipeds, and quadrupeds, and their size ranged from 50 cm to 40 meters.

Habitat and its Effect

• Habitat is a place where the basic needs of an organism are fulfilled, including food, reproduction, and safety.
• The availability of resources in a habitat affects the population of a species.
• If resources are adequate, the population of a species may increase, while a decline in resources may lead to extinction.

Graphs and Population Growth

• The rate of population growth is not always the same as the rate of growth of food resources.
• Uncontrolled population growth can lead to a shortage of food resources, resulting in control measures such as natural disasters or deaths due to competition for resources.
• The graph shows that the amount of food resources has an effect on the rate of population growth.

Darwin and his Findings

• Charles Darwin, a naturalist, proposed the theory of evolution, which revolutionized scientific thought.
• Darwin's observations during the voyage of the HMS Beagle, including the diversity of living organisms and the influence of nature on diversity, led to his theory of evolution.

Voyage of the Beagle and Darwin's Experience

• Darwin traveled around the world on the HMS Beagle, studying and gathering information about natural phenomena, habitats, and organisms.
• He observed that organisms have adapted to their environments and that there is a struggle for life everywhere.

Darwin's Observations

• Darwin observed food chains and webs, where organisms (predators) feed on others (prey).
• He found fossils of aquatic organisms and observed changes in land forms over time.
• He collected and observed different organisms, including specimens of the existing forms, and compared them with fossils of the past.

Galapagos Islands

• Darwin collected fossils and specimens of organisms on the Galapagos Islands, which helped him to study and compare forms of present organisms with those of the past.
• He observed variations in finches, including differences in beak shape and size, which were related to their food habits.

Homologous Characters

• Homologous characters are characters that indicate similar origins but have diverse functions, such as the type of beak in finches.
• Examples of homologous characters can be seen in plants, such as stems that have different functions, and in animals, such as the forelimbs of humans, dogs, and birds.

Selection and Evolution

• Darwin suggested that a process of natural selection, similar to artificial selection, occurs in nature, resulting in the evolution of one form to another.

• Natural selection is not an intentional process, but rather a result of the environment and the presence of diverse organisms.

• The process of natural selection can lead to the evolution of new species.### Evolution

• Evolution is the process by which organisms or species become better suited to their environment through variations in populations.

• Theory of Evolution suggests that organisms evolved from pre-existing organisms and selective processes in nature occurred spontaneously and non-intentionally, giving rise to diverse forms of species on Earth.

• Variations found in organisms lead to diversity in their ability to survive in nature, and those with greater ability to survive have more chances of evolving.

Artificial Selection

• Artificial selection is the process of selection of desirable characters of organisms by humans.
• Examples of artificial selection include the evolution of different varieties of rice, wheat, vegetables, and fruits.

Theory of Evolution by Darwin and Wallace

• Darwin and Wallace together suggested that:
  • Variations found in organisms lead to diversity in their ability to survive in nature.
  • New varieties of organisms may emerge suddenly from pre-existing ones due to natural calamities.
  • Various organisms have had similar ancestors, and the evolutionary relationship can be represented by a branched tree diagram.
  • Variations are found in populations of organisms, and only some variations pass on from one generation to the next.
  • Populations of organisms that have advantageous variations grow more profusely, affecting the population composition.

Process of Speciation

• Adaptation is the process of change by which organisms or species become better suited to their environment.
• Speciation is the process of evolution where organisms vary so much that they are not able to interbreed.
• The process of speciation can be fast due to natural calamities or slow otherwise.

Biological Species Concept

• A group of organisms that can interbreed sexually producing viable offspring is known as a species.
• This definition of species is considered as the biological species concept.

Key Terms

• Evolution of organisms
• Speciation
• Adaptation
• Natural selection
• Artificial selection
• Fossils
• Homologous characters
• Analogous characters