Evolution — Short Questions

Selective breeding means the process in which humans select varieties of plants or animals and breed them to produce offspring with required characteristics.

There are two main types of speciation:
i. This speciation occurs when a population is geographically separated into two or more populations.
• This speciation occurs when reproductive isolation happens within the same geographical area due to habitat preference or behaviour.

The forelimbs of mammals (forearms of human, legs of cat, flippers of whale and wings of bat) all have the same structure but different functions.

i. Variations
ii. Struggle for survival
iii. Survival of the fittest
iv. Reproduction and passing on variations
v. Gradual evolution over time

In 1859, Darwin published his work in the form of a book. 'On the origin of species' In this book, he presented his 'theory of evolution by natural selection.'

English naturalist Charles Darwin (1809-1882) went on a five-year trip around the world on a His Majesty Ship (HMS) Beagle. During this voyage, Darwin made a lot of important observations that laid the foundations of his Theory of Evolution by Natural Selection.

The following are some important observations made by Darwin:
i. Unique Species
• He observed a variety of unique plant and animal species in different regions.
• He observed that different islands and environments had their own distinct sets of species.
ii. Variations in Same Species:
• Darwin observed variations among same species living in different environments.
• He noticed that these were adaptations i.e., special variations in an organism's body or behaviour that help it survive in its environment.
• He was convinced on the role of adaptations in the survival of species.

Natural Selection Natural selection is the process through which the individuals with better characteristics (variations) are more likely to live, reproduce, and pass those variations to their offspring.

1 Giraffe's Long Neck
i. Variations: Some giraffes had slightly longer necks than others.
ii. Struggle for Survival: Food (leaves on tall trees) was hard to reach, especially during dry seasons.
iii. Survival of the Fittest: Giraffes with longer necks could eat leaves from taller trees and survived better during harsh conditions.
iv. Reproduction and Passing on Traits: These long-necked giraffes reproduced and passed the long-neck trait to their babies.
v. Gradual Evolution Over Time: Over many generations, most giraffes in the population had long necks.

Species A species is a group of organisms that can interbreed and produce fertile offspring under natural conditions. Members of the same species are similar and are reproductively isolated from other species.
Speciation: Speciation is the process by which new species arise by evolution.

Variation Variations are the inheritable differences among individuals in a population on which natural selection can act.
Sources of Variation
i. Mutations
ii. Genetic Recombination
iii. Gene flow
iv. Random pairing of gametes

Gene flow occurs when individuals from one population migrate to another and introduce new genes in that population.
Example: When plants from one area cross-pollinate with plants from a different region, they introduce new characteristics into the population, such as improved drought resistance varieties.

The similar internal structures in different species that perform different functions are called homologous structures.
Example: The forelimbs of mammals (arms of human, legs of cat, flippers of whale, and wings of bat) all have the same structure but different functions. The basic similarity of structure of these forelimbs is the evidence that they evolve from a common ancestor.

i. Human Appendix: It is a small, tube-like structure attached to the cecum. In humans, it is a vestigial structure. It might have played a more important role in the digestive system of ancestors.
ii. Ear muscles in humans: In many animals, such as cats and dogs, ear muscles move their ears to detect sounds from different directions. However, in humans, these ear muscles are largely non-functional.

Breeds The varieties of animals which are selectively bred are called breeds. Many breeds of sheep, goat, cow, hen etc. have been produced by selective breeding to increase the production of meat, milk, eggs, wool etc.
Cultivars: The varieties of plants which are selectively bred are known as varieties or cultivars. Similarly, many plant varieties (cultivars) have been produced for better quantity and quality of food.

Variation among individual is crucial for evolution because:
• It provides the raw material for natural selection.
• It allows populations to adapt to changing environments, resists diseases and survive by favouring advantageous traits, without which a species would be unable to change and might face extinction.
• These differences, arising from mutations, gene flow and sexual reproduction ensure that some individuals possess traits better suited for survival enabling them to reproduce and pass those beneficial genes to the next generation.

Fossils are crucial for understanding Earth's history by providing tangible evidence of past life, showing how species evolved, adapted to changing environments and revealing past climates, geography and mass extinctions essentially adding as snapshots in time to build the tree of life. They show evolutionary transitions (like dinosaurs to birds) reveal deep time and help geologists to date rocks and map Continents connecting ancient world to today's biodiversity

Isolation leads to new species by stopping gene flow between population mutations, genetic drift and different natural selection pressures to accumulate unique genetic changes, eventually causing reproductive isolation where they can no longer interbreed to produce fertile offspring creating distinct species. This process called speciation happens through geographic separation (allopatric) like mountains or oceans or biological barriers such as different mating rituals.