CBSE Class 12 Biology Evolution NCERT Solutions

Darwinian selection theory emphasizes that individuals within a population exhibit variations, and those with variations that provide a survival advantage in a particular environment are more likely to survive and reproduce. This process is clearly illustrated by antibiotic resistance in bacteria. When a bacterial population is exposed to an antibiotic, such as penicillin, most bacteria that are susceptible to the drug will die. However, due to random mutations, a few bacteria might possess a gene that confers resistance to the antibiotic. These resistant bacteria are better adapted to the environment containing the antibiotic and thus survive and multiply. Consequently, the proportion of resistant bacteria in the population increases over time. This phenomenon highlights how environmental pressures (the antibiotic) act as a selective agent, favoring individuals with advantageous traits (resistance) and leading to evolutionary change within the population.

Recent fossil discoveries continue to shed light on evolutionary history. For instance, the discovery of fossils from the Jurassic period has provided significant insights into the evolution of reptiles, including the lineage leading to birds and mammals. In recent years, unusual fossil finds in China have sparked discussions and controversies regarding avian evolution. One notable example is the genus Confuciusornis, a type of primitive bird roughly the size of a crow, which lived during the Cretaceous period. Such discoveries are crucial as they provide tangible evidence for evolutionary transitions and sometimes challenge existing hypotheses, prompting further research and debate within the scientific community.

A species can be clearly defined as a group of individual organisms that share the potential to interbreed with one another under natural conditions and produce viable, fertile offspring. This biological definition emphasizes reproductive isolation from other such groups as a key characteristic of a species.

Human evolution is a complex process marked by significant changes in various aspects of our ancestors' biology and behavior. Key components include:

1. Brain Capacity: There has been a progressive increase in cranial capacity over millions of years, indicating enhanced cognitive abilities.
2. Posture and Locomotion: Early ancestors like Dryopithecus had an ape-like posture. Later, Ramapithecus showed adaptations for more upright movement. Australopithecus developed an erect posture and bipedal locomotion. Homo erectus also maintained an erect posture, and Neanderthals were also upright walkers.
3. Dietary Preference: The diet evolved from soft fruits and leaves in early apes to seeds, nuts, and eventually becoming omnivorous and carnivorous in later hominids.
4. Skeletal Structure and Features: Changes in jaw structure, teeth size (canines and molars), and overall skeletal build reflect dietary shifts and adaptations for bipedalism.
5. Tool Use and Behavior: Early hominids like Homo habilis were the first known toolmakers. Homo erectus used stone and bone tools for hunting, while Neanderthals developed more sophisticated tools, used hides for clothing, and practiced burial rituals.

Here is a summary table tracing these components: