Answer:
Different types of evidences support the theories of evolution. These include morphological evidence, embryological evidence, anatomical evidence showing similarity in bones, and connecting links.
The embryos of various vertebrates such as fish, salamander, tortoise, chicken, cow, and human look alike during the early stages of development. As the embryos grow, these similarities gradually reduce. The resemblance seen in the initial stages of development indicates that all these organisms originated from a common ancestor.
Some organisms possess characteristics of two different groups and are known as connecting links. For example, the duck-billed platypus lays eggs like reptiles such as lizards and snakes, but also has mammary glands and hair like mammals. Hence, it forms a link between reptiles and mammals.
Answers:
Nearly 7 crore years ago, dinosaurs became extinct. During this period, monkey-like animals evolved that were similar to present-day lemurs. Around 4 crore years ago, these animals lost their tails. Gradual enlargement of the brain and improvement in hand structure resulted in the evolution of ape-like animals, which later developed into gibbons and orangutans. This sequence indicates that human evolution started approximately 7 crore years ago.
Speciation is the process by which new species are formed from existing species. A species is a group of organisms capable of interbreeding and producing fertile offspring. When some members of a species become separated due to geographical barriers, reproduction between the groups is prevented. Over time, these isolated populations undergo separate evolutionary changes and develop into different species.
Due to natural disasters such as floods, earthquakes, and volcanic eruptions, many plants and animals get buried beneath the earth. Their preserved remains or impressions are called fossils. Fossils include bones, shells, exoskeletons, and stone imprints.
The age of fossils can be estimated by measuring radioactive carbon (C-14). Determining the age of fossils helps scientists understand the evolution of organisms.
Von Baer studied the embryonic development of vertebrates such as fish, frog, tortoise, pigeon, chimpanzee, and human. In the early stages, the embryos of these organisms appear very similar and are difficult to distinguish. Differences become noticeable only in later stages due to the development of specialized features. These early similarities suggest that chordates have a common ancestry.
Answers:
Short Notes:
Lamarckism is the earliest theory of evolution proposed by Jean Baptiste de Lamarck. According to this theory, environmental changes cause changes in the external features of organisms. These changes occur due to frequent use of some organs and less use of others. The acquired characteristics are passed on to the next generation.
The long neck of the giraffe developed because generations of giraffes stretched their necks to feed on leaves of tall trees.
Darwin's theory states that organisms have a high reproductive capacity, which leads to a rapid increase in population. Due to limited resources, organisms compete for food and space. Only those organisms that are well adapted to their environment survive. Nature selects these fit organisms, which reproduce and give rise to new species.
Embryology is the branch of biology that deals with the study of formation and development of embryos and foetus. All multicellular organisms begin life as a single-celled zygote. The zygote undergoes repeated mitotic divisions to form morula, then blastula, followed by gastrula, which finally develops into a mature foetus.
Evolution is the slow and continuous change that occurs in living organisms over a long period of time. These gradual changes result in the formation of new species. Nature selects organisms with favourable variations. Changes occurring in the biosphere and universe are also included in the study of evolution.
Organisms that show characteristics of two different groups are known as connecting links. For example, lung fish has fins, gills, and scales like fishes, but breathes through lungs like amphibians. Therefore, lung fish acts as a connecting link between fishes and amphibians.
Answer:
Heredity is the transmission of genetic traits from parents to offspring. The traits passed from one generation to the next are called inherited traits, such as eye colour, blood group, and ear lobe structure.
Heredity includes physical as well as physiological characteristics. These traits may be expressed if dominant or remain hidden if recessive.
Mechanism of Hereditary Changes:
- Mating: Fusion of male gamete (sperm) and female gamete (ovum).
- Growth: Repeated mitotic divisions of the zygote.
- Chromosomes: Both male and female gametes contain a nucleus with 24 chromosomes each.
- Genes: Genes present on chromosomes control specific traits and are passed from parents to offspring.
- Chance factor: During meiosis, only 24 pairs of chromosomes are selected randomly, which leads to variation.
Answer:
Vestigial organs are underdeveloped and non-functional organs present in some organisms. These organs were functional in ancestors but have lost their function over time.
Appendix, ear pinna muscles, and tail bone (coccyx). These organs are functional in other animals.
Answers:
Heredity involves the transfer of genes from one generation to the next. Sometimes sudden changes called mutations occur in genes. These hereditary changes lead to variations. Over many generations, such variations result in the formation of new species, which are selected by nature. Thus, hereditary changes play a key role in evolution.
DNA produces mRNA, and mRNA synthesizes proteins. This process is known as the central dogma.
- mRNA is formed from DNA through transcription.
- mRNA carries coded information to the cytoplasm.
- Each amino acid is coded by three nucleotides called a triplet codon.
- tRNA brings amino acids according to the codons on mRNA.
- Amino acids are joined by peptide bonds with the help of rRNA.
- Multiple amino acid chains combine to form complex proteins.
According to the theory of evolution, life originated in the ocean as simple unicellular organisms. Over time, gradual changes led to the formation of multicellular and complex organisms. These changes occurred slowly over millions of years.
Similar body structures indicate common ancestry.
Similar bone structures in organs with different functions.
Useless organs indicating ancestral features.
Fossils provide information about extinct organisms.
Organisms showing characteristics of two different groups.
Some organs in different animals perform different functions but have similar internal bone structure. For example, the human hand, cat's foreleg, bat's wing, and whale's flipper perform different functions but have a similar bone pattern. This similarity suggests that these animals evolved from common ancestors.
A fossil is any preserved remain, impression, or trace of organisms that lived in the past. Fossils include bones, shells, and stone imprints.
The age of fossils can be determined by carbon dating using radioactive carbon (C-14). Fossils provide information about extinct organisms and show that complex organisms evolved gradually from simpler forms.
- About 7 crore years ago, dinosaurs became extinct.
- Monkey-like animals similar to lemurs appeared.
- Around 4 crore years ago, tails disappeared.
- Ape-like animals evolved with larger brains and better hands.
- Gibbons and orangutans evolved, followed by gorilla and chimpanzee.
- Human-like animals with erect posture appeared about 2 crore years ago.
- Ramapithecus is considered the first human-like ape.
- Skilled humans evolved around 20 lakh years ago.
- Neanderthal man was considered the first wise man.
- Cro-Magnon man evolved about 50,000 years ago.