Notes On Evolutionary Relationships II - CBSE Class 10 Science
Characteristics These are the hereditary traits transmitted from parent organisms to their offspring. Characteristics are of two types namely, homologous characteristics or analogous characteristics          • Homologous characteristics are organs that have the same basic structure and origin, but different functions. For example, mammals, birds, reptiles and amphibians have four limbs with the same basic limb layout because they have inherited the limbs from a common ancestor. These limbs have been modified to perform different functions.          • Analogous characteristics are organs that have different structures and are of different origin, but perform same functions. For example, the design of the wings of bats and the wings of birds look similar because they have a common purpose – to fly. Fossils Fossils are the remains or traces of a plant or animal that existed in a past geological age, and that has been excavated from the soil. Fossilisation is the process in which an organism is converted into a fossil. Biological convergence This is a phenomenon by which two unrelated organisms become quite alike after a period of time through few generations, if it is assumed that they have a common ancestor. The eyes of the octopus and the eyes of vertebrates have evolved independently. These similarities of structure, despite of different origins provide a classic example of biological convergence. Adaptation A characteristic of a particular animal may, post-evolution be useful for performing a totally different function. For example, long feathers were considered to provide insulation in cold weather. Some reptiles like the dinosaur had feathers but very few were adapted for flying. In the present day, birds use feathers for flight, which is an example of adaptation. Artificial selection This is the usage of plants with desirable characteristics to produce new varieties. Broccoli, kohlrabi and kale are produced from its ancestor wild cabbage by artificial selection. The tools used to trace evolutionary relationships are excavation, time-dating, studying fossils, and determining DNA sequences. These have been used for studying human evolution.

#### Summary

Characteristics These are the hereditary traits transmitted from parent organisms to their offspring. Characteristics are of two types namely, homologous characteristics or analogous characteristics          • Homologous characteristics are organs that have the same basic structure and origin, but different functions. For example, mammals, birds, reptiles and amphibians have four limbs with the same basic limb layout because they have inherited the limbs from a common ancestor. These limbs have been modified to perform different functions.          • Analogous characteristics are organs that have different structures and are of different origin, but perform same functions. For example, the design of the wings of bats and the wings of birds look similar because they have a common purpose – to fly. Fossils Fossils are the remains or traces of a plant or animal that existed in a past geological age, and that has been excavated from the soil. Fossilisation is the process in which an organism is converted into a fossil. Biological convergence This is a phenomenon by which two unrelated organisms become quite alike after a period of time through few generations, if it is assumed that they have a common ancestor. The eyes of the octopus and the eyes of vertebrates have evolved independently. These similarities of structure, despite of different origins provide a classic example of biological convergence. Adaptation A characteristic of a particular animal may, post-evolution be useful for performing a totally different function. For example, long feathers were considered to provide insulation in cold weather. Some reptiles like the dinosaur had feathers but very few were adapted for flying. In the present day, birds use feathers for flight, which is an example of adaptation. Artificial selection This is the usage of plants with desirable characteristics to produce new varieties. Broccoli, kohlrabi and kale are produced from its ancestor wild cabbage by artificial selection. The tools used to trace evolutionary relationships are excavation, time-dating, studying fossils, and determining DNA sequences. These have been used for studying human evolution.

#### Activities

Activity 1 Wonderville.ca has devised a game which allows the user to select the conditions for fossilising a dead animal. Under appropriate conditions, dead animal is fossilised. If the conditions selected by the user are not apt for the process of 'Fossilisation', bones of the animal get eroded and fossil is not formed. The animation created with SFX sound effects to thrill the user Go to Activity Activity 2 Utexas.edu has created a template which provides information about 'Phylogenetic Evolutionary Tree'. It provides the student the knowledge about evolution in the form of a tree diagram. Important concepts like 'Homologous Structures' and 'Analogous Structures' are discussed in detail. Go to Activity Activity 3 Indiana.edu has manifested a template just to explain 'Evolution of Human beings'. This template help the user to know about gradual changes which took place over millions of years which helped in Evolution of man from chimpanzee. Go to Activity

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