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Course: Science — Third Preparatory

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Science — Third Preparatory

Science — Third Preparatory

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Science — Third Preparatory 2026/2027

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Unit 1 - Force, Motion, Acceleration and Physical Quantities

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Text lesson

Unit 4 — Dating Planet Earth

Science — Third Preparatory

Unit 4 — Dating Planet Earth

1.7 Comparative anatomy

1.7 Comparative anatomy

Comparative anatomy→is the study of similarities and differences in the body structures of different species to deduce evolutionary relationships.

Compare the forelimb of a human, a bat and a whale.
Each has the same basic bones (one upper-arm bone, two forearm bones, wrist bones, finger bones) in the same arrangement, though they are used differently: a human arm for grasping, a bat’s wing for flying, a whale’s flipper for swimming.

Comparison aspect	Main idea	Example	Keywords
Homologous structures	organs with the same basic structure (and origin) but may perform different functions because organisms adapted to different environments and lifestyles. They are evidence of a common ancestor. The similar bones of the human arm bat wing and whale flipper are evidence that these animals are all mammals	—	organssamebasicorigin
Analogous structures	organs with similar function but different structure. Example: the wings of a pterosaur (extinct flying reptile) a bat (a mammal) and a butterfly (an insect). All enable flight but: a pterosaur’s wing is a skin membrane supported by one very long finger a bat’s wing is supported by four long spread fingers like umbrella ribs an insect’s wing is an extension of the exoskeleton and has no bones or muscles in it it is moved by chest (thoracic) muscles. Analogous structures show that having wings does not mean sharing a recent common ancestor it shows adaptation to a similar way of life (flying). Homologous Analogous Structure Similar Different Function May be different Similar Meaning Common ancestor Adaptation to a similar environment Example Human arm bat wing whale flipper Bat wing and butterfly wing Importance of comparative anatomy Finding common ancestors. The more similar the internal structures of two species the closer their evolutionary relationship. Fossils show that modern birds share many features with a group of meat-eating dinosaurs called theropods	hollow bones posture and feathers. Following the evolution of organs. For instance bones of the reptile jaw evolved into the bones of the middle ear in mammals. Reconstructing extinct animals. By comparing the skeleton of an extinct animal with the skeletons of living animals scientists can picture what it looked like as with Archaeopteryx which became extinct about 150 million years ago. Transitional fossils A transitional fossil shows features of two different groups and supports the idea of a gradual evolutionary change. Archaeopteryx had teeth and a long bony tail like reptiles and feathered wings like birds. It is an example of a transitional fossil between reptiles and birds	organssimilarfunctiondifferent

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