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Q10:
Using various resources such as your school Library or the internet and discussions with your teacher, trace the evolutionary stages of any one animal, say horse.
Solution :
1. Evolutionary Trajectory of Equidae (The Horse)
The evolution of the horse ($Equus$) serves as a classic example of an orthogenetic trend characterized by progressive adaptation to changing environments—specifically the transition from dense forests to open grasslands during the Eocene to the Pleistocene epochs.
2. Chronological Evolutionary Stages
| Epoch | Genus | Key Characteristics |
|---|---|---|
| Eocene (50 Mya) | Eohippus (Hyracotherium) | Size of a fox; 4 toes on front feet, 3 on hind. Browser. |
| Oligocene (35 Mya) | Mesohippus | Size of a sheep; 3 toes on all feet, middle toe prominent. |
| Miocene (25 Mya) | Merychippus | Size of a pony; development of high-crowned teeth (hypsodonty). |
| Pliocene (5 Mya) | Pliohippus | First true monodactyl (single-toed) horse. |
| Pleistocene to Recent | Equus | Modern horse; large size, single hoof, highly specialized molars. |
3. Morphological Transformation Analysis
The evolutionary process is defined by three fundamental trends [Per the Theory of Natural Selection and Environmental Pressure]:
- Reduction in Digit Count: Reduction from multi-toed limbs to a single functional digit (the third phalanx) encapsulated in a hoof. This allowed for increased speed and efficiency on hard-packed, open grasslands [Adaptation for locomotion].
- Dental Specialization: Transition from brachydont (low-crowned) teeth for browsing soft leaves to hypsodont (high-crowned) molars with complex enamel folding. This enabled the consumption of abrasive, silica-rich prairie grasses [Adaptation for diet].
- Cranial & Body Elongation: Gradual increase in total body mass and facial length, providing a greater field of vision for predator detection in open plains [Adaptation for survival].
4. Schematic Representation of Equid Evolution
5. Theoretical Justification
The evolutionary lineage of the horse demonstrates a Phyletic Gradualism, where a continuous series of transitional forms exists [Evidence documented in the fossil record]. The change in environment—from the dense forests of the Eocene to the drying, cooling climates that created vast grasslands—acted as the primary selective pressure, favoring individuals with greater cursorial (running) ability and dental resistance to abrasive vegetation.
Final Solution: The evolution of the horse from Hyracotherium to Equus represents a comprehensive transition driven by environmental shift, resulting in increased body size, limb specialization (monodactyly), and dental complexity to facilitate life in open terrestrial habitats.
More Questions from Class 12 Biology Evolution EXERCISES
- Q1: Explain antibiotic resistance observed in bacteria in light of Darwinian selection theory.
- Q1: Explain antibiotic resistance observed in bacteria in light of Darwinian selection theory.
- Q2: Find out from newspapers and popular science articles any new fossil discoveries or controversies about evolution.
- Q2: Find out from newspapers and popular science articles any new fossil discoveries or controversies about evolution.
- Q3: Attempt giving a clear definition of the term species.
- Q3: Attempt giving a clear definition of the term species.
- Q4: Try to trace the various components of human evolution (hint: brain size and function, skeletal structure, dietary preference, etc.)
- Q4: Try to trace the various components of human evolution (hint: brain size and function, skeletal structure, dietary preference, etc.)
- Q5: Find out through internet and popular science articles whether animals other than man has self-consciousness.
- Q5: Find out through internet and popular science articles whether animals other than man has self-consciousness.
- Q6: List 10 modern-day animals and using the internet resources link it to a corresponding ancient fossil. Name both.
- Q6: List 10 modern-day animals and using the internet resources link it to a corresponding ancient fossil. Name both.
- Q7: Practise drawing various animals and plants.
- Q7: Practise drawing various animals and plants.
- Q8: Describe one example of adaptive radiation.
- Q8: Describe one example of adaptive radiation.
- Q9: Can we call human evolution as adaptive radiation?
- Q9: Can we call human evolution as adaptive radiation?
- Q10: Using various resources such as your school Library or the internet and discussions with your teacher, trace the evolutionary stages of any one animal, say horse.
CBSE Solutions for Class 12 Biology Evolution
Chapters in CBSE - Class 12 Biology
- Reproduction in Organisms
- Human Reproduction
- Reproductive Health
- Principles of Inheritance and Variation
- Molecular Basis of Inheritance
- Human Health and Disease
- Strategies for Enhancement in Food Production
- Microbes in Human Welfare
- Biotechnology: Principles and Processes
- Biotechnology and Its Applications
- Organisms and Populations
- Ecosystem
- Biodiversity and Conservation
- Environmental Issues
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