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Evolution - Interpret fossil evidence, classification, and stages of evolution including human evolution

Grade 10CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Fossils are the preserved traces or remains of organisms that lived in the past. They provide direct evidence of evolutionary history (e.g., ArchaeopteryxArchaeopteryx acts as a connecting link between reptiles and birds).

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The age of fossils is determined by two methods: Relative dating (fossils found in deeper layers of Earth are older than those in upper layers) and Carbon dating (measuring the ratio of 14C^{14}C to 12C^{12}C).

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Homologous Organs: Organs with the same basic structural design and origin but different functions. They indicate 'Divergent Evolution' and common ancestry. Example: Forelimbs of a human, bird, and lizard.

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Analogous Organs: Organs with different structural designs and origins but performing similar functions. They indicate 'Convergent Evolution'. Example: Wings of a bat (skin folds) and wings of a bird (feathers).

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Evolution by Stages: Complex organs like the eye did not evolve in a single step but through gradual changes. For example, the eye-spot in PlanariaPlanaria can only detect light, while complex eyes in vertebrates provide clear images.

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Artificial Selection: Humans have evolved different vegetables from wild cabbage by selecting specific traits: Cabbage (short distance between leaves), Broccoli (arrested flower growth), Cauliflower (sterile flowers), and Kohlrabi (swollen parts).

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Molecular Phylogeny: This approach uses changes in DNA sequences during reproduction to trace evolutionary relationships. Organisms with more similar DNA are more closely related.

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Human Evolution: All humans belong to the species Homo sapiensHomo\ sapiens. DNA evidence shows that the earliest members of Homo sapiensHomo\ sapiens originated in Africa and migrated across the planet in multiple waves.

📐Formulae

Age Calculation (Radiocarbon):t=ln⁡(N0/N)λ\text{Age Calculation (Radiocarbon)}: t = \frac{\ln(N_0/N)}{\lambda}

Common Ancestry∝Similarity in DNA sequence\text{Common Ancestry} \propto \text{Similarity in DNA sequence}

Carbon Ratio=14C12C\text{Carbon Ratio} = \frac{^{14}C}{^{12}C}

Rate of Evolution=ΔGenetic VariationΔTime\text{Rate of Evolution} = \frac{\Delta \text{Genetic Variation}}{\Delta \text{Time}}

💡Examples

Problem 1:

A fossil XX is found in a layer of rock 5050 meters deep, and fossil YY is found in a layer 1010 meters deep. Which fossil is likely more recent?

Solution:

Fossil YY is more recent.

Explanation:

According to the principle of relative dating, the layers of earth are deposited over time. Fossils found in deeper layers (like XX at 5050m) were buried earlier, whereas fossils in shallower layers (like YY at 1010m) were buried more recently.

Problem 2:

Identify the type of evolution indicated by the wings of a butterfly and the wings of a bat.

Solution:

Analogous organs (Convergent Evolution).

Explanation:

The wings of a butterfly are made of a thin membrane without bones, while the wings of a bat are skin folds stretched between elongated fingers. Since their basic structures are different but they perform the same function (flight), they are analogous organs resulting from convergent evolution.

Problem 3:

A researcher is studying the DNA of three species: AA, BB, and CC. The DNA sequence similarity between AA and BB is 98%98\%, and between AA and CC is 85%85\%. Which species shared a common ancestor most recently?

Solution:

Species AA and BB.

Explanation:

In molecular phylogeny, a higher percentage of DNA sequence similarity indicates that the species have diverged from a common ancestor more recently. Since AA and BB share 98%98\% similarity, they are more closely related than AA and CC.