Evolution and Classification
NCERT Class 10 • Science • Chapter "Heredity and Evolution" | NCERT Class 9 • Science • Chapter "Diversity in Living Organisms"
Evolution and Classification
Evolution is the gradual change in the inherited characteristics of a population over many generations. It explains both why organisms are so diverse and why they nonetheless share so many features, which classification then organises into a system.
How Evolution Works
- Variation is the difference between individuals of the same species, and it arises during sexual reproduction and from changes in genes.
- Variation is essential because it gives a population something to select from when conditions change.
- Natural selection, explained by Darwin, means that individuals better suited to their environment survive and leave more offspring.
- Over long periods these small advantages accumulate and the population changes, which is evolution.
- A species is a group of organisms that can interbreed and produce fertile offspring.
- Speciation occurs when a population is separated so that gene flow stops and the two groups gradually become different species.
- Geographical barriers, genetic drift and selection all contribute to speciation.
Evidence and Classification
- Fossils are the preserved remains of ancient organisms and give direct evidence of past life and of change over time.
- Homologous organs have a similar basic structure but different functions, as in the forelimb of a human, a bat and a whale, and show common ancestry.
- Analogous organs have different structure but similar function, as in the wing of a bird and of an insect, and show adaptation to a similar way of life.
- Embryological similarity among vertebrates in early stages is another line of evidence.
- Classification arranges organisms into groups on the basis of similarities and differences.
- The hierarchy runs kingdom, phylum, class, order, family, genus, species, with similarity increasing down the list.
- Binomial nomenclature, given by Linnaeus, names every organism with a genus and a species name in Latin.
| Evidence | What It Shows | Example |
|---|---|---|
| Fossil | Direct record of past life | Fossil of an extinct reptile |
| Homologous organ | Common ancestry | Forelimb of human, bat, whale |
| Analogous organ | Similar adaptation | Wing of bird and insect |
Natural selection — the process by which individuals better adapted to their environment survive and reproduce more successfully.
Exam me kaise aata hai
- Who explained natural selection — Darwin
- Organs with similar structure but different function are — homologous organs
- Who gave binomial nomenclature — Linnaeus
- The smallest unit of classification is the — species
UPSC/State PSC ke liye
- Homologous organs argue for common ancestry while analogous organs argue only for similar selective pressure, so the two kinds of evidence answer different questions.
- Evolution does not act on individuals but on populations, since it is the frequency of traits across generations that changes.
Yahan confuse hote hain
✗ Homologous and analogous organs mean the same | Homologous share structure; analogous share function | ✓
✗ Evolution means individuals change during their lifetime | Populations change across generations | ✓
✗ Fossils show only extinct animals | Fossils also record how existing groups changed over time | ✓
Ek nazar me
- Variation plus natural selection over long periods produces evolution.
- Speciation happens when gene flow between separated populations stops.
- Fossils, homologous organs and embryology are the main evidences.
- Classification runs from kingdom to species with binomial nomenclature for naming.
Ab practice karein
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