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Biology · Unit 7

Evolution: MDCAT Notes and MCQs

Origin of life

  • Early earth had a reducing atmosphere (CH4, NH3, H2, water vapour; no free O2).
  • Oparin–Haldane hypothesis: energy from lightning/UV formed simple organic molecules in the "primordial soup" → polymers → protobionts (coacervates) → first cells.
  • Miller–Urey experiment (1953): electric sparks in CH4, NH3, H2, H2O produced amino acids, supporting chemical evolution.
  • First cells were likely anaerobic heterotrophic prokaryotes; photosynthesis later added O2 to the atmosphere. RNA is thought to have been the first genetic material ("RNA world").

Lamarckism (Jean-Baptiste Lamarck, 1809 — Philosophie Zoologique)

  • Use and disuse: organs used often develop; unused organs degenerate.
  • Inheritance of acquired characters: changes acquired during life pass to offspring.
  • Example: giraffes stretching necks to reach leaves → longer necks inherited.
  • Rejected: Weismann cut tails of mice for 20+ generations — offspring still had tails. Acquired (somatic) changes are not in germ cells.

Darwinism (Charles Darwin, 1859 — On the Origin of Species)

  • Based on voyage of HMS Beagle (Galápagos finches); Alfred Russel Wallace reached similar conclusions; influenced by Malthus (populations outgrow resources).
  • Steps: overproduction → struggle for existence → variation → survival of the fittest / natural selection → inheritance of favourable variations → over many generations → new species.
  • Weakness: Darwin could not explain the source of variation — later explained by genetics (mutation, recombination) → Neo-Darwinism / modern synthesis.

Evidence for evolution: fossils, comparative anatomy (homologous organs — forelimbs of vertebrates; vestigial organs — appendix), embryology, biochemistry (DNA/protein similarity), biogeography.

PMDC learning outcomes for this unit
  • Concept of Evolution: 7.1 Explain origin of life according to concept of evolution
  • Lamarckism: 7.2 Describe the theory of inheritance of acquired characters, as proposed by Lamarck.
  • Darwinism: 7.3 Explain the theory of natural selection as proposed by Darwin

Evolution MCQs with answers

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Q1
'Inheritance of acquired characters' was proposed by:
AWallace
BLamarck
CMendel
DDarwin
Show answer
Answer: B (Lamarck). Lamarck (1809) proposed use & disuse and inheritance of acquired characters.
Q2
Darwin's theory of evolution is known as:
AMutation theory
BSpecial creation
CNatural selection
DUse and disuse
Show answer
Answer: C (Natural selection). Darwin proposed natural selection — survival and reproduction of the fittest.
Q3
Lamarck's theory was experimentally challenged by:
AMorgan
BPasteur
CWeismann
DMiller
Show answer
Answer: C (Weismann). Weismann cut tails of mice for many generations; offspring were still born with tails.
Q4
The Miller–Urey experiment produced which important biomolecules?
AAmino acids
BLipids
CNucleic acids
DProteins
Show answer
Answer: A (Amino acids). Sparking a mixture of CH4, NH3, H2 and water vapour produced amino acids.
Q5
The primitive earth's atmosphere lacked:
AAmmonia
BWater vapour
CMethane
DFree oxygen
Show answer
Answer: D (Free oxygen). The early atmosphere was reducing; free O2 came later from photosynthesis.
Q6
Forelimbs of man, whale and bat are examples of:
AAnalogous organs
BVestigial organs
CHomologous organs
DConvergent evolution
Show answer
Answer: C (Homologous organs). Homologous organs share the same basic structure and origin but differ in function.
Q7
Darwin's book 'On the Origin of Species' was published in:
A1866
B1953
C1859
D1809
Show answer
Answer: C (1859). It was published in 1859.
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