Exercises
Explain antibiotic resistance observed in bacteria in light of Darwinian selection theory.
Answer
Darwin's theory rests on variation, struggle for existence, and natural selection of the fittest, whose heritable traits spread over generations. A bacterial population is not uniform: by chance mutation, a few cells may carry genes that let them survive a particular antibiotic. When the antibiotic is applied, it acts as the selecting agent – sensitive bacteria are killed while the resistant variants survive. With competitors removed, the resistant cells multiply rapidly and pass the resistance genes to their progeny. Because bacteria divide within minutes to hours, in a short time most of the population becomes resistant. Here the resistant type has greater fitness (more surviving progeny) under the new conditions, which is exactly Darwinian natural selection; the variation existed before the antibiotic and was selected, not created, by it. Overuse and misuse of antibiotics speed up this selection.
Find out from newspapers and popular science articles any new fossil discoveries or controversies about evolution.
Answer
(Activity – students should look up the latest reports.) Some well-known examples to start from:
(i) Tiktaalik roseae (Canada, 2004): a fish with limb-like fins and a neck, a transitional fossil between fishes and four-legged land animals.
(ii) Homo floresiensis (Flores, Indonesia, 2003): small-bodied, small-brained humans nicknamed "hobbits"; debate continues on whether they were a separate species.
(iii) Homo naledi (Rising Star cave, South Africa, 2015): a mix of primitive and modern features; claims that it buried its dead are controversial.
(iv) Feathered dinosaurs from China (e.g. Sinosauropteryx): support the evolution of birds from dinosaurs.
(v) Controversy: the discredited "Piltdown man" (a forgery exposed in 1953) and ongoing debates on whether evolution is gradual (Darwin) or happens in jumps (saltation, as proposed by de Vries).
Attempt giving a clear definition of the term species.
Answer
A species is a group of natural populations whose members are similar in structure, can interbreed freely in nature to produce fertile offspring, and are reproductively isolated from other such groups (biological species concept). Members of a species share a common gene pool. Example: all humans belong to Homo sapiens; a horse and a donkey are separate species because their offspring (mule) is sterile.
Try to trace the various components of human evolution (hint: brain size and function, skeletal structure, dietary preference, etc.)
Answer
(i) Dryopithecus and Ramapithecus (about 15 mya): hairy, walked like gorillas and chimpanzees; Ramapithecus more man-like, Dryopithecus more ape-like.
(ii) Man-like primates of East Africa (3–4 mya): not taller than about 4 feet but walked upright (bipedal).
(iii) Australopithecines (about 2 mya): lived in East African grasslands, hunted with stone weapons but mainly ate fruit.
(iv) Homo habilis: the first human-like being (hominid); brain 650–800 cc; probably did not eat meat.
(v) Homo erectus (about 1.5 mya, fossils from Java): larger brain, about 900 cc; probably ate meat.
(vi) Neanderthal man (1,00,000–40,000 years ago, near east and central Asia): brain about 1400 cc; used hides to protect the body and buried their dead.
(vii) Homo sapiens: arose in Africa and spread across continents, forming distinct races; modern Homo sapiens arose during the ice age (75,000–10,000 years ago). Cave art developed about 18,000 years ago (e.g. Bhimbetka, Madhya Pradesh), and agriculture and settlements about 10,000 years ago.
Overall trends: increase in brain size and intelligence, development of language, upright posture with changes in skeleton (pelvis, spine, free hands), reduction of jaws and face, change of diet from fruits to an omnivorous diet including meat, use of tools and fire, and social and cultural life.
Find out through internet and popular science articles whether animals other than man has self-consciousness.
Answer
(Activity.) Self-consciousness is often tested by the mirror self-recognition test: a mark is put on an animal's body where it can see it only in a mirror; if the animal touches or examines the mark on itself, it is taken to recognise itself. Animals reported to pass include chimpanzees, bonobos, orangutans, some gorillas, Asian elephants, bottlenose dolphins, killer whales (orcas) and the Eurasian magpie; recent studies even report it in a small fish, the cleaner wrasse, though this is debated. Such findings suggest that some degree of self-awareness exists in other animals, especially those with large, complex brains and social lives, though scientists still debate how far it matches human self-consciousness.
List 10 modern-day animals and using the internet resources link it to a corresponding ancient fossil. Name both.
Answer
1. Horse – Eohippus (Hyracotherium)
2. Elephant – Moeritherium
3. Whale – Pakicetus
4. Bird – Archaeopteryx
5. Camel – Protylopus
6. Dog – Hesperocyon
7. Cat – Proailurus
8. Giraffe – Palaeotragus
9. Rhinoceros – Hyracodon
10. Human – Australopithecus
Practise drawing various animals and plants.
Answer
(Activity – to be done by the student.) Useful practice for this chapter: beaks of Darwin's finches, the white-winged and dark-winged peppered moth, homologous forelimbs (whale, bat, cheetah, human), thorn of Bougainvillea and tendril of Cucurbita (homologous organs), wings of butterfly and bird (analogous organs), Australian marsupials, and stages of horse evolution. Draw neat outlines, label clearly and keep proportions correct.
Describe one example of adaptive radiation.
Answer
Adaptive radiation is the evolution of different species in a given geographical area starting from a point and radiating into other habitats. Example: Darwin's finches of the Galapagos Islands. Darwin found many varieties of small black finches on the same island. All of them evolved there from an original seed-eating ancestor. As they spread to different habitats, their beaks changed in shape and size to suit different foods, giving rise to insectivorous, seed-eating and vegetarian (cactus/fruit-eating) finches. (Another example: Australian marsupials, such as kangaroo, koala, Tasmanian wolf, marsupial mole and sugar glider, evolved from a common ancestral stock within the Australian continent.)
Can we call human evolution as adaptive radiation?
Answer
No. Adaptive radiation means many different species arising from one ancestor at about the same time in a given geographical area, each spreading into and adapting to a different habitat (like Darwin's finches or Australian marsupials). Human evolution is a sequence of successive stages along one line (Dryopithecus/Ramapithecus
⇒ Australopithecus
⇒ Homo habilis
⇒ Homo erectus
⇒ Neanderthal
⇒ Homo sapiens), with only one human species surviving today. It does not represent radiation into many coexisting forms suited to different habitats, so it is not an example of adaptive radiation.
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.
Answer
The horse lineage evolved in North America over about 60 million years:
(i) Eohippus (Hyracotherium), Eocene: fox-sized, about 30 cm tall; four toes on forelimbs and three on hindlimbs; short-crowned teeth for browsing soft leaves in forests.
(ii) Mesohippus, Oligocene: larger, about 60 cm (goat-sized); three toes on all limbs, middle toe larger; still a browser.
(iii) Merychippus, Miocene: about 100 cm tall; three toes but walked on the large middle toe, side toes not touching the ground; high-crowned grinding teeth for grazing grass on open plains.
(iv) Pliohippus, Pliocene: about 120 cm tall; the first one-toed horse with a hoof; side toes reduced to splints.
(v) Equus, Pleistocene to present: modern horse, about 150 cm tall; single-toed hoof, long legs for fast running, and teeth suited for grazing.
Trends: increase in body size; lengthening of limbs and neck; reduction of side toes to a single hoofed toe for speed on open grassland; and change of teeth from browsing to grazing, as forests gave way to grasslands.
Important Extra Questions
Differentiate between homologous and analogous organs with examples.
Answer
Homologous organs have the same basic structure and origin but different functions (forelimbs of whale, bat, cheetah and human) – divergent evolution. Analogous organs have different structure and origin but similar function (wings of butterfly and bird, eye of octopus and mammal) – convergent evolution.
Explain industrial melanism.
Answer
In England, after industrialisation, tree trunks darkened with smoke and lost lichens; dark-winged moths were camouflaged and escaped predators while white-winged moths were eaten, so the dark form became more common – natural selection in action.
State the Hardy-Weinberg principle and write its equation.
Answer
Allele frequencies in a population remain constant from generation to generation (genetic equilibrium) unless disturbed: p² + 2pq + q² = 1, where p and q are frequencies of alleles A and a.
Name the five factors that disturb Hardy-Weinberg equilibrium.
Answer
Gene migration (gene flow), genetic drift, mutation, genetic recombination and natural selection.
What did S.L. Miller's experiment show?
Answer
Using electric discharge in a closed flask of CH₄, H₂, NH₃ and water vapour at 800 °C, he obtained amino acids, supporting chemical evolution of organic molecules from inorganic ones.