Questions: Evolution

Q1 Explain antibiotic resistance in bacteria in the light of Darwinian natural selection.

Answer (English): A bacterial population has built-in variation, and some cells carry mutations that make them less affected by a particular antibiotic. When the antibiotic is used, the sensitive cells die while the resistant variants survive and reproduce, and because bacteria divide very fast the resistant variant becomes common within a few generations. The antibiotic does not create the resistance; it selects the variants that already carry it. The same logic explains why resistant strains appear in months or years, which is evolution by anthropogenic action.

Hinglish: Bacteria ki population mein pehle se variation hota hai; kuch cells antibiotic ke against resistant hote hain. Antibiotic use karne par sensitive cells marte hain aur resistant cells survive karke tezi se divide karte hain, isliye resistant strain common ho jaata hai. Antibiotic resistance banata nahi, sirf select karta hai.

Q2 What are fossils? How do fossils help us to understand the process of evolution?

Answer (English): Fossils are the remains of the hard parts of life forms preserved in rocks. Rocks form from sediments, and different sedimentary layers contain fossils of different ages. Studying the fossils of successive layers shows that life forms changed over geological time and that particular forms are restricted to particular time spans, so new forms appeared at different times. Fossils of extinct organisms such as the dinosaurs show that forms which once existed are no longer present. The age of a fossil is estimated by radioactive dating, which places the fossil in the geological time scale.

Hinglish: Fossils jeevon ke hard parts ke remains hain jo rocks ke sediments mein milte hain. Alag layers mein alag umar ke fossils milte hain, jisse pata chalta hai ki jeev samay ke saath badle aur kuch forms khaas time period tak hi rahe. Radioactive dating se fossil ki umar milti hai.

Q3 Define species. Why is the definition difficult to apply in practice?

Answer (English): A species is a group of individuals that can interbreed and produce fertile offspring under natural conditions, and that is reproductively isolated from other such groups. The definition is difficult to apply in practice because many organisms reproduce asexually, some distinct forms can interbreed in captivity, and fossil forms cannot be tested for interbreeding. Populations that live in different places may also look different without being separate species.

Hinglish: Species woh group hai jo natural conditions mein interbreed karke fertile offspring paida kar sake aur dusre groups se reproductively isolated ho. Practical mein dikkat aati hai kyunki kai organisms asexually reproduce karte hain aur fossils ka interbreeding test nahi kar sakte.

Q4 Trace the main components of human evolution, mentioning brain size and diet wherever relevant.

Answer (English): The sequence begins with Dryopithecus and Ramapithecus about 15 million years ago, hairy primates that walked like gorillas and chimpanzees. Man-like primates walked in eastern Africa about 3 to 4 million years ago, and Australopithecines lived in the East African grasslands about 2 million years ago, hunted with stone weapons and mainly ate fruit. Homo habilis, the first human-like being, had a brain of 650 to 800 cc and probably did not eat meat. Homo erectus, about 1.5 million years ago, had a brain around 900 cc and probably ate meat. The Neanderthal man had a brain of 1400 cc and used hides and buried the dead, and Homo sapiens arose in Africa and spread across continents. Cave art appears about 18,000 years ago and agriculture about 10,000 years ago.

Hinglish: Human evolution ka order: Dryopithecus/Ramapithecus (15 mya), man-like primates (3-4 mya), Australopithecines (2 mya, fruit), Homo habilis (650-800 cc, no meat), Homo erectus (900 cc, meat), Neanderthal (1400 cc), Homo sapiens. Cave art 18,000 saal aur agriculture 10,000 saal pehle shuru hui.

Q5 Describe one example of adaptive radiation.

Answer (English): Darwin's finches are the standard example. On the Galapagos Islands, many varieties of small black birds evolved on the island itself from a single ancestral seed-eating form. The beaks of the different varieties became modified, and the modified beaks allowed some forms to become insectivorous and others vegetarian. The variety of beaks in one geographical area, radiating into different feeding habits, is adaptive radiation. The Australian marsupials are a second example, with many different marsupials evolving from one ancestral stock within the Australian continent.

Hinglish: Galapagos Islands par Darwin ki finches ek hi seed-eating ancestor se bani, aur unke beaks badal kar kuch insectivorous aur kuch vegetarian ho gaye. Ek area se alag feeding habits mein radiation hi adaptive radiation hai. Australian marsupials dusra example hain.

Q6 Can human evolution be called adaptive radiation? Give a reason.

Answer (English): Human evolution is not an example of adaptive radiation. Adaptive radiation means many different species evolving from a common ancestor and radiating into different habitats, as the finches did on the Galapagos Islands. Human evolution is a progressive lineage from Homo habilis through Homo erectus to Homo sapiens, with changes in brain size, posture and diet, and it does not show the branching into many different habitats that adaptive radiation describes.

Hinglish: Human evolution adaptive radiation nahi hai. Adaptive radiation mein ek common ancestor se kai species banti hain jo alag habitats mein fail jaati hain, jaise Galapagos ki finches. Human evolution ek progressive lineage hai Homo habilis se Homo erectus aur Homo sapiens tak, isliye ise adaptive radiation nahi kehte.

Q7 What does the Hardy-Weinberg principle state? Write the equation and explain the symbols.

Answer (English): The principle states that the allele frequencies of a gene in a population remain constant from generation to generation, so the gene pool stays in genetic equilibrium. For two alleles with frequencies p and q, p plus q equals one. The frequency of the homozygous dominant genotype AA is p squared, of the homozygous recessive genotype aa is q squared, and of the heterozygous genotype Aa is 2pq, so p squared plus 2pq plus q squared equals one. A measured frequency that differs from the expected value indicates evolutionary change.

Hinglish: Hardy-Weinberg principle kehta hai ki allele frequencies generations tak constant rehti hain aur gene pool genetic equilibrium mein rehta hai. p + q = 1; p² = AA, q² = aa, 2pq = Aa; aur p² + 2pq + q² = 1. Agar measured frequency expected se alag ho to evolution ho raha hai.

Q8 List the five factors that disturb genetic equilibrium and explain any one.

Answer (English): The five factors are gene flow, genetic drift, mutation, recombination during gamete formation and natural selection. Genetic drift is the change in allele frequency that occurs by chance rather than by selection. When a small part of a population separates and builds a new population, chance can make the allele frequencies of the new population quite different from the original, and the original drifted population becomes the founder population. The effect is called the founder effect, and with enough drift the new population can become a different species.

Hinglish: Paanch factors: gene migration/gene flow, genetic drift, mutation, genetic recombination aur natural selection. Genetic drift matlab chance se allele frequency badalna; chhoti population alag ho kar nayi population banaaye to founder effect kehte hain.

Q9 Explain the industrial melanism observation in terms of natural selection.

Answer (English): In England before industrialisation, white winged moths were more common than dark winged moths, because lichens covered the trees and gave a pale background on which the white moth was hidden. After industrialisation, smoke and soot darkened the trunks, and the dark moths became more common while the white moths were picked out by predators. The change is natural selection in action: the variant that is better camouflaged survives and leaves more progeny, and the proportion of the two variants reverses. In rural areas where industrialisation did not occur, the count of melanic moths stayed low.

Hinglish: Industrialisation se pehle lichens ki wajah se ped halke the, isliye white moths chhupe rehte the. Soot se ped kaale hone par dark moths survive karte aur white plate jaate, isliye 1920 tak dark moths zyada ho gaye. Rural areas mein melanic moths kam hi rahe.

Q10 Describe the three modes of natural selection with reference to the distribution of a trait.

Answer (English): Stabilising selection favours the mean value of the trait, so more individuals acquire values near the mean and the peak of the distribution becomes higher and narrower. Directional selection favours one extreme, so the peak of the distribution shifts in that direction, as with the moth population after industrialisation. Disruptive selection favours the values at both ends of the distribution, so two peaks form and the middle values become less common. The three modes show that selection can act on the distribution in different ways depending on which phenotype is favoured in the environment.

Hinglish: Stabilising selection mean value ko favour karta hai, directional selection ek extreme ko, aur disruptive selection dono ends ko. Isliye stabilising mein peak uncha aur patla hota hai, directional mein peak ek taraf shift hota hai, aur disruptive mein do peaks ban jaate hain.

The quiz on this page has five questions on the origin of life, evidences for evolution, adaptive radiation, the Hardy-Weinberg principle and the modes of natural selection. Attempt it after writing the ten answers above.