Q.(a)
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🔒 Start your 14-day free trial to unlock the full solution →Part (a)Concept understanding — Human Evolution Evidence
Human Evolution Evidence: A First Look
Think about a detective who arrives at a crime scene long after everyone has left. There are no eyewitnesses, no videos, no confessions. Yet the detective can piece together what happened — from footprints, a strand of hair, a broken cup, the pattern of dust on the floor. That is exactly how scientists study human evolution. We cannot go back in time to watch our ancestors evolve, but we have left behind clues. The job of an evolutionary scientist is to read those clues.
What is human evolution evidence?
Human evolution evidence is any physical or biological trace left by our ancestors that helps us understand how modern humans — Homo sapiens — came to be. It is not a single thing. It is a collection of different kinds of clues that, when put together, tell a story spanning millions of years.
The NCERT textbook for Class 12 (Biology, Chapter 7) introduces this topic under "Evolution" and emphasises that the evidence comes from fossils, comparative anatomy, embryology, and molecular biology. For a humanities or commerce student, the key is to see these as different types of documents in the archive of life.
The main types of evidence
1. Fossils — the direct remains
Fossils are the most dramatic evidence. They are the preserved remains of ancient organisms — bones, teeth, footprints, even impressions of skin or feathers. When a hominid (an early human relative) died and was quickly buried by sediment, its bones could slowly turn to stone over millions of years.
What do fossils tell us? They show us the shape of the skull, the size of the brain, the structure of the jaw and teeth, and whether the creature walked upright. For example, the famous fossil "Lucy" (Australopithecus afarensis) from Ethiopia, dated to about 3.2 million years ago, had a small brain but walked on two legs. That was a revolutionary clue: bipedalism (walking on two feet) came before a large brain.
Fossils are rare. Most organisms never become fossils. The ones we find are a tiny, incomplete sample. This is why every new fossil discovery can rewrite parts of the story.
2. Comparative anatomy — the body's blueprint
If you look at the bones of a human arm, a bat's wing, a whale's flipper, and a horse's leg, you will notice something striking: they all have the same basic arrangement of bones — one upper bone, two lower bones, a cluster of wrist bones, and then digits. These are called homologous organs — same structure, different functions.
Why does this matter? It suggests that all these animals inherited this basic limb plan from a common ancestor. Over millions of years, natural selection modified the same blueprint for different uses — flying, swimming, running, grasping. The NCERT textbook uses this as a key argument for evolution: similar structures in different species point to a shared ancestry.
Do not confuse homologous organs with analogous organs — structures that look similar but have different evolutionary origins, like the wings of a bird and the wings of an insect. They serve the same function (flying) but evolved independently. That is convergent evolution, not common ancestry.
3. Embryology — the shared beginning
In the early stages of development, the embryos of fish, amphibians, reptiles, birds, and mammals look remarkably alike. All have a tail, gill slits, and a similar body plan. As development proceeds, they diverge into their distinct adult forms.
This similarity in early embryos is evidence that these groups share a common ancestor. The NCERT textbook mentions this as "embryological evidence" — the idea that the more closely related two species are, the longer their embryos will resemble each other.
4. Molecular biology — the DNA record
This is the most modern and precise type of evidence. Every living organism uses DNA as its genetic material. By comparing the DNA sequences of different species, scientists can measure how closely related they are. Humans and chimpanzees share about 98–99% of their DNA. Humans and mice share about 85%. Humans and bacteria share far less.
The NCERT textbook points out that molecular evidence has confirmed what fossils and anatomy had already suggested: humans are most closely related to the great apes (chimpanzees, gorillas, orangutans), and our evolutionary path split from the chimpanzee lineage roughly 6–7 million years ago.
Why does this evidence matter? …
Part (b)Concept understanding — Mendelian Genetics Basics
Mendelian Genetics Basics
Imagine you have a box of coloured beads — red and white. If you pick one bead from the box, you get either red or white. Now imagine that the colour of your eyes, or the shape of your earlobe, is decided by something like that: a tiny "packet" inside your cells that comes in two versions, and you inherit one from each parent. That is the core idea of Mendelian genetics.
The everyday intuition
You have probably noticed that children often look like their parents — same hair colour, same dimples, same height. But they are never exact copies. Why? Because each parent contributes half of the "instructions" for building a child. Those instructions come in pairs, one from mother and one from father. Sometimes one instruction overrides the other; sometimes they blend. Gregor Mendel, a 19th-century monk, figured out the rules by watching pea plants — tall vs short, yellow vs green seeds — and counting what appeared in the next generation.
The precise meaning
Mendelian genetics is the study of how traits are passed from parents to offspring through genes. A gene is a unit of heredity — a stretch of DNA that codes for a specific characteristic, like flower colour. Each gene comes in different versions called alleles. For every gene, you inherit two alleles: one from your mother, one from your father.
If the two alleles are identical, you are homozygous for that trait. If they are different, you are heterozygous. In a heterozygous pair, one allele may be dominant — it shows up in the appearance — and the other recessive — it stays hidden unless both alleles are recessive.
Mendel's key insight was that traits are not blended like paint. Instead, alleles remain separate and are passed on intact. A recessive allele can skip a generation and reappear later, unchanged.
Why it matters
Mendelian genetics is the foundation of modern biology. It explains:
- Why some diseases run in families (like cystic fibrosis or sickle-cell anaemia)
- How plant and animal breeders create new varieties
- Why you might have your grandmother's eyes but not your mother's
The NCERT textbook states that Mendel's work established the laws of inheritance — the Law of Dominance, the Law of Segregation, and the Law of Independent Assortment. These laws describe how alleles separate during the formation of eggs and sperm, and how different genes are inherited independently of one another.
Key terms at a glance
- Gene: a unit of heredity on a chromosome
- Allele: a variant form of a gene
- Dominant: the allele that expresses itself even when paired with a different allele
- Recessive: the allele that expresses itself only when paired with an identical recessive allele
- Homozygous: having two identical alleles for a gene
- Heterozygous: having two different alleles for a gene …
Part (a)
(i) Two characteristics of Neanderthal man (Homo neanderthalensis, near East and Central Asia, ~1,00,000-40,000 years ago):
- A large brain, about 1400 cc, comparable to modern humans.
- A robust, stocky, cold-adapted body; they used animal hides to protect themselves and buried their dead.
(ii) Identify the hominids:
- (I) Brain capacity ~900 cc, probably ate meat -> Homo erectus. (First to use fire; ate meat.) …
Part (a): Neanderthals were robust, cold-adapted hominids with ~1400 cc brains that buried their dead; Homo erectus (~900 cc) ate meat, Homo habilis (650-800 cc) was the first human-like tool-maker.
Part (b): with 36% blue-eyed (q² = 0.36), q = 0.6 so freq(B) = 0.4 (40%), heterozygotes 2pq = 48%, homozygous dominant p² = 16%.
Part (a)
(i) Characteristics of Neanderthal man.
Homo neanderthalensis lived in the near East and Central Asia roughly between 1,00,000 and 40,000 years ago, during Ice-Age conditions. Two clear characteristics:
- Large brain: the Neanderthal cranial capacity was about 1400 cc, equal to (or slightly larger than) that of modern humans.
- Robust, cold-adapted body and cultural behaviour: they were heavily built and stocky (reducing heat loss), used hides/skins to protect their bodies from cold, and buried their dead — evidence of complex behaviour.
(ii) Identifying the hominids.
- (I) Brain capacity ~900 cc, probably ate meat -> Homo erectus. This species had a brain of about 900 cc, is associated with the use of fire, and evidence suggests it ate meat. …
Showing the 12 most recent of 83 on this concept.
- CBSE 2026Set V11 markQ.Homo erectus had a brain size around ___________.
›Reveal solutionSolution
Homo erectus had a brain capacity of about 900 cc.
In human evolution, Homo erectus lived about 1.5 million years ago and had a larger brain than its ancestors, with a cranial (brain) capacity of around 900 cc. Homo erectus probably ate meat. (For comparison, Ho …
- CBSE 2026Set EG1 markQ.Who proposed the chromosomal theory of inheritance?
›Reveal solutionSolution
The chromosomal theory of inheritance was put forward by Sutton and Boveri (1902).
Working independently, Walter Sutton and Theodor Boveri noticed that the behaviour of chromosomes during meiosis exactly parallels the behaviour of Mendel's 'factors' (genes) — they occur in pairs, segregate during gamete formation and assort independently. Around 1902 they proposed the chromosomal theory of inheritance, stating that genes are located on chromosomes, and that the pairing and separation of chromosomes is the physical basis of …
- CBSE 2026Set A1 markMCQQ.Which of the following laws is based on monohybrid cross?(a) Law of dominance(b) Law of segregation(c) Law of independent assortment(d) Both (A) and (B)
›Reveal solutionSolution
A monohybrid cross reveals the Law of Dominance and the Law of Segregation; independent assortment needs a dihybrid cross.
Mendel's monohybrid cross (a single-character cross) showed that one allele masks the other in the F1 (Law of Dominance) and that the paired factors separate during gamete formation so each gamete carries only one, reappearing in the 3:1 F2 ratio (Law of Segregation). T …
- CBSE 2026Set A1 markMCQQ.Which of the following was more like ape?(a) Dryopithecus(b) Ramapithecus(c) Homo erectus(d) Australopithecus
›Reveal solutionSolution
Among these ancestors, Dryopithecus was the most ape-like; Ramapithecus was more man-like.
Dryopithecus was a hairy, ape-like primate that walked like a gorilla/chimpanzee and is regarded as more ape-like. Ramapithecus was more man-like (more human). Australopithecus and Homo erectus are l …
- CBSE 2026Set BOTANY1 markMCQQ.The genotypic ratio of F2 generation of Mendel's monohybrid cross is _____.(a) 3 : 1(b) 1 : 2 : 1(c) 2 : 2(d) 1 : 1
›Reveal solutionSolution
In a monohybrid cross, the F2 phenotypic ratio is 3:1 but the underlying genotypic ratio is 1:2:1.
In Mendel's monohybrid cross (e.g. tall (TT) x dwarf (tt) pea plants), the F1 generation is entirely heterozygous (Tt) and phenotypically tall, since tallness is dominant. When F1 plants are self-pollinated, each parent contributes either a T or a t gamete with equal probability (1/2 each). Using a Punnett square, the F2 offspring genotypes appear in the ratio:
- TT (homozygous dominant) : 1/4
- Tt (heterozygous) : 1/2 (i.e. 2/4, from Tt and tT)
- tt (homozygous recessive) : 1/4 …
- CBSE 2026Set ANNUAL1 markMCQQ.Who rediscovered the results of Mendel's inheritance of characters?(a) Devries, Correns and Tschermak(b) Sutton and Boveri(c) Schleiden, Schwann and Morgan(d) Watson and Crick
›Reveal solutionSolution
Mendel's 1865 findings were ignored for about 35 years until three botanists independently rediscovered the same laws of inheritance in 1900.
Mendel presented his laws of inheritance in 1865, but their significance was not understood at the time and the work was ignored for about 35 years. In 1900, Hugo de Vries, Carl Correns and Erich von Tschermak independently rediscovered Mendel's results while working on different plants, and gave due credit to Mendel's original work. Sutton and Boveri later proposed the chromosomal theory of inherit …
- CBSE 2026Set ANNUAL1 markQ.Fill in the blank: The brain capacity of homo habilis man was ______ cc.
›Reveal solutionSolution
Homo habilis, the first tool-using early human, had a cranial (brain) capacity of roughly 650-800 cc.
Fossils of Homo habilis, discovered in Africa, show a brain capacity of about 650 to 800 cubic centimetres (cc) - larger than earlier hominids like Australopithecus but smaller than modern Homo sapiens (~1350 …
- CBSE 2026Set ANNUAL1 markMCQQ.When the genotype of an organism contains two identical alleles, the organism is considered as(a) Homozygous(b) Heterozygous(c) Hemizygous(d) Pleiotropy
›Reveal solutionSolution
Two identical alleles at a locus (e.g., TT or tt) make the organism homozygous; two different alleles (Tt) make it heterozygous.
In diploid organisms, each gene locus carries two alleles, one inherited from each parent.
- If both alleles are identical (e.g., TT or tt), the genotype is homozygous (true-breeding) for that trait.
- If the two alleles are different (e.g., Tt), the genotype is heterozygous.
- Hemizygous refers to having only a single copy of a gene/allele (as with X-linked genes in a male, who has only one X chromosome). …
- CBSE 2026Set ANNUAL1 markMCQQ.Crosses between F1 offspring and either of their parents are called as(a) Inbreeding(b) Back cross(c) Dihybrid cross(d) Test cross
›Reveal solutionSolution
A back cross is any cross of an F1 hybrid with one of its own parents; a test cross is the specific back cross to the homozygous recessive parent used to determine genotype.
- Back cross: F1 offspring crossed with either parent (dominant homozygous OR recessive homozygous) — used generally in breeding programmes to study inheritance or improve stock.
- Test cross: a specific type of back cross — F1 (of unknown genotype for a trait) crossed specifically with the homozygous recessive parent, used to determine whether the F1 is homozygous or heterozygous for the dominant trait. …
- CBSE 2026Set ANNUAL1 markQ.............. A cross between an organism of an unknown genotype and homozygous recessive organism.
›Reveal solutionSolution
A test cross is a cross between an individual of unknown genotype and a homozygous recessive individual, used to determine whether the unknown individual is homozygous dominant or heterozygous.
In a test cross, an organism showing a dominant phenotype (whose genotype could be either homozygous dominant, e.g. TT, or heterozygous, e.g. Tt) is crossed with a homozygous recessive organism (tt). If all offspring show the dominant phenotype, the unknown parent was hom …
- CBSE 2026Set ANNUAL1 markQ.Fill in the blank: Homo sapiens arose in ______ and moved across continents.
›Reveal solutionSolution
Homo sapiens arose in Africa and spread to other continents.
According to the accepted account of human evolution, modern humans (Homo sapiens) first appeared in Africa. From there they moved out and gradually spread across the different continents of the world, adapting …
- CBSE 2026Set ANNUAL1 markMCQQ.A pure tall (TT) plant is crossed with a pure dwarf (tt) plant to produce F1 offspring. The F1 offspring are then self-crossed. What is the ratio of true-breeding tall (TT) to true-breeding dwarf (tt) plants in the F2 generation?(a) 1 : 1(b) 1 : 2 : 1(c) 1 : 3(d) 3 : 1
›Reveal solutionSolution
The F2 of a monohybrid cross gives a 1 TT : 2 Tt : 1 tt genotypic ratio; the two true-breeding types (TT and tt) are therefore in a 1 : 1 ratio.
From the CBSE/NCERT Principles of Inheritance and Variation chapter (Mendel's monohybrid cross):
- Parents: TT (tall) × tt (dwarf).
- F1: all Tt (tall).
- F1 selfed (Tt × Tt) gives the F2 Punnett square:
T t T TT Tt t Tt tt - Genotypic ratio = 1 TT : 2 Tt : 1 tt. …
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