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RC Passage
Direction for the questions 16 to 19: The passage below is accompanied by a set of four questions. Choose the best answer to each question.
When researchers at Emory University in Atlanta trained mice to fear the smell of almonds (by pairing it with electric shocks), they found, to their consternation, that both the children and grandchildren of these mice were spontaneously afraid of the same smell. That is not supposed to happen. Generations of schoolchildren have been taught that the inheritance of acquired characteristics is impossible. A mouse should not be born with something its parents have learned during their lifetimes, any more than a mouse that loses its tail in an accident should give birth to tailless mice.
Modern evolutionary biology dates back to a synthesis that emerged around the 1940s-60s, which married Charles Darwin’s mechanism of natural selection with Gregor Mendel’s discoveries of how genes are inherited. The traditional, and still dominant, view is that adaptations – from the human brain to the peacock’s tail – are fully and satisfactorily explained by natural selection (and subsequent inheritance). Yet new evidence from genomics, epigenetics and developmental biology indicates that evolution is more complex than we once assumed.
In his book On Human Nature (1978), the evolutionary biologist Edward O Wilson claimed that human culture is held on a genetic leash. The metaphor needs revision. Imagine a dog-walker (the genes) struggling to retain control of a brawny mastiff (human culture). The pair’s trajectory (the pathway of evolution) reflects the outcome of the struggle. Now imagine the same dog-walker struggling with multiple dogs, on leashes of varied lengths, with each dog tugging in different directions. All these tugs represent the influence of developmental factors, including epigenetics, antibodies and hormones passed on by parents, as well as the ecological legacies and culture they bequeath.
The received wisdom is that parental experiences can’t affect the characters of their offspring. Except they do. The way that genes are expressed to produce an organism’s phenotype – the actual characteristics it ends up with – is affected by chemicals that attach to them. Everything from diet to air pollution to parental behaviour can influence the addition or removal of these chemical marks, which switches genes on or off. Usually these so-called ‘epigenetic’ attachments are removed during the production of sperm and eggs cells, but it turns out that some escape the resetting process and are passed on to the next generation, along with the genes. This is known as ‘epigenetic inheritance’, and more and more studies are confirming that it really happens. Let’s return to the almond-fearing mice. The inheritance of an epigenetic mark transmitted in the sperm is what led the mice’s offspring to acquire an inherited fear.
Epigenetics is only part of the story. Through culture and society, humans and other animals inherit knowledge and skills acquired by their parents. All this complexity points to an evolutionary process in which genomes (over hundreds to thousands of generations), epigenetic modifications and inherited cultural factors (over several, perhaps tens or hundreds of generations), and parental effects (over single-generation timespans) collectively inform how organisms adapt. These extra-genetic kinds of inheritance give organisms the flexibility to make rapid adjustments to environmental challenges, dragging genetic change in their wake – much like a rowdy pack of dogs.
Full RC Video Analysis
RC Line-wise Explanation
Paragraph 1
"When researchers at Emory University in Atlanta trained mice to fear the smell of almonds (by pairing it with electric shocks), they found, to their consternation, that both the children and grandchildren of these mice were spontaneously afraid of the same smell."
Explanation: Researchers at Emory University trained mice to associate the smell of almonds with electric shocks, and surprisingly, both their children and grandchildren also feared the same smell.
"That is not supposed to happen."
Explanation: This outcome was unexpected and goes against what was traditionally believed in biology.
"Generations of schoolchildren have been taught that the inheritance of acquired characteristics is impossible."
Explanation: It has long been taught that traits acquired during an organism's life (such as learned fears) cannot be passed on to offspring.
"A mouse should not be born with something its parents have learned during their lifetimes, any more than a mouse that loses its tail in an accident should give birth to tailless mice."
Explanation: According to traditional beliefs, a mouse shouldn’t inherit a fear learned by its parents, just as a tailless mouse wouldn’t give birth to offspring without tails.
Paragraph 2
"Modern evolutionary biology dates back to a synthesis that emerged around the 1940s-60s, which married Charles Darwin’s mechanism of natural selection with Gregor Mendel’s discoveries of how genes are inherited."
Explanation: Modern evolutionary biology, which emerged between the 1940s and 1960s, combined Darwin’s theory of natural selection with Mendel’s work on inheritance of genes.
"The traditional, and still dominant, view is that adaptations – from the human brain to the peacock’s tail – are fully and satisfactorily explained by natural selection (and subsequent inheritance)."
Explanation: The dominant belief is that adaptations in organisms, such as the human brain or a peacock’s tail, are fully explained by natural selection and genetic inheritance.
"Yet new evidence from genomics, epigenetics and developmental biology indicates that evolution is more complex than we once assumed."
Explanation: However, recent discoveries in genomics, epigenetics, and developmental biology show that evolution is more complicated than previously thought.
Paragraph 3
"In his book On Human Nature (1978), the evolutionary biologist Edward O Wilson claimed that human culture is held on a genetic leash."
Explanation: In his 1978 book, Edward O. Wilson argued that human culture is controlled by our genetic makeup.
"The metaphor needs revision."
Explanation: This metaphor needs to be updated to better explain the relationship between genes and culture.
"Imagine a dog-walker (the genes) struggling to retain control of a brawny mastiff (human culture)."
Explanation: A new metaphor: imagine genes as a dog-walker trying to control a strong dog (human culture), showing the struggle between genetic influences and cultural factors.
"The pair’s trajectory (the pathway of evolution) reflects the outcome of the struggle."
Explanation: The outcome of the struggle between genes and culture determines the path of evolution.
"Now imagine the same dog-walker struggling with multiple dogs, on leashes of varied lengths, with each dog tugging in different directions."
Explanation: The metaphor is expanded: now the dog-walker (genes) must deal with multiple dogs (factors like epigenetics and culture), each pulling in different directions.
"All these tugs represent the influence of developmental factors, including epigenetics, antibodies and hormones passed on by parents, as well as the ecological legacies and culture they bequeath."
Explanation: These "tugs" represent various factors influencing development, such as epigenetics, parental antibodies and hormones, and cultural and ecological legacies passed down.
Paragraph 4
"The received wisdom is that parental experiences can’t affect the characters of their offspring."
Explanation: The traditional belief is that what parents experience does not influence the traits of their offspring.
"Except they do."
Explanation: However, this is not the case, as parental experiences can indeed affect offspring.
"The way that genes are expressed to produce an organism’s phenotype – the actual characteristics it ends up with – is affected by chemicals that attach to them."
Explanation: Gene expression, which determines the organism’s characteristics (phenotype), can be influenced by chemicals that attach to genes.
"Everything from diet to air pollution to parental behaviour can influence the addition or removal of these chemical marks, which switches genes on or off."
Explanation: Factors like diet, pollution, and parental behavior can add or remove these chemical marks, turning genes on or off.
"Usually these so-called ‘epigenetic’ attachments are removed during the production of sperm and eggs cells, but it turns out that some escape the resetting process and are passed on to the next generation, along with the genes."
Explanation: Normally, these epigenetic marks are erased when sperm and egg cells are created, but some of them can persist and be passed to the next generation.
"This is known as ‘epigenetic inheritance’, and more and more studies are confirming that it really happens."
Explanation: This phenomenon, where epigenetic marks are inherited, is called "epigenetic inheritance," and numerous studies confirm its occurrence.
"Let’s return to the almond-fearing mice."
Explanation: The passage then revisits the example of the almond-fearing mice.
"The inheritance of an epigenetic mark transmitted in the sperm is what led the mice’s offspring to acquire an inherited fear."
Explanation: The fear of almonds in the mice’s offspring was caused by the inheritance of an epigenetic mark in the sperm.
Paragraph 5
"Epigenetics is only part of the story."
Explanation: Epigenetics is just one factor in the larger story of inheritance.
"Through culture and society, humans and other animals inherit knowledge and skills acquired by their parents."
Explanation: Humans and other animals also inherit knowledge and skills passed down through culture and society, not just through genetics.
"All this complexity points to an evolutionary process in which genomes (over hundreds to thousands of generations), epigenetic modifications and inherited cultural factors (over several, perhaps tens or hundreds of generations), and parental effects (over single-generation timespans) collectively inform how organisms adapt."
Explanation: Evolution is influenced by a combination of factors, including genetic inheritance, epigenetic changes, cultural inheritance, and parental effects, all working together to help organisms adapt.
"These extra-genetic kinds of inheritance give organisms the flexibility to make rapid adjustments to environmental challenges, dragging genetic change in their wake – much like a rowdy pack of dogs."
Explanation: Non-genetic inheritance allows organisms to quickly adapt to environmental challenges, pulling genetic change along, much like a chaotic group of dogs pulling in different directions.
RC Paragraph Explanation
Paragraph 1 Summary
Researchers discovered that mice, who were trained to fear the smell of almonds, passed this fear down to their offspring and grandchildren, challenging the traditional belief that acquired characteristics cannot be inherited.
Paragraph 2 Summary
While the dominant view in evolutionary biology has been that adaptations are fully explained by natural selection and genetic inheritance, new research in genomics and epigenetics suggests that evolution is more complex than previously thought.
Paragraph 3 Summary
Edward O. Wilson’s metaphor of human culture being controlled by genes is expanded to illustrate how multiple factors, including epigenetics and cultural influences, contribute to evolution, with these factors pulling in different directions.
Paragraph 4 Summary
Parental experiences can influence offspring through epigenetic inheritance, where chemical marks on genes affect gene expression and are passed down to future generations, as seen in the almond-fearing mice.
Paragraph 5 Summary
Epigenetics is just one part of the inheritance story. Cultural knowledge, skills, and parental effects, alongside genetic and epigenetic factors, collectively shape how organisms adapt to environmental challenges.
RC Quick Table Summary
| Paragraph Number | Main Idea |
|---|---|
| Paragraph 1 | Mice trained to fear almonds passed this fear to their descendants, challenging the belief that acquired traits cannot be inherited. |
| Paragraph 2 | New research in genomics and epigenetics suggests that evolution is more complex than just natural selection and genetic inheritance. |
| Paragraph 3 | The influence of genes, epigenetics, and culture on human evolution is illustrated with a metaphor of multiple factors pulling in different directions. |
| Paragraph 4 | Epigenetic inheritance shows that parental experiences can influence offspring, as demonstrated by the almond-fearing mice. |
| Paragraph 5 | Evolution is shaped by a combination of genetic, epigenetic, cultural, and parental influences, providing flexibility to adapt to environmental changes. |
RC Questions
Ques 16. The Emory University experiment with mice points to the inheritance of:
Ques 17. Which of the following best describes the author's argument?
Ques 18. Which of the following, if found to be true, would negate the main message of the passage?
Ques 19. The passage uses the metaphor of a dog walker to argue that evolutionary adaptation is most comprehensively understood as being determined by:
