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.
Q.1: The Emory University experiment with mice points to the inheritance of:
- psychological markers
- acquired characteristics
- personality traits
- acquired parental fears
Q.2: Which of the following best describes the author's argument?
- Darwin’s and Mendel’s theories together best explain evolution.
- Mendel’s theory of inheritance is unfairly underestimated in explaining evolution.
- Wilson’s theory of evolution is scientifically superior to either Darwin’s or Mendel’s.
- Darwin’s theory of natural selection cannot fully explain evolution.
Q.3: Which of the following, if found to be true, would negate the main message of the passage?
- A study affirming the influence of socio-cultural markers on evolutionary processes.
- A study highlighting the criticality of epigenetic inheritance to evolution.
- A study indicating the primacy of ecological impact on human adaptation.
- A study affirming the sole influence of natural selection and inheritance on evolution.
Q.4: The passage uses the metaphor of a dog walker to argue that evolutionary adaptation is most comprehensively understood as being determined by:
- extra genetic, genetic, epigenetic and genomic legacies.
- socio-cultural, genetic, epigenetic, and genomic legacies.
- ecological, hormonal, extra genetic and genetic legacies.
- genetic, epigenetic, developmental factors, and ecological legacies.
1. This is a very easy question and right at the start of the passage the clue to the right answer can be found. The passage says “a mouse should not be born with something that its parents have learned during their lifetime”. Thus the author suggests that they should not have been born with acquired characteristics during their lifetime. We should not be tempted with option 4 because though it looks good, it is not the right choice. Fear is just one characteristics that is likely to be inherited, while the passage points at a broader conclusion that can be derived from this experiment. So the inheritance may not necessarily be of fears, but of anything that the parents might have acquired in their lifetime.
2. The hint to the right answer can be found in the second paragraph of the passage. The second para says: 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. .
Thus 1 is the best choice, as the author attributes inheritance to much more than natural selection and mendelian gentics. The other negative opinions expressed in the other
options cannot be seen anywhere in the passage.
3. To answer this question correctly, we have to understand the main message of the passage. The main idea is that there is a lot more to inheritance than just natural selection and genetics. So if there is a study that affirms the sole influence of natural selection and inheritance on evolution than the author’s main argument would be weakened.
We can see clear evidence in these lines: 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.
4. This too is an easy question, the clue to the right answer can be seen here in these lines: We can see clear evidence in these lines: 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.