Table of Contents
BEST IELTS General Reading Test 487
IELTS GENERAL READING TEST 487 – PASSAGE – 3
IELTS GENERAL READING TEST – 487
READING PASSAGE – 3
DARWIN’S THEORY OF EVOLUTION
Darwin’s theory entails the fundamental ideas of evolution. Darwin’s original contributions were the mechanism of natural selection and copious amounts of evidence for evolutionary change from many sources. He also provided thoughtful explanations of the consequences of evolution for our understanding of the history of life and modern biological diversity. Species (populations of interbreeding organisms) change over time and space. The representatives of species living today differ from those that lived in the recent past and populations in different geographic regions today differ slightly in form or behavior as they evolve. These differences extend into the fossil record which provides ample support for this claim.
All organisms share common ancestors with other organisms. Over time, populations may divide into different species, which share a common ancestral population. Far enough back in time, any pair of For example, humans shared a common ancestor with organisms shares a common ancestor. Chimpanzees about eight million years ago, with whales about 60 million years ago, and with kangaroos over 100 million years ago. Shared ancestry explains the similarities of organisms that are classified together. Their similarities reflect the inheritance of traits from a common ancestor.
IELTS General Reading Test
Evolutionary change is gradual and slow in Darwin’s view. This claim was supported by the long episodes of gradual change in organisms in the fossil record and the fact that no naturalist had observed the sudden appearance of a new species in Darwin’s time. Since then, biologists and paleontologists have documented a broad spectrum of slow to rapid rates of evolutionary change within lineages.
Darwin’s process of natural selection has four components.
1. Variation- Organisms within populations exhibit individual variation in appearance and behavior. These variations may involve body size, hair color, facial markings, voice properties or number of offspring. On the other hand, some traits show little to no variation among individuals for example, number of eyes in vertebrates.
IELTS General Reading Test
2. Inheritance- Some traits are consistently passed on from parent to offspring. Such traits are heritable, whereas other traits are strongly influenced by environmental conditions and show weak heritability.
3. High rate of population growth- Most populations have more offspring each year than local resources can support leading to a struggle for resources. Each generation experiences substantial mortality.
4. Differential survival and reproduction- Individuals possessing traits well suited for the struggle for local resources will contribute more offspring to the next generation.
IELTS General Reading Test
Galapagos finches are the famous example from Darwin’s voyage. Each island of the Galapagos that Darwin visited had its own kind of finch (14 in all), found nowhere else in the world. Some had beaks adapted for eating large seeds, others for small seeds, some had parrot-like beaks for feeding on buds and fruits, and some had slender beaks for feeding on small insects. One used a thorn to probe for insect larvae in wood, like some woodpeckers do. Six were ground-dwellers and eight were tree finches.
This diversification into different ecological roles is thought to be necessary to permit the coexistence of multiple species. To Darwin, it appeared that each was slightly modified from an original colonist, probably the finch on the mainland of South America, some 600 miles to the east. It is probable that adaptive radiation led to the formation of so many species because other birds were few or absent, leaving empty niches to fill and because the numerous islands of the Galapagos provided ample opportunity for geographic isolation.
IELTS General Reading Test
These are the basic tenets of evolution by natural selection as defined by Darwin.
– More individuals are produced each generation that can survive.
– Phenotypic variation exists among individuals and the variation is heritable.
– Those individuals with heritable traits better suited to the environment will survive.
– When reproductive isolation occurs new species will form.
IELTS General Reading Test
Variation is a feature of natural populations and every population produces more progeny than what its environment can manage. The consequence of this overproduction is that those individuals with the best genetic fitness for the environment will produce offspring that can more successfully compete in that environment. Thus the subsequent generation will have a higher representation of these offspring and the population will have evolved.
Darwin’s general theory presumes the development of life from non-life and stresses a purely naturalistic undirected descent with modification. That is, complex creatures evolve from more simplistic ancestors naturally over time. In a nutshell, as random genetic mutations occur within an organism’s genetic code, the beneficial mutations are preserved because they aid survival a process known as natural selection. These beneficial mutations are passed on to the next generation. Over time, beneficial mutations accumulate and the result is an entirely different organism which is not just a variation of the original, but an entirely different creature.
IELTS General Reading Test
Questions 27-34
Choose NO MORE THAN ONE WORD from the above text for each answer.
Darwin’s theory points out that life of living 27……………………. is related and has descendents from a common 28……………………. whether birds and bananas, fishes and flowers, all are related. Darwin’s theory also says that complex creatures 29……………………. from more simplistic ancestors naturally over the time. Therefore, we can say that genetic 30……………………. randomly occur with an organism’s genetic code and the mutation that is benefited is 31……………………. because they aid survival and this process is known as 32……………………. selection. Also, these beneficial mutations are 33……………………. to the future generation. With the 34……………………. the mutation that is benefited accumulates and a different organism is formed. According to Charles Darwin, natural selection acts to preserve and accumulate minor advantageous genetic mutations.
IELTS General Reading Test
Questions 35-40
Do the following statements agree with the information given in the text above?
In boxes 35-40 on your answer sheet, write
TRUE – if the statement agrees with the information
FALSE – if the statement contradicts the information
NOT GIVEN – if there is no information on this
35. The coexistence of multiple species in nature requires diversification into different ecological roles.
36. The contemporaneous naturalists were already working on the ‘species problem’ when Darwin began his research.
IELTS General Reading Test
37. The fact that no naturalist had observed the sudden appearance of a new species upheld Darwin’s theory.
38. The fossil records do not buttress the indagation of the Darwin’s theory of natural selection.
39. Each generation experiences prodigious mortality due to ebbing food resources.
40. Geographic isolation was not responsible for the variation in finches on the islands of the Galapagos.
IELTS General Reading Test
IELTS General Reading Test
ANSWERS
27. ORGANISMS
28. ANCESTOR
29. EVOLVE
30. MUTATIONS
31. PRESERVED
32. NATURAL
33. PASSED
34. TIME
35. TRUE
36. NOT GIVEN
37. TRUE
38. FALSE
39. TRUE
40. FALSE
IELTS General Reading Test