IELTS READING LEVEL 6.5 – When Fish First Walked

When Fish First Walked

by ReadWorks

 

 

A few hundred million years ago, the competition for food between fishes was fierce. So much so that gradually, some fish developed the ability to get out of the water and reach food sources that none of the other fish could get to. They survived long enough to successfully reproduce, and passed this characteristic on to future generations. In fact, from these fish eventually originated the animals with two pairs of limbs, including human beings.

This is an example of natural selection. An organism that develops a trait that helps it survive in its environment will have a better chance of reproducing and passing that trait on to the next generation. As a consequence, organisms with this helpful trait will become more prominent while other organisms of the same species die out. Why do giraffes have long necks? Why do rabbits produce so many offspring? Natural selection can help us understand why some species are the way they are.

The term “natural selection” was coined by Charles Darwin, who developed the scientific theory of evolution. Darwin was born in England in 1809 and spent his life observing animals and plants from around the world. He explained the theory in his landmark book On the Origin of Species.

Sometimes, the changes that occur among a group of organisms will seem very small but still play an important role in their survival. Take, for example, the peppered moth. The peppered moth was light in color and had speckled wings. It was hard to pick out against many of the trees and buildings in England and could camouflage itself easily. But during the Industrial Revolution, London became polluted, and the smog turned everything black. Now the moths could be seen more easily by predators; they had nowhere to hide. Around this time, dark-colored peppered moths, which are almost invisible against a dark background, began to appear and soon became widespread. The lighter moths, on the other hand, became scarce in these sooty industrial areas.

Another case that has to do with survival through camouflage involves the little deer mouse. Typically, deer mice are dark brown, which makes it easier for them to hide from owls and other predators in the dark soil of the woods. The deer mouse that lives in Nebraska’s light-colored Sand Hills, however, has gone from brunette to blonde so it can blend in and have a better chance at survival. It took thousands of years for these mice to change the color of their coats, which may sound like a long time, but when it comes to evolution, that’s pretty quick!

One interesting case study is that of the Galápagos finches, about 14 species of bird that were studied by Darwin on the Galápagos Islands. Often referred to as “Darwin’s finches,” these birds look very much alike. The most significant difference among them is the size and shape of their beaks. Every different beak evolved the way it did so as to be suited to a particular feeding task. When, in 1977, a drought hit the island, vegetation withered and the only seeds left were large and tough. The finches with deeper, stronger beaks were able to crack through these seeds, and many more of them survived than their smaller-beaked brothers. However, in the mid-1980s, during an especially rainy time, smaller, softer seeds flourished. The birds best adapted to eat them had smaller beaks and they fared much better.

Where have all the dull male peafowl (peacocks) gone? Well, female peafowl (peahens) choose their mates based on the color and brightness of their plumage. This means that peacocks with impressive tail feathers are able to find mates more easily. A few thousand years ago, there were many more males with dull feathers, but they kept getting passed over by the females and did not reproduce. Their numbers therefore began to dwindle. These days, they’re quite rare.

Darwin’s theory teaches us that an animal or plant that adapts to its environment and remains alive long enough to procreate will thrive. The dodo bird, which has gone extinct, was not lucky in this respect. A lack of predators for thousands, and maybe even millions, of years meant that the dodos never learned to fly. When humans finally arrived to their home on the island of Mauritius, the dodos had no way of protecting themselves and, in the 17th century, were wiped out. It isn’t easy being on the wrong side of natural selection. Fortunately for us humans, the fish with the fleshy, leg-like fins came out on top.

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Vocabulary

 

adapt       a ·dapt

Advanced Definition

transitive verb

1. to make fit or suitable for a particular need or condition; adjust.

They adapted the reading room so they could hold meetings there.

The school water fountains are adapted for children.

intransitive verb

1. to become adjusted.

The children of the immigrants adapted quickly to their new surroundings.

Spanish cognate

adaptar: The Spanish word adaptar means adapt.

These are some examples of how the word or forms of the word are used:

1. One by one, the other races have gone extinct. The hypothesized reasons range from an inability to adapt to climate change to murder at the hands of more advanced humans.
2. Zoe had specialized in behavioral ecology during her studies at university, so when she applied for a job at the zoo, she specified that she was very interested in the ways animals adapt their behavior to changing environmental factors.
3. Another way animals adapt to life in the rainforest is by camouflaging themselves to hide from predators.
4. Scientists feel that there are many possible reasons that led to the extinction of the Smilodon, all of which are highly debated. Some think it was due to climate change. As the air began to heat up quickly around planet Earth, animals needed to adapt.

 

evolution       e ·vo ·lu ·tion

Advanced Definition

noun

1. the continuous modification and adaptation of organisms to their environments through selection, hybridization, and the like.
2. the theory or study that describes this process as the cause of species’ existence and characteristics. (See Darwinian theory.)

the dispute over evolution vs. creation

3. a gradual process of change and development that something goes through, usu. becoming more complex and sometimes better.

the evolution of electronic weaponry

Spanish cognate

evolución : The Spanish word evolución means evolution.

These are some examples of how the word or forms of the word are used:

1. Before the breakup of Pangaea, many scientists believe, all of life was situated in one ecosystem, and did not have any reason to adapt to change. Once Pangaea broke up, it was possible for evolution to happen at an increased rate.
2. Charles Darwin, the famous biologist who first proposed the scientific theory of evolution, described the coral reef as an oasis in the desert of the ocean.
3. When the famous naturalist Charles Darwin, who helped develop the theory of evolution, visited the Galapagos Island in the 1830s, he made an interesting discovery about native birds.
4. Tiny bacteria used the sulfur from the vents to make food – a process called “chemosynthesis.” Other animals, like worms and shrimp, then ate this bacteria. A whole ecosystem exists there. Finding this life made scientists reconsider the power of evolution.
5. Prehuman evolution has wound its way through two genera (groups of related species) during the past 5 million years. The first genus, Australopithecus, existed roughly 5 million to 2 million years ago. The second genus, Homo, arose 2.5 million to 2 million years ago.
6. Sexual selection is an example of natural selection. That’s the principle that animals with advantageous traits are more likely to survive and pass those traits to the next generation. Natural selection drives evolution.
7. Hazen’s background is studying minerals-solid, crystalline materials that form naturally through geological processes and make up rocks. He’s using that knowledge to figure out how ancient minerals might have been involved in the evolution of the first primitive life-forms.

 

reproduce       re ·pro ·duce

Definition

verb

1. to make a copy of.

The designer made a model, and the company reproduced it.

2. to make a new plant, human, or animal. In humans, to reproduce is to produce children.

Plants reproduce in a different way from humans.

Advanced Definition

transitive verb

1. to make a copy or duplicate of.

The furniture maker reproduced a chair made hundreds of years ago.

2. to produce again.

Can you reproduce that sound you just made?

3. to create (new plants or animals of the same kind) by means of a sexual or an asexual process.
4. to have a mental image of, or to bring to mind again.

intransitive verb

1. to go through a process of copying, duplication, or reproduction.

This design will reproduce well.

2. to create offspring.

Turtles reproduce by laying eggs.

Spanish cognate

reproducir: The Spanish word reproducir means reproduce.

These are some examples of how the word or forms of the word are used:

1. All plants, animals and other living things reproduce, resulting in new offspring or organisms.
2. Jansen claims to be creating new forms of life. He originally hoped that the beasts would be able to reproduce, perhaps by feeding on plastic and making offspring inside themselves.
3. Natural selection is based on the idea that animals with specific biological traits well-suited to survive in an environment, will reproduce at a much faster rate than animals with biological traits that are poorly suited to an environment.
4. Charles Darwin outlined the idea of natural selection in his 1859 book, On the Origin of Species, where he explained there are certain characteristics that help an animal survive, such as a sharp beak that allows birds in the Galapagos Islands to better find and eat their food. These sharp-beaked birds survived long enough to reproduce, and their offspring had sharp beaks too.
5. In the habitat, there will be plants and trees also native to Africa, as well as rock formations (like caves) that replicate a lion’s natural surroundings. Similarly, if you visit an aquarium, you can look through thick panes of glass to shark tanks, complete with large swimming turtles, rays and other fish that live peacefully among sharks. These are attempts to reproduce the conditions in which the animals we see on display evolved-in so doing, they highlight biodiversity.

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