The goby of the genus Eviota, a minute fish, is one of the smallest vertebrates in existence, only about a centimeter long and less than 1/10th of a gram in weight. It’s about a million times smaller than an average human being, though comprising similar elements: a spinal cord, a bony skull, a brain, a liver and a pair of kidneys. Excepting gills and lungs, the tiny fish and a human share similar set of organs.

By contrast, the whale shark or the Rhincodon typus, is not only the largest living fish but also truly gigantic by anyone’s standards. Adults at their prime weigh up to 34 tons, more than 300 times an average human’s. The difference in weight between the tiny goby and the whale shark is as startling as it could be. Such massive disparities in animal sizes have fascinated biologists for more than a century.

Apparently, there are enormous advantages that come with being large. Big animals have an easier time avoiding predators. They can also invest more in reproduction: while a female goby’s body produces only about 250 tiny eggs to hatch into larvae per lifetime, a female whale shark can give birth to a few hundred fully developed shark pups over its lifetime, each more than half a meter in length. In large warm-blooded animals, maintaining a constant body temperature is easier due to their better surface-to-volume ratio. In large herbivores, the larger volume of the intestines leads to more effective fermentation processes, which are needed to break down plant tissues.

Biologists do not feel surprised that many lineages of animals have vastly increased in size during the course of their evolution. This trend is called Cope’s rule, named after the 19th-century American palaeontologist Edward Drinker Cope. Prominent examples of lineages following Cope’s rule are dinosaurs, which originated from an already sizeable two-meter-long reptile alive in the mid-Triassic (231 million years ago). During the following 165 million years, dinosaurs evolved into the largest land animals ever, the Titanosaurs (up to 37 meters long), and the largest land predator ever, the mighty Tyrannosaurus rex.

Another striking example is the cetaceans, the whales and dolphins. These secondary marine mammals descended from a cat-sized amphibious omnivore roaming around India 48 million years ago called Indohyus. When becoming fully aquatic, the cetaceans’ size increased, with the ancient Basilosaurid whales already up to 25 meters long 41 million years ago. The size increase of baleen whales further accelerated during the past 10 million years, and today’s blue whale is the largest animal to ever live, with adults attaining lengths of up to 30 meters and weighing close to 200 tons.

Given all these advantages of large body sizes, it becomes natural to ask why all animal species are not big. One reason is that species of small animals give rise to new species more rapidly. It is a well-established fact that small animals are more numerous (there are more gobies than whale sharks in the ocean). Larger populations give rise to new species – a process called speciation – at a faster rate. Hence, some animal species evolve towards larger body sizes (following Cope’s rule), but the remaining small species multiply much more rapidly into new small species. That keeps the majority of animal species small.

It is also worth noting that ‘laws’ and ‘rules’ in biology are generally softer than the laws of physics, to which there are no exceptions. Exceptions to Cope’s rule definitely occur, since the advantages conferred by large body sizes can be nullified by ecological or anatomical conditions. For example, the early lineages of birds in the Mesozoic did not increase in size because flying is notoriously harder with a bigger body. North American freshwater fishes even decreased in size over the course of evolution, perhaps due to the fact that many of them had invaded smaller bodies of waters where food is scarcer.

Another ecological situation that favors smaller body sizes is mass extinction. The mass extinction at the end of the Cretaceous, for instance, is thought to have been caused by a meteorite impact 66 million years ago, which darkened the skies, cooled the atmosphere, and upset the ecological balance on Earth. The event eliminated dinosaurs living on land and, with the exception of a few cold-blooded crocodiles and turtles, no land animal larger than 25 kilograms survived.

1. The primary purpose of the passage is

A. to expound the advantages of being large in size.
B. to compare the advantages of being large to the disadvantages of being small.
C. to discuss the reasons for a certain kind of diversity observed in the animal kingdom.
D. to anticipate the direction of evolution, with regards to size and weight, in future.
E. to present a hypothesis about how the mean size or weight of a species affects its chances of survival



2. Which of the following is least supported by the passage?

A. Human beings stand somewhere in the middle in terms of size or weight.
B. Fermentation is an organic process that may happen inside an animal as well outside.
C. Edward Cope studied the connection between living animals and the extinct ones.
D. Biologists don’t frame rules or laws regarding the phenomena they study.
E. Baleen whales were about 25 meters long 41 million years ago.



3. Which of the following is most supported by the passage?

A. Evolutionary changes appear only once in a generation in a species.
B. Difference among individual members of a species contributes to the pace of speciation.
C. All adult crocodiles living 66 million years ago were less than 25 kilograms in weight.
D. Birds first appeared in the Mesozoic age.
E. The size of a bird does not provide it with any advantage over other birds.