People tend to view evolution as a linear process that has led up to humans, the most "advanced" animal. ( 29 ), we are not surprised when very close evolutionary relatives of humans, such as chimpanzees, demonstrate intelligence. In recent decades, however, researchers have noted intelligence in creatures with a more remote connection to humans: cephalopods, a group that includes octopuses and squid.
Octopuses in particular show signs of intelligence. They collect rocks, shells, and other items to use as tools for protection and shelter. Given a jar containing food, an octopus will quickly work out how to open the lid. Furthermore, octopuses seem to ( 30 ). Biologists Jennifer Mather and Roland Anderson recorded the reactions of 44 octopuses over a two-week period to a number of stimuli, such as being touched with a brush. Not only did responses vary greatly from octopus to octopus, but each animal was consistent in the way it responded. An octopus that responded in a shy, timid manner, for example, did so every time.
Scientists believe intelligence in cephalopods ( 31 ) than in animals with backbones, known as vertebrates. Intelligent vertebrates are generally social and long-lived, and their brainpower enables them to handle complicated social relations. Cephalopods, however, live short, solitary lives. One of many theories proposed by scientists is that they began to acquire intelligence as they lost their protective shells. Exposed to attack, they would have needed to react quickly and cleverly to various situations in order to survive.
(29) 1 Nevertheless
2 For this reason
3 On the contrary
4 In exchange
(30) 1 learn from their mistakes
2 change their behavior frequently
3 seek attention from humans
4 have distinct personalities
(31) 1 evolved more slowly
2 is easier to explain
3 developed for different reasons
4 causes more problems