ACT Reading Jun. 2016 72F - Passage IV

Questions 31-40 are based on the following passage.

NATURAL SCIENCE: This passage is adapted from the article "Swarm Savvy" by Susan Milius (©2009 by Society for Science & the Public).

Only a few millimeters long, rock ants (Temnotho-

­rax albipennis) prove difficult to track in the wild but

excellent for the tabletop world of the laboratory.

When something terrible happens to a rock ant
5 home, such as a researcher lifting off the roof, the

majority of ants cluster in the ruins. A quarter to a third

of the colony scurries out looking for new possibilities.

"I think of the ants as a sort of search engine," ant

biologist Nigel Franks says. In one set of tests, he and
10 his students disrupted a nest and watched to see what

the ants would make of a series of new possibilities that

improved with distance. The best nest was almost three

meters distant, nine times as far from the original home

as a nearby but less appealing choice. "It was just such
15 fun doing this experiment because the ants won,"

Franks says.

In spite of the epic distances, the ants typically

found and agreed to move into the best nest. "They're

fantastic at it," Franks says.

20 Franks and Elva Robinson, both of the University

of Bristol, monitored rock ants by fitting them with

radio-frequency identification tags. The data suggest

that each scout follows a simpler rule than previously

thought, Robinson, Franks and their colleagues
25 reported online in Proceedings of the Royal society B.

Instead of making direct comparisons between

sites, a scout follows a threshold rule. If she finds a

poor site, she keeps searching. When she finds a site

that exceeds her "good enough" threshold, she returns
30 to the original nest

Next, previous work shows, the scout recruits a

new scout to join her on a trek to the good site. She

dashes around tapping her antennae on other ants and

releasing a pheromone from her sting gland, explains
35 Stephen Pratt of Arizona State University in Tempe.

Usually she finds a volunteer within a minute or so, and

the two set off tandem running.

Scout A, who knows the way, runs back toward the

nest while her follower, B, jogs closely enough to tap
40 antennae against the leader. Should A sprint a little too

fast and dash beyond antennae range, she slows until

her partner catches up. Periodically the two ants stop,

and the newbie looks around as if learning landmarks.

It's a slow way to get to the site, and Franks argues that
45 it qualifies as animal teaching.

When the ants do reach the possible site, the

recruit explores it and, depending on her assessment,

returns to recruit yet another scout.

As with bees, it's the quorum of scouts at the sites
50 that matters. When enough of them gather at a particu­-

lar place to encounter each other at a sufficiently high

rate, they've got a decision.

Once scouts reach that decision, their behavior

changes. Each scout dashes back to the nest, but instead
55 of coaxing a nest mate for a tour, she just grabs some­-

body. She uses a mouthpart hook, an over-the-shoulder

throw, and off she goes with the passive nest mate

curled on her back in an ant version of the fetal posi­-

tion. Carrying takes about a third as long as leading
60 would, and scouts can haul the rest of the colony to a

new home within hours. The ants shift from the inde­-

pendent info gathering of scouts to group implementa­-

tion of the quorum's decision.

Rock ants' willingness to thrive in the lab allows
65 experiments on finer points of collective decisions

making, Pratt says. For example, forcing a crisis among

the ants demonstrates that they will, in a pinch, trade

accuracy for speed. When researchers destroy an old

nest so that ants are completely exposed, the ants scope
70 and relocate within hours. Other experiments that just

offer the ants a better nest but don't ruin their current

one can result in days of deliberation. Speed has its

costs, and ants in a hurry now and then make mistakes,

such as splitting the colony between two nests. Slower
75 moves prove more accurate.

The quorum system could be widespread in group

behavior in nature, Pratt says. Overall it's a beautiful

tool, allowing for carefully balanced independence plus

some shortcut speed. Yet the system "has a dark side,"
80 he acknowledges. Once individuals have made their

independent assessments and then a quorum has

reached agreement, fellows copy the quorum behavior.

The chances are low that the whole quorum will reach

the same wrong decision. But flukes can happen. In
85 most uses of a quorum, "it's going to make a decision

more accurate," he says, "but it also slightly increases

the incidence of these rare events when you get it really

spectacularly wrong."

Question 31 The passage makes clear that a main objective of the research of Franks and Robinson was to