What is Safety in numbers?
[[File:Critical_Mass,_San_Francisco,_April_29,_2005.jpg|thumb|Critical Mass, San Francisco, April 29, 2005 and Muni Metro tram on J Church line]] Individuals that are part of a larger group are less likely to be the [[victim]] of an [[accident]], [[attack]], or other bad event. This idea is called '''safety in numbers'''. Related theories show that mass behaviour can reduce accident risks. In the case of [[traffic]] safety, the effect really reduces the [[danger]], rather than simply distributing it over a larger group. == In biology == The mathematical biologist [[W.D. Hamilton]] proposed his selfish herd theory in 1971. This theory tries to explain why [[animals]] seek central positions in a group: each individual can reduce its own danger by putting itself in a position with neighbours all around. So it moves towards the centre of the group.<ref>{{Cite journal|last=Hamilton|first=W.|date=1971|title=Geometry for the selfish herd|journal=Journal of Theoretical Biology|volume=31|issue=2|pages=295–311|doi=10.1016/0022-5193(71)90189-5|pmid=5104951|bibcode=1971JThBi..31..295H}}</ref> The effect was tested in [[brown fur seal]] [[predation]] by [[Great white shark|great white sharks]]. Decoy seals were used, and the distance between them was varied to produce different levels of danger. The seals in greater danger had (as predicted) an increased risk of shark attack.<ref>{{Cite journal|last1=De Vos|first1=Alta|last2=O'Riain|first2=M. Justin|year=2010|title=Sharks shape the geometry of a selfish seal herd: experimental evidence from seal decoys|journal=Biology Letters|volume=6|issue=1|pages=48–50|doi=10.1098/rsbl.2009.0628|pmc=2817263|pmid=19793737}}</ref> [[Defence against predators|Antipredator adaptations]] include behaviour such as the flocking of [[birds]], [[herding]] of [[sheep]],<ref>{{Cite journal|last1=King|first1=Andrew J.|last2=Wilson|first2=Alan M.|last3=Wilshin|first3=Simon D.|last4=Lowe|first4=John|last5=Haddadi|first5=Hamed|last6=Hailes|first6=Stephen|last7=Morton|first7=A.Jennifer |year=2012|titl