There are many species that live alone, who show signs of agitation around others who invade their territory and who only come together in order to reproduce (1), this way of life is a successful survival strategy for a large majority of solitary species, as on average they produce more offspring (2). However, a common feature of many animals is social grouping of family species, this happens for reasons such as clumped food resources (3). We can trace the evolution of grouping back to types of algae such as Merismopedia, which forms complex structures by living together as a group in regular rows (4), this level of organization can be correlated to the close grouping of cells that make up tissues. In a similar way, schooling fish such as silver-side (Menidia menidia) live a large proportion of their lives in groups, born with a genetic behavioral trait to synchronize their movements with other fish of its species. They form a close grouping, like the cells do in tissues, resembling a larger organism which they use to intimidate predators. This type of grouping contains no distinct leader and the fish continuously change their positions whilst they swim, making it hard for predators to catch them (5).
Another aquatic animal that lives in groups are the dolphins, and unlike schooling fish dolphins have a hierarchy, containing a leading larger dolphin who dominates the smaller dolphins, which are usually female. There are however differences between the dolphin species, where marine species such as the pacific spotted dolphin can collect in groups of several thousand, whereas freshwater species travel in small groups and are almost solitary creatures (6). Not all animals are so flexible with their social groupings. The baboon is an animal which has social grouping directly influencing its chances of survival, if a baboon were to be left behind from a group it would quickly die (7). This shows how grouping can provide protection with numbers, and there are also reproductive advantages, as it is easier to find a mate, and protecting your own family protects your own genetic line. Also an interesting note is that although social living transmits diseases and parasites (2), baboons have turned the disadvantage of parasites into a socially beneficial grooming behavior.
There are however disadvantages in groups, such as more reproductive competition, and dominant males are likely to father most of the offspring. Female completion can also be seen within groups such as egg tossing, where females such of the Acorn Woodpecker (Melanerpes formicivorus) destroy other female's eggs, therefore reducing completion for their own offspring (2). Animals that group together can also be more of a target to predators because they are more easily seen and the predator has a higher chance of catching prey if they are in large numbers, such as dolphins, and other predators that attack schools of fish, and pick them away from the group one by one. This image also portrays the last disadvantage of social groups, which is completion over food resources and energy lost through competing with your companions. Animal groupings are usually only energy efficient in species where energy is used the unsure the survival of the group and its genes under harsh environmental conditions.
Social insect societies expend a large amount of energy to maintain communities of overlapping adult generations, for example ants cooperate in hierarchies to take care of the next generation, in what seems an altruistic fashion. The offspring are highly genetically related to one another because daughter ants are more genetically close to their sisters than they would ever be to their own offspring, so in caring for the new younger sisters they are increasing their genetic fitness (8). There would be little social evolution if animals were unable to communicate with one another, ants use chemicals for communication, pheromones are secreted and such communication can quickly gather thousands of workers when needed.
The evolution of animal social groups has occurred many times independently within the different classes of animals. The continuous manifestation suggests that social grouping is beneficial to a species and increases its chances of survival against selection pressures. Animals that live within groups do so because their environmental conditions creates a situation where the animals are more genetically protected from predators. The disadvantage of reproductive competition only affects the spread of genes of specific individuals, groupings on the whole give rise to more offspring overall because mates are easier to find.Species group because it increases their chances of survival and reproductive potential in an environment where predators have the advantage.
1.William T. Keeton(1980). Biological Science 3rd eddition, W.W.Norton & company, Inc, New York, London.
2.John Alcock (2005). Animal Behaviour An Evolutionary Approach 8th edition, Sinauer Associates, Inc, Sunderland, Massachusetts U.S.A.
3.Richard J.Cowe & John R.Krebs, edited by R.M Anderson, B.D Turner & L.R. Taylor (1979), 20th Symposium of the British Ecological Society Population Dynamics, Blackwell Scientific Productions, London, Melbourne.
4.Peter Bell & Christipher Woodcock (1978), The Diversity of Green Plants 2nd eddition, Edward Arnold, London.
5.Evelyn Shaw (1962), Scientific American Animal Societies and Evolution, W.H. Freeman and company, San Francisco.
6.Bernd Wursig (1979), Scientific American Animal Societies and Evolution, W.H. Freeman and company, San Francisco.
7.S.L.Washburn and Irev Devore (1961), Scientific American Animal Societies and Evolution, W.H. Freeman and company, San Francisco.
8.David Grimaldi & Michael S. Engel (2005), Evolution of the Insects, Cambridge Uniiversity Press, Cambridge, New York.