Written by Dr Juliet Turner
I like to think of myself as an ant colony. Each cell is ant, and many different cells (ants) work together to form the complex higher entity that is Me (the ant colony). This might sound a bit insane, but it has a real scientific basis, and one that I explored in depth during my DPhil.
Ant colonies and multicellular bodies
So why do I think of myself as an ant colony? To justify this, I need to go back to basics. All complex life depends on division of labour and cooperation between smaller parts. Genes cooperate in a genome. Cells cooperate in a multicellular organism. Organisms cooperate in colonies or societies.
In a multicellular organism such as a human being, there are two broad categories of cell. First, the somatic cells -skin cells, blood cells and so on. Second, the germline cells -sperm and eggs. Somatic cells replicate through asexual reproduction (mitosis) but ultimately die when you do. Germ cells, however, undergo sexual reproduction (meiosis). If you die, your germ cells can live on, having built themselves into a new cellular arrangement – a baby.
Ant colonies have a similar system. Worker ants are sterile, like somatic cells. Queens are vessels for propagating genes to the next generation, like our germline cells. Just as somatic cells cooperate to ensure the survival of your germline, workers cooperate to ensure the survival and reproduction of their queen. New colonies are formed when queens disperse, mate, and settle down to produce a brood. That brood eventually develops into a colony.
If you ever had an ant farm as a child, and captured worker ants but not the queen, what you had was not a true colony. It is similar to how a petri dish containing skin, fat, and blood cells is not a human being. Queens and workers have total mutual dependence. Reproduction itself has been allocated as a specific role for only a subset of the population. Just as our bodies are colonies of cooperating and mutually dependent cell types, ant colonies can be thought of as higher-level individuals, made up of cooperating castes. The division of individuals into reproductive and non-reproductive castes is called reproductive division of labour – a key focus of my thesis.
There can also be additional division of labour among the non-reproductive individuals. Somatic cells are divided into skin cells, muscle cells, blood cells, etc.. Ant workers are divided into soldiers, foragers, gardeners. This is called non-reproductive division of labour. In the very socially complex leafcutter ants of the Neotropics, there are specialised foragers that bring food into the nest -just as we bring food into our body for digestion. Others remove waste from the centre of the nest and deposit it in a designated landfill area -analogous to our digestive system. A soldier caste defends against intruders - like our immune system.
Sometimes ant workers go rogue. They neglect their obligations to the colony and instead try to just replicate themselves. In social evolution, we call this ‘cheating’ behaviour. These workers reproduce asexually, laying unfertilised eggs that develop into clones of themselves. In our cellular bodies, when cells do this we call it cancer. A cell that multiplies uncontrollably forms a tumour. Both ant colonies and human bodies have ways of dealing with these ‘cheats’ – immune cells suppress cancer, and ant workers police each other; patrolling the colony and destroying any eggs not laid by the queen.
An organism is a cooperating assemblage of cells. An ant colony is a cooperating assemblage of organisms, called a superorganism. Understanding these parallels shows how cooperation underpins life at every level – from cells to societies.