Are humans one single organism, or a fact a colony or society of cooperating organisms of many different types, including both many specialised human cells, and even cells that are not even human?
A Single Living Organism?
What constitutes a living organism is not so easy to define. Being able to reproduce is usually seen as the defining trait of a living organism. But then, is a honey bee a living thing, or is the bee hive a living thing? Individual worker bees do not actually reproduce, only the hive reproduces. Even in terms of intelligence, the bee hive in many ways displays an intelligence totally beyond the intelligence of an individual bee. Individual bees cannot continue to live without the hive. But we still think of the individual bee as the living organism, and do not tend to think of the hive as the organism and individual bees as effectively just cells. Perhaps this is because the bees can be physically separated from each other?
Another example is ‘slime mold‘. Unlike bees or ants, individual slime mold do not appear specialised to perform different functions within their ‘hive’ or ‘nest’, but again they do not reproduce as individuals. However they do (to quote wikipedia) ‘assemble into a cluster that acts as one organism’. Others even form a single membrane around such clusters giving the clear appearance of a single organism. When we view slime mold, we very often do perceive the ‘clusters’ as the living organism even though technically the cluster can be seen as many individuals.
Blurring the line perhaps even more confusingly, are some jellyfish like sea creatures which even in science have varied definitions as to what constitutes the organism. Unlike bees, we are not in the habit of thinking of a ‘Portuguese man of war‘ in the same manner as a hive of individual bees, but rather as a single organism. In practice, they are ‘not a single multicellular organism, but a colonial organism made up of specialized minute individual organisms called zooids‘.
The point is the line between a collection of living units being individual organisms or collectively constituting a single organism is not clear. In the same manner it is useful to consider light as waves and at other times as particles, I suggest it is sometimes useful to consider an entire ants nest as one organism and at other times to consider each ant as a separate organism.
So is a human a collection of cells which all should be considered as individual organisms or collectively as a single organism. As with photos and the alternate wave/particle perspectives, I suggest both views of the human body have merit. Most people probably normally think of the human body as one single organism already, but may find considering the human body as a colony novel. All the human cells in the body share the basically the same DNA, but so do the all the bees in a bee colony. Cells within the same body take on different highly specialised roles, but again the same principle is seen with bees or ants if not to the same specialised extent. Some cells even demonstrate independence and keep growing after the ‘colony’ is dead.
Aliens in the Mix.
For the Portuguese man of war example of a colonial animal, not all the individual components of the organism have the same DNA or are even the same species. The same with humans! Consider that within a human body there are ten times more non human cells than there are human cells. Although not by number of cells, we are still mostly human. Our human cells are far more complex and significantly larger than those other cells, so by mass that ratio almost reverses. Again, like the Portuguese man of war, it is symbiotic and we do need most of those other non-human cells to survive. Until recently we still considered every non-human cell in our body as a disease, and did not understand the essential role of many bacteria to our very assistance.
Then consider something like Toxoplasma gondii. ‘Alien’ organisms estimated to exist within 30-50% of humans. These aliens are also thought to be able to alter behaviour of the host human being.
Consider next time you meet a friend, that you are meeting a colony of a multitude of organisms, many working together to keep functioning as unit, others with their own agenda.
The Evolving Colony.
There have been circulating stories that the human body is totally replaced every 7/10/other number of years. The real picture is more complex, and the average age of the cells in our body is suggested to around 7-10 years but there are some cells believed to last our entire lifetime. The average is lower by the fact that most cells last significantly less than 7-10 years.
In fact our cells live from only a few hours through to our whole lives. Blood cells live from around 10 hours (white) about four months (red cells), through to over a year (lymphocytes). Stomach cells only live for about up to four days. Skin cells live about two or three weeks. Bone cells can live twenty years and brain cells are thought to usually last for our entire life.
So the truth is we are a mix of all different ages, so the ‘colony’ we meet at a later date has some of the same members, and many, many very new members. However, like bees within a bee colony, new members tend to be little different from the previous ones. Using the colony metaphor also has far more profound implications. If we consider the cells as individual living things with often far shorter life-cycles, we realise that the DNA of the colony can evolve not only at the birth of the colony, but at the birth of any individual cell. More than a billion times many more chances of taking place. Of course such evolution may produce faulty cells which then multiply with a negative consequence that we call cancer, or other more subtle effects. We can begin to have multiple variants of any given cell type, and one variant just may turn out to be a better adaptation. This evolution of ‘the colony’ during ones lifetime can give rise to what seems like like Lamarck evolution, the inheritance of acquired traits, for the specific case where a trait is acquired genetically by mutation during ones lifetime. Rare, yes, but evolution through mutation is rare, but also essential.
There is often no clear line between a colony of organisms being one complete living organism, or between each component of the colony being a living organism. In fact their can be a benefit from considering both viewpoints. I still suggest a beehive is the animal, not the bee 🙂
May your colony have a great day.