Ancient Greek philosopher Aristotle made what may be the first known attempt to define life. He said that something is alive if it grows, is animated and nourishes itself. A more recent definition suggests the important characteristics being “the capacity for growth, reproduction, functional activity and continual change preceding death.”
There are other attempts, but they all fail in some way. Both of these definitions, for example, would consider fire to be alive and mules, which are born sterile, not to be alive. All that said, most of us have an instinctive understanding of what it means to be alive. If you see a bug or a bird or even an amoeba, you are certain it possesses life.
None of this, however, tells us anything about how life first started or whence it came. Again, there are countless thoughts about this, such as life resulting from a stroke of lightning zapping just the right elements at the right time. Some believe radiation was the instigator, and some suggest that early life forms arrived on Earth aboard rocks from outer space. No one knows for sure.
However, there is research that shows the possibility of creating the basic building blocks of life, amino acids and proteins, from basic inorganic compounds by simulating the conditions that must have prevailed at Earth’s beginning. And research in cell biology has established some remarkably likely facts about how we became human.
It’s all about cells?
A cell is the smallest functional unit of every living thing; we are made from trillions of them. The cell has a jelly-like liquid called cytoplasm enclosed in a membrane. Within the cytoplasm are structures with functions similar to our organs, and they are called organelles, or little organs, with names like mitochondria, lysosomes and others. With these, the cell can perform for itself all the same functions that we need for life: respiration, reproduction, waste removal, energy conversion and more.
Some cells have an organelle called the nucleus inside the membrane, as well. These are called eukaryotes, meaning to have a true (eu) nucleus (kary). A nucleus is important, as it contains most of the cell’s genes that are part of its DNA molecules; DNA is packaged in the form of chromosomes in order to fit into the nucleus. Other cells are called prokaryotes, meaning to exist before (pro) a nucleus occurs; bacteria are prokaryotes. They, too, have DNA, but it’s located directly in the cytoplasm.
The organelles are like computer programs, apps, in that they can perform specific functions, but they have to be started by a brain. The important fact is that cells are intelligent, and their brain is the cell membrane. The membrane includes tens of thousands of IMPs (integral membrane proteins) that receive and send signals from and to their environment, directing the organelles to do their thing and so create the complex behavior of a living cell.
A brief timeline
Earth was created about 41/2 billion years ago, but it wasn’t until 3.8 billion years ago that single-cell prokaryotes appeared. That is, the bacteria have been here a seriously long time.
The eukaryotes evolved from prokaryotes, appearing about 21/2 billion years ago, and the kind of life forms we experience today are only about 600 million years old. There were no mammals until about 200 million years ago, and we, Homo sapiens, have been around for a mere 200,000 years. So, what happened to get from the first eukaryotes to us?
For the first 3 billion years that there was life on Earth, it consisted of independent single cells, monads. They were bacteria, they were algae, they were protozoans and some fungi. It was long thought that they were solitary.
Research has shown, however, that the signals they use to organize their own physiology can be released into their environment, creating a kind of long-distance communication. For example, amoebas consuming food release a particular molecule that informs other amoebas of a supply of food to which many are then drawn. Other signal molecules like hormones were in use by these single-cell critters, as well.
As time passed, monads learned to increase the number of IMPs in their membrane and started to assemble themselves into close-knit cellular communities for survival. As the size and complexity of these multicellular communities grew, they became highly organized and parceled out specific functions to specialized groups of cells: forming body tissues and organs, building nervous and immune systems, etc. And so there evolved the complex organisms we recognize as plants and animals.
As the more complex animals evolved, there were specialized cells that became responsible for monitoring and regulating the flow of signaling among other cells. This central information processor became the brain that controls the overall interaction and behavior of all the cells in the body. We commonly believe that our mind is the same as our brain and is located our head. However, neuroscientist and pharmacologist Candace Pert’s elegant experiments showed that the mind is distributed throughout the body.
We as humans, and, in fact, all mammals and some others, are an advanced stage of this kind of community organization. Of special interest is the development of a region of the brain called the prefrontal cortex. In this, we find the capacity for thinking, planning and decision-making, as well as the seat of self-consciousness.
And so ...
Cellular communities continue to evolve, giving new perspectives on what it means to be alive.
Bob Keller maintains a holistic practice in Newburyport. He offers medical massage therapy for pain relief, as well as psychological counseling, dream work and spiritual direction. Many patients call him Dr. Bob and accuse him of doing miracles, but he is not a medical doctor nor a divinity. His expertise is medical massage therapy, understanding this miracle we call the human being. He can be reached at 978-465-5111 or firstname.lastname@example.org.