The nervous system in general is a marvel of evolution – the human nervous system in particular is considered to be the most complex structure in the universe.
Perhaps you have stood in awe and wondered: What is the nervous system about?
This super highway of nerve fibers reaches all parts of your body, in order to monitor both internal and external conditions. Its general purpose is to gather sensory information about your surroundings and sending it to the brain, where that it is interpreted.
Here we will focus on the part of the nervous system that engages with the external environment and to get an idea how this amazing system came to be.
Depending on how the information is interpreted, the brain will transmit a response through nerve fibers that will reach the muscle fiber, which will be prompted to react to the given stimuli (information).
In essence our nervous system continually keeps our brain updated with data about our immediate surroundings, as well as what’s happening inside our bodies.
The brain in turn transmits what it thinks will ensure our survival; for example, we sweat in response to running on a hot day; here the brain instructs our pores to open and sweat glands to release liquid in order to cool our body down, and hence not over heat.
In order to try to understand our nervous system, I believe we first have to set our sight on the distant past. The longest living animal is the sea sponge; so it makes good sense to start there.
Freshwater sponges have been providing some answers. They are more accessible to investigators, and better to manage in the laboratory when compared to sea sponges.
In general, sponges are sedentary animals. They live their lives fixed in one place; still, they do respond to their surroundings. This ability has been central to their survival for the last 600 million years.
Sponges don’t have a nervous system or any organs at all, but do have the ability to respond to conditions in their surroundings. What’s really interesting is that these ancient creatures possess the same genes that instruct the formation of a nervous system in ourselves as well as the rest of the animal kingdom, yet don’t do so in themselves .
Let me elaborate how sponges shine a light on the evolution of the nervous system.
Back In Time
To begin to understand what is the nervous system about, you have to go to the point in time when signs of it first appeared. Your journey will take you to the distant past – about 600 million years ago. At this time sea sponges had become the first multi cellular organism to inhabit the earth – a momentous achievement for life here on earth.
This great leap from single cell life forms to multi-cellular organism resulted in the sea sponges – our earliest ancestors. Thankfully these awesome creatures are still with us today; giving us a tremendous opportunity to trace the origins of our nervous system So far only one family of sponge has revealed some secrets about the origins of our nervous system.
Natural sponges can be found in two general varieties – sea sponges and freshwater sponges. As of late, one type of freshwater sponge (spongillids) have been found to be more manageable in the lab than other sponges – including the marine variety.
Sponges in general are extremely difficult to keep in tanks; the reason being is that these animals filtrate a tremendous amount of water daily. It’s next to impossible to provide such a great amount of water that’s pure enough for a sponge.
Other reasons that can make a sponge difficult to study in the lab include the sponge’s unpredictability regarding reproduction. This in turn makes it difficult for investigators to study the sponge’s genome, which contains the animals genetic information.
This data contained in the animal’s genome determines all aspects of an animal’s physical make up – including any predisposition for the formation of a nervous system.
You may remember studying Mendel’s heredity experiments when you were in Junior High School. From his work we learned that while animals (including ourselves) have a great number of genes, only a given number are expressed.
This explains why while we may lack some of our parents’ features, they may be present in our own children. This is evidence that while we carried that particular gene, it wasn’t expressed – in our child, however the gene was revealed.
How You Do That?
It’s not easy for us to imagine spending our entire lives anchored to one spot. Hey, if all the food you needed came close enough for you to simply absorb it via a vacuum or simply snare it (as is the case with the carnivorous sponge) then maybe you can begin to see the possibilities.
What if you didn’t have to move in order to reproduce, but can do so by sending your genes to meet with those of your mate. I know It’s a very simplified scenario, but this is how the most successful animal on earth has been surviving for 600 million years without a nervous system.
In large part, these amazing creatures have survived this long by being able to respond to either threats or the condition of the water in which they live. They use powerful chemical cocktails, which makes them inedible to almost all animals, except for the Hawkbill turtle.
Another way sponges respond to their environment is by greatly reducing the amount of water that’s being filtered in response to elevated levels of pollution or sediment suspended in the water.
Sponges clearly react to threats and/or conditions without a nervous system. They do so by having specialized groups of cells working together to form special types of tissues that are able to efficiently carry out the given task. So, this definitively has been a very successful strategy for the sponge, but are there indications of the origins of a nervous system?
I Like Your Genes
As you remember from science class, we all carry genes in our DNA. We also know that these genes carry within them the instructions for making, among many other things, a host of physical characteristics like hair color, eye color and the features of one’s face.
Not all our genes get to be expressed. This is why we may not have some of our parent’s features, but our child does. That happens because we passed that gene to her and it was expressed. In other words, the particular gene instructed the building of a certain protein that in turn will do the work required to make your eyes color hazel for example.
You are also aware that all life on earth carries genes, including the sponge.
Researchers have discovered that sponges carry the genes that are responsible for giving rise to the nervous system (National Geographic). We humans (and all animals) also carry those same genes; in us, however, they are expressed and thus we grow a nervous system. For reasons not yet determined, the same genes in sponges are not expressed.
As magnificently impressive as the nervous system is (the overwhelming majority of animals have one), the sea sponge has survived and thrive without one for 600 million years; that’s longer than any other animal in the known history of the earth.
We can confidently assume that the nervous system has been in the works since the first animal (the sponge) first arrived in our world. Sea sponges saw no need for the nervous system, while at the same time evolution “knew” that there will be a great demand for it, to put it mildly.
It is noted that once an organism becomes mobile, it requires a nervous system. The reason being is that the animal will be confronted with more unpredictable challenges than a sessile creature would be, by virtue of regularly moving from one place to another.
It follows that the more complex the animal is (such as ourselves) the more developed the nervous system will need to be. We humans not only navigate through our environment, we also think and extrapolate. As far as we know we are the only life form in the history of earth that has had this ability.
So far us humans are the most complex of all the animals with the most highly developed nervous system. Yet this system began being created within our distant and seemingly more primitive ancestor the sea sponge.
We are very fortunate to have our original ancestor (the sea sponge) existing with us today. These living fossils offer us a peek into our distant past. They offer us a great help when we seek to better understand our nervous system. Yet, the number of sponges capable of assisting us is currently limited.
Sea sponges are next to impossible to keep in a tank due to the great amount of water they consistently filter. It’s not feasible to maintain their water clean enough for this sensitive creatures.
Their breeding behavior is very unpredictable as well, making it difficult for scientists to have access to the gemnules. These pods released by sponges contain all the cells that will grow into a whole new organism. Making them ideal to study the genetic make-up of the creature.
Investigators have found one type of freshwater sponge (Spongilla) to be a good subject for research. In other words, it’s possible to maintain this sponge in a water tank and it’s method of reproduction is predictable enough to allow for some investigative work.
Even though sponges don’t possess a nervous system they can, nevertheless, respond to changes in their surroundings – whether it is a threat or elevated levels of pollution in the water. This is made possible by specialized cells that gather to form specialized tissues which are responsible for the given task, such as filtering nutrients from the water for example. This, however, is not nervous system; for clues to that we have to dig deeper.
What sponges do have are genes – as all living beings do. Included are a number of genes responsible for the formation of a nervous system. Why then, don’t they have a nervous system? Part of the answer has to do with the way genes work. Not all of an organism’s genes get the chance to express themselves. In the case of the sea sponge, her genes that would otherwise give rise to a nervous system are not being expressed and hence no brain, no nerves, or nerve cells.
When you consider that sponges – the most primitive animals – carry the “blueprints” for what is thought to have the highest level of complexity in the universe – the human nervous system – It’s a humbling experience.
It is as if life itself knew that millions of years into the future more complex animals will exist. And these new creatures will move throughout their world, and to do that safely and effectively they will need a biological system that will be highly efficient in collecting information about the environment and executing appropriate responses so as to maximize the animal’s survival.
This became known to us as the nervous system and it appears to have been planned within the humble sea sponge eons upon eons ago.
What do you think of the fact that the foundation of our highly evolved nervous system is found in the sea sponge?
What are some traits from your parents that you don’t notice in yourself but see them in your children, nieces or grandchildren?
Do you think the human nervous system will continue to evolve? If so, how will it function?
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Thank you for your time,