Why is one memory ability knocked out and not the other? Has evolution created this split state? If so, what's the evolutionary purpose?
|Scooped by Mi Stenberg|
An evolutionary theory of dementia
Recently, we have been able to read in many news sites that various forms of dementia have become the leading cause of death. A close relative of mine is over 90 years old and his short-term memory is deteriorating. Meanwhile, his long-term memory is stunning in detail and precision. It is strange to sit by his side and experience this mysterious duality of memory's capacity. And it raises questions within me: Why is it just short-term memory that disappears and not vice versa?
Dementia is a generic name and a diagnosis of a range of symptoms caused by brain cells gradually withering and dying. The most common form of dementia is Alzheimer's disease. The reason why more people are becoming demented has mainly to do with the population growing and that we are living longer than before.
But aging and the history of dementia is at least as long as history itself. Greek and Roman doctors developed detailed diagnoses that can be seen as early versions of our modern concept of dementia. Cicero was 62 years old when he the year 44 BC wrote "Thoughts on Old Age." He dedicated the book to his 65-year-old friend Titus Pomponius Atticus, and it was about the 84-year-old Cato. During the period 330 - 1453 AD, according to medical historians, 7 of 87 Byzantine monarchs had turned far over seventy years and showed symptoms that we today would call dementia. In other words, dementia is nothing new.
My 90-year-old relative can, in detail describe when he was fifteen years old and worked as a brakeman on the railroad. When the driver signaled, he rolled on a worn black knob to lock or unlock the wagon brakes. He can accurately describe how he, as a young kid, built a skate sail of sheets and sticks and how he turned and struck the sail on a special way so as not to lose his balance on the ice. But when I ask him what day it is today, it’s hard for him to find an answer.
I am not an evolutionary theorist, but during and after the conversation with my dear relative, it starts me thinking as one. Why does only one memory ability become knocked out and not the other, or why not both? Could it be that evolution has somehow created this very special split state to more effectively push humanity forward? If so, what is the evolutionary purpose? Who or what benefits from dementia in a larger perspective?
Evolutionary changes take time to become widespread. A popular example, as New Scientist wrote about some time ago, is lactose tolerance, ie the ability to break down the milk (lactose and sugar). Fossil finds have shown that 7000 years ago very few people had that ability. It is still the same in most parts of the world except Northern Europe, where about 90 percent have the ability. Researchers explain this with a genetic mutation that broke through in connection with northerners starting to breed cows.
Evolutionary theorists believe that today's man is primarily a result of genetic modifications which have been developed to overcome recurring obstacles in the historic environment. The favorable inheritable characteristics, which affect reproductive success and survival, are gradually increasing in the population and, as the time goes by various obstacles are crossed.
Developmentally today's humans should therefore have their roots in both hunter-gathering and agricultural societies. Milk tolerance gene was developed for obvious reasons in the agricultural community. Is it possible to apply a similar development to dementia as well? How did people live in agricultural societies? Three generations on a farm or maybe three generations as craftsmen in a village. Handing over from generation to generation was probably a central and obvious issue. The elders handed over the land, property and knowledge to the generation after. That generation, in their turn, would eventually hand over to their children and so on.
In such a society it was extremely important for the young generation to learn from the olders experience how to manage the farm or perform the particular craft in the best way. The older generation's knowledge was worth gold, especially in bad times. Where did you find water during the drought back in time? How did you survive during the famine? How did you produce medicine from this or that plant? In short, how to survive when unexpected problems arise? Important questions that need to be answered once they show up.
At the same time, it is absolutely vital for the generation taking over to dare to innovate and operate in their own manner. That is development. In this case you don’t want older, conservative parents who demand control and adjust according to their old conservative rules.
That’s the interesting dilemma.
As terrible as it might sound, dementia is a perfect solution to this. The takeover generation has access to one or two elderly people with brilliant memories for the past, a kind of wikipedia full of history and problem solutions.
At the same time the elder with dementia has zero track of the present, he or she will not disturb and interfere with their new generations daily and hopefully innovative routine. The future development for the family can thus be relatively peacefully moved forward.
The losers are the farmers or craftsmen in the neighboring village where the three generations are living, and their elderly are still vital without dementia. The takeover generation may not have the same chance to pursue his or her line and renew. Instead, one can easily imagine devastating conflicts between the generations.
Dementia eases the takeover and helps future generations to survive and develop. If this theory is true and therefore a possible reason for the growth of dementia then one may ask what happens when man developmentally catches up to today's modern society where the concept of handing over hardly exists.