Discussion of everything related to the Theory of Evolution.
Hello, i'm a first year biology student (so no flaming please!)
I was just thinking of this: why average age of women is higher than men's...
In Norway the average life- expectancy for women is 81,4 years, and for men, "only" 76 years.
Why is it that women live longer than men, when most women stop reproducing at the age of 40 (?), when many (?) men can reproduce almost all their life?
For a long time, i have known that women live longer, but it does not make sense to me. After all, they are the one's who have to cary children and give birth, often several times, "wasting" tons of energy.
Many fish die after giving birth (or at least they die after "making sure" their eggs is not eaten by some other fishes).
The obvious reason we live so long today, at least in the west is becouse we have so much food, and also good helth- care. I did a search for the life expectancy at birth in Sierra leone ( won the price for the most shitty country to live in 2009) and it was for men 39,2 years and for women 43,6 years... And they don't have anything to eat, nor a very good health- care system Also a women in SL produces 5,88 children on average...
how can this be?
here are som demography for Sierra leone
1) the men are little (much) more endangered by life style, that is wars, hunting, nowadays many adrenalin sports, motorbikes and cars...
2) if human women died after giving birth, we wouldn't be here anymore, because human kids are unable to do anything, so women must take care of them. But not only in the first generation, but also in the second generation (as grandmothers), so that they help mothers to take care about family and they can thus have more kids
Cis or trans? That's what matters.
This is due to several factors. Like JackBean said, the life style of men is something that cuts off several years from their average life expectancy. This is especially prominent in some countries, such as in Russia where the difference in favour of women is almost 14 years.
However, there certainly are genetic factors involved, because even in countries where there is realitvely little "unhealthy" activites among men (such as Japan), the difference in life expectancy is several years.
It appears that men are simply more prone to "acute" medical emergencies such as heart attacks, whilst women are more likely to succumb to long-lasting ailments such as cancer or dementia.
Why this is so? I think it is not known for sure, but e.g. sex hormones may play an important role. Also, this is just speculation, but it might have something to do with metabolical rates: men, on average, have higher energy consumption due to bigger muscle mass (even if measured per unit of weight). In nature, animals with high metabolism tend to die quicker when compared to similar-sized animals with slow metabolism. Maybe this can also contribute to the fact that men kick the bucket so soon :)
I think that, before answering this question you need to ask another question. What causes people to die naturally?
I honestly don't know what are the latest findings there but I'd bet we don't know for sure and answering this question is essential to answer yours.
For example, is there a timer in our DNA that stipulates when we're supposed to die? What causes the hormonal changes through the course of our lives? What can influence those causes? Can an intrinsic hormonal difference accelerate the process? Is it something hardwired in the Y chromosome?
you can check the CDC mortality rates or the WHO also has some stats. Basically, men get in more accidents and have problems such as prostate cancer
Living one day at a time;
Enjoying one moment at a time;
Accepting hardships as the pathway to peace;
There is quite a lot of knowledge on this, but it is true that why we need to die is still unclear.
The shortening of telomeres is a long-known phenomenom which ensures that at some point our cells cannot replicate any more. However, the body has enzymes to rebuild telomeres but in most cells the genes for this enzyme are downregulated, meaning that it is never expressed and the cells eventually die. So at least to some extent it seems that the body "intends" to die. But then again, it has been suggested that the lack of telomerase is there to prevent cells from dividing uncontrollably - cancer cells typically are able to express telomerase enzyme and replenish their telomers, and thus become "immortal". So maybe we die of old age because our cancer-preventing mechanisms prevent also sufficient tissue regenration eventually. Though of course the gradual build-up of mutations in our genomes means that if nothing else kills us, cancer eventually does.
Most hormones and their effects are also fairly well known. And some of the phenomena related to hormonal functions are indeed hardwired in the Y chromosome, or more precisely, are dictated by the genes in the Y chromosome even if the final gene product was coded for in another chromosome. For example, the manifold levels of testosterone production in men may be one of the reasons why the male body "burns out" faster.
Cancers, in general, are bit more common in women but this has probably much to do with the fact that women just live longer. More importantly, men are about twice as likely to have a cancer associated to poor life style, such tobacco smoking or excessive alcohol use. Thus, if there were no lifestyle differences between the sexes, women would have more cancer and many men would probably die of cardiovascular disease or such before they even have time to develop cancer.
Finally, one could argue that there is no such thing as a "natural" death (or the other way round: death is always natural - it is only natural that you die if you receive a shot in the head or have a terminal cancer). If you think about it, people basically always die of some disease or trauma: for very old people it is typically cancer, pneumonia or respiratory/circulatory failure. None of these events are "natural" causes of death, they are either contageous diseases or medical emergencies. If a child or a middle-aged adult had such a condition, it would never be termed "natural" death. And how can you determine the point when someone is so old that it is just fine to die of one of those reasons? Nobody just dies because the "time is up", they die because their body suffers some kind of trauma that is big enough to end their life. The likelihood of such an event just is much bigger for old people but that aside there is no real difference.
Humans are simply the host bodies for genes. I think our dna is probably programmed to end renewal of cells at a certain age as it would not be of benefit to the next generation of genes to be in host bodies that were struggling to survive against overcrowding and over competion of resources before they had had chance to reproduce the next host body.
Some pretty good answers here, thanks!
Is it so that DNA is instructed to make leathal mutations (cancer) at "a late stage" in a Gene- host's life?
I think it's a pretty big sacrifice for our genes to destroy it's host- body (in humans today at least), becouse only 50% of a parents gene's are past on, than 25% etc. in the end, the "origanal" genes are "wiped out" through the generations. On the other hand, if lats say somone that can live forever, like an elf, is killed thats it for the genes...
For the genes it would be best to live forever in one organism, than instruct the organism to stay in one place away from any danger for the rest of time
As far as I know, this often suggested idea that organisms die in order for their offspring to have more resources and less competition is wrong. The latest view (though not probably accepted by everybody) is that the genes only function to reproduce themselves. They do not function for the good of the species or for the good of the offspring of their "host". They do not want to actively kill their "host" organism, because that would kill them as well.
Why we die of old age and why the telomeres keep shortening apparently has more to do with protecting the host from succumbing to cancer before the genes have had time to multiply (i.e. to have children). The multicellular body has created means to prevent uncontrolled cell division. Also, our bodies accumulate harmful mutations that eventually break down the integrity of the body. If it was possible, the host body would live forever and keep producing more and more offspring (i.e. copies of the original genes). The genes in us do not know when all the space is filled and resources used - that is where competition via mutations takes place. For the same reason, the genes do not work for the good of the species, the individual or their offspring. Their only "goal" is to replicate their own copies.
This can actually be seen in many "lower" organisms, such as bacteria: they do not die of old age. They simply multiply and multiply and multiply as long as they can. If the genes wanted to "make way" for their offspring, the bacteria should also die of old age so as to allow the offspring have more room and resources. Of course, with organisms multiplying by binary fission it is bit hard to tell who is the parent and who is the child, but if you think of the process as kind of "budding" (bit like in the yeast, for example), the idea may become more clear.
So, apparently, complex multicellular organisms die of old age because their bodies have developed these "suicidal" means of preventing cancer or maybe some other similar problems, not because they wanted to make room for others. If the genes in you or I got to choose, they'd replicate themselves forever and fill the Earth with their own copies. Only because of mutations and chance events there is such a big competition that it cannot happen :)
No, as far as I have understood, this is not the case. Most of the mutations happen because the DNA fails to repair itself - with few exceptions (like B lymphocytes), the cells always try to repair the mutations. Even in the B cells all other mutations except somatic hypermutation are corrected if possible. So in this light, mutations are an unwanted and potentionally disastrous event for the cell. But they do happen, and that is what gives tools for evolution.
It is a popular view, though, that the host bodies are just "discarded" after they have fulfilled their purpose (that is, they have had children). But I have read quite a few prominent evolution biologists and geneticists saying that this might not actually be the same (see my previous answer in this thread).
For example, a human male can basically have children during his whole life, so why would the genes destroy this "replication machine" on purpose if it is working? Unless, of course, some other reasons force them to do so (mechanisms that limit cell division and regeneration).
Of course, there are dozens of species that apparently live just to breed: the salmon in North America that die almost right after they have laid their spawn, or male spiders and praying mantises that often become food for their spouse. Even these cases have an explanation, but unfortunately I don't remember exactly how they are explained.
This is a very complex topic and I'm not sure if I can explain it properly, but I hope you got my point! And of course it is possible that there is much that we still do not know and the real situation is something between these two views. Nonetheless, this is an extremely curious topic.
In evolutionary terms, the main theory as to why women live longer is the 'grandmother' theory.
This theory says that humans evolved long life so that women can survive long enough to help their grandkids. In this way they enhance the survival and eventual reproduction of their grandkids, which (of course) means their own genes survive. Thus, women living long enough to be grandmums, and care for their grandkids, is selected for in evolution. There is a lot of empirical evidence that, in primitive societies, children who have living grandmothers, are more likely to survive.
In lots of ways, the real problem is why men live as along as they do. There is little empirical evidence that having grandad around enhances the grandkids chances of surviving. It may be that males live as long as we do by sheer accident. Because we share enough genes with the women to share the benefit of long life. However, this question is still moot.
I think...While both men and women have testosterone and estrogen, men have higher testosterone levels and women higher estrogen levels. Estrogen tends to increase immune system activity, whereas testosterone can dampen it. Also, estrogen causes women to have more HDL (good) cholesterol and less LDL (bad) cholesterol than men on average, which decreases their risk for heart disease and stroke. However, engaging in regular exercise can shift the balance, increasing HDL and decreasing LDL and HGH also play an important role in it...
Last edited by JackBean on Thu Feb 03, 2011 11:04 am, edited 1 time in total.
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