Viagra & Evolution

Hi Peg,This is really pretty simple. People living in the modern day are able to get incredibly old.Our ancestors, both pre-human hominids and early humans, lived a very different lives to us. They had to live on their wits, hunting and gathering, making shelter, moving over great distances and avoiding predators. Their lives were very hard.The upshot of this is that they tended to live shorter lives, compared to us. Forty years old would be pretty venerable for an early human.Erectile dysfunction is one of the many effects of ageing. It tends to happen to older men. Early humans and hominids would be unlikely to survive to such a ripe old age that they need worry about such things. Thus, natural selection would not select strongly against them.For an organism to claim evolutionary success, it need only breed and pass on its genes. It need only breed successfully once to do this.Erectile dysfunction doesn't kick in until late in life, so the chances are that any individual will have already bred successfully before it ever becomes an issue. From an evolutionary point of view, it doesn't matter if Granpa can't get it up; he has already done everything that evolution needed him to do in having children.Example. An allele that caused erectile dysfunction at the age of ten and up would be disastrous to the individual's chances of reproducing. It would destroy the man's chance of reproducing before he even reached sexual maturity. Natural selection would select very strongly against such an allele.An allele that caused erectile dysfunction at the age of sixty however would be pretty harmless to the man's chance of reproducing. He could reproduce before the dysfunction struck and pass on his genes (including the erectile dysfunction allele) without hindrance, only to die when it was past breeding age anyway. There is nothing for natural selection to work on here and the allele would likely persist in the population.It may be frustrating for Granpa, but it is not a problem for the theory of evolution.This is actually the kind of process that is thought to lie behind the ageing process itself. Genes that cause problems in old age just aren't very strongly selected against, so they accumulate. I hope this helps.Mutate and SurviveEdited by Granny Magda, : Typo in title. In the word "title" appropriately enough.

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"The Bible is like a person, and if you torture it long enough, you can get it to say almost anything you'd like it to say." -- Rev. Dr. Francis H. Wade

Hi Percy, I was under the impression that the usual explanation for that was the effects of pollutants. Oestrogen, metals and various synthetics from plastics are the usual suspects. Their effect would not be much to do with evolution, but rather environment, especially exposure during embryonic development.Mutate and SurviveEdited by Granny Magda, : No reason given.

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"The Bible is like a person, and if you torture it long enough, you can get it to say almost anything you'd like it to say." -- Rev. Dr. Francis H. Wade

Hi rueh,Sorry for the delay in reply, I've had a busy couple of days. I completely agree. The distinction I was trying to make was more that the increase in male fertility/sexual problems is usually directly attributed to environmental factors (pollution) rather than genetic. Makes sense to me, but only if there is a genetic basis for resistance to the appropriate pollutants. If alleles exist that can protect against environmental damage during development, I suppose we would expect to see the trend you describe. I would say though that medical know-how can fix some of these problems, allowing couples with infertility problems to have children nonetheless. That would presumably dilute the effect.Unfortunately, I think the trend is currently still toward an increase in male infertility etc., so I can't imagine that genetics is a significant factor as yet.Mutate and Survive

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"The Bible is like a person, and if you torture it long enough, you can get it to say almost anything you'd like it to say." -- Rev. Dr. Francis H. Wade

Peg, Yes. Another way of saying that is that less than 10% of sufferers are under 30. Note that I said "It tends to happen to older men. My earlier points still stand.Evolution will always act to reduce the frequency of harmful traits in a population, but there is no reason why it would necessarily wipe them out entirely. So long as the population as a whole can survive the negative impact of a trait, it may persist, especially if the trait is not expressed in everyone who carries it (such as in the case of a trait controlled by a recessive gene).Remember, all this is only really relevant where there is a genetic basis for the dysfunction. As has been noted above, there are a number of other causes for erectile dysfunction, infertility, etc. and telling cause from effect in so complicated a phenomenon is way beyond my meagre talents. Mutate and Survive

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"The Bible is like a person, and if you torture it long enough, you can get it to say almost anything you'd like it to say." -- Rev. Dr. Francis H. Wade

Hmmm... Is that a simple explanation? I'm not so sure it is. What would the mechanism be? What cues would "tell" the body that it is living in an overpopulated environment?The world may be more overpopulated than ever, but it is hard to see how individuals living in cities are any more crowded than those who have lived in urban environments for centuries.I'm not saying that your explanation is wrong; I've heard it many times before and it is a tempting conclusion. I just find it hard to picture how it would actually work on the ground.Mutate and Survive

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"The Bible is like a person, and if you torture it long enough, you can get it to say almost anything you'd like it to say." -- Rev. Dr. Francis H. Wade

Hmm again...I'm still not entirely convinced, but I do see where you're coming from. I do agree that whatever is happening, it's happening at a developmental level, either in adults, pubescent teens or in the womb (or maybe all three).Your points about stress, dominance behaviours and over-crowding are well made, but I still don't see that there is any huge difference in those issues between today and say, the nineteenth century and especially the early twentieth.The pictures illustrate your point very well, but imagine a Victorian factory or slum, a crowded market place or a mine. All very crowded and extremely stressful.To my mind, the most tempting hypothesis is pollution, with the drop in fertility starting at about the same time as a boom in novel chemicals and industrial processes. Molybdenum for example, has been implicated in infertility (study here).Another study plays down the pollutant connection, showing only a small effect.

quote:

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To test the hypothesis that environmental contaminant exposure was associated with enhanced risk of infertility, data concerning trends in fertility and infertility rates were examined to assess the impact of exposure of developing gametes to environmental contaminants. The relationship between exposure and reproductive outcomes was then examined to illustrate the range of adverse effects for reproductive toxicants with data sets of divergent depth and reliability. Data showed that only a weak association between exposure to environmental contaminants and adverse effects on human fertility exists. However, it is postulated that evidence of chemical exposure and potential health consequences of these exposures highlight the need for further research in this area.

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Source It also mentions that fertility rates have actually been going up recently. It certainly would. A study comparing either anxiety or infertility against urban/rural location would be interesting.I couldn't find one for infertility. It does occur to me though, that areas with higher population density are going to be more polluted, possibly confusing the issue. I found this study that suggests a link between urban living and worse mental health. That would seem to support the anxiety-based explanation.It would also be interesting to see if there were a correlation between levels of anxiety and infertility over the past few decades.So to sum up, I'm not really convinced either way. Not enough data yet to make a decision, so I'm going to maintain an open mind on this one. It's probably a combination of factors anyway.Mutate and Survive

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"The Bible is like a person, and if you torture it long enough, you can get it to say almost anything you'd like it to say." -- Rev. Dr. Francis H. Wade