“Dextrose is glucose plus glucose”
From Wikipedia:
“Two isomers of the aldohexose sugars are known as glucose, only one of which (D-glucose) is biologically active. This form (D-glucose) is often referred to as dextrose (dextrose monohydrate), especially in the food industry. This article deals with the D-form of glucose. The mirror-image of the molecule, L-glucose, cannot be used by cells”
Ouch. You got me.
Maltose is what I was thinking of. Sorry about the dextrose.
The Disaccharides article at Wiki points out that the lesser known sugars trehalose and cellobiose are also formed with two glucose molecules, but the three varieties are distinct because the way they are bonded is different.
With pleasure. I’m having problems finding more than brief abstracts to technical papers on the topic (so much for open source with regard to medical science) but here’s a series of links (If I get the chance this week I’ll go to the Millikan library or out to UCLA and pull up some peer-reviewed citations):
Huntington Reproductive Center:[ul][li]Pregnancy rates begin to decline slowly, beginning in the early 30s. []Throughout the late 30s and early 40s there is an even greater decline in pregnancy rates. []Few pregnancies are recorded after the age of 45.[]By the age of 30, 7% of couples are infertile.[]By the age of 40, 33% of couples are infertile.[/ul][/li]
WebMD: The number of infertile couples rises with increasing age. Women are born with a finite number of oocytes (eggs). Thus, as the reproductive years progress, the number and quality of the oocytes diminish. The chances of having a baby decrease by 3-5% per year after the age of 30. This reduction in fertility is noted to a much greater extent after age 40.
Men also experience reduced fertility in their thirties, though at a more gradual rate:
While declines in physical fitness may be “gradual” in modern society, a small decline in capability in a marginal, hand-to-mouth lifestyle can be a breakpoint between survival and death. In large social groups under more than marginal conditions it is not an undue burden to provide for older or less capable members. However, this type of highly cooperative living and support is, in evolutionary terms, a fairly modern innovation (e.g. from H. ergaster onward), and probably has had a modest impact on adaptive survival into extended non-reproductive lifespan.
It’s also worth noting that we enjoy the benefits of modern nutrition and public health unseen in any wild population, which significantly impacts fertility and mortality. Looking at chimpanzees (our closest primate relatives) their lifespan in the wild is slightly over 30 years, with a maximum of around 40, whereas in captivity the average age is in the late 50s to low 60s, with an observed maximum in the mid-70s–not dissimilar to that of humans and our hominid predecessors. That we live much longer beyond reproduction is more likely a result of our sociological environment than an evolutionary adaptation.
True, but again, repairing tools, fixing dwellings, et cetera, are fairly modern behaviors. I can agree that this could have some moderate bearing on post-reproductive fitness which improves the survivability of the group as a whole (although the so-called “Grandmother Hypothesis” has some significant problems, at least from a gene-centrist point of view) but not to the point of extending lifespan into chronic, disabling age-related maladies. It is, as I’ve pointed out before, generally a mistake to make sociobiological rationales for evolutionary adaptations; by being developmentally and intellectually adaptive H. sapiens has often short-cut past “natural” selection in a purely biological sense and has migrated to a Lamarckian-type of memetic adaptation, where “acquired characteristics” in the form of skills passed from generation to generation tend to predominate. In other words, it is often better to be smart than lucky, because luck (of being evolved the “right way” to deal with any general challenge) runs out, where as “smart” lets you figure out a way to perform a task using tools and cooperation that you coudn’t do alone.
So I’ll admit to a bit of hyperbole–clearly, there is some benefit, even from an adaptive point of view, to keeping post-prime-breeding-age members of the species around, for both child-rearing and general benefit to the clan–but this is such a recent development and occurs on a more abstract level that I doubt it has had a signficant effect on fundamental biological processes of aging and longevity, and the incidence of chronic illness is more a result of “artificial” longevity due to better nutrition and a less stressful, less hazardous lifestyle than a disorder that comes from eating foods with the enzymes cooked out of them.
As a contrarian point to my own argument, I’ll note that certain groups are noted for their longevity and reduced incident of chronic, age-related illness based upon diet and lifestyle, specifically, the traditional culture of Okinawa (although signficant criticisms have been made regarding the famous study performed there). It is certainly possible, by living a healthier lifestyle than enjoyed by the majority of the population of modern H. sapiens, to substantially reduce the incidence of chronic illness and improve quality of life by avoiding foods and behaviors (smoking, drinking, sedentary lifestyle) which contribute to such illnesses. But it does not necessarily follow that this is due to the anti-senescence effects of food enzymes.
Well, for every characteristic there are biomechanical limits; a giraffe, for instance, could not be bred to have a neck twice the length of existing giraffes, simply because the skeletal structure and cardiovascular system couldn’t possible support it. It is highly unlikely that you could, by enforced breeding (much less natural selective impetus) double the natural lifespan of a human being and normalize the fertility and physical fitness across that increased span. But beyond that, you have to realize that men aren’t just in competition with each others’ genes, but in direct competition with each other as well, and in various states of fitness and fertility in relation to age. If we assume that female hominids (like chimps and bonobos) are nonmonogomous in nature, they’ll have sex with as many sufficiently fit males as possible to increase the likelyhood of having a fit offspring. Barring some kind of reproductive anomoly, no 40 year old man is going to have the same fertility as a healthy 20 year old, and so the 20 year old will have a natural advantage, regardless of the actual superiority at the gene level, and will probably be more aggressive about pursuing intercourse. On the other hand, (despite years of attempts by revisionist so-called feminist sociobiology to deny it) women in general tend to prefer somewhat older men for their socioeconomic maturity and stability in providing support for said child, so there’s a saddlepoint there.
Stranger
Stranger On A Train the references you have provided have contradicted everyhting you have claimed, and are in exact agreement with everything I have ever been seen.
In summary people experience continual declines in fertility and health from puberty to middle age. Although the rate of increase (ie second derivative) increases with with age there is no sudden point at which fertility declines and health deteriorates. There is no significant decline from the age of 30-40 compared to the decline from 19-29, just a gradual decline. Women in the 27-29 bracket had a lower chance of pregancy than women in the 19-26 bracket, demonstrating a slow and steady decline with age, not a drastic drop at age thirty as you stated. A woman has a finite number of oocytes, and hence fertility declines gradually from menarche onwards.
For men your reference are even more contradictory of your claims, and even more clear that the decline is gardual with age. Fertility declines 2%/annum after age 24. The significant delcine at age 30 that you claim exists clearly does not exist at all. Similarly the oxygen capacity of the blood declined steadily by 2-6%/decade for men in their twenties and thrities. No dranmatic decline at age thirty is noted.
And you have in no way provided any refernce to support your extraordinary claim that hunter gatherers cease to be net food producers at age 30.
I wonder if you actually read your own references, or you simply failed to understand what they actually say? Quite simply people don’t have any notable decline in reporductive abilities at age 30. Reproductive decline begins in the late 20s at the latest accoridng to tghe refrences you supplied, and I have seen a lot of evidence that the declien beins in the mid-late teens. Your claim that reproductive decline begins in the thirties is simply untrue.
Added to that the body’s repair ability doesn’t begin any special decline in the late thirties. The body also begins to decline in the early 20s according to your own references.
And hunter gatherers remain net food producer well into middle age if not old age.
I have no idea where you got your contrary ideas from, but at this stage all the evidence so far presented refutes them all.
Many people mistake average life expectancy with actual life span. High infant mortality pushes the figures way down in some times and places, so if you look at LE in the same population starting at age 15 (out of childhood, starting into maturity) you get much higher figures. The assumptions about past life expectancy have had to be revised anyway, since some of the starting assumptions were flawed.
This paper, Antiquity of Postreproductive Life: Are There Modern Impacts on Hunter-Gatherer Postreproductive Life Spans? (PDF), goes into efforts to estimate ancient people’s lifespans. Most surviving HG people are as active and healthy—or more so—than first-world people. There are quite a few people in most groups that are older than 60, and pretty much anyone with interest in this area knows that most modern hunter-gatherers are living in really marginal areas, where pretty much no one wants to live. I don’t think it’s a stretch to say that people living in better areas than desert and arctic tundra would have an easier time of it, and might have more surviving oldsters.
This page also details how false assumptions led past researchers to underestimate the ages at death of remains that they’ve found. Ancient people lived longer than we thought they did, were more active, and more healthy than most people who live in an industrial society would like to believe they were.
A point well worth making, and one that pretty much kills any suggestion that all HGs become burdens on the tribe as soon as they turn 40.
That is prety dubious for two reasons.
Firtsly better areas suported denser populations, so the amount of resoucres per individual was the same or, more commonly, even less than in marginal areas.
Secondly better areas were more highly sought after and disputed, leading to a state of constant wafare.
As a result people living in more productive areas would generally have had a harder time of it than people in marginal envrionments.