Size rules biology to a great.extent. . When things get bigger, their length increases linearly but their surface area increases by the square and their volume by the cube. So when the proportions, properties and performances of organisms, such as body shape, life span or speed of movement, are plotted against size or weight in log-log graphs, they fall on straight lines. The relationship between weight and strength dates back to Galileo, who calculated the effect of increases in animal size on body proportion.
In general life is shorter, hence the time flies faster, the smaller the organism.. And the bacteria zipping around in the water sample under a microscope are not an optical illusion; rather, they are moving at more than a hundred body lengths a second — equivalent to 720 kilometres per hour for a 2-metre-sized organism like humans. The same rate as planes .
What made size matter in the first place? Selection by predators is the most obvious reason, with increasing size. Selection by predators with increasing size a way to escape. Also there is always room at the top, implying that organisms can always get bigger. But the bigger they are, they harder they fall, so it is the small ones that are less vulnerable in the long run.
Victor Smetacek Nature vol 445, February 22 9 821 writing about the book
Why Size matters, from Bacteria to blue whales John Tyler Bonner Princeton University Press.
Height may be of importance, but much more important from the health point of view is obesity and the corollary of this anorexia nervosa. Will people born in the developed world in the 1990s have shorter lives than those born 60 years ago? The upward trend in life expectancy over the past century is set to reverse unless the life style of young people dramatically improves. The steady-rise of childhood obesity in the USA is likely to reduce life expectancy by 2 to 5 years by the middle of the century, with enormous increases in morbidity from type 2 diabetes, heart disease and other vascular disorder. Obesity during pregnancy may well have consequences for the foetus.
The average stature and physique of humans from different parts of the world reflect the local nutritional regime by processes that are established in utero and transmitted to succeeding generations. It seems that obesity and its consequences are likely to emerge when there is freely available food.
In the developing world, those released from the grip of historic poverty are most affected, whereas in the developed world, for reasons that are less well understood, the victims are the least educated and the least affluent.
The Pima Indians of Arizona and the inhabitants of the Pacific island of Nauru. until a few decades ago were lean and fit and free of diabetes. Now the majority of their young adults are obese, develop diabetes and die prematurely of heart disease. There may be a genetic predisposition to diabetes but the abrupt decline in strenuous physical activity along with the loss of the traditional foods by energy-dense food is the real cause. .
We have to return to a different way of life, in our new context. The food styles of our ancestors, clean food, water and decent sanitation, accompanied by exercise appropriate to our age and stage of life.
Michael Sargent reviewing Mismatch: Why Our World No Longer Fits Our Bodies
by Peter Gluckman & Mark Hanson ; Oxford University Press. 2006. 304 pp in Nature vol 445, pp 600
The terrible scourge of obesity in children is reviewed in the BMJ 2006, vol 33 pp1207-10 in a review article ( JJ Reilly and D Wilson )
They define obesity as an excessive body fat content with an increased risk of morbidity. BMI is probably the best measure of obesity., overweight being a BMI > than 91st percentile using the UK BMI charts and obesity > 98th centile. The epidemic of childhood obesity began in the UK in the 1980s.In 2004 14% of 2-11 year old children are obese and 25 % of 11-15 year olds obese.
The health consequences of this is wide. Psychological health health , cardiovascular overload, asthma, diabetes, orthopaedic problems,
And these persist into adult life with worsening seriousness and added the risk of diabetic problems.
Guide lines to prevention are complex and must be introduced with compassion and care.
The family as an entity must be treated and overall dietary changes are needed. A restriction in high energy foods to eating only at meals especially low energy containing foods is important.
- Martin Eastwood