I have recently mentioned an analogy between the heritability of height & weight. That is, the proportion of variance of the trait which can be explained by variance in the genes. How closely do parents resemble offspring. A new paper in PLoS ONE, How Humans Differ from Other Animals in Their Levels of Morphological Variation, look at how this variation among human populations compares to other animals:
Animal species come in many shapes and sizes, as do the individuals and populations that make up each species. To us, humans might seem to show particularly high levels of morphological variation, but perhaps this perception is simply based on enhanced recognition of individual conspecifics relative to individual heterospecifics. We here more objectively ask how humans compare to other animals in terms of body size variation. We quantitatively compare levels of variation in body length (height) and mass within and among 99 human populations and 848 animal populations (210 species). We find that humans show low levels of within-population body height variation in comparison to body length variation in other animals. Humans do not, however, show distinctive levels of within-population body mass variation, nor of among-population body height or mass variation. These results are consistent with the idea that natural and sexual selection have reduced human height variation within populations, while maintaining it among populations. We therefore hypothesize that humans have evolved on a rugged adaptive landscape with strong selection for body height optima that differ among locations.
In other words, it is particularly in the domain of variance in heights within populations where humans are atypical. The authors suggest that selective forces are driving human populations toward phenotypic optimums, and we inhabit a "rugged adaptive landscape." That is, in some places it pays to be short, and in others it pays to be tall. Of possible related interest: Anthropometry of Love: Height and Gender Asymmetries in Interethnic Marriages.
Citation: McKellar AE, Hendry AP (2009) How Humans Differ from Other Animals in Their Levels of Morphological Variation. PLoS ONE 4(9): e6876. doi:10.1371/journal.pone.0006876
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It's not hard to imagine what would cause that rough landscape. Size has obvious advantage with regard to competition. We like the story of David and Goliath because we know the Goliaths typically win on that field of combat. But size also has obvious disadvantages: Though size brings strength in absolute measure, it means less strength relative to the body's own mass. And size requires more calories to sustain. That last is easily forgotten in the modern world where calories are cheap and abundant. That circumstance is the exception of human history, not the rule.
How did the workers choose to define "populations"? They are not large groups that are rather like extended families, are they?
How did the workers choose to define "populations"? They are not large groups that are rather like extended families, are they?
no.
Humans walk upright. It makes sense that the selective pressures that apply to body length in quadrupeds are different from those that apply to body height in upright animals.
Follow-up studies on large birds, kangaroos, or even theropod dinosaurs suggest themselves. I can almost hear the sound of furious grant proposal typing.
And how did they control for between-group differences in nutrition?
I've looked at the tables and I am none the wiser as to how the authors defined "populations". Their list includes The Netherlands, the Japanese Air Force, the British employees of BP Ltd, US University students, a city in Iran and various tribes around the world.
In other word you are talking about IBM and correct my if i'm wrong, size brings strength in absolute measure, it means less strength relative to the body's own mass. And size requires more calories to sustain.