Wyz_sub10

I have a "friend" on a track message board who loves to generalize about races. He's a pretty good guy, but he has some incredibly ignorant ideas about "races" being built this way or that.

The speed issue always comes up, and I can deal with that well enough.

But he mentioned the heights (tall and short) of certain African populations. Now, I understand that height is far more influenced by nutrition than genetics, and I have read the reports on the increase in the height of the Dutch population, or decrease in American height, etc. But I have a couple of questions:

1. What about nutrition causes the increase/decrease in height?

2. How much of height is genetic?

3. Two things I often hear attributed to better nutrition/housing/economics are an increase in height, and an earlier onset of menarche. I may be mistaken, but aren't both of these more visable in the black inner-city populations in the US? If so, doesn't this run counter to the theories?

Thanks all.

keyser_soze

Not sure I would jump on the american decrease in height. I am astounded at the height of kids in middle school and high school nowadays. I visit a school, and where I used to be average height, 14 year olds now tower over me! No, I think height overall is increasing everywhere....but it is only a personal opinion.

ps418

Ah, this gives me a chance to explain that the question "how much of [trait x] is genetic," is meaningless. What I think you really want to know is, is how much of the variance in height between individuals is due to genetic differences. The answer depends upon the particular population and the various environmental infuences that impinge upon it. In a population where some people are starving and others arent, the variance associated with nongenetic factors will be larger. In a population where virtually everyone has decent nutrition, genetic factors explain much more of the population variance. In all populations that have been examined, the heritability of height is considerable, with genetic factors accounting for between half to 90% or more of individual differences for this trait. The Ober et al (2001) paper estimates both the narrow and broad heritability of adult height in their Hutterite community to be 0.83, for example, which means that differences in height in that community are due almost solely to genetic differences. The graph below compares the relationship between average parental height (mean of mother and father's height) and child height. As you can see, parental height predicts child height very well:


From this page.

There is considerably less information on the sources of between-group differences in height, but there is no reason to think that the mean height differences between, say, Inuits and Masai tribesman, or between African Masai and African Pygmies are due solely to nutritional differences (some of the tallest and shortest populations, respectively).

Refs

Carmichael and McGue, 1995. A cross-sectional examination of height, weight, and body mass index in adult twins. J. Gerontol. A Biol. Sci. Med. Sci. 50, 237–44.

Finegold et al, 2000. Heritability of height and assortative mating in the Framingham Study. Am. J. Hum. Genet. Suppl. 67:A235

Ober et al, 2001. The genetic dissection of complex traits in a founder population. Am. J. Hum. Genet. 69:1068-1079.

Phillips and Matheny, 1990. Quantitative genetic analysis of longitudinal trends in height: preliminary results from the Louisville Twin Study. Acta Genet. Med. Gemellol. (Roma) 39: 1,143–63.

Preece, 1996. The genetic contribution to stature. Horm. Res. 45 Suppl 2, 56–8.

Silventoinen et al, 2000. Relative effect of genetic and environmental factors on body height: differences across birth cohorts among Finnish men and women. Am. J. Public Health 90, 627–30.

Wyz_sub10

ps418,

Thank you for the detailed reply.

I'm still a bit confused - I thought that much of the increase in height over the past 200 years has been attributed to nutrition?

If this is the case, than I'm missing the genetic connection. Is the genetic connection, perhaps, one in which body types are more likely to respond to better nutrition with an increase in height?

In other words, is it possible that instead of "expression 'x' of gene 'y' will result in increased height", the situation is "expression 'x' gene 'y' will result in increased height if nutrition 'z' is continually present"?

Sorry if this sounds novice, but I seem to be reading conflicting opinions on why, say, population 1 is taller on average that population 2.

God Fearing Atheist

The secular trend in height, like the Jensen-Flynn effect in IQ, is almost certainly environmental. This does not mean, of course, that height is entirely environmental in nature, or group differences can be explained in a similar way.

ps418

Actually, it is not clear that environmental effects alone are responsible for group differences in age of menarche. For instance, girls or european descent experience menarche on average a bit later than 'Hispanic,' Asian/Pacific Island and African-American girls, even when dietary differences are controlled for (Koprowski et al, 1999). In many different ways, Africans physically mature slightly more quickly than Europeans.

Koprowski et al, 1999. Diet, body size and menarche in a multiethnic cohort. British Journal of Cancer 79, pp 1907-1911.

Patrick

Oolon Colluphid

Apologies that this hasty reply isn’t as erudite as Patrick’s... but then, few are!

IMO the height increase over the last however-long is dietary. The famous Nariokotome Boy Homo ergaster skeleton, an 11-ish-year-old, was 5’3’’ (iirc), and is estimated to have topped six foot if he’d lived to adulthood. Unless he was exceptional -- and fossils are taken as being generally representative, because it’s most likely that an average individual will get fossilised, just because there’s most of them (by definition!) -- he’s probably a rough guide to the height of our (African) ancestors.

As I understand it, the agricultural revolution enabled many more people to be fed... but not very well. It seems that ‘we’ were taller in our more natural hunter-gatherer environment; we dipped once agriculture kicked in; and we’ve climbed back again as health care and nutrition have improved.

Cheers, Oolon

God Fearing Atheist

Right. See also Hermann-Giddens, et al. (1997). Secondary sexual characteristics and menses in young girls seen in office practice. Pediatrics 99: 505-512.

Percentage of girls that have breast development/public hair at age 8:

Girls of largely African decent - 45%
Girls of largely European decent - 15%

Age 45% of girls, largely of European decent, have some breast development/public hair: 10

-GFA

ps418

It is, and this is not in conflict with the high heritability of height. Heritability is simply an index of the extent to which differences in a trait in a population are due to genetic differences. In fact, even if heritability were .99, the mean population height could still theoretically increase dramatically.

I should clarify that the above references refer to within-group differences. Though within all populations so far studied height differences are largely the result of genetic differences, you cannot necessarily say on the basis of the studies I cited that between-population differences are almost completely genetic, because the environmental influences may be very different between populations. You'd need a different type of evidence to make that inference. For instance, if between-group differences persist when environmental differences such as nutrition and childhood illness are controlled for (either statistically or by being raised in the similar environments), this raises the likelihood that the between group differences are the result of genetic differences.

As I said, though, I see no reason to think that between-population height differences are soley the result of nutrition differences, though they probably partly responsible. For instance, the Masai tribes are some of the tallest populations in the world, yet I highly doubt that they are better nourished and experience less childhood illness than the average European, or than the African Pygmies for that matter.

Patrick

Majestyk

Some of this thread is confusing me. If, we accept that evolution is the process of genetic mutations being retained by the population due to their contributing in the proliferation of its inheritors, then how can we say that race, has no relation to genetic makeup? Doesn't this contradict the notion of inherited traits? And are not inherited traits the foundation of evolution?

Not to dismiss the role of environmental conditions, such as nutrition but I would speculate that race must have some root in genetics whether it be a single gene or the subtle interaction of a multitude of genes.

I'd hate to see the attempt by some to use this as a means of claiming superiority of one race over another, to adversely affect the science itself.