A Study Of Temperature Variation On Sea Slugs Can Explain Why People Are Taller In Colder Environments

While I was doing research for something else, I stumbled upon a nice study abstract which seems to make the connection between the effect of temperature on the growth rate and ultimate size of an organism to Bergmann’s Rule and why it seems that people from the Nordic Countries are taller than people from countries closer to the equator. The study is below…

Contemp Top Lab Anim Sci. 2005 May;44(3):31-5.
Temperature effects on growth, maturation, and lifespan of the california sea hare (Aplysia californica).
Stommes D, Fieber LA, Beno C, Gerdes R, Capo TR.

Division of Marine Biology and Fisheries, National Resource for Aplysia, University of Miami Rosenstiel School of Marine and Atmospheric Science, Miami, Florida 33149, USA.


We conducted a hatchery growth study to describe the variability in growth rates, spawning, and mortality of Aplysia californica in regard to rearing temperature. Animals were housed at a standard hatchery density of five animals per cage, at temperatures of 13, 15, 18, and 21 degrees Celsius. Animals reared at 13 or 15 degrees C grew as much as four times as large, lived twice as long, matured later, and spawned longer than did animals reared at 18 or 21 degrees C. At age 170 to 205 days the fastest growth rates occurred at 18 and 21 degrees C, and the slowest at 13 degrees C. As animals at 18 and 21 degrees C reached sexual maturity at ages 190 to 197 days, or approximately 60% through their lifespans, their growth rates slowed such that by age 260 days, the fastest growth rate was at 13 degrees C, and the slowest was at 21 degrees C. Animals reared at 13 and 15 degrees C reached sexual maturity at 242 and 208 days, respectively, or at approximately 40% of their life spans. Lifespan and maximum average animal weight were significantly inversely correlated with temperature (P </= 0.0001). However, there were no significant differences at any temperature in the age at which maximum animal weight was reached when this age was expressed as a percentage of the life span: animals reached their maximum weight at approximately 80% of their life span. Aging rate was highest for animals reared at 21 degrees C, while the mortality rate doubling time was lowest at this temperature. This would be expected for the accelerated lifecycle observed at higher temperatures.

PMID: 15934721

Analysis & Interpretation:

From a very quick glance at the abstract, it shows that when the sea slug is placed in an environment that is colder, their maximum size ends up being much bigger, and that they mature slower, and age slower, and might even live longer.

Many anecdotal evidence suggest that this type of phenomena which is called Bergmann’s Rule can be said about humans as well. People who are ethnically main from colder countries or nations like the Northern European countries are in general taller than people whose ethnicity come from places closer to the equator.

Common sense shows that land or countries closer to the equator get much more sunlight and heat than people who live further away from the equator. So their countries are generally warmer. I know from hearing people say that the Philippines can be very warm, even for the natives. This is also true in the Middle East and such.

Many people I know have suggested that Northern Chinese people are taller than Southern Chinese people. The application of the effect of temperature may explain why. Other people also anecdotally state that Koreans are taller than the Chinese on average, and this again can be explained from a geographically point of view. South Korea is situated further away from the equator, meaning that they get less sun and the temperature is lower, so they grow slightly longer and taller. Since the countries of Vietnam, Laos, Cambodia, and Thailand are closer to the equator,  the temperature is higher, so it would suggest that the national average height should be slightly lower. I have not checked the CIA national database for these numbers but it is something interesting to note.

So can we just make the sort of heuristic rule of thumb that people from nations and places further away from the equator tend to be taller? There is a weak correlation to back up that claim at this point.

It is interesting to note that the opposite is also true. There is also a Southern Hemisphere of Earth. And we know that the Southern most part of the world which has been hospitable for habitation for humans was in South America, in the Patagonia region in Chile and Argentina. Of course from my research in the past, I note that Patagonia is famous for the fact that European sailers saw that the humans living in this region were very tall, like giants. The name Patagonia even means something like the “land of the giants”.

We could also say that Australians are on average quite tall, but that could just be from the White European settlers which came there a hundred years ago. This South Hemisphere country/continent should also have tall native people, but there doesn’t seem to be much evidence of it.

So this little fact give even more credibility to the idea that the further your ethnicity are from the heat, to colder places in the world, the bigger your genetic lineage might become.

Of course, we I cam talking about is me trying to make connection and correlations in multiple unrelated areas of study and I could be completely wrong in my conclusion and will be proven wrong from some anthropological or sociological experiment a few decades from now.

2 thoughts on “A Study Of Temperature Variation On Sea Slugs Can Explain Why People Are Taller In Colder Environments

  1. bdbuilder

    According to guiness world records which do most accurate thorough measurements worlds tallest man Sultan Kosen has gained significant height increase well into his adult years in 2010 he was measured 8ft 1inch and 2012 8 ft 3 inch meaning he is still gaining 1 definite inch per year .why would you think this is possible at his age.

    1. admin

      spinal curvature decreased probably. Just look at how slouched over Brahim is who stands at 8′ 1″.


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