Increase in Human Height: How Does It Affect Organs?

[Dooga Blackrazor]

I believe it's true to say that over time humans have achieved greater average heights. I'm just curious if the organs are increasing in average size or ability to make up for the height increase.

 

[Phobos]

Well, skin is an organ. And greater height means greater skin coverage.

Off the top of my head, I would assume that most organs scale up with body size. It would get interesting if the organs started to change form/function in order to accommodate the new body size (i.e., evolution).

 

[hitssquad]

Digging Lamarck back up from his grave

Well, skin is an organ. And greater height means greater skin coverage.

Off the top of my head, I would assume that most organs scale up with body size. It would get interesting if the organs started to change form/function in order to accommodate the new body size (i.e., evolution).

That certainly would be interesting, since it would demonstrate Darwin's theory of natural selection wrong and Lamarck's long-since-abandoned theory of natural-selection-free evolution correct.

 

[ryokan]

Size and form are related

All is integrated in the organism.
There isn't first enlargement and then adjustment of organs.
In an individual, the dimensions must be adequate to functions. And functions are related to some exponent of longitudinal dimension, being some functions (as cortical activity or gut absorption) more dependent from surfaces and others (as thermogenesis) more dependent of volumes.
For this reason an insect couldn't retain its form if its size were greater.

 

[selfAdjoint]

The intestine is twisted the way it is to provide its necessary length in the volume of our torsoes. Contrary to hitssquad, this does not imply Lamarkism. Individuals born (or even developing in the womb) with an innapropriate length will simply not survive, and so we are all dscended from individuals who did have this trait, produced by a random variation in some genes, and strongly selected for.

 

[Phobos]

hitssquad - I was not implying that a big individual is born with "normal" sized organs and then organs shift to accommodate it in that individual, and then the new trait is passed down. I meant a Darwinian shift over time (over many generations) in which organ morphology changed along with body size at the same time. Didn't mean to confuse things!

With substantial body size changes, you can't simply scale up the body plan without limit (unlike small variations in body size within a species' normal range). With large-scale changes, there is also a shift in body structure to accommodate the new weight, heat capacity, calorie requirement, etc. If the overall body structure does not work as well, then the variation is selected against, as selfAdjoint said.

 

[hitssquad]

Elephant red in tooth and claw

hitssquad - I was not implying that a big individual is born with "normal" sized organs and then organs shift to accommodate it in that individual, and then the new trait is passed down. I meant a Darwinian shift over time (over many generations) in which organ morphology changed along with body size at the same time. Didn't mean to confuse things!

You're still confusing things.

1. Where is the random variation?
   
2. Where is the environmental pressure?
   
3. Where is the macabre selection process?

With large-scale changes, there is also a shift in body structure to accommodate the new weight, heat capacity, calorie requirement, etc.

Agreed. Overall size change causes a ratio change between bulk and surface area.

However, you are missing random variation, environmental pressure to select among those random variations, and a macabre selection process, and therefore you are not describing Darwinian evolution.

If the overall body structure does not work as well, then the variation is selected against, as selfAdjoint said.

I'm looking around and I don't see any environmental pressure in a world where random variations are accommodated by technology. If we have a problem with heat variation, instead of killing off the 999,999,999 out of every billion of us that does not have the appropriate large floppy ears and wrinkled skin otherwise needed to accommodate the greater heat-dissipation needs of a lower body-surface to body-bulk ratio, we can simply turn up the air conditioners.

 

[Phobos]

hitssquad - I think you're getting beyond the scope of the OP. It sounds like you are questioning the premise that modern humans can evolve (an interesting discussion we've had here a couple times as well as in a Physics Post article) whereas D.B. was asking if there was any known changes in human organs associated with our increased height over time.

FWIW, I'd say that our technology has slowed, but not eliminated natural selection. The selection process is still with us. Perhaps you could start a new topic on that debate point.