[Taxacom] barcode of life: PS

Stephen Thorpe stephen_thorpe at yahoo.co.nz
Sun Jul 4 23:37:06 CDT 2010


surely height is not a bell curve - it is for "normal people", but the existence of recognised medical conditions like dwarfism (http://en.wikipedia.org/wiki/Dwarfism) is something over and above (no pun intended!) the normal bell curve. It must surely mean that there are more dwarves than by chance alone (i.e., more than just the tail of the bell-curve, so there is a little hump on the tail).

anyway, I fear you are missing the point. The point is that IF the human height frequency distribution was flat (which it isn't), then the concept of short/average/tall would have less "reality" than it actually does, and could only be purely arbitrary. On the other hand, if everybody were to die out except for a narrow band around the average and at each extreme, then the short/average/tall distinction would be far more real than it actually is. As it is, it is not completely arbitrary, but not that good either.

So, similarly, the reality of species distinctions depends on what is out there in the world. If reproductive isolation is mostly either all or nothing, then species are very "real". If it is mostly 50% (or random) then species do not represent reality very well at all. I say it is pretty good. Rich seems to disagree, and says things which sometimes suggest complete arbitrariness (like shortness on a flat height distribution) ...

Stephen




________________________________
From: Curtis Clark <lists at curtisclark.org>
To: taxacom at mailman.nhm.ku.edu
Sent: Mon, 5 July, 2010 2:28:12 PM
Subject: Re: [Taxacom] barcode of life: PS

I also disagree. Height *is* a bell curve 
(http://www.garyweeks.com/designing_bar_stool.htm, bottom of the page). 
What makes tall people stand out is that we ordinarily see so few of 
them; they are one of the two tails of the distribution. Natural 
distributions that are tail-less (with the exception of truncated 
distributions where one end is structurally fixed, such as "zero 
progeny") are so uncommon as to have had no role in shaping human 
perceptions.

On 7/4/2010 7:02 PM, Jim Croft wrote:
> This isn't really true is it?  Aren't notion(s) of short/tall,
> dark/light, fat/thin, etc. and other continua are dependent on the
> range, not on the distribution of the attribute within that range?
> Most distributions of characters in nature follow a bell curve, but
> what if they didn't?  Say the distribution was flat - individuals
> clustered towards end would still be considered tall, the other short.
>  What if it was an inverse bell curve?  Don't tell me... different
> species at each end, for sure... :)
>
> Even with a bell curve, the notion of short vs tall vs normal is
> arbitrary. You can pick your working percentile and I can pick mine.
> And it applies a flat distribution as well.  If you are a 25% person
> and I am 33% person all it impacts is the number of individuals each
> of us would call short of tall.
>
> jim
>
> On Mon, Jul 5, 2010 at 10:11 AM, Stephen Thorpe
> <stephen_thorpe at yahoo.co.nz>  wrote:
>    
>> Analogy: if there were an equal proportion of people for every possible height, then there would be no useful concept of "tall people" or "short people". Of course you could arbitrarily set a particular height such that anybody above it was a "tall person", but this would not be a "real" distinction. A person who is 7ft tall really is a tall person simply because there is a distinct gap in nature between that and the normal range of heights (which is NOT to suggest that there aren't a few people with each "in between" height). Note that a 7ft tall person would still be a tall person if lots of people were 7ft. tall, provided only that there were relatively few people of heights somewhat less and then more again below that, so it isn't just about the rarity of 7ft. tall people, but about the whole frequency distribution of heights.
>>
>> It is all about finding (describing) patterns in nature - patterns which "really are out there" (and need not have been if things were different)
>>      
>    


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