BURR EVOLUTION

Back in early November - when I brushed by a 5 foot high dry weed - my orange polar fleece [1] (needle-punched non- woven fabric) [2] vest was silently loaded up with hundreds of securely embedded seeds.   I was flabbergasted by the physical effectiveness of the seeds in hitching a ride on my (left photo above ) vest .  There were so many seeds visible I had to put the vest away – I’d look a little hicky if I wore it out.

THE BRILLIANCE OF EVOLUTION –   GOOD DESIGN BY TRIAL AND ERROR

 The photo on the right above is a magnified view of a  seed cluster on the stem of the weed.   Each seed has two “horns” on the outer end of the seed (the spread-apart horns look like the antenna on a beetle).   Each “horn” has dozens of microscopic needle-like backward facing “hooks”.  When the seed is pulled on, or flexed, the “horns” break away from the seed at an abscission [3], staying embedded in the fabric.    Unlike Velco [4]  (which imitates thistle) [5] , it is impossible to pull this burr “horn” out backward.  

In my experience I have found example after example of nature solving engineering tasks with evolutionary elegance.    With this weed the task was seed dispersal.  Dandelion seeds use the wind to disperse.  Edible berries are dispersed through scats.  And these burrs are hitchhikers.

TESTING HUMAN DESIGN BY ITS COMPATIBILITY WITH A NATURALLY EVOLVED SYSTEM

It dawned on me that fleece must be structurally very much like animal fur – because the burrs  had evolved to attach to passing animals – not to fabric – yet they attached to the fabric very, very effectively.   So, in a reverse twist, the fact that burrs attach to a non-woven fabric like  fleece is a demonstration that fleece is  very similar to animal fur.   Animal fur – by the fact that fur is an evolutionary design system which is used by a vast number of species -  is obviously a very effective protective layer and insulator.   So the  close similarity between fleece and fur  suggest that fleece is probably a engineering design which is very close to the most effective fabric man can design.   Fleece breaths, it it soft and flexible, it is a good insulator, it wears well.     

So for me the burrs attaching to fleece is a “consumer test” for fleece – and the fleece passes with a high score.

  OTHER HUMAN DESIGNS WHICH IMMITATE THE BURR “HORNS” -  FORM FOLLOWING FUNCTION

Each individual horn looks almost exactly like a whale harpoon [6].  And when you consider that the harpoon  was engineered – just like this burr -  to prevent pull out – it is not surprising that the harpoon design is identical  to that of the spiny burr “horn”.

Another man made design which imitates the dual horns of the burr is the fishing spear [7] used in the Pacific Northwest by Indians.  Again, the fishing spear was intended to attach itself to fish and not let go.   I would think that the weed burr evolved long before the fishing spear was developed – did the Indians merely look at furry animals, see the burr seeds in the animal fur, get curious like I did today – and then make the segway from burr to spear?   Here is another fishing spear [8] which looks almost identical to one of the burr’s “horns”.

Plagiarizing evolution.  That’s the best way to get to superlative design. 

Next evolutionary photo episode – the tortoise and the hexagonal-barked desert plant….stay tuned!