1. The Many Arseholesofthe Box JellyfishandEye Evolution
ProfessorDan-EricNilsson hasstudiedeyesfor35years. He has an assuredand conversational way
of speaking,impressinguponyouhis deep understaningof thisfieldof study. Hisseminar,‘Eye
Evolution –How, Why,When’,exploresthe processesandpathwayswhichhave ledtothe classesof
visionwe see today,illustratedwithmanyexamplesandhisownresearch. A particularlycolourful
example of the box jellyfishwhichhas fourbrains,twentyfoureyes and“60 arseholes”alsorevealsa
sense of humourwhichonlyaddsto the qualityof the talk.
He talked of the basicstructure of differenteyesandthere development. How photoreceptorshave
evolvedindependentlyroughly60-65 times. The differenttypesof opsinsusedinphotoreceptors;
rhabdomeric,ciliaryandthe more recentlydiscoveredGO opsinandhow all three are presentin
some formthroughoutall organismsbutonlyone will be expressedinthe eye. ThatPax-6and other
masterregulatorygenesdefine eyedevelopment.
He thenled ontoexamplesof differenttypesand levelsof vision. Compoundvscameravision,and
whycompoundis“shittier”due tothe lawsof physics. The structure of compoundeyeslimitsthe
amountof lightenteringthe eye leadingtoa worse image whereascameraeyeshave the abilityto
focusmore lightontothe retina. Many examples of basicor primitivevisionwere given,suchassea
urchins. These creatureshave simple photoreceptorsacrossthe entire surface of theirbodygiving
thema 3600
fieldof visionbuttheycanonlyresolve areasof lightordark,thisisusedby themto
findreefsandcan be definedashabitatlocation. Anotherexample isthe scallop,whichhasupto a
100 simple eyeswhichcontaintwosimpleformsof retina,one todetectlightandone todetect
abrupt darknesssuchas the shadowof a predator. The abruptdarknessisinterpretedasathreat
and initiatesaresponse,inthiscase closingof the shell. Theycannotresolve shapesbuttheirability
to detectsuddendarknessprotectsthemfrompredators.
These examplesleadustothe mainthrust of the lecture. That complex behaviourandcomplex
visiongohandin handand that behaviourisadriverinthe evolutionof vision. Converselythey
illustrate thatsimple behaviourand,aswe shall see later,simplebodystructuresare alsorelated.
Take for example the seaurchin. Itdoesnothave complex visionbecauseitdoesnotneedit. What
use are eyesthatcan see predators comingwhenitcannotmove away fastenough? Needdefines
vision,functiondefinesits complexity.
He characterisesphotoreceptorcontrolledbehaviourintofourclassesdefinedbydegree of vision,
resolutionandthe speedof the photoreceptorsi.e.the timeittakestointegrate animage :-

2.  Class I - Non-directionalphotoreception
 Class II - Directional photoreception
 Class III- Low-resolutionvision
 Class IV- High-resolutionvision
The classesare alsodefinedmorphologicallywithClassIhavingsimple lightdetectorsandefficient
signalling. ClassIIhave membrane stackingandscreeningpigments. ClassIIIhave more efficiently
structuredeyes,bothcompoundandcamera,capable of low resolutionimages. ClassIV,the eyes
we see withtoday,are highlycomplex andhave lenses.
Notonlyis complex visiontiedinwithbehaviourbutalsoa complex bodystructure. Duringthe
CambrianExplosion,aneraof seeminglyrapidevolutionanda resultanthostof new species,key
componentsevolvedwhichwouldallowthe evolutionof highervision. Skeletal systemsevolved,
whichallowedthe formation andattachmentof more muscles. These neededtobe guidedbymore
complex nervoussystems, whichinturnneededtobe informedbymore advancedsensorysystems.
Thisis where the foundationwaslaidforthe evolutionof highervision. The abilitytomove about
more demandedthe processingof informationfromthe environmentmore rapidlyandalsoledto
more complex behaviours,suchasfoodgatheringviahuntingorherbivory,avoidance of predators
or the seekingof mates. These eventsledtoevolutionof the complex eyewithwhichwe see with
today.