, whileridingthroughtheparkonhiswaytothelibrary, Martindismountedfromhiswheelandlistenedtothearguments, ', , heknewnotwhy, thereseemedsomethingvitalaboutthestuffofthesemen', whoslaughteredEnglish, gesticulatedlikelunatics, andfoughtoneanother'sideaswithprimitiveanger, , .

MartinhadheardHerbertSpencerquotedseveraltimesinthepark, butoneafternoonadiscipleofSpencer'sappeared, , amidthesmokingofmanycigarettesandtheexpectorationofmuchtobacco-juice, whereinthetrampsuccessfullyheldhisown, evenwhenasocialistworkmansneered,"ThereisnogodbuttheUnknowable, andHerbertSpencerishisprophet." Martinwaspuzzledastowhatthediscussionwasabout, butwhenherodeontothelibraryhecarriedwithhimanew-borninterestinHerbertSpencer, andbecauseofthefrequencywithwhichthetramphadmentioned "FirstPrinciples," Martindrewoutthatvolume.

, andchoosingthe "PrinciplesofPsychology" tobeginwith, , , afteralgebraandphysics, andanattemptatasonnet, hegotintobedandopened "FirstPrinciples." , whenhetriedthehardfloor, readingonhisback, thebookheldintheairabovehim, , anddidhiswritingnextmorning, andthenthebooktemptedhimandhefell, readingallafternoon, .

, , , observingdetachedphenomena, accumulatingfragmentsoffacts, makingsuperficiallittlegeneralizations—; butithadneverenteredhisheadtotrytoexplaintheprocesswherebybirds, asorganicflyingmechanisms, , .

Andasitwaswithbirds, , , andtheonlyideahehadgatheredwasthatevolutionwasadry-as-dusttheory, ; thatscientistsnolongerdisagreedaboutit, theironlydifferencesbeingoverthemethodofevolution.