The Order of Man: A Biomathematical Anatomy of the Primates

CHAPTER 4 Biological 'Meaning' of Structures

CHAPTER 4 Biological 'Meaning 5 o f Structure s Abstract - 'Biologica l meanings ' o f structur e The importanc e o f internal , developmental , factor s The al l pervasiv e effect s o f functio n - Structur e - Functio n the structural-functiona l interfac e - Anima l Mechanic s - A direc t approac h Functional morpholog y - A n indirec t evaluatio n The structural-functiona l associatio n revisite d — Som e practica l example s Average biomechanica l situation s - Locomoto r classification s - A n alternative , the regiona l functiona l spectru m - A spectru m o f uppe r lim b functio n A spectru m o f lowe r lim b functio n - A summar y The classificatio n versu s th e spectru m - Th e desig n o f observation s Observational design , som e precaution s - Application s t o fossil s Primitive an d derive d feature s Limits, fo r fossil , t o th e functiona l argumen t - Summary Abstract. I n thi s chapter is discussed wha t we can learn from studie s of structure. Of course, many studies of structure lead t o th e understandin g o f matter s suc h a s heredit y an d development . But , fo r th e post-crania l skeleton , man y investigations reflect th e functions tha t the structures subserve. Though direct information abou t function i s produced by the studies of animal mechanics, indirect insights can come from observin g the way in which animals with differen t behaviours ar e arranged b y structures. For this purpose th e attempts t o quantify an d analys e structure, as in the last chapter, ar e s o critical . Arguments about the nature of the association between structure and function ar e discussed and lead to the concept of the 'structural-functional interface ' an d th e 'average biomechanical situation ' actin g upon a structure. One form o f average biomechanica l situatio n i s reflecte d i n th e classificatio n o f locomoto r patterns : th e clusterin g o f animal s according t o similaritie s i n locomoto r patterns . I n th e pas t suc h idea s hav e bee n quit e useful . But consideration o f the deficits of such classifications lead s to the idea of the functional spectru m and to the notion that suc h spectr a ar e limite d t o individua l anatomica l regions . This , i n turn , lead s t o th e ide a tha t searchin g fo r relationships betwee n structur e an d functio n ca n hav e a stric t 'desig n o f observations' tha t parallel s th e desig n o f experiments whic h ha s lon g bee n know n t o b e critica l i n direc t experimenta l studie s o f animal mechanics . The application o f these concepts to the study of structures, the functions o f which are unknown (i.e . the structure s of fossils), has limits over and beyon d thos e applying to the study of living forms. Of course, some of these limits stem from th e fragmentary natur e o f much fossi l data , bu t no t inconsiderable part s ste m fro m th e problems o f prediction. Biological meaning s o f structur e Once difference s i n structur e hav e bee n defined , as, fo r instance , b y th e method s o f the las t chapter , we ca n tr y t o asses s thei r biologica l (evolutionary ) meaning. Fo r som e worker s th e fac t an d natur e o f structural difference s ar e alon e th e resul t o f th e process o f evolution , an d speculatio n abou t evolu tion i s therefor e mad e directly . Bu t fo r th e grea t majority o f biologists, discoverin g structura l differ ences i s merel y th e first ste p i n makin g evolution ary assessments . A s nex t steps , suc h biologist s expect tha t variation s i n structur e ca n b e weighte d according t o whethe r o...