Optimization of two-joint arm movements: a model technique or a result of natural selection?
The fossil record of early hominids suggests that their Arm length, and presumably stature and weight, had a tendency to increase. Using the minimum jerk principle and a related formulation of averaged specific power, ASP, with regard to selected two-joint Arm movements, the current paper explores relationships between ASP, hand trajectory length (or Arm length, or body mass) and mean movement speed, deriving relationships which indicate that ASP is proportional to cubic mean movement speed, but inversely proportional to hand trajectory length (or Arm length, or 1/3 power of body mass). Accordingly, an ;ecological niche' is modeled in a three-parameter space. Either ASP maximization for fixed movement time, or ASP minimization for fixed mean movement speed, taken as selective optimization criterion, allows the increasing of human Arm length during evolution, regardless of the arm-to-forearm length ratio.
Secco
Emanuele Lindo
EL
Dipartimento di Informatica e Sistemistica, Universitá di Pavia, Via Ferrata 1, 27100 Pavia, Italy. Emanuele@bioing.unipv.it
Valandro
Luca
L
Caimmi
Roberto
R
Magenes
Giovanni
G
Salvato
Benedetto
B
D000465:Algorithms; D001132:Arm / Q000502:physiology*; D005075:Biological Evolution; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D008297:Male; D008954:Models, Biological; D008962:Models, Theoretical; D009142:Musculoskeletal Physiological Phenomena; D012641:Selection, Genetic