Notes on Dawkin's "Extended Phenotype"Prior to chapter eleven the book is mainly concerned with butressing the theories expoused in "The Selfish Gene".
Pg.197/8: A genetisist need not care about the exact pathway between gene and phenotypic effect, simply on the difference between alleles and their effects on end products/outcomes - because 'natural' selection is applied in exactly the same way - taking the existence of a pathway, one even routing through several bodies, for granted.
Say a fish builds a little 'house' out of stones on the river bed. The colour of the stones chosen is dependent on a single allele. Change that, chage the hue of the house. How exactly is that mechanism any different from a gene that governs the colour of skin or hair..? save in extention..?
Same with spider webs. A larger mouth at less energetic cost. Beaver dams, and the lake they form, and the ecology that lake promotes, should be thought of as extentions of the beaver phenotype, as surely as if that lake were enclosed inside their skins.
Note: Convergent evolution // behavioral mimicry of optimal physiology.
A three-jointed human arm has only seven degrees of freedom, which are defined as the types of movements each joint can perform. Your shoulder and wrist each have three degrees of freedoms—each can tilt up and down, turn left and right, and can roll in a circular motion. Your elbow, however, only has one degree of freedom, which is tilting up and down.
Scientists consider each of an octopus' eight arms to possess a virtually infinite number of degrees of freedom, allowing them to bend and twist freely. But when it's time to eat, octopuses use their flexible muscles to form temporary, quasi-articulated joints that work similar to how human joints function.
Researchers recorded muscle activity in octopus limbs, and found that an arm generates two waves of muscle contractions that propagate toward each other. When the waves collide, they form a part-time joint.
This process occurs three times, forming a shoulder where the arm meets the body, a wrist where the suckers have grasped their food, and an "elbow" somewhere in between. The elbow typically exhibits the most movement during food retrieval.
The researchers say this is a remarkably simple and apparently optimal mechanism for adjusting the length of arm segments according to where the food item is grasped along the arm.
The similarity of structural features and control strategies between jointed vertebrate arms and flexible octopus limbs suggests that these configurations evolved separately in octopuses and vertebrates, a result scientists call an example of convergent evolution.
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