Kevin MacDonald, Ph.D.
CSULB, Department of Psychology
PSYCHOLOGY 346IC
HUMAN SOCIOBIOLOGY: BASIC IDEAS ON EVOLUTION
ARTIFICIAL SELECTION: BREED ANIMALS OR PLANTS FOR PARTICULAR PURPOSES;
E.G., DOGS, CATS, COWS, RACE HORSES OR CORN PLANTS
REQUIRES THAT THE TRAITS ARE INFLUENCED BY GENETIC VARIATION. BREEDER SIMPLY
SELECTS ANIMALS WITH DESIRABLE TRAITS TO BREED. Usually, that would mean selecting animals at one
end or the other of the normal distribution curve.
NATURAL SELECTION:
1. ANIMALS VARY IN THEIR CHARACTERISTICS;
2. ANIMALS VARY IN THEIR REPRODUCTIVE SUCCESS (RS), I.E., SOME HAVE NO OFFSPRING OR FEWER OFFSPRING THAN OTHERS. ANIMALS THAT SUCCESSFULLY REAR 3 OFFSPRING WILL DRIVE ANIMALS THAT SUCCESSFULLY REAR 2 OFFSPRING TO EXTINCTION
GIRAFFES WITH LONGER NECKS AND EAGLES WITH BETTER EYESIGHT AND GAZELLES WITH BETTER RUNNING ABILITY HAD A REPRODUCTIVE ADVANTAGE OVER THOSE LESS ENDOWED. Therefore the eagles we see now have great eyesight. Notice that it's not that giraffes keep stretching their necks and this trait is then passed on to their offspring. It's that if a genetic mutation causes a giraffe's neck to get longer, there is natural selection for the mutation and it spreads in the population because animals with that mutation have more offspring.
3. ALL ANIMAL SPECIES ARE CAPABLE OF OVER-PRODUCING OFFSPRING; I.E., THEY ARE CAPABLE OF MORE THAN SIMPLY REPLACING THEMSELVES. E.G., IF EACH MALE AND FEMALE HAD 4 OFFSPRING, THE POPULATION WOULD INCREASE EXPONENTIALLY (2, 4, 16, 256 . . .).
4. THEREFORE, COMPETITION WITHIN EACH SPECIES IS INEVITABLE.
5. ANY ADVANTAGE IN THIS COMPETITION WILL BE SELECTED. THIS IS NATURAL SELECTION.
Tinbergen's Four Causes
(1) PROXIMATE CAUSATION: THE DIRECT CAUSE IN A MECHANICAL SENSE; HOW DO GENES, PHYSIOLOGICAL SYSTEMS AND ENVIRONMENTS CAUSE BEHAVIOR?
Example: What neurotransmitters are involved in hibernation? What is the biochemical basis of love?
(2) ULTIMATE CAUSATION: THE ADAPTIVE SIGNIFICANCE OF A BEHAVIOR OR PHYSICAL STRUCTURE. WHY DID THE BEHAVIOR OR STRUCTURE EVOLVE?
ADAPTATION = A BEHAVIOR OR MORPHOLOGICAL FEATURE DESIGNED BY NATURAL SELECTION IN ORDER TO PERFORM A PARTICULAR FUNCTION
EXAMPLE: ATTACHMENT IN HUMANS IS AN ADAPTATION THAT FUNCTIONS TO KEEP THE INFANT CLOSE TO MOM IN ORDER TO AVOID PREDATORS (BOWLBY). IT WAS DESIGNED BY NATURAL SELECTION IN THE SENSE THAT GENES FAVORING ATTACHMENT SPREAD IN THE POPULATION BECAUSE INDIVIDUALS WITH THESE GENES HAD MORE OFFSPRING.
Example: The eagle's beak is an adaptation that functions to enable the animal to tear flesh. It has been designed by natural selection to solve the eagle's need to get food.
(3) DEVELOPMENTAL (ontogenetic) CAUSE: HOW DOES A BEHAVIOR OR STRUCTURE DEVELOP IN AN INDIVIDUAL?
Example: Attachment in human infants develops gradually over the first six months of life. Full-fledged attachment appears only with the development of fear of strangers in the second half of the first year.
(4) PHYLOGENETIC CAUSE: WHAT IS THE EVOLUTIONARY HISTORY OF AN ADAPTATION? For example, it is possible to trace the evolution of the horse's hoof over many millions of years by examining the fossil record.
FITNESS = RELATIVE REPRODUCTIVE SUCCESS (RS); I.E., RELATIVE TO SOME OTHER GENOTYPE
EXAMPLE: FRUIT FLY WITH A MUTATION THAT AFFECTS WING VIBRATION DURING COURTSHIP IS LESS FIT (HAS LOWER RS) THAN NORMAL GENOTYPE.
GENOTYPE: NN Nn nn
RELATIVE RS: 1.0 .80 0.67
IF N DOMINANT: 1.0 1.0 0.67
BEHAVIOR IS DESIGNED BY NATURAL SELECTION TO MAXIMIZE FITNESS IN THE ENVIRONMENT OF EVOLUTIONARY ADAPTEDNESS (EEA).
EEA = ENVIRONMENTS THAT THE SPECIES EVOLVED IN AND WHICH PRESENTED THE
PROBLEMS SOLVED BY THE SET OF ADAPTATIONS POSSESSED BY THE ANIMAL.
For
example, the EEA for attachment was presumably an environment with predators and
other dangers for infants. Infants who had a strong attachment system survived
better because they stayed closer to mom and avoided these dangers.
SPECIES-TYPICAL BEHAVIOR = BEHAVIOR COMMON TO ALL MEMBERS OF THE SPECIES
SPECIES-TYPICAL BEHAVIOR IS USUALLY FIT BEHAVIOR IF THE ENVIRONMENT IS LIKE THE EEA.