NATURAL SELECTION

IN MOST SPECIES, MANY MORE OFFSPRINGS ARE PRODUCED THAN CAN POSSIBLY SURVIVE. THIS OVER PRODUCTION CAUSES COMPETITION BETWEEN THE OFFSPRINGS CREATING A STRUGGLE FOR EXISTENCE. THE SUPERIOR GENOTYPES WILL MAKE A RELATIVELY LARGER CONTRIBUTION  TO THE GENE POOL OF THE NEXT GENERATION. THE RESULT OF DIFFERENTAL SURVIVAL AND DIFFERENTIAL  REPRODUCTION IS POPULARLY KNOWN AS  SURVIVAL OF THE FITTEST. NATURAL SELECTION  FAVOURS THOSE VARIATIONS THAT ARE ADAPTIVE, AND THEREBY FOSTERS THE CONTINUED EXISTENCE AND IMPROVED REPRODUCTION OF THE SPECIES.

EVOLUTION OCCURS BY THE PROCESS OF NATURAL SELECTION. IN THE STRUGGLE FOR SURVIVAL, SOME LIVING THINGS ADAPT BETTER TO THE CONDITIONS. THESE INDIVIDUALS  ARE MORE LIKELY TO SURVIVE AND PRODUCE OFFSPRING. IF THE OFFSPRINS INHERIT THE SAME FEATURES, THEY TOO HAVE A GREATER CHANCE OF SURVIVAL. IT IS AS IF NATURE  CHOOSES  WHO WILL SURVIVE WHO WILL NOT.

EVOLUTION BY NATURAL SELECTION EXPLAINS THE BODILY FEATURES AND BEHAVIOURS OF LIVING ORGANISMS. THE LONG, COLOURFUL FEATHERS OF A MALE BIRD OF PARADISE MAY SEEM A DRAWBACK . THEY MAKE HIM MORE OBVIOUS  TO PREDATORS AND LESS ABLE TO ESCAPE FROM THEM. BUT THEY ALSO ATTRACT FEMALES FOR BREEDING, AND SO THIS FEATURE IS PASSED ON TO HIS OFFSPRING.

BEHAVIOUR PATTERNS AND CHARACTERISTICS FROM GENERATION PARTLY THROUGH GENETIC MECHANISMS AND PARTLY BY IMPRINTING,CONDITIONING, OR TRAINING THE YOUNG TO BEHAVE IN PARTICULAR WAYS. 

VARIATION IN POPULATION CHARACTERISTICS

DIFFERENCE IN STRUCTURE, FUNCTION AND BEHAVIOUR BETWEEN INDIVIDUALS BELONGING TO THE SAME SPECIES ARE COMMON. IN FACT, NO TWO INDIVIDUALS BELONGING TO THE SAME SPECIES ARE COMMON. IN FACT, NO TWO INDIVIDUALS, EXCEPT PERHAPS IDENTICAL TWINS, HAVE EXACTLY SIMILAR CHARACTERISTICS. IT IS THE GRADUAL ACCUMULATION OF MANY VARIATIONS OVER MANY GENERATIONS WHICH EVENTUALLY GIVES A POPULATION REPRODUCTIVE ISOLATION AND, CONSEQUENTLY SPECIES IDENTITY.

POPULATION MAY VARY IN CHARACTERISTICS  AS ADAPTATIONS TO LOCAL HABITAT CONDITIONS. AN INCREASE OR DECREASE IN THE FREQUENCY OF A GIVEN CHARACTERISTIC  APPEARS TO BE A RESULT OF VARIATIONS  IN THE SELECTIVE PRESSURE OF THE ENVIRONMENT, PERMITTING INDIVIDUALS WITH CERTAIN CHARACTERISTICS OR GENE COMBINATIONS TO SURVIVE AT ONE TIME OR PLACE; OTHER INDIVIDUALS, AT OTHER TIMES AND OTHER PLACES.

MOST SPECIES DIFFER NOT BY SINGLE GENES BUT BY HUNDREDS AND THOUSANDS OF GENES. WHEN FREE BREEDING, PREVAILS  IN A SPECIES, THESE GENES MAY BE ARRANGED IN ALL SORTS OF COMBINATION TO FORM AN ALMOST INFINITE MIXTURE OF CHARACTER MODIFICATION. HETEROZYGOTE ARE, THEREFORE, MUCH MORE FLEXIBLE IN ADAPTIVELY RESPONDING TO THE ENVIRONMENT  THAN ARE HOMOZYGOTE. THE MORE CHARACTERS FOR WHICH AN INDIVIDUAL IS HETEROZYGOUS, THE MORE ADAPTABLE ITS OFFSPRINGS ARE LIKELY TO BE. THESE POPULATIONS ARE MORE EFFICIENT IN EXPLOITING THE ENVIRONMENT THAN ARE GENETICALLY UNIFORM ONES.

SPECIATION

GENETIC VARIATION LEADS TO EVOLUTION OF NEW SPECIES OR SPECIATION. SPECIATION IS THE PROCESS THAT SEPARATES GENETIC VARIATION INTO DISTINCT UNITS, OR SPECIES. IN SPECIATION, THE ORIGINAL POPULATION OF ORGANISMS WITH SIMILAR GENES, CALLED GENE POOL, IS DIVIDED INTO TWO OR MORE GENE POOLS. EACH OF THIS GENE POOL ACQUIRES A NEW SET OF CHARACTERISTICS THROUGH MUTATION AND SELECTION. SPECIATION FOLLOWS MOST COMMONLY FROM THE PHYSICAL DIVISION OF A GENE POOL. THE SEPARATION INHIBITS INTERBREEDING BETWEEN INDIVIDUALS  IN TWO POPULATIONS. IN TIME, ONE OR BOTH POPULATIONS CHANGE ENOUGH TO PROHIBIT INTERBREEDING.

SPECIATION IS THEREFORE THE PROCESS OF EVOLUTIONARY DIFFERENTIATION BETWEEN POPULATIONS, WHICH MAY RESULT IN ONE OLDER SPECIES BECOMING SPLIT INTO TWO OR MORE NEW ONES.

GENETICISTS DEFINE A POPULATION  OF SPECIES  AS A ' A REPRODUCTIVE COMMUNITY SHARING A COMMON CHARACTERISTIC GENE POOL.' EACH LOCAL POPULATION IS DIFFERENT FROM THE OTHER; THROUGH NOT EASILY DISTINGUISHABLE FROM  ONE ANOTHER, AND THEREFORE ARE GIVEN NO FORMAL NAMES.

MUTATIONS

MUTATION IS THE PROCESS IN WHICH THE GENETIC MATERIAL OF A PERSON, PLANT OR AN ANIMAL CHANGES IN STRUCTURE WHEN IT IS PASSED ON TO THE OFFSPRING. THE RATE AT WHICH ANY ONE GENE MUTATES VARIES GREATLY FROM ONE GENE TO ANOTHER. MUTATIONS OF DIFFERENT SORTS APPARENTLY OCCUR HAPHAZARDLY AND ARE NOT INFLUENCED BY ENVIRONMENTAL CONDITIONS. ADAPTION OF A SPECIES TO A PARTICULAR HABITAT OR NICHE IS AFFECTED THROUGH NATURAL SELECTION OF THE FAVOURABLE MUTATIONS OUT OF THE MANY THAT OCCUR. THE SIZE OF THE POPULATION AND THE RATE AT WHICH A PARTICULAR GENE MUTATES AFFECTS THE ODDS OF MUTATION THAT A GENE ESTABLISHES ITSELF IN A POPULATION.