1. MECHANISMS OF EVOLUTION

2.  After studying Malthus, Darwin realized that if more individuals are produced than can survive, members of a population must compete to obtain food, living space, and other limited necessities  Described as the “struggle for existence” TARGET #3- I CAN EXPLAIN HOW VARIATION CONTRIBUTES TO AN ORGANISM’S SURVIVAL

3.  Variation plays a vital role in the struggle for existence  Individuals have natural variations among their heritable traits  Darwin hypothesized that some of these variations are better suited to life in their environment than others  Ex: a lion with longer claws and higher endurance is a better hunter than a lion without those traits

4.  Adaptation: any heritable characteristic that increases an organism’s ability to survive and reproduce in its environment.  Includes  Body parts  Claws  Wings  Coloration  Bright colors  Camouflage  Mimicry  Physiological functions  Photosynthesis  Brain capacity TARGET #4- I CAN DESCRIBE AN ADAPTATION

5.  Darwin recognized that there must be a connection between the way an organism “makes a living” and the environment.  Differences in adaptations affect an organism’s fitness  Fitness: how well an organism can survive and reproduce in relation to others of the same species within it’s environment  Individuals with adaptations that are well suited to their environment can survive and reproduce more offspring  Individuals with characteristics that are not well suited to their environment either die without reproducing or leave few offspring  The difference in rates of survival and reproduction is called “survival of the fittest” TARGET #5- I CAN EXPLAIN WHY ORGANISMS WITH GREATER FITNESS GENERALLY LEAVE MORE OFFSPRING THAN ORGANISMS THAT ARE LESS FIT

6.  Natural Selection  The process by which organisms with variations most suited to their local environment survive and leave more offspring  The environment influences fitness

7.  Natural selection occurs in any situation in which more individuals are born than can survive, there is a natural heritable variation, and there is variable fitness among individuals  Does not make the organism “better”  Does not move in a fixed direction  A process that enables species to survive and reproduce in a local environment  If local conditions change, some traits may become adaptive  If conditions change faster than a species can adapt, the species may become extinct TARGET #6- I CAN SUMMARIZE HOW NATURAL SELECTION ALLOWS ORGANISMS WHICH ARE MORE ADAPTED SURVIVE IN THEIR ENVIRONMENT

8.  Adaptations and variations among individuals in populations of species does not begin in the environment  Step 1: a mutation occurs within the DNA of an organism  Step 2: that mutation leads to the production of a protein that either does not function, over functions, or has a different function than originally intended  Step 3: the mutation is passed down to an offspring where it is expressed in the offspring’s phenotype TARGET #7- I CAN EXPLAIN HOW A POPULATION OF ORGANISMS IN A SPECIES UNDERGOES NATURAL SELECTION

9.  Step 4: the mutated phenotype is naturally selected by the environment as being more advantageous, and that individual has more offspring than the non-mutated individuals  Step 5: the mutation is passed down, generation to generation, until the population of organisms in that species retain that mutation  **Step 6: if enough mutations collect within a population of individuals in a given species, then a new species is formed

10.  Within the species black bear (Ursus americanus), there is a subspecies (Ursus americanus kermodei)  There are about 400 individuals in this subspecies  About 10% of this subspecies is homozygous recessive for a mutation that turns their coats whitish  Caused by a mutation in a pigment gene, known as MC1R (Melanocortin receptor)  MC1R is involved with the synthesis of the pigment eumelanin  A mutation in this gene in humans results in red hair)  Evolutionary Advantage  Better at catching fish during the day than their dark bear counterparts  Are considered sacred by the local people, the Tsimshian, so they are hunted less EXAMPLE- THE SPIRIT BEAR

13.  Natural selection depends on the ability of organisms to reproduce, or to leave descendants  Lineage can be traced back over many generations  Over many generations, adaptation could successfully lead to the evolution of new species  Darwin proposed that living species are descended with modification from common ancestors  Known as descent with modification TARGET #8- I CAN EXPLAIN WHAT DARWIN’S MECHANISM FOR EVOLUTION SUGGESTS ABOUT LIVING AND EXTINCT SPECIES

14.  Means that life as been on earth for a long time  Basis for the explanation of the diversity of life  According to the principle of common descent, all species, living and extinct, are descended from ancient common ancestors