-Upon his return, he became interested in natural selection –a procedure in which particular
animals are deliberately mated to product offspring that possess especially desirable
characteristics. He looked at this practise in pigeons and bred pigeons himself for a while.
-He wondered if it was possible to produce such different varieties of pigeons that it would
result in a new species.
-He was struck by the idea of natural selection –the consequence of the fact that, because
there are physical and behavioural differences among organisms, they reproduce differentially,
Within a given population, some animals – the survivors – will product more offspring than will
-He came to this realization in 1838 but did not publish his findings until 20 years later.
Natural Selection (61)
-The ability of an individual to produce offspring defines that individual’s reproductive
success –the number of viable offspring an individual produces relative to the number of viable
offspring produced by other members of the same species.
-The two aspects of natural selection, variation and competition, are the critical factors that
determine whether any animals will be reproductively successful.
-Variation refers to the differences among members of a species, including physical
characteristics such as size, strength, or physiology, and behavioural characteristics such as
intelligence or sociability.
-What factors are responsible for these sorts of variations? Genotype and phenotype.
-An individual organism’s genetic makeup, or its genotype, differs from that of all other
individuals (except for twins). As a result of these genetic differences, an individual organism’s
physical characteristics and behaviour, or its phenotype, also vary from every other individual.
-Every individual’s phenotype is produced is produced by the interaction of its genotype with
-Although evolution occurs over the long run, natural selection can produce important changes
in the short run – in the space of only a few years.
-Phenotypic diversity is very important for a species survival because it ensures that if an
unexpected natural disaster occurs, the species will not go extinct.
-Competition is a striving or competing with others who share the same ecological niche for
food, mates, and territory.
-Competition can be for mates, territory, food and all factors affect the animal’s success.
-Over time, competition for food and other resources will allow only the best-adapted
phenotypes to survive, thereby producing evolutionary change.
-These changes can be measured using techniques based on correlational methods.
Part 2: Heredity and Genetics
-Genetics is the study of the genetic makeup of organisms and how it influences their physical
and behavioural characteristics.
-Closely related to genetics is heredity –the sum of the traits and tendencies inherited from a
person’s parents and other biological ancestors.
-Following Darwin’s The Origin of Species, Mendel uncovered the basic principles of heredity.