UNIT I EVOLUTION

Introducing Evolution Evolution  the change in the genetic makeup of a population over time… many, many generations Note: The characteristics of living things change with time Change is directed by Natural Selection

Population Changes Organisms constantly face environmental challenges that limit their ability to survive  severe weather, famine, competition Diversity within species and interaction with the environment can explain how populations can change over time Survival Extinction

Adaptations & Survival Adaptation: a structure, behaviour, or physiological process that helps an organism survive and reproduce in a particular environment E.g. camouflage E.g. hibernation

Mimicry Mimicry: a structural adaptation in which a harmless species resembles a harmful species in coloration or structure E.g. Viceroy vs. Monarch Butterfly

Development of Adapations Adaptations are the result of gradual, accumulative changes that help an organism survive and reproduce. Result of: random, heritable mutations in DNA over generations Variations: differences between individuals, which may be structural, functional or physiological Postive/ negative/ no effect  depending on environmental condition

Environment affects adaptation Environments change Climate, droughts, floods, famines, human activities This can cause variation to lead to adaptation E.g. The English Peppered Moth & Pollution

Variation within a Species Genetic variation in a population results from the variety of genetic information in all individuals of the population Mutations: a permanent change in the genetic material of an organism; the only source of new genetic variation Affect on gametes leads to passing on this mutation to offspring  starting point of genetic variation in populations

Selective Advantage Selective Advantage: a genetic advantage (over a competitor), that improves an organisms’ chance of survival, usually in a changing environment Over time the organism is favoured in terms of survival and reproduction Helps an organism survive the changing environmental conditions and reproduce

Selective Advantage & Bacteria E.g. Staphylococcus aureus bacterium Reproduce asexually very rapidly (every 30 minutes) Mutation can lead to antibiotic resistance **Populations change, not individuals**

Natural Selection Natural selection: the process by which characteristics of a population change over many generations as organisms with heritable traits survive and reproduce, passing their traits to offspring Requires diversity within a species

Selective Pressure An abiotic (non-living) environmental condition can be said to select for certain characteristics in some individuals and select against different characteristics in other individuals Selective pressure: environmental conditions that select for certain characteristics of individuals and select against other characteristics

Natural Selection is Situational Does not anticipate change in environment In one situation a particular trait has no relevance to survival but in another situation helps certain individuals survive and reproduce

Fitness Fitness: the relative contribution an individual makes to the next generation by producing offspring that will survive long enough to reproduce An organism with many viable offspring has high fitness, an organism that has few or no viable offspring has low fitness

Artificial Selection Artificial Selection: selective pressure exerted by humans on populations in order to improve or modify particular desirable traits E.g. Selective breeding Biotechnology: the use of technology and organisms to produce useful products *In natural selection, the environmental conditions determine which individuals in a population will survive and reproduce in current conditions

Artificial Selection & Food Crops Selective breeding  rice, corn, wheat, vegetables E.g. Brocciflower = cauliflower + broccoli Increase nutritional value and harvest yield; develop drought and pesticide resistance

Consequences Respiratory problems in bulldogs Reduction in genetic diversity Dangers of monoculture: extensive plantings of the same varieties of a species over large expanses of land

Selective Breeding in Farm Animals

Sample issue: Selective breeding of agricultural crops can benefit populations in less-developed countries by producing hardier crops, increasing food supplies, and improving the nutritional content of food. However, opponents of artificial selection technology believe that it affects the natural ability of a species to reproduce, which negatively affects biodiversity.

Sample issue: An increase in forest fires in some areas of North America has affected the reproductive success of some species as their food supplies decrease and they are forced to adapt to adverse habitat conditions. Yet, forest fires also naturally promote changes in plant and animal species over time as the environment becomes more suitable for other species.

Sample questions: How has selective breeding of specific crops helped to increase the yield of the crop and decrease the need for chemicals in the fields? How has the introduction of genetically engineered species in the horticultural industry affected other species planted in the same areas? In what ways do the characteristics of today’s farm animals, such as cattle, pigs, and chickens, differ from those of earlier farm animals? What are the reasons for the differences?

Sample questions: Why has a decline in the milkweed population, as a result of urbanization and pesticides, affected the migration of monarch butterflies? How has the introduction of bacteria and viruses in inland lakes affected the life cycle of carp? What impact has the loss of bamboo forests to urbanization had on the giant panda’s ability to breed and live?