Percorso interdisciplinare di avviamento al CLIL Darwin s theory of evolution by natural selection CLASSE 5^B Prof. A. Le Piane Prof. F. Minissale
Theory of Evolution Evolution: the process of change over time Specifically, a change in the frequency of a gene or allele in a population over time
Charles Darwin (1809-1882) Father of Evolutionism He proposed the theory of evolution by natural selection Darwin went on a five-yearlong voyage to the South Seas aboard The Beagle He was a naturalist and studied organisms in South America and the Galapagos Islands He published his theory in a book: On the Origin of Species by Means of Natural Selection (1858)
Darwin s voyage to the South Seas (1831-1836)
Natural Selection Natural selection is a process which allows organisms that are best adapted to an environment to survive and reproduce more than others.
Darwin s theory of evolution by natural selection is based on six points: Overproduction Competition Variation Selection Adaptation Speciation
1. Overproduction Each species produces more offspring that can survive EXAMPLES: Fish that lay millions of eggs, sea turtles. Sea turtles lay from 70 to 190 eggs (depending on the species). Only about 1 out of 100 survive.
2. Competition Because of overpopulation, organisms of the same species, as well as those of different species, must compete for limited resources such as food, water and a place to live. Interspecific competition between different species Intraspecific competition between the same species
3. Variation Differences occurring among members of the same species. Each individual has a unique combination of inherited traits. No two individuals are exactly alike. These variations are passed onto the next generation.
Why is Variation important? Because the environment changes. The more variation within a species, the more likely it will survive EX: If everyone is the same, they are all vulnerable to the same environmental changes or diseases The more variation of types of species in an habitat, the more likely at least some will survive EX: Dinosaurs replaced by mammals
Which community has a better chance of surviving a natural disaster? Community A Community B
4. Selection The individuals with the best traits / adaptations will survive and have the opportunity to pass on its traits to offspring. Natural selection acts on the phenotype (physical appearance), not the genotype (genetic makeup) Ex: When a predator finds its prey, it is due to the prey s physical characteristics, like color or slow speed, not the alleles (BB, Bb)
Survival of the Fittest Individuals in a species with good traits that give them an advantage are better able to compete, survive and reproduce. Individuals with bad traits that are not well suited to their environment either die without leaving offspring or leave few offspring. Natural selection occurs through Survival of the fittest Fitness: the ability to survive and reproduce
5. Adaptation The accumulation of characteristics that improve a species ability to survive over long periods of time. Allows organisms to become better suited to their environment.
There are three broad categories of adaptations: 1. Physiological 2. Behavioural 3. Structural
1. Physiological Physiological adaptations involve what is going on inside the body. Examples: - hibernation of bears. - cow s ruminant digestive system. - pesticide-resistant insects. - antibiotic resistant bacteria.
2. Behavioural An organism s behaviour may provide it with a better chance of surviving and reproducing. Examples: - Storage of nuts by squirrels. - Plants bending towards light. - Animals playing dead. - Migration of Canada geese.
3. Structural Structural adaptations involve an organisms anatomy. Examples: - Webbed feet of ducks for swimming. - Talons on eagles for grasping. - Camouflage: this can be used to benefit both predator and prey. - Mimicry.
Example of camouflage Phasmatodea (walking stick insect)
Example of mimicry Moth resembles owl to scare off predators.
6. Speciation Origin of new species. Over numerous generations, new species arise by the accumulation of inherited variations. When a type is produced that is significantly different from the original, it becomes a species. A species can reproduce successfully with its own kind.
Evidence for Evolution: Fossil Record Homologous Body Structures Vestigial Organs Similarities in Embryology Biochemical Evidence
The Fossil Record Fossils: a record of the history of life on earth Fossils provide evidence of the history of life on earth and they show how different groups of organisms have evolved over time
Homologous Body Structures Homologous Body Structures: similar anatomy in different types of animals because of a common ancestry e.g. wing of bat, human arm, leg of turtle
Homologous Body Structures
Homologous Body Structures
Vestigial Organs Vestigial Organs: traces of homologous organs in other species Organ that serves no useful function e.g. Appendix
Similarities in Embryology Embryology: embryos of all vertebrates are very similar, providing evidence that they share a common ancestry
Embryological development
Biochemical Evidence Biochemistry: DNA with more similar sequences suggests that species are more closely related EX: Humans and chimpanzees share more than 98% of identical DNA sequences
Learning Goals 1. Define "Evolution" & "Natural Selection". 2. Describe the 6 steps of Natural Selection, giving an example of each. 3. Explain the importance of "Variation". 4. Does Natural Selection act on an organism phenotype or genotoype? Explain! 5. List the 5 evidences that support the Theory of Evolution.