Charles Darwin - PowerPoint PPT Presentation

Charles Darwin

• Darwin was not the first to present the concept of evolution
• Word first appeared in 1647
• Ancient Greeks inferred that species had descended from a common ancestor
• Darwin referred to evolution as “descent with modification”
• Explained it as the differential survival of organisms following their naturally occurring genetic variation
• Natural Selection

• Charles Lyell – geologist
• Proposed that plant and animal species had arisen, developed variations over time and then became extinct
• Also believed that earth’s physical landscape had changed over time
• Thomas Malthus – proposed that populations outgrew their food supplies, causing competition between organisms and a struggle for one species to survive against another
• Applied theory to humans, Darwin applied to all animal species

• Darwin’s trip on the Beagle stopped in the Galapagos
• Contained endemic species, not found anywhere else on earth
• The species there looked similar to mainland species
• But somehow specialized to their particular environment
• proposed that changes were dependent on the environment

• 1st: Adaptations  traits occur within organisms and allow them to be more successful in the environment
• Darwin reasoned that the importance of these adaptations was to insure the survival of reproduction of the species
• Successful adaptations help organisms to both survive and reproduce, so these adaptations are passed on to future generations
• Natural Selection is the mechanism that explains how changes occur within a population with favorable variations for that particular environment surviving, reproducing and passing these variations on to the next generation
• (environments are constantly changing)

• 2nd Speciation – organisms on the Galapagos Islands had become geographically separated from one another
• Produced reproductive isolation so that there is no interbreeding between organisms of same species
• separates the gene pools of the populations
• Darwin theorized that within a populations of species, adaptations would arise because of reproductive isolation and would develop adaptations specific to their particular environment over time
• Eventually this would lead to new species evolving on the different islands
• Which is what was observed

• All begins when a group becomes reproductively isolated from the rest
• May be geographic, temporal or behavioral
• It is most obvious in distant islands, such as the Galapagos or Hawaiian island
• Mountains, rivers, lakes and other natural barriers can also geographically separate populations that once belonged to the same species

• Temporal isolation occurs when there is a time difference between two species
• Such as one species of flower opening up for pollination in the morning and another at night
• Behavorial isolation occurs when the behavior of one species does not match another
• One mating song for one bird is not recognized by another
• Geographic isolation is the most common method of separating two populations of a species
• Depends on the animal involved as to what is needed to separate it

• Classic example of speciation is the 13 species of finches on the Galapagos Islands
• Each species, descended with modifications, from an ancestral species
• Today, the different species of finches on the island have distinct habitats, diets and behaviors depending on the current climate conditions
• Which determines what food is available to the birds

• The Origin of Species – Presents Darwin’s theory (1859)
• Has undergone modification and expansion and is now supported by studies in genetics and molecular biology