Darwin’s Theory of Evolution

What is Theory ?? Most people think of it as a guess “It’s just a theory.” In Science a theory is not a guess. A hypothesis is more like a guess than a theory In Science a theory is a well tested and well supported explanation

What is a Theory? A well supported testable explanation of phenomena that have occurred in the natural world. The Theory of Evolution

Evolution “Change over Time” Geological Evolution Organic Evolution Change in non living characteristics of the earth over time Examples = Climate & Continental Drift Organic Evolution Change in species over time Change (in DNA) over time

Evolution: Key Concepts History: Darwin, Lamarck , Hutton, Lyell Natural Selection : Survival of the Fittest Evidence: Fossils Geographic Distribution of Species Homologous Structures Embryological Development Evolution and Genetics History of the Earth : Geologic Time Scale Classification

Can an Individual Evolve? No! Individuals are born with a set of chromosomes that determine their characteristics. This set does not change Individuals Develop Populations EVOLVE

Charles Darwin Age 22 set sail on the H.M.S beagle (1831) Chart coast line of South America and some pacific islands Voyage took 5 years Most significant observations were made on Galapagos Islands He returned convinced that species evolve

Voyage of the Beagle

Survey made by the Beagle

Current Survey

Galapagos Island Finches

Galapagos Island Tortoise

Intermediate Shell Pinta Island Saddle-backed shell Hood Island Dome-shaped shell Isabela Island

What Island does this Tortoise come from? Isabela

Modern Evolution spurred from?? Darwin’s Publications of …… On the Origin of Species by means of Natural Selection Published in 1858 Nearly 25 years after the beagle returns home

6 Main Points of Darwin’s Theory Variation Overproduction Competition Adaptations Natural Selection Speciation

Earlier Theories of Evolution James Hutton (1785) Earth is shaped by geological forces over millions of years not thousands of years Charles Lyell (1831 ) Writes about how the earth can be shaped (volcanoes , earthquakes) Influences Darwin’s thinking If the earth can change why can’t species

Lamarck’s Theory of Evolution Jean-Baptiste Lamarck (1809) Selective use or disuse of organs, organisms acquired or lost certain traits during their life time. Traits passed onto offspring Over time this leads to change in a species DISPROVEN

Jean-Baptiste Lamarck believed… Was based on the idea that individuals adapt during their own lifetimes and transmit traits they acquire to their offspring. Offspring then adapt from where individuals left off, enabling evolution to advance. As a mechanism of adaptation , Lamarck proposed that individuals increased specific capabilities by exercising them, while losing others through disuse.

Lamarck’s Giraffe

Lamarck vs. Darwin

Back to Darwin’s Six Principles Species tend to overproduce This leads to competition There is variation in a population Some of these variations are positive adaptations Natural selection means that those best adapted tend to survive and reproduce This process of natural selection changes the gene pool

Variation Individuals in a species do not have identical characteristics Darwin observed this fact but he could not explain the mechanisms that caused variability Darwin did not know about DNA and Genetics

Overproduction Habitats have limited resources Habitats can only support a limited number of individuals Species tend to produce more offspring than can survive in a given environment

Competition Overproduction leads to competition Members of a species compete for limited resources

Adaptations Adaptations are positive traits That increases an individuals ability to survive in a given environment Individuals with adaptations have higher fitness They tend to survive and reproduce most successfully

Natural Selection The environment selects those individuals with the best adaptations to be the parents of the next generation Those less fit cannot compete and they reproduce less (Survival of the Fittest) Over many generations natural selection causes changes in the characteristics of species

Speciation New species arise from existing species through the process of natural selection

Summary of Darwin’s Theory Individual organisms differ from one another. More offspring are produced than can survive. Members of a species compete for limited resources. Each unique organism has different advantages and disadvantages in the struggle for existence. Individuals best suited to their environment survive and reproduce most successfully. Species change over time. Natural selection causes changes in characteristics of species. New species arise, and other species disappear. Species alive today have descended with modification from species that lived in the past. All organisms on Earth are united into a single tree of life by common descent.