DARWIN’S THEORY ON EVOLUTION UNIT #5 EVOLUTION

Charles Darwin (1809 – 1882) Born in Shrewsbury, Western England He always had a consuming interest in nature His father saw no future for him as a naturalist and sent him to medical school He quit medical school to become a clergyman at Cambridge University Became the protégé of John Henslow, a botany professor After he graduated, he worked with Captain Fitzroy on the HMS Beagle for a long voyage around the world.

HMS Beagle

Darwin’s Voyage The mission was to chart the unknown stretches of the S. American coastline.

Darwin’s Voyage Spent most of his time on shore collecting plants and animals Described how different features of organisms made them well suited to their environment Spent most of his time reading Lyell’s Principles of Geology After experiencing earthquake, he observed that rocks and fossils along the coast had been raised by several feet

The Galapagos Islands A group of volcanic islands near located near the equator Noticed several kinds of finches. Most of Galapagos species were not known anywhere else in the world However, the animals on Galapagos were similar to species living on the South American mainland Darwin hypothesized that the Galapagos Islands had been colonized by organisms coming from South America

Darwin’s Views on Adaptation Adaptations – inherited characteristics of organisms that help their survival and reproduction in specific environments. Chameleons – camouflage Snakes – Fangs to attack on prey Bats – Night hearing An organisms’ body and behavior adapts to the specific foods located on their home land

Natural Selection Natural Selection – A process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits Lizards – the ability to climb tall trees to avoid floods “Survival of the Fittest”

Darwin’s Publications By 1840s, Darwin wrote out the major features of his hypothesis and set these ideas on paper Wrote about descent with modification and natural selection Darwin published it immediately before anyone could come to the same conclusion and publish it first.

Alfred Russel Wallace (1823 – 1913) By 1858, Darwin’s fear came true Darwin received a paper from Wallace Wallace had developed a paper on natural selection similar to Darwin’s Wallace asked Darwin to evaluate his paper and send it to Lyell for publication In 1858, Lyell and a colleague presented both Wallace’s paper and Darwin’s unpublished essay to the Linnean Society of London

Darwin’s Publications Meanwhile, Darwin quickly finished his book, titled On the Origin of Species by Means of Natural Selection and published it the next year Although Wallace had submitted first, Wallace thought that Darwin developed and explained the idea of natural selection much better Wallace thought that Darwin should be credited for this new theory Darwin’s book convinced most scientists at the time that life’s diversity is the product of evolution.

The Basics of Darwin’s Theory In his book, Darwin made three broad observations about nature Unity of Life Diversity of Life Relationship between Organisms and their Environment .

Descent with Modification In the 1st Edition of The Origin of Species, Darwin never used the word “evolution” The final word in the book is “evolved” Instead, he wrote about descent with modification, a phrase that showed his point of view of life Due to organisms sharing many characteristics, he perceived a unity in life He attributed the unity of life to the descent of all organisms from a common ancestor in the past Darwin reasoned that descent with modification eventually led to the diversity of life that we see today

Darwin’s Tree Darwin viewed the history of life as a tree Multiple branching's from a common trunk out to the tips of the youngest twigs

Artificial Selection Darwin proposed the idea of natural selection to explain patterns of evolution He created his argument carefully to persuade readers First he discussed selective breeding of domesticated plants and animals. Artificial Selection – the process in which humans have modified other species over time by selective breeding of individuals containing desired traits.

Observations and Inferences “Members of a population often vary in their inherited traits” Inference #1 “Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals” Observation #2 “All species can produce more offspring than their environment can support and many of these offspring fail to survive and reproduce” Inference #2 “This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over genetics”

Thomas Malthus (1766-1834) Wrote about human suffering – disease, famine and war He believed that human suffering resulted from human population’s potential to increase faster than food supplies and other resources Darwin realized that the ability to over reproduce was a characteristic of all species. .

Heritable Traits Heritable Traits – traits that can be passed down to offspring An organism’s heritable traits not only affects its own performance, but it can also affect how well its offspring copes with environmental challenges .

How rapid does change occur? Darwin believed that if artificial selection can create a dramatic change in such a short period of time, then natural selection can cause change over hundreds of generations.

Natural Selection Recap Natural Selection – a process in which individuals with certain heritable traits tend to survive and reproduce at higher rates because of those traits. If an environment changes or if an organism moves to a new environment, natural selection can result in adaptations to those new conditions – giving a rise to new species

Natural Selection Recap Even though natural selection occurs through interactions between organisms and their environment It is NOT the individuals that evolve but the POPULATION that evolves Favored traits can vary from place to place over time These traits depend on the context in which a species lives and mates in