Evolution: History and Theory

What is Evolution?: Fact vs. Theory Evolution is the change in the genetic make up of populations over time. All living things change. Evolution is a fact. Populations evolve, not individuals. The mechanism for evolution (how it happens) is a theory. The theory of natural selection is a well supported, testable explanation of how evolution occurs.

Common beliefs in the 19th century Many believed that Earth was only a few thousand years old. Most people believed that neither the planet nor the species that inhabited it had changed since the beginning of time.

Challenges to Common Beliefs During Darwin’s time, many fossils were being discovered which challenged the notion that plants and animals had not changed since Earth was formed.

Jean-Baptiste Lamarck (1744-1829) First scientist to propose a mechanism for how organisms change (1809). Realized that organisms are adapted to their environments. Theory of Acquired Traits Through time, a generation would use an organ more than previously, and would pass those traits on to their offspring.

Lamarck’s Assumptions 1. Organisms have a desire to change. They have an inborn urge to better themselves for their environment. Ex.: Birds tried to fly and eventually grew wings because of their efforts.

Lamarck’s Assumptions 2. Organisms can change shape by using or not using their bodies. Ex.: The wings of a bird that does not fly would get smaller from generation to generation and the wings would eventually disappear.

Lamarck’s Assumptions 3. Organisms can pass on acquired traits to their offspring. Ex.: If an animal developed muscles from running during its lifetime, it could pass those muscles on to its offspring.

Why was Lamarck wrong? Lamarck did not know about the inheritance of traits through the passing of genes. Acquired traits can NOT be inherited. Behavior has no effect on an organism's heritable characteristics.

Who was Charles Darwin? (1809-1882) English naturalist. Traveled around the world on the Beagle (1831). Recorded observations and collected specimens. Observed and collected many species and fossils – he was astonished by diversity. Devised a hypothesis about the way life changes over time of evolution (but only published it years later in 1859). Now known as the Theory of Evolution.

Journey of the Beagle

Species of Interest The Galapagos Finches Tortoises http://www.rit.edu/~rhrsbi/GalapagosPages/Pictures/LandBirds/FinchTypes.jpeg

Observations made by Darwin Darwin noticed that the shape of turtle shells was different for each island and could be used to determine which island they inhabited.

Observations made by Darwin The finches on each island had different types of beaks. Darwin reasoned that the finches had adapted beaks that were well suited to eat the type of food available on their island.

Darwin hypothesized that these finches had started as one species, but had adapted to the environments of each island over large periods of time. He developed the theory of natural selection.

Charles Darwin was influenced by the work of others. Thomas Malthus – Populations. James Hutton and Charles Lyell – Geological Record. Farmers – Selective breeding.

Thomas Malthus Essay on the Principle of Population (1798) Predicted that the human population would grow faster than space and food available to sustain it. Stated that the only checks on the human population were war, famine, and disease.

Influence of Malthus Malthus’ theory of population growth was observed by Darwin in other animal populations as well. In nature, Darwin saw many organisms that produced many offspring. Most died. Darwin wondered what determined which individuals would survive and reproduce.

James Hutton and Charles Lyell Hutton is the father of modern geology. Based on layers found in rock structures, he proposed the Earth was millions of years old (1785). Lyell proposed that geological features could be built up or torn down over long periods of time (1833). Grand Canyon, Arizona

Influence of Lyell After reading Lyell’s book, Darwin was convinced that the Earth was very old. Darwin reasoned that if geological phenomena could change the Earth, then life on Earth could change as well. He also realized it would have taken a very long time for organisms to change in the ways he suggested.

Influence of Farmers Within a population, there is natural variation. Farmers improved their plants and animals through selective breeding.

Influence of Farmers Farmers bred the plants or animals with the most desired traits. This process of humans allowing only the organisms with the most desirable variation to reproduce was called artificial selection by Darwin.

Survival of the Fittest Fitness is the ability of an organism to survive and reproduce in its environment. Ex.: An animal that can easily avoid predators and mates regularly has higher fitness than an individual that does not mate. Adaptation is any inherited characteristic that increases an organism’s chance of survival. Individuals in nature with characteristics best suited to their environment survive the struggle for existence (competition for food and other necessities). This principle is called Survival of the Fittest.

Natural Selection Natural Selection: Those best adapted to their environment are more likely to survive and produce offspring (pass genes on to the next generation). Natural selection causes changes in the inherited characteristics of populations (adaptations) over time because of changes in their environment (selection pressures). These changes increase a species’ fitness in its environment. I have called this principle, by which each slight variation, if useful, is preserved, by the term Natural Selection.    —Charles Darwin from "The Origin of Species"

Descent with Modification - through a series of adaptations, each new species arises from another. Darwin suspected that all species present on earth had begun as one species, and through a series of adaptations over millions of years, had diverged into all the species present today.

Populations evolve, individuals DO NOT!!! REMEMBER! Populations evolve, individuals DO NOT!!!

Two Varieties of Peppered Moth Light color and dark color. There must be genetic variation in order for natural selection to occur. carbonaria typica

Peppered Moth Prior to the industrial revolution, tree trunks were light colored. Predators were more likely to pick the dark moths. As a result, the moth population was primarily light.

Peppered Moth After the industrial revolution, trees were covered in soot making them dark. Now, predators were more likely to pick the light moths. As a result, the population shifted from being primarily light to primarily dark.

Darwin’s Theory – A Summary Individual organisms differ, and some of this variation is heritable. Organisms produce more offspring than can survive. Thus, organisms have to compete for resources. Only the most fit organisms survive and reproduce. The most fit organisms pass on their heritable traits to their offspring. Species alive today are descended with modification (change) from ancestral species.

Darwin vs. Lamarck Contrast how Darwin and Lamarck would explain the evolution of the giraffe.