Evolution 15

The Big Idea

The theory of natural selection explains evolution and the diversity of life.

Main Idea #1Charles Darwin developed a theory of evolution based on natural selection.

The 1st Scientific Hypothesis of Evolution

• French biologist Jean Baptiste de Lamarck offered the first complete explanation of evolution in 1809.

• He was the first to argue that fossils were the remains of extinct animals.

• His concept was transformational, meaning individuals transform their own traits in order to evolve.

Uniformitarianism• Geologist Sir Charles Lyell - the principle of uniformitarianism.

• Two parts:

• laws of physics and chemistry remain the same throughout earth’s history

• past geological events occurred by natural processes similar to those that observed today

• He said Earth’s age must be measured in millions of years.

Charles Robert Darwin1809-1882

• In 1831, Darwin sailed aboard the very small ship the HMS Beagle.

• During his 5-year voyage, he collected a wide variety of flora and fauna from South America and surrounding islands.

• He found long extinct fossils, including seashells in the Andes Mountains at an altitude of 13,000 feet.

• He also witnessed earthquakes and severe erosion that helped to confirm his ideas about geology.

Darwin & The Galapagos Islands

• These volcanic islands are on the equator, 600 miles west of Ecuador.

• Each island varied in tortoises, iguanas, mockingbirds, and ground finches.

• The islands had similar climate, but varied greatly in vegetation.

• Darwin inferred that island species originated in South America, and were modified over many years under the varying conditions of different islands.

• Darwin conducted the remainder of his work at home in England, where all of his notebooks had been sent home ahead of him in October 1836.

• His travel journal, The Voyage of the Beagle, was published three years later, but he continued his research on the evolution of species by natural selection.

• Darwin first presented his ideas in a paper in 1844, but did not began writing the larger volume until 1856. By 1858, he had received a manuscript from Alfred Russel Wallace summarizing his ideas on natural selection.

• Geologist Lyell was instrumental in convincing Darwin to publish a joint paper with Wallace.

• Darwin’s book On the Origin of Species by Means of Natural Selection was published in 1859. All printed copies sold out in one day.

Darwin (continued...)

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• Darwin’s work actually included 5 separate theories

• Perpetual Change is the basic theory of evolution on which the others are based stating that the world is constantly changing.

• Common Descent (controversial theory) states that all forms of life descended from a common ancestor.

• Multiplication of Species - species divide and split into different species, which can no longer interbreed

• Gradualism - large differences actually originate from an accumulation of many smaller differences

• Natural Selection - explains the selective processes of the environment, through a phenomenon called adaptation.

Darwin’s Theory of Evolution

Natural Selection & Speciation

Natural Selection

• The Ideas Behind Natural Selection

1. Individuals in a population show variations.

2. Variations can be inherited.

3. Organisms have more offspring than can survive on available resources.

4. Variations that increase reproductive success will have a greater chance of being passed on.

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Types of Evidence of Evolution

1. Fossil Record

2. Comparative Anatomy

• Homologous Structures - similar structures inherited from a common ancestor

• Vestigial Structures - structures that are reduced forms of functional structures in other organisms; get smaller over generations

• Analogous Structures - structures that have similar function, but not similar shapes; not inherited from a common ancestor

Evidence (continued...)

3. Comparative Embryology - many embryos share characteristics that are not alike in the adult form

4. Comparative Biochemistry - the more closely related two species are, the more amino acid sequences they will share

5. Geographic Distribution - evolution may be closely linked to climate and geographical characteristics

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Speciation• Speciation is the evolutionary process by which new

biological species arise.

• Allopatric speciation - a physical barrier divides one population into one or more populations

• mountain ranges, lava flows, channels between islands, wide rivers

• believed to be the most common type of speciation

• Sympatric speciation - no physical barrier separates the populations

• the ancestor species and new species live side by side

Types of Evolution

• Chemical Evolution - formation of organic molecules from inorganic substances

• primordial soup; chemicals in the early ocean giving rise to organic, and eventually, living matter

• Organic Evolution - changing of a species into something different by the accumulation of small changes over time