Chapter 16 – Darwin’s Theory of Evolution

16.1: Darwin’s Voyage of Discovery Darwin was born on February 12, 1809 in England. Darwin was the first man to develop and publish a theory of evolution. Evolution: a scientific theory that explains how modern organisms evolved over long periods of time through decent from common ancestors. This theory arose first when he visited the Galapagos islands and other locations around the world in 1831 on the ship H.M.S Beagle and collected samples of the life there.

On his journey, Darwin noticed three general patterns of biological diversity 1. Species vary globally Different, yet ecologically similar, animal species inhabit separated, but ecologically similar, habitats around the globe Example- the flightless bird the rhea in the grasslands of South America and the flightless bird the emu in the grasslands of Australia.

On his journey, Darwin noticed three general patterns of biological diversity 2. Species vary locally Different, yet related, animal species often occupied different habitats within a local area. Example- the tortoises of the Galapagos.

On his journey, Darwin noticed three general patterns of biological diversity 3. Species vary over time By collecting fossils (preserved remains or traces of ancient organisms) Darwin came to realize that fossils of extinct animals were similar to living species. Example- the armadillo and the long-extinct Glyptodont.

16.2: Ideas that Shaped Darwin’s Thinking Geologists James Hutton and Charles Lyell greatly influenced Darwin’s thinking Hutton and Lyell concluded that the Earth is extremely old and that the processes that changed Earth in the past are the same processes that operate in the present.

James Hutton Hutton explained geological change of rocks, mountains, and pressure.

Charles Lyell Lyell published a book called Principles of Geology in 1830 that explained the theory of uniformitarianism- that the geological processes we see today shaped the Earth long ago, as well.

Jean-Baptiste Lamarck Lamarck suggested that organisms could change during their lifetimes by selectively using or not using various parts of their bodies. He also suggested that individuals could pass these acquired traits on to their offspring, enabling species to change over time. His ideas were published in 1809. His hypotheses was concluded incorrect in several ways.

Thomas Malthus In 1798, English economist Thomas Malthus noted that the world was becoming overcrowded. He reasoned that if the human population grew, unchecked there wouldn’t be enough living space and food for everyone.

Artificial Selection In artificial selection, nature provides the variation, and humans select those they find useful. Most common example is with plant and animal breeders

16.3: Darwin Presents his Case Described his theory in a book called On the Origin of Species published in 1859. He spoke about the struggle for existence The theory of adaptation- any heritable characteristic that increases an organism’s ability to survive and reproduce in its environment. Survival of the fittest and fitness- describes how well an organism can survive and reproduce in its environment.

Natural Selection And, most importantly, as the mechanism for evolution, natural selection- the process by which organisms with variations most suited to their local environment survive and leave more offspring. Natural selection occurs in any situation in which more individuals are born than can survive, there is a natural heritable variation, and there is variable fitness among individuals.

Common Decent According to the principle of common descent, all species – living and extinct – are descended from ancient common ancestors.

16.4: Evidence of Evolution Biogeography is the study of where organisms live now and where they and their ancestors lived in the past. Patterns in the distribution of living and fossil species tell us how modern organisms evolved from their ancestors.

There are two biogeographical patterns 1. Closely related species differentiate in slightly different climates. Example- finches (birds) of the Galapagos. 2. Very distantly related species develop similarities in similar environments. Example- similar ground dwelling birds in the grasslands of Europe, Australia, and Africa.

The Age of Earth and Fossils Radioactive dating indicates that the Earth is about 4.5 billion years old – plenty of time for evolution and natural selection to take place. Many recently discovered fossils form series that trace evolution of modern species from extinct ancestors. Example- a fossil of the Eocene whale Ambulocetus natans dates back to 49 million years old.

Homologous Structures Structures that are shared by related species and have been inherited from a common ancestor are called homologous structures, Evolutionary theory explains the existence of homologous structures adapted to different purposes as the result of descent with modification from a common ancestor. Example- common structures are found in chicken wings and alligator legs, probably dating back to an ancient, lobe-finned fish.

Structures Vestigial Structure: inherited from ancestors but have lost much or all of their original function due to different selection pressures acting on the descendant. Analogous Structure: body parts that share a common function, but not structure.

Embryology Similar patterns of embryology, or the study of the similarity of embryos provide further evidence that organisms have descended from a common ancestor.

Genetics and Molecular Biology At the molecular level, the universal genetic code and homologous molecules provide evidence of common descent. The genetic code of RNA and DNA is nearly identical in bacteria, yeast, plants, fungi, and animals. Genes, proteins, and cells can be homologous, too.

Real Life Most changes take place over millions of years, and evidence won’t be seem overnight. Bacteria in a lab can display the effects of natural selection, so scientists can understand evolution through a lab setting.

Darwin’s Finches Darwin’s finches are the most stunning example of natural selection. First Darwin hypothesized Then, he collected evidence for over 35 years The Grants took over his work and have documented that natural selection takes place in wild finch populations frequently, and sometimes rapidly.

Further Study The Grant’s work shows that variation within a species increases the likelihood of the species’ adapting to and surviving environmental change It is important to understand that any questions that remain are about how evolution works – not whether evolution occurs.