Chapter 16 Darwin’s Theory of Evolution
Section 1 Darwin’s Voyage of Discovery
Be Able To:
● Explain what was Charles Darwin’s contribution to science.
● Explain the three patterns of biodiversity that Darwin noted on his voyage on HMS Beagle.
Key Terms: evolution and fossil
Darwin’s Epic Journey
● Charles Darwin developed a scientific theory of biological evolution that explains how modern organisms evolved over long periods of time through descent from common ancestors.
● Darwin’s path to his theory on evolution started in 1831 when the HMS Beagle started its 5 year voyage to map the coastline of South America.
● His role on this voyage was to serve as a naturalist, collecting samples of plants and animals.
● Many agree that this historic voyage led to the
“single best idea anyone has ever had”.
Observations Aboard the Beagle
● Darwin filled his notebooks with observations about the characteristics and habitats of the different species he saw.
● Darwin noted three distinct patterns of biological diversity:
○ Species vary globally
○ Species vary locally
○ Species vary over time
● Darwin noticed that different, yet ecologically similar, animal species inhabited separate but ecologically similar habitats around the globe, ie flightless birds
● Darwin noticed that different, yet related, animal species often occupied habitats within a local area.
● Darwin also collected fossils, the preserved remains or traces of once living organisms, and noticed that some fossils of extinct animals were similar to living species.
● Darwin’s evidence suggested that species are not fixed and could change by natural processes.
Chapter 16 Darwin’s Theory of Evolution
Section 2 Ideas that Shaped Darwin’s Thinking
Be Able To:
● Explain Hutton’s and Lyell’s view of Earth’s history.
● Explain Lamarck’s ideas on how species evolve.
● Describe Thomas Malthus’s view on population growth.
● Explain how inherited variation is used in artificial selection.
Key Term: artificial selection
An Ancient, Changing Earth
● James Hutton and Charles Lyell concluded that Earth is extremely old, older than the view of the day which was a few thousands years, and that process that changed Earth in the past are the same the operate in the present.
● Hutton concluded that the Earth’s history stretches back further than we can
comprehend which he called deep time.
● Lyell’s view founded the concept of uniformitarianism.
● Charles Darwin applied their theories to what
he observed on his travels.
Lamarck’s Evolutionary Hypotheses
● Jean Baptiste Lamarck, in 1809, published his idea that suggested that organisms could change during their lifetimes by selectively using or not using various parts of their bodies and could pass on these acquired traits onto their offspring.
● Lamarck thought all organisms were driven to become perfect and that an individual organism could evolve.
● Although incorrect, Lamarck was one of the first scientist to suggest that species were not fixed.
Population Growth and Artificial Selection
● In 1798, Thomas Malthus reasoned that if the human population grew unchecked, there wouldn’t be enough living space and food for everyone, therefore war, famine, and disease would control the human population.
● Darwin applied Malthus’s ideas to other populations to explain why some survive to reproduce while others do not.
● Darwin studied artificial selection, selective breeding of plants and animals to promote occurrence of desirable traits in offspring.
● Darwin did not what the heritable unit was or how heredity worked but he had all the information he needed to publish his ideas.
Chapter 16 Darwin’s Theory of Evolution
Section 3 Darwin Presents his Case
Be Able To:
● Explain what conditions are needed for natural selection to occur.
● Relate Darwin’s mechanism for evolution to living and extinct species.
Key Term: adaptation, fitness, natural selection
Evolution by Natural Selection
● 20 years after he completed his draft on The Origin of Species by Means of Natural Selection, Darwin published his ideas.
● Was Darwin’s decision to publish in 1859, many years after his initial discovery, the perfect time or due to a similar theory proposed by naturalist Alfred Wallace?
● Darwin described evolution through a process or a mechanism that required four conditions:
○ Struggle for existence
○ Variation and adaptation
○ Survival of the fittest
○ Natural selection
● Natural selection is the process by which organisms with variations most suited to their local environment survive and leave more offspring than those with less suitable traits.
Common Descent
● Every organism alive today is the descendant of parents who survived to reproduce.
● Darwin proposed that over many generations, adaptation could cause successful species to evolve into new species and that living
species are descended, with modification, from common ancestors.
● The diversity of life is based on species
change over time and a “single” tree of life
links all living organisms to a common ancient
ancestor, the principle of common descent.
Chapter 16 Darwin’s Theory of Evolution
Section 4 Evidence of Evolution
Be Able To:
● Explain how the geographic distribution of species today related to their evolutionary history.
● Explain how fossils help document the descent of modern species from their ancient ancestors.
● Explain the difference between homologous and analogous structures in relationship to evolutionary relationships.
● Explain how modern technology helps trace the process of evolution.
Key Term: biogeography, homologous structure, analogous structure, and vestigial
structure.
Biogeography
● Biogeography is the study of where
organisms live today and why 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.
● Darwin’s theory of evolution was based on two biogeographical patterns:
○ Closely related species differentiate in slightly different climates.
○ Distantly related species develop
similarities in similar environments.
The Age of the Earth and Fossils
● Evolution takes a long time, which posed a
potential difficulty for Darwin because in his day the estimate on the age of Earth was young.
● Today, radioactive dating indicates that Earth is 4.5 billion years old.
● The fossil record was and is incomplete,
however many recently discovered fossils form
series that trace the evolution of modern species
from extinct ancestors, ie relationship between
birds and dinosaurs or land-dwelling extinct
mammals and whales.Comparing Anatomy & Embryology
● Homologous structures are anatomical features that are shared by related species inherited from a common
ancestor.
● Evolutionary theory explains the existence of homologous structures adapted to different purposes as the result of descent with modification from a common ancestor.
● Body parts that share a common function but not structure are analogous structures, which do not indicate common ancestry, that suggest convergent evolution.
● Vestigial structures are inherited from ancestors but have lost much or all of their original function due to different selective pressures acting on descendants.
● Similar patterns of embryological development provide further evidence that organisms have descended from a common ancestor.
Genetics and Molecular Biology
● Darwin had no idea how heredity worked and now the strongest evidence of evolution
comes from genetics.
● At the molecular level, the universal genetic code and homologous molecules provide evidence of common descent.
● Because the genetic code is nearly identical for all species, that in itself provides evidence that all organisms evolved from a common ancestor.
● Homologies also exist in genes and proteins,
ie cytochromes found in the electron transport
chain and Hox genes.
Testing Natural Selection
● Some kinds of evolutionary change have been observed and have been studied in the lab and in controlled outdoor
environments.
● It begins with an hypothesis:
○ Darwin misidentified the Galapagos finches as warblers and realized that the finches and warblers could have descended from a common ancestor.
● One long term evolutionary study on the Galapagos finches, found exactly what Darwin thought was needed for evolution to take place:
○ Heritable variation in traits
○ Variations in traits must produce different fitnesses
● Advances in other fields of biology along with other sciences have confirmed and expanded on Darwin’s hypotheses.
● Because evolutionary theory is theory, it is constantly reviewed and revised as new data is collected.
