Chapter 10

Where did we come from?


10.1 What is Evolution? - The Process of Evolution

§ Biological evolution – change in the characteristics of a population of organisms that occurs of over the course of generations.

§ Evolutionary changes are inherited via genes

§ Other changes may take place because of environmental changes and are not necessarily evolutionary.


§ Pesticide resistant lice are an example of biological evolution.


§ Populations evolve, NOT individuals.

§ In the lice example, the genetic structure of the population of lice changed.

§ Individuals without a gene for resistance died

§ Over time, the population changed to mostly resistant individuals


§ Natural selection – the differential survival and reproduction of individuals in a population.

§ Process by which populations adapt to varying environments

§ Examples:

§ Pesticide resistance in crop-eating insects

§ Antibiotic resistance in infectious bacteria


§ Microevolution – changes that occur within a species and the characteristics of a population. Easily observed, relatively non-controversial.

§ Macroevolution – changes that occur, as a result of microevolution, over long periods of time and result in the origin of new species. Controversial among non-biologists.


10.1 What is Evolution? - The Theory of Evolution

§ Ambiguity of the word “theory”

§ Everyday usage:  theory = best guess, or tentative explanation

§ Scientific usage:  theory = body of accepted general principles, supported by many lines of evidence.

§ Examples: atomic theory, gravity, germ theory.


§ All species present on earth today are descendents of a single common ancestor, and all species represent the product of millions of years of accumulated evolutionary changes.


10.2 Charles Darwin and the Theory of Evolution

§ Theory of Evolution is sometimes called “Darwinism” because Charles Darwin is largely credited with introducing the concept to mainstream science.


10.2 Charles Darwin and the Theory of Evolution - Early Views of Evolution

§ Charles Darwin did not “invent” the idea of evolution.  Many philosophers of science had notions of organisms changing over time.

§ Anaximander – Greek philosopher who suggested that humans evolved from fish that had moved onto land

§ Lamarck – published ideas about inheritance of acquired traits in 1809


10.2 Charles Darwin and the Theory of Evolution - The Voyage of the Beagle

§ At age 22, Darwin set sail as ship’s naturalist aboard the HMS Beagle on a five year long trip.

§ Darwin’s job was to collect and observe “anything worth to be noted for natural history.”

§ Darwin had a book by Lyell, Principles of Geology, which postulated earth was old and changes occurred over long periods of time.


§ The following had influences on Darwin during the voyage:

§ Rainforests of Brazil

§ Fossils that he collected

§ Birds and reptiles of the Galapagos Islands


§ Galapagos islands tortoises vary with their environments.


10.2 Charles Darwin and the Theory of Evolution - Developing the Hypothesis of Common Descent

§ Darwin returned to England in 1836, but did not publish his ideas immediately.

§ Spent about 20 years refining his ideas

§ Learned about animal husbandry (selective breeding)

§ Finally published On the Origin of Species in 1858


10.3 Examining the Evidence for Evolution

§ Theory of common descent is controversial.  There are some possible alternative hypotheses that can be tested against available data:

§ Static model hypothesis

§ Transformation hypothesis

§ Separate types


§  Graphical representations of theory of common descent and alternative hypotheses:


10.3 Examining the Evidence for Evolution - An Overview of Evidence for Evolution

§ Several lines of biological evidence point to a common ancestor:

§ Biological classification

§ Anatomical similarities between organisms

§ Useless traits in modern species

§ Shared developmental pathways

§ DNA similarities

§ Distribution of organisms on earth (biogeography)

§ Fossil evidence


§ Biological classification implies common ancestry.


§  Anatomical similarities between organisms.  Mammalian forelimbs have the same set of bones. The underlying structure is similar despite the very different functions.


§ Useless traits in modern species.  Vestigial, but similar, structures in ferns and flowering plants.


§ Shared developmental pathways.  Similarity among chordate embryos.


§ DNA similarities.  Birds in same genus have DNA that is more similar to one another, while distantly-classified birds have DNA that is less similar.


§ Distribution of organisms on earth.  Different species of mockingbird found on Galapagos all resemble another species found on the mainland.


§ Fossil evidence. Horse fossils provide a good sequence of evolutionary change within a lineage.


10.3 Examining the Evidence for Evolution - A Closer Look

§ The same lines of evidence that support common descent can be used to look for the closest relatives of humans.

§ Are humans related to apes?


§ Linnean classification

§ Basis of modern biological classification

§ Named after Carl von Linne

§ Hierarchical: large groups share general characteristics, and small groups share many characteristics.

§ Humans are classified with apes because they share many biological characteristics


§ Linnean classification of humans


§  Shared characteristics of humans and apes


§ Anatomical and developmental similarities

§ Tail – great apes and humans have tailbone, but no tail


§  Anatomical and developmental similarities

§ Goosebumpsarrector pili are small muscles at base of body hair.  When tensed cause hair to stand up.  Useful for heat conservation or in aggressive social exchange.


§ Evidence from molecular homology


§  Bipedal humans have some unique anatomical traits, such as features of hips, knees, and skull.


§ Early hominim fossils such as “Lucy” provide evidence that the earliest human ancestors arose in Africa.


§ Evidence from fossils

§ Radiometric dating

§ Used to determine age of rocks

§ Relies on decay of radioactive isotopes into daughter products


§ Evidence from fossils


§ Using radiometric dating, scientists have estimated the age of fossil hominims.


§  Trends in human evolution

§ Larger brains

§ Flatter face

§ Reduced jaw size


10.4 Are Alternatives to the Theory of Evolution Equally Valid?

§ Weighing the Alternatives


§ The Origin of Life

§ Evolution is the study of how life changes

§ It doesn’t really address issue of how life began

§ Experiment evidence does give some clues about beginnings of life


§ The Miller-Urey experiment demonstrated that complex molecules can spontaneously form from simple chemicals.


§ Evolutionary theory informs all aspects of modern biology.  It is important to understand it because it helps scientists grapple with modern issues.

§ Evolutionary theory helps us understand the function of human genes

§ Evolutionary theory is important to understanding species interactions

§ Evolutionary theory is important for predicting the biological consequences of climate change