Evolution in Action
- Evolutionary Theory is a unifying theory of life- it seeks to explain the diversity of life forms and their
- Diversity of life forms is explained by a process called natural selection
- Charles Darwin, Origin of the Species (1859)
- Alfred Russell Wallace (1859)
Two Big Questions
1) Why are there so many different kinds of life?
2) Why do plants and animals appear so well adapted to their environment?
Foundation of the Theory of Evolution
- Before Evolution emerged as a theory, certain ideological elements had to be in place :
- Recognition that the world was ancient
- Acceptance that the Earth and its life were formed by natural processes that are still
- Specifying a process by which life forms change over time
From Fixity to Mutability of Species
- Fixity of Species: species were believed to have been created at the same time and had always existed
-Mutability of Species: Some scientists challenged the fixity of species on the basis of the fact that so
many species looked alike.
In the 1800’s, people began to question why would God make so many species alike. Why are there 43
species of parrots? (The only reason they are “alike” is because they are the same species, they are all
really quite different)
- By the late 18 Century, many scientists recognized that species could change over time
- They also concluded such small changes had something to do with adapting to or coping with different
environmental conditions (polar bears vs. brown bears)
Discovery of Fossils and Ideas about Time: Europeans’ discovery of the dinosaur fossils in 1700s lead
scientists and eventually the public to believe the earth to be older
- In 1819, Charles Lyell wrote The Principles of Geology and he estimated that the earth was several
million years old (It’s really 4.5 billion years old!) The Questions: How do Species Change over Time
- Jean Baptiste LAMARCK (1744-1824) was a biologist who believed in the antiquity of the earth and in
the mutability of species
- He argued that organisms were powered by a “will” to adapt
- According to Lamarck, somehow, they were able to make changes in their bodies during their lifetime
to cope more efficiently with their environment. (I don’t believe that)
- Lamarck’s theory was undone by the observations that acquired physical characteristics are not passed
on to offspring
- People who lose a limb in an accident do not produce children without limbs
- Note: cultural change does work this way
Charles Darwin (1809-1881) wrote what is to date the most controversial book in the history of science
Darwin’s Finches: Adaptive Radiation
When species adapt by evolving biological features that enables it to survive in a new environment or
Niche- an environment that supplies the factors necessary for the survival of an organism or species
- Types of beaks that finches have of the different Galapagos islands, they adapted depending on the
different food they were eating (how does this happen? –Darwin) Through the process of adaptation,
global climate change, adaption etc.
Heritability of Traits
- It was well accepted that inherited characteristics of animals (and people) could be passed on to their
- Breeders used the knowledge of heritability of traits to select animals that possessed desirable traits.
(ex: types of dogs breed for aggressiveness/ with cattle. )
Thomas Malthus-The Principle of Population 1798
- Malthus argued that populations have a tendency to increase exponentially (or geometrically) while
available resources remain more or less finite or increased much more slowly.
- Food does not reproduce exponentially, we will eventually run out of food, said we should not feed the
poor (just let them die off)
- Darwin took from this that we are competing for finite resources, if we weren’t then evolution would
not matter!! There would be no competition.
- Populations inevitably reach the limit of the envir