Download origin of species

“At last gleams of light have come, and I am
almost convinced (quite contrary to opinion I
started with) that species are not (it is like
confessing a murder) immutable … I think I
have found out… the simple way by which
species become exquisitely adapted to
various ends.”


He knew that his theory of evolution would be
controversial and challenged. In June 1858, he
received a letter from a young biologist working
in Malaysia named Alfred Russell Wallace.
Wallace outlined his own theory and happened
to match Darwin’s theory.
After much hesitation and encouragement from
others, Darwin finally published his book “On
the Origin of Species by Means of Natural
Selection or the Preservation of Favoured Races
in the Struggle for Life”, which sold out on the
first day.

Natural selection: the way in which nature
favours the reproductive success of some
individuals within a population over others.

Evolution is the result of natural selection
Observations
In each generation,
populations produce more
offspring than there are
adults
Inferences
Theory of Natural
Selection
Individuals within a population
compete for resources
Popluations do not continue
to grow in size
Food and many other sources
are limited
Over time the population changes as
advantageous heritable characteristics
become more common generation after
generation
Individuals withing all
populations vary
Some individuals will inherit
characteristics that give them a
better chance or surviving and
reproducing
Many variations are hertiable
These were Darwin’s key observations:
 All healthy populations produced far more
offspring than could survive and reproduce
 Individuals exhibited heritable variability
 Ie. a slow cheetah vs a faster cheetah

Survival of the fittest: a phrase that has been used
to describe the process of natural selection

This might be misleading because you might think
someone who has lived a long life is fit, but the
term is used to describe reproductive success

Adaptation: a characteristic or feature of a species
that makes it well suited for survival or
reproductive success in its environment

All scientific theories must be explanatory, have
predictive powers and be testable.
Explanatory Powers
 Darwin used the evolution of large-billed finches
 An ancestral population with medium-sized bills arrives
on the island. They eat medium-sized seeds. With no
initial competition, the finches establish a growing
population on a small island where there are some
medium seeds but mostly plants with larger seeds
 The finch population grows until it reaches the limit of
its food supply. Each year, many eggs are laid, but the
island can’t support all the birds. The birds are not all
alike – exhibit variation. Some birds have slightly smaller
and larger beaks than average beaks.
 Most of the birds must compete for the medium-
sized seeds, but the ones with the larger beaks are
also able to feed. They have little or no
competition. The environment favours these
larger beaks and lays more eggs on average
because they are healthier. Their young are more
likely to be born with larger beaks.
 As this process is repeated generation after
generation, the average beak size continues to
increase. This is evolution by natural selection.
Prediction
 The theory allows scientists to make predictions about
how species may change over time, which are
associated with changing environments
 Ex. The evolution of antibiotic resistance in bacteria
 Ex. Darwin made predictions that fossils of the most
primitive human ancestors would be found on the African
continent. His predictions were proven correct
Testing and Falsification
 Science theory must be testable – the possibility of
being proven wrong
 There are examples that could falsify the theory:
p. 303 #1, 2, 4, 7, 8
p. 307 #1(b), 2, 4, 5(a,b,d,f)