Darwin’s Dangerous Idea
The Struggle for Existence,
Natural Selection & Descent With
Modification
Who Was Charles Darwin?
• Born in 1809 to a wealthy English family
• A below-average student at school
• Trained as a doctor, but dropped-out
• Trained eventually as a country clergyman
• Loved travel & the outdoors
– “You care for nothing but shooting, dogs and
rat-catching, and you will be a disgrace to
yourself and all your family!” (Darwin’s dad!)
Darwin’s Travels
• In 1831, aged 22, Darwin was invited to join a
5yr round-the-world expedition as an unpaid
naturalist on HMS Beagle
“Woe unto ye, beetles of South America…”
The Galapagos Islands
Darwin was amazed that any wildlife had reached such a remote place, and
suspected that the ALL the birds, plants and animals had arrived during the
past from the mainland
Galapagos Wildlife
Tortoises: each island, and even specific
mountains within an island, had a tortoise
with a unique shell shape. Were they all
descended from one ancestral tortoise?
Finches: every island had a variety of
finches, each with different size beaks,
adapted to eating different sized seeds.
One type was usually more common on
each island. Were they all descended
from one ancestral finch?
Darwin’s Idea
In the same way that dog-breeders and farmers “altered” the
appearance of animals by careful breeding (Artificial
Selection), Darwin proposed that there was also a NATURAL
mechanism which accomplished the same thing in nature…
The Origin of Species
• Darwin knew that his ideas were controversial: most scientists of the
day believed that each organism was “specially created” and “fixed”
in its form. He was very reluctant to publicize his ideas.
• In 1858, after reading about Wallace’s research in the Malay
Archipelago, Darwin decided to “go public” with his dangerous idea
• In 1859, Darwin published his ideas in a book called “On the Origin
of Species by means of Natural Selection, or the Preservation of
Favoured Races in the Struggle for Life”
5 Points of Darwin’s Theory
• Individual organisms differ, and some of
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this variation is heritable (offspring tend
to look similar to their parents)
Organisms produce more offspring than
can survive, and many survivors do not
reproduce
Because more organisms are produced
than can survive, they compete for
resources (“Struggle for Existence”)
Individuals best-suited to their
environment survive (“Survival of the
Fittest”) and reproduce most
successfully. These individuals then
pass on their heritable traits to their
offspring (“Natural Selection”).
ALL species alive today are therefore
“descended with modification” from
ancestral species that lived in the distant
past. This process unites ALL organisms
on Earth into a single tree of life.
Darwin’s original ideas on
how organisms might have
descended from each other
The Public Reaction
• Many scientists were
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appalled at the idea of
humans evolving from
ancestral apes. A fierce
debate ensued.
Research in geology,
paleontology,
biogeography and
breeding continued, as
scientists sought to either
confirm or reject Darwin’s
hypotheses
Darwin’s Legacy
• “There is a grandeur in this view of life,…that…from so
simple a beginning, endless forms so beautiful and
wonderful have been and are being evolved”
• This belief has fuelled research on every continent for
over 100 years…