Download While at Cambridge College studying theology, Charles Darwin

SBI3U Evolution – 2
Geologist Charles Lyell proposed that geological processes operated at the same rates in
the past as they do today in a process called uniformitarianism. Lyell, therefore rejected
catastrophism and theorized that slow, subtle processes could happen over a long period
of time and could result in substantial change. For example, floods that happened in the
past had no greater power than floods that occur today. This idea inspired naturalist
Charles Darwin and others. If Earth is slowly changing, they wondered, could slow, subtle
changes also occur in populations?
French naturalist Jean-Baptiste Lamarck compared current species of animals with fossil
forms and observed what he interpreted as a line of descent, or progression, in which a
series of fossils (from older to more recent) led to a modern species that increased in
complexity over time. Lamarck hypothesized that organisms could become progressively
better adapted to their environments. For example, it was thought that giraffes
stretched their necks to reach the foliage in tall trees and that this stretched neck
condition was passed on to their offspring, resulting in tall giraffes that can eat from the
tops of trees. Although this is not the way giraffes developed their long necks, Lamarck
called this idea the inheritance of acquired characteristics. Lamarck also suggested that
body parts not used would eventually disappear.
At the time there was little understanding of cell biology and no understanding of
genetics. Lamarck provided a hypothesis for how the inheritance of characteristics from
one generation to the next might happen. More importantly, he noted that an organisms
adaptations to the environment resulted in characteristics that could be inherited by
offspring.
In 1831, Charles Darwin sailed aboard the HMS Beagle, a British survey ship. The primary
purpose of this voyage was to map the coast of South America but this journey provided
Darwin with an opportunity to explore the natural history of various countries and
geographical locations. At first, Darwin did not understand the significance of many of
his observations but years later, many of them became important to his theory of
evolution by natural selection.
After his trip, Darwin began to propose answers to his questions and to compile his and
others’ observations into a comprehensive theory to explain how species change over
time. British naturalist Alfred Russel Wallace, reached conclusions that were similar to
Darwin’s as they both accepted that populations changed as time passed, but they were
unclear how they changed.
An essay by economist Thomas Malthus called Essay on the Principles of Population,
proposed that populations produced far more offspring than their environments could
support. Malthus said that these populations were eventually reduced by starvation or
disease. This gave Darwin and Wallace a key idea because according to them, individuals
with traits that helped them to survive in their local environments were more likely to
survive to pass on these traits to offspring.
They reasoned that competition for limited resources between individuals of the same
species would select for individuals with favorable traits – traits that increased their
chances of surviving to reproduce. Therefore, these traits would appear in later
generations, and as time passed, the entire population would have them. This is the idea
of survival of the fittest, and Darwin called this process natural selection.
Darwin proposed that all life descended from some unknown organism and as descendants
of this organism spread out over different habitats over many years, they developed
adaptations to help them better survive in their local environments. His ideas were
published in 1859 in a book called The Origin of Species. Darwin’s theory of natural
selection showed how populations of individual species became better adapted to their
local environments over time.
His ideas can be summarized as:

Organism’s produce more offspring than can survive. Therefore, organisms
compete for limited resources.

Individuals of a population vary extensively, and much of this variation is heritable

Individuals that are better suited to local conditions survive to produce more
offspring

Processes for change are slow and gradual.
Darwin did not use the word evolution in the original copy of The Origin of the Species.
Instead, he used the term descent with modification as he felt the word evolution implied
progress. Darwin did not believe that natural selection demonstrated progress but rather
is the result of the ability of certain individuals in any population to survive local
environmental conditions and to pass on traits that helped them survive in the first place.