The evolution of species by “descent with modification”
Darwin’s time: changing our world view
Darwin was born at a time when scientific enquiry was changing
the way we view the world and ourselves. When Europeans were
exploring and “discovering” far away lands with huge diversity of
animals, plants, and people.
Charles Lyell proposed that gradual processes acting over long
periods of time can lead to great changes in the Earth’s landscape
(uniformitarianism). Resembles the theory of evolution: gradual
and constant processes bring big changes over long time periods.
Pre- “Origin of species” ideas on evolution of species: Darwin
was not the first to propose that species had changed through
time or that species evolved from others.
Jean Baptist Lamarck – simple species are continuously
created by spontaneous generation and then adapt by passing
onto offspring advantageous traits acquired by parents
(disproved).
Robert Grant – evidence for common descent of species by
looking for homology among different organisms.
Robert Chambers – fossils in different stratigraphic layers
changed over time, becoming increasingly complex, leading to
the ascent of humans.
Origin of Darwin’s theory
Darwin travelled around the world and visited the Galapagos
Islands. Finches caught his attention as they were very diverse –
he noticed that each island was inhabited by different species/
combination of species of finches, and that their beaks were
different and seemed to be the most adept shape to pick their food
source.
He suggested that species had not been designed, but instead
that species changed, with species evolving from other ancestral
forms.
The evolution of species by “descent with modification”
Organisms have variations in a number of traits, and these
traits can be passed on from one generation to the next.
Evolution of species by “descent with modification” refers to
changes in the prevalence of these traits in a population over
several generations.
For example: beetles on a diet – because of food restrictions due
to drought, the beetles in the population are a little smaller than
the preceding generation of beetles (NOT evolution because due to
Darwin’s time: changing our world view
Darwin was born at a time when scientific enquiry was changing
the way we view the world and ourselves. When Europeans were
exploring and “discovering” far away lands with huge diversity of
animals, plants, and people.
Charles Lyell proposed that gradual processes acting over long
periods of time can lead to great changes in the Earth’s landscape
(uniformitarianism). Resembles the theory of evolution: gradual
and constant processes bring big changes over long time periods.
Pre- “Origin of species” ideas on evolution of species: Darwin
was not the first to propose that species had changed through
time or that species evolved from others.
Jean Baptist Lamarck – simple species are continuously
created by spontaneous generation and then adapt by passing
onto offspring advantageous traits acquired by parents
(disproved).
Robert Grant – evidence for common descent of species by
looking for homology among different organisms.
Robert Chambers – fossils in different stratigraphic layers
changed over time, becoming increasingly complex, leading to
the ascent of humans.
Origin of Darwin’s theory
Darwin travelled around the world and visited the Galapagos
Islands. Finches caught his attention as they were very diverse –
he noticed that each island was inhabited by different species/
combination of species of finches, and that their beaks were
different and seemed to be the most adept shape to pick their food
source.
He suggested that species had not been designed, but instead
that species changed, with species evolving from other ancestral
forms.
The evolution of species by “descent with modification”
Organisms have variations in a number of traits, and these
traits can be passed on from one generation to the next.
Evolution of species by “descent with modification” refers to
changes in the prevalence of these traits in a population over
several generations.
For example: beetles on a diet – because of food restrictions due
to drought, the beetles in the population are a little smaller than
the preceding generation of beetles (NOT evolution because due to
