Transcript Natural Selection Notes

Natural Selection Notes
Charles Darwin
• In 1831, Darwin traveled to South
America
on the ship the HMS Beagle as a
naturalist. His job was to collect
specimens to be studied.
• Darwin collected a large number of
species from the Galapagos Islands, off
the coast of Ecuador.
• After returning to England and studying the
species that he collected, Darwin noticed that
many of the species were similar to those
found in other countries, but were different
enough to be unique species.
• He hypothesized that the species from the
mainland must have changed after reaching
the island.
Questions

What observations lead Darwin to
develop the theory of evolution by
natural selection?
Darwin was hesitant to publish his theory
because he knew how controversial it was.
Alfred Russel Wallace came up with a similar
theory at the same time, which
encouraged Darwin to publish his work.
Darwin was not the first person to consider
the theory of evolution, he was the first
person to offer a plausible method for it
to occur.
The Theory of Natural Selection
• Adaptation – a beneficial trait that allows an
individual to survive better than others
• Adaptations may help individuals to compete for
food or other resources or to avoid predators.
• Those individuals are then also able to have more
offspring.
• If these traits are hereditary, then the offspring
would also have these traits.
• In the next generation, there will be more
individuals with the beneficial trait.
• Natural selection – Individuals with
better adaptations have a better chance
of survival and are able to produce more
offspring, therefore, future generations
will have more individuals with that
trait.
• Darwin’s Dangerous Idea video clips (From
PBS Evolution series)
First 2 sections:
On your notes, answer the following
questions:
1. What evidence does Darwin give for an old
earth?
2. What explanation does he give for the
differences in the birds?
3. What explanation does he provide for how
life has developed?
4 Principles of Natural Selection
1. Variation: individuals in a population differ from one
another.
2. Heritability: individuals pass down their traits to their
offspring. If these traits are beneficial and allow an
individual to leave more offspring, more offspring in
the next generation will have the beneficial trait.
3. Overproduction: more offspring are produced than
can survive.
4. Struggle for survival: limited resources, predators and
harsh conditions all make survival difficult.
Evolution
• Evolution is the build up of genetic changes in a
population of a species over many generations.
• Scientists believe that natural selection leads to small
changes that build up and add up to large changes in
species – this is evolution.
In other words: natural selection leads to
evolution.
Do not confuse these two terms, natural selection and
evolution ARE NOT the same thing.
• Microevolution – small changes in a species
(attributed to natural selection)
• Macroevolution – development of a whole new
species, typically called evolution
People rarely argue that microevolution occurs,
we see evidence of this. Macroevolution is
where the controversy lies.
Darwin’s Dangerous Idea video clips (From PBS
Evolution series)
On your notes, answer the following
questions:
3rd section:
4. What are the researchers looking at and
observing in Ecuador?
4th section:
5. What idea have they provided evidence for?
6. What have they not provided evidence for?
Phylogenetic Trees
• Phylogeny – evolutionary history,
generally drawn in the form of a
family tree
phylo – race, tribe, kind
gen -
• Organisms that are more closely
related are drawn more closely on the
phylogenetic tree.
• Which 2 taxa (groups) are most
closely related?
• A didn’t evolve from B. A and B
share a common ancestor. They both
evolved from that common ancestor.
• In the same way, man is not believed
to evolve from apes, man and apes are
believed to share a common ancestor.