Download Evolution by Natural Selection

Evolution by Natural
Selection
15-1 & 15-2
What is Evolution?
= A change in a species over time
= A change in a population over time (micro)
Examples:
Drug resistant bacteria
Snails with different shell thicknesses
= A change in the community over time (macro)
Dinosaurs replaced by what we see today
Mechanisms of change
• How did/do these changes come about?
• What mechanisms are responsible for
generating the diversity of species we
observe?
Science looks for mechanisms that can bring
about the changes or diversity
Charles Darwin
• British Naturalist
• Hired as a naturalist
to collect specimens
on a voyage around
the world
• Voyage on HMS Beagle in 1831
Darwin’s Voyage
What got Darwin thinking?
• Organisms seemed well suited to their environments
– how?
• Species don’t always appear where you would
expect based on habitat – why?
• Similar species located close to each other show
slight differences in appearance – why?
• Galapagos Tortoise shells and neck lengths
• Wide diversity of beetles in Brazilian Rain Forest
• Fossils of previously unknown creatures
Galapagos Tortoises
Beetle Diversity
Darwin influenced by other scientists
• James Hutton & Charles Lyell: Earth is shaped by
normal geologic forces over a long period of time.
• Alfred Wallace is also speculating about how
species could be shaped by natural forces over time
• Domesticated animal breeds were shaped by
breeding (artificial selection)
• Darwin publishes his idea in a book (1859):
“On the Origin of Species…”
Lamarck’s idea
Lamarck’s ideas
1) Traits can be acquired from use or need
2) Traits can be lost through non-use or lack of
need
3) Acquired traits can be passed on from parents to
offspring
Errors:
1) Acquired traits cannot be passed on because they
have no genetic basis (DNA)
2) Traits are not likely to appear due to need or
disappear from non-use
Name that breed!
A game of great skill
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Artificial selection
How are dog breeds created?
1) Find parents that display the traits you want
2) Let them mate and reproduce
3) Observe the offspring and select those you
wish to breed in the future (traits)
4) Eventually some traits become very common
and pronounced while other traits are
eliminated
What is natural selection?
= organisms that reproduce most successfully will
pass on more traits to the next generation
- Future populations will have the traits of the most
successful reproducers from the previous
generations
- Think about the snails!
- Organisms that are best adapted for survival in the
environment will probably be the best reproducers
- Not necessarily strongest & fastest
- Why are male and female birds colored differently?
Red-winged Blackbird (R)
Male
Female
Male vs. Female Birds
• Males draw lots of attention to themselves to advertise for
mates
• Bright colors,
• long, loud songs
• Singing from a prominent perch
• Females avoid attention so as not to advertise the presence
of a nest
• Camo coloration
• Less vocal, short calls
• Stay secluded
• From an evolutionary standpoint, the males have developed
traits that make them an easier target for predators but they
result in better reproductive success.
Natural Selection – 3 conditions needed
1) Variability exists in a certain trait
- new variations can come from immigrants or mutation
Natural Selection – 3 conditions needed
2) The trait must be heritable (not acquired) to be
passed down
Heritable
Acquired
Natural Selection – 3 conditions needed
3) Selective Pressures in Environment lead to Differential
Reproduction
Differential reproduction = some individuals with one
version of the trait produce more offspring than others with
the other version
• Fitness = offspring an individual contributes to next
generation
• A good trait that leads to better fitness = adaptation
Natural Selection – the result
4) Given enough time, the most advantageous traits should
become common in a population