Species
• Species: group of organisms that can
interbreed and produce fertile
offspring
– Different species rarely breed
– Interspecies breeding often
results in sterile offspring
• Ex: Horse x Donkey = Mule
• Ex: Lion x Tiger = Liger
• Acquired Inheritance: Early theory where organisms could
acquire and pass traits after birth
• Cause: environmental changes forced individuals to change
• Early Belief: Giraffes & Long Necks
– Long necks are result of stretching to reach leaves
– Extra length was passed on to offspring
• Problem: Traits acquired after fertilization cannot be
passed to offspring
Geologic Change
• Early belief:
– Earth ~6,000 years old
– Life remained unchanged
• “New” Observations
– Rock layers (strata) contained
differing fossils
– Deeper fossils (older) less
complex
– Environmental changes
thought to affect life
characteristics
Charles Darwin
• Observed:
– Organisms have variations based upon environment
– Similarities between extinct fossils & modern life
– Marine fossils atop mountains
• Natural Selection: Process where organisms with favorable
traits survive and reproduce
• Major concept in biology published in The Origin of Species
(1859)
Adaptation & Variation
• Variation: Inherited traits that make an individual
different from others
– Green, flat wings of the insect above
• Adaptation: Variation increases the chance of
survival
– Ability to blend with environment
Causes of Genetic Variation
• Genetic variation increases chances some survive in changing
environments
• Gene Pool: All alleles within a population
• Two main causes of genetic variation:
1) Mutations: Random genetic changes may affect phenotypes
2) Recombination(crossing over): During meiosis, genes recombine in varying
patterns
Variation: 4 Different Gametes
Chromatids
copied
Crossingover
CrossingOver
finished
Genetic variation!
Four differing chromatids
Review
1)
2)
3)
4)
5)
When are two organisms considered a different species?
Even though incorrect, why is Lamarck’s theory still relevant?
How can the general age of rocks (and fossils) be determined?
How does a variation and adaptation differ?
What is natural selection?
• Features of a species
can evolve, or change
over time
• Natural selection is
when favorable traits
allow survival &
reproduction
• Variations allow an
organism to be better
suited to its
environment