Chapter 22 Descent with Modification

CHAPTER 22: DESCENT WITH MODIFICATION

Questions in This Course
How did life on earth become the way it is today?
What differences exist among living organisms?
What drives biodiversity?
How are structures related to function?

Life: The Why and the How
Ultimate vs. Proximate questions:
Ultimate: Why?
Why are we here?
Why does life exist?
Proximate: How?
How did we get here?
How did life become what it is today?
Philosophy and religion—Ultimate questions
Science—Proximate questions, few ultimate

Evolution
Many ways to define
Descent with Modification—modern descendants are different from ancestors
Change in genetic makeup of a populations

Early Ideas About “Evolution”—Aristotle (384 – 322 BCE)
Species are fixed, unchanging
Scala naturae—“ladder” of life, from least to most complex
Matches well with creationism/ intelligent design—living thing were created perfect and match their environment perfectly

Linnaeus’ View
1707-1778, Swedish, physician/ botanist
Classify diversity of life to discover God’s plan
Binomial nomenclature—method of naming organisms
Genus and species
Ex. Homo sapiens, Tyrannosaurus rex
Sometimes name tells something about it, sometimes a person
Similar species grouped together no based on relatedness, but “createdness”

Charles Darwin
Born in Shrewsbury, England 1809
Interested in nature all his life
Father sent him to medical school
Found it boring and horrifying
Enrolled at Cambridge to become clergyman
After graduating, went on Beagle to survey South America

Influence on Darwin: Fossils
Paleontology—study of fossils
Georges Cuvier (1769 – 1832) saw that older fossils were less similar to extant (existing) species
Extinctions common
Opposed evolution
Proposed catastrophism: boundaries due to local catastrophes

Influences on Darwin: Geology
James Hutton (1726 – 1797)
Geologic features we see today are due to long, slow process of erosion
Charles Lyell (1797 – 1875)
Uniformitarianism: mechanisms of change are constant over time
Forces in past same as today
Theses ideas of slow, continuous change strongly influenced Darwin

Darwin’s voyage on The Beagle
Started December 1831 (Darwin was 22)
Darwin spent most of his time observing and collecting plants and animals
Noted characteristics that made them well-adapted to where they lived
Also noted they were more similar to each other than ones found in similar habitats overseas

The Galapagos
Some animals looked like ones on mainland, but different
Others were similar to each other, but with unique traits
Darwin’s finches
Colonization and isolation?
Idea of adaptation

Adaptations
Adaptations—inherited characteristics that enhance survival and reproduction
Can gradual accumulation of adaptations lead to new species?

Origins of The Origin
Darwin was afraid to publish his ideas
Public outcry?
Advised to just go ahead and publish them before someone else did…
Like Alfred Russell Wallace

Darwin vs. Wallace
Wallace sent Darwin his manuscript on natural selection
Very similar to Darwin’s
Darwin hurried and finished The Origin of Species
Wallace admired Darwin, said he

The Origin of Species
“Evolution” never used in first edition
Focused on descent with modification
All modern life came from ancient ancestor
As its descendants lived in different habitats, they accumulated adaptation  new species
History of life is like a

Natural Selection
One of several processes that drive evolution
“Survival of the fittest”
Two Key Components:
Members of a population vary in their inherited traits
All species can “over-populate/ reproduce,” but only a few individuals survive and reproduce
Most survive long enough to reproduce
Short vs. long-lived strategies?

Examples of Natural Selection
What helps survival?
Defending itself
Things that help them in their environment
What helps reproduction?
Attracting it to something

Artificial Selection
Like natural selection, except the selecting agent is us
Dog breeds
Crops

Important Note:
Natural selection acts on individuals
Individuals do not evolve, populations evolve
Natural selection only works if a trait is both heritable and variable
If heritable but identical, no natural selection

Evidence for Evolution
How can someone prove evolution is real?
Homologous structures
Vestigial traits
Fossils
Direct observation
Biogeography

Evidence: Homologous Structures
Developmental, physiological, molecular
Structures that derive from common ancestry
But may have different functions now!
DNA, etc. sequences
New way to construct trees

Warning: Analogous Structures
Structures that have same function, and may appear similar
NOT due to common ancestry
Insect and bird wings
Eyes in vertebrates and eyes in squids

Evidence: Vestigial Traits
Traits that were used in the past, but no longer serve a function
Examples?
Appendix
Wisdom teeth
Flightless birds
Eyeless cave animals

Evidence: Fossils
Similarity between extinct and extant species
“Missing links”

Evidence: Direct Observation
Best source of evidence
Artificial selection speeds up process

Examples of Observed Evolution: MRSA
Methicillin—resists S. aureus
Staphylococcus aureus
Certain strains become “fleshing-eating”
Became resistant to antibiotics over time
How?
Heritable variability in cell wall protein—Natural Selection
“99.99%”
Evidence: Biogeography
Geographic distribution of species
Continental drift
Pangaea—single large continent 250 million years ago
Prediction of fossil locations
Explains why islands have lots of endemics—found nowher else
Ex. Australia
No placental mammals
Has lots of marsupials
Explanation?
Marsupials came first since we don’t have them here, we have placental animals while they don’t