CHANGE OVER TIME
LS CH 6
REVIEW: HYPOTHESIS, THEORY, LAW
• Hypothesis• Testable statement about what should happen in an investigation
• “What should happen.”
• Law• A statement that describes what happens in nature
• “What will happen.”
• Theory• An explanation for natural phenomena
• “Why it happens.”
• Based on:
• Repeated testing or observations and several confirmed hypotheses
• Theories explain Laws. They do not become Laws.
BIOLOGICAL EVOLUTION
• A scientific theory (explanation)
• Definition: The change in the frequency of alleles in a population over time.
• Restated: The changes in traits in closely related organisms over time.
• Most explanatory power of any theory in biology.
• “Nothing in biology makes sense except in the light of evolution.” –Theodosius
Dobhansky (Russian Biologist).
• Supposed for hundreds of years, but lacked a mechanism
• That is, a method for why it occurs
EARLY IDEA ABOUT EVOLUTION
• Jean-Baptiste Lamarck (1744-1829)
• Hypothesis: Inheritance of acquired traits
• Believed that offspring inherited traits that parents
had gained in their lifetimes
• This is closer than anyone before him, but wrong
CHARLES DARWIN
• 1800’s British Scientist
• Wrote several books
• On the Origin of Species (1859)
• H.M.S. Beagle
• Chart coastlines of South America
• Darwin collected specimens of plants
and animals
DEVELOPMENT OF DARWIN’S THEORY
• Erasmus Darwin, his grandfather, believed that organisms changed over
time, but didn’t know how
• Darwin learned this reading his grandfather’s writings
• Darwin also read Lemarck’s works, but thought it unlikely
• A lot of people criticized Lemarck’s idea
• Around this time, a lot of fossils were being discovered
• Geology was making tons of discoveries, including that the earth was much
older than was thought
CONTINUED
• Maybe the most influential to
Darwin was Thomas Malthus, an
economist
• Malthus was one of the first to
realize that food production
cannot keep up with population
growth
• Carrying capacity
• The maximum number of organisms
that can be supported by the
environment
ARTIFICIAL SELECTION
• Also called selective breeding
• Humans breeding organisms for desired traits
• Cows with more milk
• Strong horses
• Friendly wolves
• Many more
• Over time, offspring will have desired trait
DARWIN’S JOURNEY
• H.M.S. Beagle
• Collected plant and animals from different regions
• Galapagos Islands
• Learned that species varied by island, but were similar
• Also similar, yet different, to those in South America
• The location of the organisms depended on the types of food available
DARWIN’S FINCHES
DARWIN’S PRINCIPLES
• Based on what he had learned, and what he had seen on his journey, Darwin
came up with 4 basic principles
• 1. The reproductive potential of a species (the number of offspring that could be
born) exceeds the amount that can be supported by the environment
• 2. There is variation in all species
• Different traits (recall, Darwin did not know about genes or DNA)
• 3. Offspring resemble parents
• Traits are inherited
• 4. Organisms with traits better suited to their environment will survive, and have
a better chance of passing their traits on
NATURAL SELECTION
• Darwin’s great insight into the natural world
• The process by which organisms with variations that help them survive in
their environment have a better chance to survive long enough to
reproduce, passing the traits on.
• Restated: If an organisms has a trait that allows it to survive better in its
environment, it will likely survive better…
• Nature (i.e. environmental change) chooses which species survive
VARIATION AND ADAPTATION
• Variations are the inherited differences within a species
• Height, color, speed, etc.
• Beneficial variations are selected for; negative variations are selected against.
• Adaptations are variations that give organisms an advantage in their
environment
• Beneficial variations
• Increase the chance for survival and reproducing
• Keeps the species alive
• These are what natural selection acts on
TYPES OF ADAPTATIONS
• Structural Adaptations:
• Involve physical characteristics, such as color, size, shape, anatomy, etc.
• Examples: Camouflage, speed, strength, better teeth for meat eating, etc.
• Behavioral Adaptations:
• Involve how an organism behaves or acts
• Nocturnal hunters limit competition and are able to attack while prey sleep
• Functional Adaptations:
• Involve internal, biochemical changes
• Hibernation, photosynthesis, etc.
EXAMPLES OF ADAPTATIONS
• Camouflage- Being able to blend in with surroundings
• Mimicry- Looking like another species
• One that is venomous, poisonous, or tastes bad
IMPORTANCE OF DARWIN’S THEORY
• Darwin did not invent the idea of evolution
• He came up with the way that evolution happens
• It was already accepted that species change over time
• Nobody knew how
• Darwin answered the question
• Nature (environmental conditions) determine which traits will survive and which will not
• In the 150 years since Darwin published his Theory, it has been one of the
most tested and studied theories in science
• It has continually passed
PREDICTIONS FROM DARWIN’S THEORY
• A method of inheritance would be discovered to explain how traits are passed
• Mendel came up with this around the same time Darwin was completing his Theory,
unaware of Darwin’s ideas
• Mendel actually tried communicating his idea to Darwin, but it never reached him
• Species will continually be formed and will continually go extinct from changing
environmental conditions
• Happens all of the time
• All life is related
• Confirmed by DNA studies
SPECIATION
• The formation of new species
• A species is a group of organisms that can reproduce and have fertile offspring
• Evolution occurs in populations (members of a single species in an area)
• If a population is reproductively isolated (split from initial population) they
may evolve to the point where they are no longer able to reproduce with
members of their original species
• At this point, a new species has been born
• This is speciation
EVOLUTION VS. EXTINCTION
• Species have 2 possible outcomes: staying alive or going extinct
• Extinction is the death of the final member of a species
• It is final… for now
• When environmental conditions change, species must adapt, or will go extinct
• There have been several mass extinctions (death of >50% of Earth’s species in
a geologically short period of time)
• We are currently part of another one driven by changing environmental conditions
• Which we are causing…
BIOLOGICAL EVIDENCE FOR EVOLUTION
• Often takes a long time, so often relies on indirect evidence
• Though it has been observed, many times, even recently
• Evidence includes:
• Fossils (best evidence for past instances)
• Comparative anatomy
• Vestigial structures
• Embryology
• DNA evidence
FOSSILS
• Remnants of past organisms
• Location of the fossil tells us about organism
• Deeper in rock layers=older
• Can tell us about cause of death
• Sometimes found with food or eggs
• Even if incomplete, good clue to past
• Many different types
• Not always bones
• Can be an imprint, a cast or mold, an organism preserved in amber
COMPARATIVE ANATOMY
• Similarities between organisms
• Homologous structures-similar structures found in different organisms
which are not closely related
VESTIGIAL STRUCTURES
• Structures an organism has that no longer serve their original function
• May still do something, but not what it used to do
• Examples:
• Appendix-Used by some organisms to digest large amounts of cellulose (plant
materials)
• In humans, it holds some bacteria, but is not necessary to our survival
• Can actually kill us…
• Goosebumps- Makes fur-covered organisms look bigger (cats)
• No purpose in humans
• Wisdom teeth- Were useful for ancestors that relied on coarse, rough foods
• Now only cause problems
• Actually disappearing from human population
• 35% of people born will never have Wisdom Teeth
• Many others will only get 1 or 2
EMBRYOLOGY
• Study of embryos during development
Tail
Gills
DNA EVIDENCE
• All organisms have DNA similarities
• All use the same 4 bases (A,T,G,C)
• Similar genes for cellular jobs
• Sequence of nucleotides shows strong similarities
• Follows “tree of life” pattern of visible features
• Molecular clocks
• Predictable mutations to DNA show speciation events