Evolution By Natural Selection Flashcards
Patterns observed in Life
- Although species are diverse, there is unity among organisms.
- Species are adapted to their environments.
- Similar species are typically found relatively near to each other.
- Species are not perfect.
In 1858, Charles Darwin and Alfred Russel Wallace:
A. Made the claim that evolution has occurred, that species have changed through time.
B. Proposed a mechanism of evolution called natural selection.
A scientific revolution challenged what
Challenged special creation, the leading explanation for the diversity of life for over 2000 years.
Special creation proposes that:
A. Species were created in dependently by God as recently as 6000 years ago.
B. Species were unchangeable and thus had been unchanged since the moment of their creation.
The evolution of evolutionary thought
A. Plato: typological thinking
B. Aristotle: typological thinking + scale of nature
C. Lamarck: change through time + scale of nature
D. Darwin and Wallace: change through time + common ancestry
Plato
Types are created and immutable (no evolution) Variation within types not important.
Aristotle
Types can be ranked higher and lower based on complexity.
Lamarck
Species change through time from low to high; individuals evolve
Darwin and Wallace
Species change through time and are related via a common ancestor (tree- thinking); populations evolve (population- thinking); variation within populations important
Darwin’s voyage
- A five-year voyage (1831-1836) around the world as a naturalist on the HMS Beagle.
- He studied the animals, plants, and fossils in different parts of the world.
- He identified patterns in the diversity of life and identified a process to explain them.
Two components of Darwin’s theory of evolution
A. Decent with Modification
B. Natural Selection
Darwin’s observations
- There is competition among individuals in a population to survive and reproduce.
- Variation in traits exists in population.
- Certain traits give individuals a survival or reproductive advantage.
- Many traits are heritable (can be passed on to offspring).
Darwin’s conclusions
- Individuals with an advantageous trait are more likely to survive and reproduce.
- Over time, more individuals in the population will have the advantageous trait (if heritable).
Natural selection results in
Evolution
Natural selections occurs when
- individuals with certain traits produce more offspring that survive than do individuals without those traits.
- The selected traits will increase in frequency in the population from one generation to the next, causing evolution.
Darwin’s theory can be condensed into two statements:
Evolution by natural selection occurs when:
1. Heritable variation leads to
2. Differential success in survival and reproduction.
Natural Selection (3 steps)
- Population with varied inherited traits
- Elimination of individuals with certain traits
- Reproduction of survivors
Step 4: evolution
Increasing frequency of traits that enhance survival and reproductive success.
Population thinking
- Darwin proposed that change in species through time is fueled by variation in traits among individuals in populations.
- Populations evolve, not individuals.
Natural selection produces
- Adaptations
- An adaptation is any trait [what is a trait?] that increases the fitness of a population: ability to survive and reproduce offspring that also survive and reproduce.
Fitness vs. Adaptation
- Population with varied inherited traits
- Elimination of individuals with certain traits
- Reproduction of survivors
- Increasing frequency of traits that enhance survival and reproduction success
What increases your fitness?
Traits that allow you to survive and reproduce more offspring (that also survive and reproduce) can become adaptations.
Adaptations can help an individual
- Survive
- Attract a mate
- Produce healthy offspring
- Help offspring survive
Nature selects by
- exerting pressures
- Nature puts pressure on the survival and reproduction of individuals in a population.
These selection pressure come from:
A. Physical environment.
B. Interactions with another species.
These selection pressure can vary:
A. From one environment to another.
B. In the same environment from one time to another.
Physical Environment
- Climate
- Availability of resources
Interaction with other species
- Competition (for food, living space)
- Predator/prey relationships
- Mutualism
- Parasite/host relationships
Each side produces selection pressures for the other and results in coevolution.
We’re Darwin and Wallace the first to propose evolution?
No. Others had proposed that evolution did occur.
However, most did not formally propose a mechanism for evolution.
Jean-Baptiste de Lamarck (1744- 1829) was the first to propose a formal hypothesis of evolution including a mechanism in 1809.
Lamarck’s mechanism of evolution
He also recognized a match between organisms and their environment.
To explain Lamarck’s evolution he suggested that:
- Individuals change in response to characteristics to their environment via use and disuse.
- Pass on these acquired characteristics to their offspring
Lamarck’s pattern and process of evolution has been refuted by our understanding of genetics.
Decent with modifications
Makes two (2) claims about the nature of species:
1. Species change through time.
2. Species are related by common ancestry.
Evidence that species change through time
- Fossil Record
A. Life is Ancient
B. Extinction
C. Transitional Features - Vestigial Traits
- Current Examples
1A. Fossil Record: Life is Ancient
- Fossils are traces of organisms that lived in the past.
- The many fossils that have been found, described, and dated make up the fossil record.
- The fossil record indicates that life is ancient.
1B. Fossil Record
- species have gone extinct; fossils ressemble extant species in same region
- Many fossils provide evidence for extinct species, those that are no longer living.
Fossil data indicates
that extinctions have occurred continuously throughout Earth’s history and suggest that over 99 percent of all the species that have ever lived are now extinct.
Extinct species in fossils
typically resemble extant species in the same geographic location.
Early palaeontologists such as Cuvier
were not advocates of evolution and explained extinction by catastrophism and explained fossils resembling extant species as the law of succession.
1C. Fossil Record
- transitional features
- The fossil record includes many transitional features.
- Transitional features are structural forms that are intermediate between earlier and later species.
Many transitional features found in the fossil record provides
the “missing link” to help support hypotheses about evolutionary histories.
Vestigial traits
- A vestigial trait is one that is typically incompletely developed in an organism with no or reduced function, but is clearly similar to more developed, functioning traits in closely related species.
- Is a type of homology and so also provides evidence for common ancestry.
Example of vestigial traits
A. The human tailbone is a vestigial trait (incompletely developed; no function)
B. Goose bumps are a vestigial trait (developed; reduced function)
Current example of change in species through time
Hundreds of today’s populations have been documented undergoing evolutionary change.
For example:
A. Artificial selection in animals and plants.
B. Viruses, bacteria, fungi, insects, plants have evolved resistance to chemicals.
C. Numerous studies where populations have changed in our lifetime.
Artificial selection
• In artificial selection, changes in populations occur when humans select which individuals will produce the most offspring.
• Repeating this process over generations results in changes in the characteristics of a domesticated population over time.
Morphological changes in Galapagos finches
Drought in 1977 and wet year in 1983 caused population of finches to change.
Evidence that species are related
- Homology
- Bio geographic relationships
- Speciation occurring today
3 types of Homologies
- Genetic homology: similarity in DNA, RNA or amino acid sequences due to inheritance from a common ancestor
- Developmental homology: similarity in embryonic form or developmental processes due to inheritance from a common inheritance
- Structural homology: similarity in adult organismal structures due to inheritance from a common ancestor
Biogeographic relationships
- Biogeography is the study of the geographical distribution of organisms today and over time.
- Biogeography reveals that similar species ( extant or extinct) are linked by geography.
- In many cases, explanation also requires knowledge of movement of tectonic plates over geological time.
- Supports the idea that similar species involved from a common ancestor inhabiting the same area.
Islands and evolution
- Geographical isolation makes islands “hotbeds” for different selective pressures and studying evolution.
- Over time populations isolated on islands with different environments diverge into new species that look different from each other and their ancestors that may exist on the mainland.
Darwin’s observations concerning islands
Species have different traits that match their specific environments (e.g., beak shape for food source) but similarities to species in neighboring islands and to mainland.
Darwin’s hypotheses concerning islands
Islands are colonized by species from the nearest mainland as they are formed, and these colonists eventually give rise to new species as they adapt to their new environments via natural selection.
Wallace Line
Wallace’s hypothesis on evolution was heavily influenced by biogeographical evidence.
Contradicting Evidence?
- Can be explained by Convergent evolution
- Results in species with similar characters but are not derived from a common ancestor. Character is an analogous structure (homoplasy) not a homology.
- Demonstrates that organisms with separate ancestors may show similar adaptations due to similar selection pressures.
Examples of convergent evolution
Similarities between species of eutherian (placental) mammals and marsupial mammals arose independently not from a common ancestor due to similar niche adaptations.
Prediction 1
Species are not static, but change through time
Prediction 2
Species are related, not independent
Phylogenies can be built using many tools
- Data from independent tools: fossil dating, homologies, transitional features, vestigial traits suggest that whales evolved from a terrestrial ancestor that also gave rise to hippos
Individuals
Do not evolve, populations do
Acclimatization
(change in an individual) ≠ evolution.
Bigger and stronger
≠ more fit; loss of traits can be adaptive.
There is no such thing as
a more evolved or higher organism as all organisms have been evolving for the same amount of time.
An adaptation
does not occur because an organism needs it
Not all traits are
Adaptive
Adaptations are limited by:
- Fitness trade-offs: cannot maximize one trait without negatively affecting another because of energy and resource limitation
- Genetic constraints: gene pool in a population is limited
- Historical constraints: some adaptations are built from exaptations
- Environmental constraints: environments change and so perfection is a moving target.
Theory of evolution by natural selection:
A. Proposes change through time
B. Proposes decent from a common ancestor
C. Proposes that adaptations are due to natural selection
D. Is scientific and testable
Theory explains:
A. The diversity of life
B. The unity of life
C. The match between species and their environment
D. Biogeographical relationships of species
E. The imperfection of species
Fitness
If an individual is able to survive and reproduce in a given environment or condition, it has a high fitness
Adaptation
An adaptation of an organism depends on its fitness. If an organism can adapt to changes, it increases its fitness.
