Evolution Flashcards
Define: EVOLUTION
biological change in the characteristics of a population over time
(genetic change in population over generations)
What is Small-scale Evolution
changes in gene frequency in a
population from one generation to the next
What is Large-scale Evolution
the descent of different species from a common ancestor over
many generations
Darwin & Wallace’s basic evolutionary theory CONDITIONS
- Intrinsic increase in number of individuals within a species
- Competition for limited resources
- Survival of the few
4 Evolutionary Forces:
- Natural selection
- Mutation
- Gene flow (migration & reproduction)
- Random genetic drift
Darwins 5 Observations:
- Organisms have great potential fertility, which permits exponential growth of populations (source: Thomas malthus)
- Natural populations normally don’t increase exponentially but remain about the same
- Natural resources are limited
- Variation occurs among organisms within populations
- Variation is heritable
Darwin’s 3 Inferences
Inference 1: A struggle for existence occurs among organisms in a population (Source: Thomas Malthus)
Inference 2: Varying organisms show differential survival and reproduction, favouring advantageous traits (= natural selection).
Inference 3: Natural selection, acting over many generations, gradually produces new adaptations and new species
Population Definition
A group, within a species of interbreeding individuals and their offspring in the same geographic location
Gene Definition
The unit of inheritance affecting the characteristics of a trait
Allele Definition
– One of two or more alternative expressions of a gene
Genotype Definition
The Genetic Makeup of an individual
Phenotype Definition
The expression of the genotype & environment
Gene Pool
All genes in the eggs & sperm in a population
HOW DO NEW TRAITS ARISE? (Mutation - Definition)
Mutation – A spontaneous error in DNA replication leading to a heritable change in an individual’s genome – It is NOT “a change in the genetic code” (Relethford)
For mutation to be heritable it must occur in sex cell. If occurs in body cell (somatic cell, cannot be passed on)
heritable change in DNA
HOW ARE NEW GENETIC COMBINATIONS CREATED?
- Crossing over during meiosis
* Sexual reproduction
Fitness
Fitness = survival + reproductive success
Natural Selection Definition
“The preservation of favourable individual differences and variations, and the destruction of those which are injurious, I have called Natural Selection” – Charles Darwin, “The Origin of Species”
SELECTION PRESSURES:
• Biotic factors o Competition o Predation o Disease • Abiotic factors o Climate o Topography
Habitat Selection pressures:
- act on the phenotype
- act on all stages of the life cycle
- may act for many generations
Types of Natural Selection
o Stabilising selection
o Directional selection
o Disruptive selection
o Sexual selection
Stabilizing Selection
Selects against extreme phenotypes
Directional selection
Phenotypic character shifts in one direction
Disruptive Selection
Selects against average phenotypes
Sexual Selection
Selection of traits that give an individual an advantage in attracting mates, even if these traits are neutral or harmful for survival.
Artificial selection
(domestication)
Artificial selection has produced numerous breeds of dogs, which descended from wolves, Canis lupus about 15,000 years ago.
Species Definition
Definition of species varies and may include several criteria
• Members descend from a common ancestral population
• Interbreeding occurs within a species but not among different species
• Genotype and phenotype within a species is similar
Speciation
the evolutionary process or event by which new species arise
1: no barrier; one species
2: barrier allows differences to develop in two populations
3: Differences are so great that two species are evident
4: When barrier is removed, species do not interbreed
Gradualism
Gradualism: Large differences in anatomical traits that characterize species originate through the accumulation of many small incremental changes over very long periods of time.
ANAGENESIS
Punctuated equilibrium
Long periods of evolutionary stasis (no change) followed by relatively short periods of rapid evolutionary change
CLADOGENESIS
EVIDENCE FOR EVOLUTION
- Fossil Record (even tho incomplete)
- Stratigraphy – Fossils in deeper rock are older than those above, and their position within these rock layers gives them a chronological age relative to older (deeper) or younger (surface) fossils.
- Radiometric Dating: Method of determining the age of rocks
- Radiocarbon‐14 dating
Radiometric Dating
Potassium‐40 > argon‐40 & calcium‐40: half‐life = 1.3 billion years
Uranium‐235 > lead‐207: half‐life = 713 million years
Radiocarbon-14 Dating
- Half‐life of Carbon‐14 = 5,730 years
- C‐14 produced in the upper atmosphere
- C‐14 > plant tissue > food chain
- C‐14 uptake stops at death > C‐14 begins to decay
- Difference between C‐14 (atmosphere) & C‐14 (fossil) is proportional to the age of the fossil
- C‐14 dates the fossil not the rock it is embedded in
- = direct measure of the age of a fossilised organism
FOSSIL RECORD
a) If species were created independently there would be no order to the fossil record
b) The fossil record is a dated sequence of morphological change
- SHOWS EVOLUTIONARY TRENDS
- EVIDENCE OF INTERMEDIATE FORMS
- EVIDENCE OF EVOLUTIONARY STABILITY
- EVIDENCE FOR EVOLUTIONARY FAILURE
EVOLUTIONARY TRENDS
Evolutionary trends are directional changes in features & diversity of organisms • Perpetual Change • Common ancestry • Anagenesis Evolutionary trends in horses: • increased size of molars • loss of toes • increase number of species (diversity)
intermediate forms
Archaeopteryx ‐ The original feathers have long since disintegrated, but their impressions left in the surrounding rock confirm that the associated bones are those of a bird.
• Cladogenesis
Evolutionary Stability
Lingula, a marine organism (brachiopod) occupying vertical burrows in sand and mud has survived morphologically unchanged for approx. 400 million years
The horseshoe crab, an inhabitant of marine shores, has lived morphologically unchanged for approx. 250 million years
Evolutionary Failture
Extinction of dinosaurs ‐ After their demise at the end of the Cretaceous, dinosaurs were replaced as dominant land vertebrates by birds and mammals.
What is Phylogenetic constraint?
- Evolution is constrained by ancestry
- A species may inherit particular traits or developmental systems that constrain the possible variation that forms the basis for new adaptations
Homologous Features
“the same organ in different organisms under every variety of Form and function”
• Vertebrate forelimb: Although the vertebrate species differ, the underlying pattern of the forelimb is fundamentally the same.
o Common descent
o Phylogenetic constraint
Comparative Embryology
• Homologies – common ancestry
• Phylogenetic constraint
human - gill slits, tail
Vestigial Features
Anatomical characters which have decreased in size and complexity because their original function is no longer required
a) Whales evolved from terrestrial ancestors with four legs. But in whales, the hips and hind limbs are reduced to small bones with no function.
b) Snakes evolved from lizards with four legs. But in primitive snakes, the remnants of hindlimbs persist (forelimbs are absent).
c) The human appendix is a vestigial structure, reduced from the cecum of primate ancestors, which was involved in digestion of significant plant material.
auricular muscles, appendix, coccygeal vertebrae
Atavistic Features
a) Modern horses have only one enlarged digit on each foot. Their single toe evolved from ancestors with 3 or 4 toes. During the course of their evolution, the peripheral toes were lost and the central toe emphasized.
(b,c) On rare occasions these “lost” toes or their remnants reappear, testifying to the lingering presence of the underlying ancestral developmental pattern.
(d) On rare occasions, a modern horse is born with additional toes.
Analogous features
- Similar features evolve independently through similar environmental selection pressures
- Convergent evolution – separate lineages that were quite different but become similar because of similar lifestyles. Features that are similar in function but evolved independently are called analogous features.
The wings of bats, butterflies, and birds evolved independently, through convergent evolution, not from a recent common ancestor. But they have a similar function, flight, and so are analogous.
Homoplasy
Homoplastic structures are similar in appearance. May or may not also be homologous or analogous
ADAPTIVE RADIATION
- Evolution of several ecologically diverse species from a common ancestral species
- Galapagos finches illustrate adaptive radiation on an oceanic archipelago
- Convergent evolution
Anagenesis
evolutionary change within a lineage
The evolution of human brain size is an example of straight line evolution
Convergent evolution
– separate lineages that were quite different but become similar because of similar lifestyles. Features that are similar in function but evolved independently are called analogous features.
