Evolution 1 Flashcards
What is evolution? What does it encompass?
Evolution is a change in the genetic composition of a population over successive generations. Includes:
Descent with modification
Change over periods of time
Variety between individuals in a species
Variety between species
What are the theories of gradualism and uniformitarianism?
Gradualism and uniformitarianism were thought up by James Hutton and Charles Lyell
The idea was that Earth can only change slowly, and thte uniform, constant change of our planet could be a model for the change in species
Fossils had indicated that species had gone extinct and changed previously
What is the theory of catastrophism?
Thought up by Georges Cuvier
The idea that changes on Earth could, at times, be fast and drastic, such as in earthquakes and volcanoes
Local changes can be much faster than global changes
The strata of Earth were coherent with successive catastrophes, proven by fossils found in each layer
Geirges Buffon did what?
Geirges Buffon laid down the groundwork for the theory of evolution.
Geirges Buffon studied animals body structure
He noticed that some animals have structures in their bodies which are not useful
E.g., pigs have extra toes which do not reach the ground
His theory was that, in the past, pigs might’ve used these digits, but now no longer need them.
Information about the HMS Beagle Voyage
Between 1831 - 1836
Gave Darwin the opportunity to extensively research organisms and fossils worldwide
The Galapagos Islands:
Unique organisms forced Darwin to think about their origins
Only inhabited by birds and reptiles
Who came up with “struggle for existence?” What is it?
Thomas Malthus
If left alone populations grow exponentially, but no single species is overruning the Earth
Limited resources mean those who obtain them are most fit to survive
Not necessarily the traits which are strongest, just the ones which are most efficient
What is “Use or Disuse” theory? Who came up with it?
Jean Baptiste de Lamarck
“Use or Disuse” determines which traits would become prominent
Change could come by a wanted or perceived need
Giraffe example: Giraffes gained their long necks by willing them into existence after a shortage in ground foliage.
This theory is not correct with the addition of the last point
Although incorrect, this theory included the important detail of traits being heritable, which aided in the discovery of evolution theory.
What is natural selection?
Natural selection is the way in which nature favours that reproductive success of some individuals over others; The survival of those most fit to live in an environment because of their specific traits. Formulated by Darwin, rests on three principals
What are the three principals of natural selection?
- Natural Variation
- Reproductive Success
- Environmental Influences
Natural variation.. (Natural Selection)
There must be variations in organisms, otherwise all organisms will be equally matched and nothing will be favoured.
Variation is caused by genetic mutations, and can be advantageous, disadvantageous, or neutral.
Without an environmental context, you can’t establish the value of a given variation.
(Natural selection is less important in a day to day human life because we have created technologies to correct our disadvantages).
Reproductive success.. (Natural Selection)
Reproduction is furthering the success of a species because it is increasing genetic variation.
Organisms are reproductively successful if they survive to the reproductive age, can attract a mate, and can produce viable offspring.
This is important because, without reproductive success, no species would be able to survive past the first generation.
Favourable traits lead to reproductive success.
Environmental influences.. (Natural Selection)
The favourablility of traits depends on many environmental factors, including other organisms, resource scarcity, climate, etc..
Sexual selection
Species with sexual dimorphism, which means there are drastic differences in appearance or behaviours between males and females. This is often seen in the colours of birds.
Often means the males compete and the females choose a mate
Kin selection
Species with very strong social structures, such as wolves and meerkats
Can jeopardize their own reproduction/exclusive fitness and survival to help their kin survive
Artificial selection
Domestic species
In this form of selection, humans are the selective agents
Traits we choose are not always advantageous to the organism, but they get passed on because they are selected by people
Cast vs Impression fossils
Impression fossils:
Impression fossils form when an organism dies. Before entirely decomposing, it is covered in silt, mud, or ash.
The flesh then decomposes inside of this casing, leaving minerals in a ‘negative imprint’
Certain parts of the organism may mineralize
Cast fossils:
Cast fossils start the same, with a dead organism cast in silt, mud, or ash. However, large or tough structures, such as bones, remain after the decomposition of the flesh.
Over time, minerals seep in and replace the bones
The new remains are now petrified, or ‘made of stone.’
These fossils are really only rocks shaped like organisms
How are fossils evidence for evolution?
Fossils can tell us about change over time. Different fossils are found in different strata or materials, telling us that they happened over different time periods.
The problems of fossil evidence
Fossilization needs a specific set of conditions to occur. If things do not fossilize, we won’t have any record of them.
Incomplete or fragmented fossil records, which are inconsistent over different strata. Why do some strata have many fossils, while others have none?
If there is only one or two fossils found for a certain species, does it accurately represent the whole?
Analogous vs Homologous vs Vestigial
Analogous structures = Same use, different structures
Homologous structures = Similar structures, different uses
Vestigial structures = Present structures which have lost function
Embryology
Vertebrate embryos all start out very similar, then diverge in form. The longer similarities last between any two embryos, the more closely related the two organisms are.
In Darwin’s time, it was thought that embryonic development was a form of mini-evolution.
“Ontogeny Recapitulates Phylogeny” means that the development of an embryo imitates the evolution of that organism/species. In other words, each embryonic stage represents an evolutionary milestone in that organism, and imitates their ancestors.
If members of phyla evolved from a common ancestor, then their embryology should be similar
Biogeography
Similar environments cause similar selective pressures on species.
Biochemistry
Not available in Darwin’s time.
DNA analysis can be used to asses the similarities between species. For instance, humans and chimpanzees are 98% similar.
Hemoglobin analysis is another indicator. Human and chimp HB are identical; human and horse HB are an 80% match.
What is speciation?
The formation of a new species, which can evolve from a variety of different circumstances. Always includes the evolution of distinct features which isolate the species genetically and reproductively.
What is microevolution, and what does it look at?
Microevolution refers to changes in the gene pool of a population over time, which results in relatively small changes to the organisms in the population. These changes do not result in the new organisms being considered a separate species.
Microevolution mainly looks at the changes in gene/allele frequencies and phenotypic traits within a population and species. E.g., the frequency of a certain fur colour in a species over time.
Evolution at this scale may be observed over short periods of time; as short as between two generations: E.g., the frequency of a gene for pesticide resistance over two generations of crop pests
This type of change could come about through mutation, migration, natural selection, or genetic drift.
What is macroevolution, and what does it look at?
Macroevolution refers to changes which are significant enough that the newer organisms could, over time, be considered a new species.
Microevolution happens over very (comparatively) small scales of time. When microevolution changes build up over millions of years, they translate into macroevolution.
Macroevolution encompasses the grandest trends and transformations in a species, such as the origin of mammals.
Macro patterns are what we generally see when looking back at the large-scale history of life
All of the changes, diversifications, and extinctions that happened over the course of history are patterns of macroevolution.
What are the patterns of macroevolution?
Stasis, Character Change, Speciation, Extinction
What is stasis?
Many lineages exhibit stasis, meaning they don’t change for long periods of time.
Multiple have not changed for so long they are considered “living fossils”: E.g., Coelacanths are a species of fish which were thought to have been extinct for over 80 million years until they were found in 1938. This lineage therefore exhibits over 80 million years of morphological stasis
What is character change?
Single changes within a lineage that make this lineage unique from others.
Lineages can change quickly or slowly.
Character change can occur in a single direction, such as evolving additional segments, or it could reverse itself by gaining and losing segments.
What is speciation?
Patterns of lineage splitting can be examined and tracked through phylogeny
Phylogeny may reveal that a particular lineage has undergone unusually frequent speciation, unusually infrequent speciation, or a burst of speciation all at once.
What is extinction?
Extinction is extremely important
In can be frequent or rare within a lineage, or it can occur simultaneously across many lineages, known as mass extinction.
Every lineage has a chance of going extinct, with over 99% of all species across time being extinct.
What are the (5) mechanisms of change?
Mutation
Migration/gene flow
Genetic drift/finite population
Natural selection
Non-random mating
What is migration/gene flow?
Refers to the movement of alleles/genes between populations due to either the movement of individuals or their gametes
Organisms which migrate into a population may have new alleles or new proportions of existing alleles
What is genetic drift/finite population?
Random events which lead to changes in allele frequency
For instance, a random event which leads to only 100 survivors in a species, with 90 of them having a certain genotype. That genotype will now be the most prevalent among the species, even if it wasn’t before the event.
What is non-random mating?
In non-random mating, organisms may prefer to mate with others of the same genotype or of different genotypes. Non-random mating won’t make allele frequencies in the population change by itself, though it can alter genotype frequencies.
What is mutation?
Ultimate source of variation
- Rate of mutation in eukaryotes is 1
in 10000 DNA base pairs, on
average.
- Many mutations are neutral, but
others are not; these are the ones
subject to natural selection.
- Low rate of mutation = slower ability
of a species to adapt
- High rate of mutation = more
variability in the species, and faster
ability to adapt.
The isolating mechanisms are:
Geographic
- Behavioural
- Ecological
- Reproductive
(Two populations, isolated long enough from one another, and subject to Genetic Drift, will become separate species. This is Speciation.)
What are the three selection mechanisms? What do they each mean?
Stabilizing: keeps things the same; the
intermediate phenotype is most adaptive & selected for.
- Disruptive/Diversifying: Leads to change & speciation; intermediate is selected against, extremes are favoured.
- Directional: One extreme is more adaptive & selected for.
What is the founder effect?
One part of a population breaks off from the
main population & establishes a new group
elsewhere. For example:
- Some female deer follow a young male to a new
territory.
- Songbirds forced into new habitats
- Human Colonists
What is a genetic bottleneck?
Like founder effect, but after some extreme
environmental change
- Drastic reduction in population
- Limited genome left behind
Two types of speciation:
TRANSFORMATIVE – one species changes into a new one (a -> b)
DIVERGENT – one species splits into two (a ->b + c)
What are the prezygotic mechanisms of isolation?
Behavioural isolation
Different species using different courtship/mating clues to find and attract mates
Temporal isolation
Different species breeding at different times of year
Ecological isolation
Very similar species may occupy different habitats within a region
Mechanical isolation
Difference in morphological features which make two species incompatible
Physically different sex organs which cannot come together
Gametic isolation
Male gametes may not be able to recognize and fertilize an egg of a different species
More common in marine animals such as coral or clams, which release their sperm/eggs into open water. If the sperm cannot recognize the egg.
What are the postzygotic mechanisms of isolation?
Zygotic mortality
Mating and fertilization are possible, but there are two many genetic differences between the two species for a zygote to continue to develop
Hybrid inviability
A hybrid individual develops but either dies before birth or will not survive to maturity
Hybrid infertillity
Hybrid offspring remain healthy and viable, but are not fertile
What is allopatric speciation?
The formation of a new species as a result of geographic isolation
Once populations are physically separated, they can no longer exchange genetic information
Over many generations, the populations will become less alike
Different areas result in different forms of natural selection
This process is often very slow
What is sympatric speciation?
The formation of new species within the same population in the same geographic area
Polyploidy?
Polyploidy -> mutation which results in doubling of the number of chromosomes in an individual
What are the patterns of evolution?
Adaptive radiation
Divergent evolution
Convergent evolution
Coevolution
What is adaptive radiation?
Relatively rapid evolution of a single species into many new species, filling a variety of empty ecological niches
This occurs when a variety of new and plentiful resources become available
Darwin’s finches are a good example of this process
What is divergent evolution?
The large scale evolution of a group into many different forms
Results in the minimization of competition
What is convergent evolution?
The evolution of similar traits in distantly related species; ANALOGOUS traits
This usually occurs so similar ecological niches can be occupied
What is coevolution?
The process in which one species evolves in response to the evolution of another species
