genomes to ecosystems lecture 3- evolution and natural selection Flashcards
what is does pattern mean?
the change we see in the fossil record overtime. infer evolutionary relationships between different fossil organisms and their living descendants.
assumption that all organisms, extinct or extant are in some way related
what is the process?
natural selection and ecological opportunity.
eg ecological opportunity in the shallow equatorial tethys ocean, abundant marine food sources in the shallows
what is Mutationalism?
Species emerge in large jumps
Also ‘saltationism’
Hugo de Vries 1900
what is Orthogenesis?
Directional force driving evolution
Evolution is non-reticulate
Various proponents
what is Theistic evolution?
Divine creation
God generating beneficial mutations
Asa Grey and others
what is Scalae Naturae?
A solid march towards ‘perfection’
Slime moulds at the bottom, us at the top
what is catastrophism?
Series catastrophic events defines the fossil record
Georges Cuvier (1812)
what is Lamarckianism?
Individuals loose characters they don’t require
Acquired traits are heritable
JB Lamarck (1809)
what happens when Mendel meets Darwin?
Mendel studies inheritance of seven phenotypic traits
Developed two key ‘rules’ of inheritance 1) law of segregation (gametes), 2) law of independent assortment (prophase 1). Described genes as ‘factors’
Darwin posited that a portion of inter-individual variation must be heritable
Darwin developed ‘pangensisis’ theory of evolution involving ‘gemmules’ which were produced by all tissues. Pangenesis had a Lamarckian twist
what is Darwins big idea?
On the Origin of Species’ published 1859
Broad support among scientists (scientific naturalism)
Skepticism from the church and the establishment (natural theologists)
The result of 30 years of careful natural observation and synthesis
what is darwins theory in a nutshell on natural selection?
Individuals in a population vary significantly from one another and much of this variation is heritable
Individuals less suited to the environment are less likely to survive and less likely to reproduce; individuals more suited to the environment are more likely to survive and more likely to reproduce and leave their heritable traits to future generations, which produces the process of natural selection
This slowly effected process results in populations changing to adapt to their environments, and ultimately, these variations accumulate over time to form new species
why does population size stay the same?
Every species is fertile enough that if all offspring survived to reproduce, the population would grow
Despite periodic fluctuations, populations remain roughly the same size
Resources such as food are limited and are relatively stable over time
how does selection act on phenotype?
A hypothetical population of organisms
‘Trait’ is the phenotype under selection (e.g. tail length)
Variation in trait values might be normally distributed without selection
what is Selection type 1 – Stabilizing or ‘purifying’ selection (when the graph reaches a high peak in the centre)
Selection against extreme trait values
Phenotypic variation lost from population
Mean trait value stays the same
what is selection type 2- directional selection (when the value of a trait moves direction but the graph remains the same shape)
Mean trait value moves in response to the direction and intensity of the selection
what is Selection type 3 – Disruptive Selection (when the peaks are high on either sides but have a dip in the middle where it peaked previously)
Selection against mean trait
The result is a multimodel trait distribution
what is sexual selection?
Darwin noted that some characteristics in sexually dimorphic species could not readily be explained by natural selection.
what is intrasexual selection?
Intrasexual selection, or competition between members of the same sex (usually males) for access to mates (accepted immediately)
what is intersexual selection?
Intersexual selection, where members of one sex (usually females) choose members of the opposite sex (ridiculed for 80 years!)
how is heritability used to predict evolutionary change?
The essence of the modern synthesis is that selection due to environmental pressures can be propagated via heritability through evolutionary time
what is the breeders equation?
R = h2 x S The greater the heritability of a trait, the faster a species can respond to selective pressure
what does each letter stand for in the breeders equation?
R = the evolutionary response - change in phenotype between generations
h2 = selection differential - change in phenotype due to selection
S = heritability - transmissibility of phenotype
how is the h2 value calculated?
the heritability (h2) of any given trait is the ratio of the genetic variation to total phenotypic variation
h2 = VG / VP
Variability against the same genetic background = phenotyic plasticity
how do we use heritability to predict evolutionary change?
A way of directly measuring heritability is to look at how well trait values correlate between generations
strong heritability= a high gradient and weak= low gradient
