Natural selection Flashcards
Adaptation.
Example of adaptation?
Function of a trait that has been evolved by natural selection
Example of White and black pepper moths- white ones died out post-industrial revolution since soot covering some meant ‘black’ ones were better camouflaged against trees
Evolution as improvement. Think of the Scala Naturae- true or false?
False. Evolution just means change.
The Great Chain of being is now known to be incorrect, we are not above all of the rest of the animal kingdom. Evolution is branch not a chain
Thomas Huxley- what did he do?
with Alfred Russel came up with the first plausible mechanism of evolution, Darwin not actually first to propose the idea
Darwin’s theory in short
In ‘Origin of Species’- He believed evolution happened in humans too. Drew a powerful analogy in the paper between artificial selection (I.e. for breeding animals with favourable characteristics) and natural selection (both select for traits).
In essence ‘multiple, vary, let strongest live and the weakest die’
4 core principles of E by NS
Heritability- genes must be transmitted within a species. Darwin needed to overcome issue of ‘blended inheritance’ idea (he didnt know about genes - which dont blend). Traits that are adaptive would be lost if blended inheritance were true
Variability- individuals of species must differ- it gives something for natural selection to act on. Variability must be vertical transmitted (from one generation to next). Lamarkianism is incorrect
Surplus offspring- more offspring produced than can be supported by environment (many die off)
Non-random survival and reproduction- 9remember blind watch makers idea - complexity in environment like a watch face, can’t have arisen by chance. So survival & reproduction are not random- individuals with traits better suited to current environment on average more likely to survive and produce viable offspring.
Mutations which are adaptive are not random- they will continue to be transmitted
Lamarkianism proposes what?
Inheritance of acquired characteristics - but this is incorrect as only genes can be inherited
Vertical transmission
Genetic transmission from one generation to the next
Blending inheritance
The discredited theory that inheritance of traits from two parents produces offspring with characteristics that are intermediate (blended) between those of the parents. as opposed to dominant traits inherited)
The Four Fs
Fighting, feeding, fleeing, reproduction (fornication)
Absolute and relative fitness
Fitness is the differential survival and reproduction of individuals of a species
Absolute- total number of gene copies transmitted to the next subsequent generation or the total number of viable, surviving offspring they produce in their lifetime.
Relative-
survival rate of a genotype/phenotype relative to the maximum of another (how well you do compared with others)
2 types of genetic drift
mechanism of evolution in which allele frequencies of a population change over generations due to chance. May result in the loss of some beneficial alleles or rise of others
Population bottlenecks- drastic reduction in size of population. May be due to environmental facors, hunting to point of extinction, loss of habitat
Founder effect-
reduced genetic diveristy which results when a population is descended from a small number of colonising ancestors. Often they are non-adaptive characteristics i.e. Amish people have an extra finger/toes (due to their colonising founder having an extra toe/finger)
2 levels of explanation for causation
Proximate- the immediate, closest circumstances for causing an event
Ultimate- higher level distal, deeper cause. Refers to evolutionary levels of explanation, often thought to be the real cause
Timbergen’s 4 WHYs- explain them a bit more
Ultimate causation-
Function (fitness value of trait, evolution (phylogeny- evolutionary history of a trait)
Proximate causation- development (ontogeny-traits variation through development), causation (mechanism)- immediate circumstance affecting a trait i.e. stimuli elicit a response, neurology)
Explain Mendelian inheritance
Gregor Mendel showed how genes are inherited without blending (which Darwin could not understand). By studying the cross-breeding of pea plants (focusing on simple variants i.e green/yellow, smooth/wrinkled), he found discrete ‘particles’ now known as genes that are passed down and express a characteristic
What’s Neodarwinism, a different name for it
The Modern Synthesis- Fusion of Darwinian evolution by natural selection and mendelian inheritance. But with the addition that populations change not individuals
Dominance, recessive, genotype, phenotype
dominance- some versions of genes (alleles) can mask the expression of others
Recessive- trait won’t be expressed when paired with a dominant allele
Phenotype- observable traits (expressed)
Genotype- genetic basis for traits
Law of segregation (Mendel’s 1st law)
Every individual has 2 versions of the ‘particles’ (gene) for a trait. Pairs of these particles separate (segregate) and get passed into different sex cells (gametes). They are then united with another particle after fertilisation to form a zygote.
In other words, one one of a pair of alleles is passed on to each of the offspring. Genes for different characteristics are passed on individually rather than being attached to each other (they are segregated)
Law of independent assortment (Mendel’s 2nd law)
particles for different traits assorted independently (different genes are not connected). Phenotypic features occuring in adults will not necessarily appear together in the offspring
Difference between homozygous, heterezygous
Homozygous- two of the same alleles for a gene (pp, PP)
Heterozygous- have one of each of two alleles (Pp)
Polygenic
More than one gene controls a trait
Chromosome theory- gametes, alleles
Genes from each parent jointly determine traits. Genes carried on chromosomes. Gametes carry single copies of parental chromosom. When gametes formed, variants of genes equally likely to be transferred.
An allele is a variant form of a gene
Chromosome theory- gametes, alleles
Genes from each parent jointly determine traits. Genes carried on chromosomes. Gametes carry single copies of parental chromosom. When gametes formed, variants of genes equally likely to be transferred.
An allele is a variant form of a gene
A gene occupies a unique position on chromosome (locus)
DNA chemical basis of inheritance
DNA is where genes are carried. A gene is a segment of DNA- which specifies the sequence (code) of amino acids to make proteins via messenger RNA.
Only 2% of your DNA actually codes for proteins, the rest is ‘junk’ non-elements. These may be helping regulate other genes’ expression
Epigenetics
non-genetic change that can aid gene expression (the non-coding bunch
Gene studies can be done by what methods?
Genetic manipulation, gene sequencing, gene expression,
Twin studies-
monozygotic (identical) twins- from a single fertilised egg so share 100% of genes
dizygotic (non-identical)- twins coem from 2 different eggs and 2 different sperm so share same amount of genes as a brother/sister
How is evolution termed by a population geneticist?
Changes in allele frequency over time
Explain what homologies and analogies are
Homologies (similar by design) - the same /similar traits in animals, derived from a common ancestor
Analogies (similar by decent)- structures in different species which perform the same function, have similar appearance and structure but are not evolved together; therefore do not share a common ancestor
i.e. wings of a bird, moth, butterfly
Explain what vestigial traits are and some examples.
Examples of behavioural vestigial traits?
characteristics that have lost their function i.e. appendix, tonsils, sinuses, wisdom teeth, tail bone
Behavioural vestigial traits- arachnophobia, trynophobia (fear of holes, ethan)
What does exaptations mean
shift in the function of a trait from one things to another i.e. bird feathers initially for temp control then later became useful for flight
What does maladaptions mean
adaptation of a trait specific to your environment (but not necessarily for adaptive reasons, more comfort) i.e. preference for sweet sugary things in humans
What is meant by developmental by products
no adaptive requirement for the trait in an animal i.e. men have nipples, hyenas clitoris looks like a penis
What’s phylogenetic inertia
adaptation can only evolve within a species to a certain degree i.e. cant get a gigantic flying insect
Expand on the misunderstandings of: inevitability, Hume’s Is/Ought law, evolution for good of the species?
Inevitability- the complexity of traits combined with certain traits are not destines, but if we go back in time evolutionary traits could have panned out differently.
Hume’s Is/Ought law- normative (is) does not always follow the descriptive (ought)
Does evolution/our genes determine our fate?
genes, evolution and our nature do NOT determine our fate
The non-debate between ?
our genes AND environment play influence on every trait we possess (a false dichotomy to consider them as divided)
What is social spencerism?
Herbert Spencer coined the term ‘survival of the fittest’. He believed Darwinian principles could be applied to human society i.e. justifies application to economic/political systems
What’s meant by Eugenics?
breeding for certain traits and breeding out of undesired traits for the good of your species - moral imperatives based on genetics (i.e. think of Nazi germany and the ideal Aryan race)
What is the naturalistic fallacy?
goodness (morality) cannot be reduced to natural properties i.e. desires, pleasures
(tendency to believe that what is natural is good)
