Evolution & Genetics Flashcards
1
Q
Theory of evolution
A
- Charles Darwin & Alfred Russel Wallace
- The central idea of biological evolution is that all life on Earth shares a common ancestor. It does not mean we have evolved from apes, but more that humans and great apes share a common ancestor.
- Organisms are (successful) adaptations of previous generations – Natural Selection
2
Q
Requirements for the evolution of populations
A
- Principle of inheritance
- Physicial or behavioural traits that we can provide to the next generation → heritability
- Principle of variation
- Individuals within a species show variation in their traits e.g. hair colour, chronotype/diurnal preference
- Principle of adaptation
- Some versions of traits are more adaptive than others e.g. lack of blondes around the equator as being brunette has an advantage because it protects your head from sunburn
- Principle of evolution
- As a consequence of being better adapted to an environment, some individuals will survive and produce more offspring, who will inherit the same advantages. This is called ‘fitness’ (natural selection).
3
Q
Adaptation to the environment
A
- Stabilising selection: the individuals with the middle expression of a variation are favourite in terms of adaptation to the environment - stabilisation of the population
- Directional selection: one end of the distribution is particularly well adapted. e.g. polar fox evolve because they were adapted to white snowy environment
- Diversifying selection: the population is split in two different populations which will eventually lead to new species → the current theory of human evolution states that humans have evolved from the diversifying selection of a common ancestor whereby geographical changes in Africa led to the differentiation of environments between West Africa (rainforest environment) and East Africa (savannah, dry environment). Apes continued as normal in West Africa whilst in East Africa, upright walking position was beneficial to the dry environment.
4
Q
Natural selection & reproduction
A
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Individual selection
- Animals behave to maximize the number of copies of their genes left in the next generation by reproduction → Individual self-reproduction
- E.g. male peacock has bright blue wings for sexual selection, to attract females
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Kin selection
- Reduce the reproductive success of an individual to increase the success of a relative because you share more common genes
- e.g. in a beehive, the queen bee is in charge of reproducing the genes of the entire population so all the other bees help the queen to reproduce herself
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Reciprocal altruism
- An organism acts in a manner that temporarily reduces its fitness while increasing another organism’s fitness, with the expectation that the other organism will act in a similar manner at a later time → synergistic behaviours
- E.g. monkeys grooming each other with the expectations that other monkeys will return the favour
5
Q
Evidence in support of the theory of evolution
A
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Biogeography: Distribution of organisms on Earth; evolution of unique species on islands e.g. koalas in Australia
- Evolution has been observed in progress. For example an 18-month drought on one of the Galapagos Islands left only large, difficult to eat seeds and increased the beak size in one species of finch (=bird).
- Fossils: selection in various forms in progress e.g. reptiles and bird fossiles have shown they have evolved from a common ancestor, fossils in West and East Africa have provided evidence for evolution from a common ancestor with the great apes
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Structural similarity: two types of structure
- Homologous structures are those organs whose underlying similarity arises from their being derived from a common ancestral structure. For example, the wing of a bird and the forelimb of a human are homologous.
- Analogous structures are those whose similarity comes from their performing a similar function, rather than their arising from a common ancestor. Therefore, for example, the wing of a butterfly and the wing of a bird are analogous. → evolution’s way to solve the same problem in different ways - diverisfying selection
- Embryology: embyos of different species roughly at the same developmental stage, we can see they all have similar organs e.g. even human embryos have tails
- Molecular biology: At the most basic level, all living organisms share: a genetic code, genetic material - DNA; basic process of gene expression (transcription and translation); the same molecular building blocks, such as amino acids → homologous structure serving different functions with the same build-up
- Human genome project: If evolution is true then we might also expect that closely related organisms will be more similar to one another than more distantly related organisms → evidence of common ancestor
6
Q
Characteristics of human evolution
A
- Evolution is a slow process
- Evolution has no ‘aim’ nor is any part of it a pinnacle.
- Not all existing behaviours or structures are adaptive
- Spandrels—phenotypic characteristic that is a byproduct of the evolution of some other characteristic, rather than a direct product of adaptive selection (e.g., human chin, redness of blood have no adaptive purpose)
- outdated adaptations to previous environments (e.g., humans used to be endurance running but no longer need to be, which explains why we still have the ability to do so →ironman competitors. Bramble & Liebermann, 2004 found an African tribe that still uses endurance running as their main method of hunting)
- Evolution is gradual vs punctuated equilibrium (=what we see and observe, not to be confused with pinnacle)
- Social Psychology: ‘maladaptive’ behaviours (e.g. psychopathy, aggression, jealousy, rape)
- Evolutionary Psychology : potential adaptive benefits? e.g. obesity can be explained by ancestors having a beneficial survival advantage if they had the capacity to eat more when food was available, as food was not always available as it is now
7
Q
Evolution of the brain
A
- Roth & Dicke, 2005:
- Homo brain is proportionally much bigger to other species, relative to its body weight
- Homo neanderthalensis is the only species with a bigger brain:body weight ratio than homo sapiens
8
Q
Behaviourism
A
- Skinner & Watson, 1950s
- All behaviour is the product of learning (nurture)
9
Q
Ethology
A
- The study of animal behavior in the wild instinctive (nature) behaviours
- Originated in Germany in the 1950s
10
Q
Nature vs nurture debate
A
- Many factors other than genetics (nature) or learning (nurture) have an impact on behaviour
- “Nurture” now encompasses learning and environment
- Generally accepted that behavior is a product of nature and nurture
- Ill-posed question: how much is determined by each
- Genetic and experiential factors do not merely combine in an additive fashion → interactionism
11
Q
Genes and evolution
A
12
Q
DNA molecules
A
- Forms the genotype of an organism
- Information bank found within the nucleus of every cell
- Every time an organism grows a new cell a new copy of the DNA is created
- It is important that every copy of the DNA is identical, since any errors copying the genotype may prevent the cell from functioning properly.
- In 1953, Watson and Crick figured out that DNA had a double-helix structure and showed how it copies itself with such amazing accuracy.
- When DNA replicates, the helix unwinds and each strand produces an exact mirror image copy of itself. This ensures that each copy is identical to the original.
- DNA segments = genes
- Segments are organised in different base pairs
- 3 segments code for a gene
- DNA exists in form of chromosomes
- DNA is copied/replicated from one generation to the next (almost) errorless
- In evolution, the emphasis is on almost
13
Q
Chromosome
A
Thread-like strand of DNA that contains the genetic code
14
Q
Genotype
A
The genetic constitution of an individual organism
15
Q
Human chromosomes
A
- 23 chromosome pairs
- 22 identical pairs
- 1 different pair: sex chromosomes
- Female: homogametic sex (XX)
- Male: heterogametic (XY)
- Each chromosome carries genes
- Each inherited factor is a (combination of) gene(s)
- Genes occur in pairs
- Genes that control the same trait are called alleles
- Homozygous – 2 identical alleles
- Heterozygous – 2 different alleles
- dominant alleles/traits and recessive alleles/traits
17
Q
Selective breeding of “maze-bright” and “maze-dull” rats study
A
- Cooper & Zubek, 1958
- Two groups of rats that were separated based on their performance in a standardized maze problem.
- Those that performed best were bred with each other, as were those that performed most poorly.
- Over relatively few generations, there was a complete separation in performance, with none of the maze-bright rats overlapping in scores with maze-dull rats.
- However, the selective breeding appeared to be specific to the maze tests that were used and did not affect learning ability more generally; moreover, maze-dull rats reared in an enriched environment could perform as well as maze-bright rats.
- Highlights the importance of the interaction between the environment and the genes
18
Q
Minnesota twin study
A
- Shields, 1962
- Study of monozygotic MZ (identical i.e. exact same DNA) and dizygotic DZ twins (not identical - different DNA)
- Minnesota study of twins reared apart showed that identical twins are more similar to each other than fraternal twins on all psychological dimensions
- Correlations of the IQ’s of identical twins whether raised together or apart is larger than that of
fraternal twins raised together - Critique:
- Multiplier effect – genetically similar individuals seek out similar environments. Twins when reared apart will typically be given to parents from upper-middle class, so similar environments. → environment effect is underestimated
- Turkheimer et al. (2003) showed that the heritability of IQ was near 0 in impoverished twins and near 1 (maximum) in affuent twins ⇒ effect cannot be generalised to populations from dissimilar environments
