Lec 5 slides and reading Flashcards
why was argument of design incorrect
Before Darwin and Wallace, adaptations appeared to require a creator
There seemed no other way to account for the detail and perfection of many aspects of living organisms (just as the complexity of a watch could not be a purely natural production - argument from design)
Term adaptation used to describe the observation that living things have structures that are useful to them
Argument from design overlooks the possibility that there could be natural processes, in addition to those that produce minerals and rocks, etc, which can account for living creatures as complex natural productions, without the need for a designer
The biological explanation of the origin of adaptation replaces the idea of a designer and is central to post-Darwinian evolutionary biology
Artificial selection and heritable variation
The modification of organisms by humans is possible and can produce the same appearance of design that we see in nature
Achieved by artificial selection or selective breeding from animals and plants with desirable characteristics
Artificial selection is possible because heritable variation exists within populations and species
Individuals within domesticated species must have been different from each other, and many differences can be passed from parents to offspring (heritable)
Many characteristics of those individuals are affected by environmental circumstances and are influenced by heredity
kinds of heritable variation
Artificial selection is strong evidence that many kinds of character differences in animals and plants are heritable
Variation originates by processes of random mutation in the DNA sequences of genes, similar to those that produce human genetic disorders
Most mutations are deleterious but some are advantageous (disease resistance)
Heritable differences in humans controlled by differences in single genes and unaffected by environmental circumstances (e.g. colour blindness → genetic difference)
Behavioural characteristics can be heritable as well (e.g. whether fire ant colonies have single or multiple queens seems to be controlled by a polymorphism that affects recognition by ants of other individuals
Amount of genetic variability can be measured from resemblances between relatives of different degrees → useful in animal and crop plant breeding, allows breeders to predict characteristics like milk yield of cows
molecular polymorphism
→ some individuals in the pop. have a variant sequence of the gene, the difference will show up in some of the comparisons
Variation is generally higher in the less important regions of the genome that don’t code for proteins than in the coding parts of genes
Many natural species live in different, geographically separated populations and the amount of diversity in such species as a whole is greater than within a single population, because there are differences between populations
E.g. certain blood groups are more common in some human races than in others and same is true for other genetic variants
Increased mobility in the modern world is quickly reducing any differences between populations
natural selection and fitness
Fundamental idea in evolution theory is that some heritable character differences affect survival and reproduction
Our ability to modify plants and animals by artificial selection depends on the characteristic of having a heritable basis
Provided that there are heritable differences → successful individuals in the wild will pass their genes (and good traits) to their offspring, which will possess the adaptive traits (e.g. speed)
Many different aspects of organisms contribute to fitness (e.g. alertness, ability to attract pollinators)
changes in genetic variability
Given genetic variability for many characteristics and environmental differences, natural selection will inevitably operate and the genetic make-up of populations and species will change over time
Changes are slow in terms of years because it takes many generations for a genetic variant that is rare to become the majority type in pop.
Despite the slowness of evolutionary change in terms of years, natural selection can produce rapid changes on the timescale of the fossil record
Advantageous traits can spread throughout a population from a very low starting frequency in less time than that between successive layers in the geological strata
describe how natural selection never stops and how even humans are still evolving
For functions that are no longer used intensively, changes are expected and it could become vestigial
Individuals carrying genes that lower their survival or reproductive success will not pass on those genes
Variability and selection are very general properties of many systems, not just individual organisms
Certain parts of genetic material are maintained, not because they increase fitness but because they can multiply within genetic material itself, just like parasites in the body of their host
situation in which natural selection drives evolutionary change within an organism
Another important situation in which natural selection drives evolutionary change within an organism occurs in cancers
Cancer is a disease in which a cell and its descendants evolve and multiply, and cells can become resistant to drugs that suppress their growth
Caused by a mutation that increases the mutation rates of other genes
Different rates of extinction of species with different sets of characteristics
E.g. species with large body sizes, which tend to have low population sizes and low rates of reproduction, are more vulnerable to extinction than species with small bodies
Theory of evolution by natural selection explains…
features of organisms as a result of the successive accumulation of changes, each giving higher survival or reproductive success
how/why is evolution gradual
Radical changes can easily be produced by mutations → these major changes can disrupt normal development, reduce survival and fertility and won’t become favoured by natural selection
For this reason, we expect evolution to proceed by small adjustments
When new adaptations evolve, they will usually be modified versions of pre-existing structures, and will at first often not be the optimum function
true/false: Species that evolve to occupy an extremely specialized type of habitat are vulnerable to extinction if that habitat disappears due to environmental change
true
Example of a natural case of selection
Darwin’s finches differ in their beak size and shape, but due to drought, plants only produced large seeds and only the birds with large beaks survived and had high fitness → new evolved trait
stabilizing selection
Even in a constant environment, selection acts on every gen against mutant genes (that encode mutant proteins or ones that are expressed in the wrong place/time/amount)
New individuals with mutations arise in every generation, but non-mutants tend to leave more offspring and so their genes remain the most common, with the mutated versions remaining at low frequencies in the population
This is stabilizing selection
E.g. the gene that codes for one of the proteins involved in blood clotting, some changes to the sequence of the protein result in an inability of blood to clot following a cut (haemophilia)
