Definition
Evolution - cumulative change in the heritable characteristics of a population.
Evidence for evolution
Fossilization
Petrification - organic matter of the dead organism is replaced by mineral ions
Mould - organic matter decays, but the space left becomes a mould, filled by mineral matter
Trace - an impression of a form, such as a leaf or a footprint, made in layers that then harden
Preservation - of the intact whole organism; for example, in amber (resin exuded from a conifer, which then solidified) or in anaerobic, acidic peat
Fossilization is rare because predators, scavengers and bacterial action normally break down dead plant and animal structures before they can be fossilized. Some are destroyed by weathering and other factors.
If a fossil is found though, or rocks around it, Carbon-14 and Potassium-Argon dating may be used to relatively determine the age of the fossil.
Artificial selection
Involves identifying the largest, the best or the most useful of the progeny for the intended purpose, and using them as the next generation of parents. The continuous culling out of progeny deficient in the desired features, generation by generation, leads to deliberate genetic change in the population
Comparative anatomy
Show that although adapted to different habitats or life styles, often their underlying organization is similar (homologous structures). They share a common ancestor and adaptive radiation. On the otherhand, fundamentally different structures have similar functions show only superficial resemblances - called analogous structures.
Populations and offspring
Populations tend to produce more offspring that the environment can support.
Consequences of potential overproduction of offspring
Population size is naturally limited by restraints we call environmental factors.
Factors - space, light, availability of food; never-ending competition for resources results in the majority of organisms failing to survive and reproduce, so environment can only support a certain number of organisms.
Variations
Members of a species show variation.
Sexual reproduction and variation
Random assortment of paternal and maternal chromosomes in meiosis (process of gamete formation).
Crossing over of segments of individual maternal and paternal homologous chromosomes (new ombinations of genes on chromosomes of haploid gametes)
Random fusion of male and female gametes in sexual reproduction.
How natural selection leads to evolution
Theory of natural selection put out by Charles Darwin - survival of the fittest.
Genetic variation within population (must be inherited).
Competition for survival (populations tend to produce more offspring than the environment can support).
Organisms with beneficial adaptions will be more suited to their environment and more likely to survive to reproduce and pass on their genes.
Over generations there will be a change in allele frequency within a population (evolution).
Evolution in response to environmental change
1) Multiple antibiotic resistances in bacteria
In a large population of a species of bacteria, some may carry gene for resistance to the antibiotic in question; sometimes it is spontaneous mutation; sometimes it is sexually reproduced between bacteria of different populations.
However, in absence of antibiotic, antibiotic resistance bacteria have no selective advantage as they need to still compete for resources with non-resistant bacteria.
Resistant bacteria give rise to future progeny which are all resistant.
2) Heavy metal tolerance in plants
In mining sites, heavy metals such as zinc, copper, lead, and nickel are present as ions dissolved in soil moisture at concentrations that generate toxic conditions for plants normally present on surrounding unpolluted soils. However, an organism such as Agrostis tenuis (bent grass) may be tolerant of toxic concentrations of copper. They have developed a selective ability to avoid uptake of heavy metal ions; accumulation of ions that enter in insoluble compounds in cell walls by formation of stable complexes with wall polysaccharides; transport of toxic ions into the vacuoles of cells, membranes of which are unable to pump them out again, so avoiding interaction with cell enzymes.
In a large population of a species of bacteria, some may carry gene for resistance to the antibiotic in question; sometimes it is spontaneous mutation; sometimes it is sexually reproduced between bacteria of different populations.
However, in absence of antibiotic, antibiotic resistance bacteria have no selective advantage as they need to still compete for resources with non-resistant bacteria.
Resistant bacteria give rise to future progeny which are all resistant.
2) Heavy metal tolerance in plants
In mining sites, heavy metals such as zinc, copper, lead, and nickel are present as ions dissolved in soil moisture at concentrations that generate toxic conditions for plants normally present on surrounding unpolluted soils. However, an organism such as Agrostis tenuis (bent grass) may be tolerant of toxic concentrations of copper. They have developed a selective ability to avoid uptake of heavy metal ions; accumulation of ions that enter in insoluble compounds in cell walls by formation of stable complexes with wall polysaccharides; transport of toxic ions into the vacuoles of cells, membranes of which are unable to pump them out again, so avoiding interaction with cell enzymes.
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