EVOLUTION

EVOLUTION

1. Evidence For Evolution

   • Evolution occurs when heritable characteristics of a species change
     • The fossil record provides evidence by revealing the features of an ancestor
       • Evidence For Evolution: Fossils
       • Fossil record is incomplete: Few organisms become fossils, only the hard parts of the organism are preserved and old assumptions are constantly challenged
   • Change over time linked to adaptation
   • Selective breeding: a form of artificial selection where man intervenes in the breading of a species
     • Example: Dogs and cows
     • Selective breeding provides evidence of evolution as targeted breeds can show significant variation in a short period
   • Comparative anatomy of groups of organisms may show certain structural features that are similar, implying common ancestry
     • Anatomical features that are similar in basic structure despite being used in different ways are called homologous structures
   • Speciation
     • If two populations of a species become geographically separated then they will likely experience different ecological conditions
       • Over time, the two populations will adapt to the different environmental conditions and gradually diverge from one another
         • The degree of divergence between geographically separated populations will gradually increase the longer they are separated
           • the two populations will diverge to an extent where they can no longer interbreed if returned to a shared environment: Speciation

2. Natural Selection

   • survival of the fittest
     • Inherited Variation: There is genetic variation within a population that can be inherited
       • Natural selection can only occur if there is variation among members of the same species
         • Mutations: Changing the genetic composition of gametes (germline mutation) leads to changed characteristics in offspring
         • Meiosis: Via either crossing over (prophase I) or independent assortment (metaphase I)
         • Sexual reproduction: The combination of genetic material from two distinct sources creates new gene combinations in offspring
     • Competition: There is a struggle for survival
       • species tend to produce more offspring than the environment can sustainably support
         • a stable population will inevitably outgrow its resource base, leading to competition for survival
           • any trait that is beneficial for competitive survival will be more likely to be passed on to offspring according to natural selection
     • Selection: Environmental pressures lead to differential reproduction within a population
     • Adaptations: Individuals with beneficial traits will be more likely to survive and pass these traits on to their offspring
       • Adaptations are features of organisms that aid their survival by allowing them to be better suited to their environment
         • Structural, Behavioural, Physiological, Biochemical or Developmental
       • Adaptive radiation describes the rapid evolutionary diversification of a single ancestral line
     • Evolution: Over time, there is a change in allele frequency within the population gene pool
     • Individuals that are better adapted tend to survive and produce more offspring while the less well adapted tend to die or produce fewer offspring

3. Classification of Biodiversity

   • The binomial system of nomenclature is the formal system by which all living species are classified (taxonomy)
     • It makes it easier to collect, sort and group information about organisms(taxonomy)
     • Genus is written first and is capitalised
       • Species follows and is written in lower case
         • Some species may occasionally have a sub-species designation
   • All organisms are classified into three domains
     • Eukarya:eukaryotic organisms that contain a membrane-bound nucleus
       • The principal taxa for classifying eukaryotes are kingdom, phylum, class, order, family, genus and species
     • Archaea: prokaryotic cells lacking a nucleus and consist of the extremophiles
     • Eubacteria: Prokaryotic cells lacking a nucleus and consist of the common pathogenic forms
   • Natural classifications help in identification of species and allow the prediction of characteristics shared by species within a group
     • Artificial classification involves arbitrarily selecting unifying characteristics first and then grouping organisms accordingly
     • Natural classification involves grouping organisms based on similarities first and then identifying shared characteristics
   • Kingdoms
     • Plantae
       • Bryophyta: Has no ‘true’ leaves, roots or stems (mosses and liverworts)
       • Filicinophyta: Have leaves, roots and stems. Reproduce by releasing spores from clusters called sori on the underside of the leaves Examples include ferns
       • Coniferophyta: Have leaves, roots and stems. Reproduce by non-motile gametes (seeds) which are found in cones Examples include pine trees and conifers
       • Angiospermophyta: Have leaves, roots and stems. Reproduce by seeds produced in ovules within flowers (seeds may develop in fruits) Examples include all flowering plants and grasses
     • Animalia
       • Invertebrates
         • porifera, cnidaria, platyhelmintha, annelida, mollusca and arthropoda
       • Vertebrates
         • All vertebrates belong to the phylum chordata

4. Cladistics

   • A clade is a group of organisms that have evolved from a common ancestor
     • Clades can be organized according to branching diagrams (cladograms) in order to show evolutionary relationships
   • Evidence for which species are part of a clade can be obtained from the base sequence of a gene or the corresponding amino acid sequence of a protein
     • Amino acid sequences are typically used to compare distantly related species, while DNA or RNA base sequences are often used to compare closely related organisms
   • Evidence from cladistics has shown that classification of some groups based on structure did not correspond with the evolutionary origins of a group or species