Biology Chapter on Natural Selection and Speciation

Natural Selection

• Natural selection is the process where organisms better adapted to their environment tend to survive and produce more offspring.
• This leads to changes in the genetic makeup of a population over time.
• Key components of natural selection include variation within a population, inheritance of traits, differential survival and reproduction, and adaptation over time.
• Environmental pressures drive natural selection, selecting for traits that enhance survival and reproduction.
• Organisms with advantageous traits are more likely to pass those traits to their offspring.
• Over many generations, these advantageous traits become more common within the population, resulting in adaptation to the environment.

Speciation

• Speciation is the evolutionary process by which new biological species arise.
• It involves the splitting of one ancestral species into two or more descendant species.
• Speciation can occur through various mechanisms, including allopatric speciation (geographic isolation), sympatric speciation (speciation within the same geographic area) and parapatric speciation which occurs between populations with some gene flow but separated by an environmental gradient.
• Reproductive isolation is a crucial component of speciation, preventing gene flow between newly formed species. This can result from behavioural, geographical, temporal, or genetic differences.
• Reproductive isolation mechanisms ensure that species remain distinct and prevent interbreeding.

Mutation and Genetic Drift

• Mutations are random changes in the DNA sequence.
• These changes can be beneficial, harmful, or neutral.
• Mutations introduce new genetic variation into a population, providing raw material for natural selection to act upon.
• Genetic drift is a random change in the frequency of alleles in a population, particularly pronounced in small populations.
• It can cause the loss of rare alleles from a population, or the fixation of other alleles.
• Genetic drift has a bigger influence on smaller populations than larger ones. Random events can significantly alter allele frequencies in a small population over time.

Evidence of Evolution

• Fossil records provide a chronological sequence of life forms, illustrating lineages and extinctions.
• Similar anatomical structures (homologous structures), both in their presence and their variations, suggest common ancestry between species.
• Comparative embryology reveals similarities in embryonic development across various species across a variety of lineages.
• Molecular biology demonstrates the genetic similarities between organisms. Matching up the DNA and proteins of different species reveals evolutionary relationships.

Evolutionary Trees

• Evolutionary trees (phylogenetic trees) visually represent the evolutionary relationships among species.
• They depict branching patterns, showing how lineages diverge over time.
• Nodes on the tree represent common ancestors.
• Branch lengths often represent the time elapsed since divergence, although this is not always a direct correlation.
• Evolutionary trees are constructed based on shared characteristics and genetic similarities. They provide a framework for understanding the history of life on Earth.
• Modern evolutionary trees utilize molecular data to more accurately portray the evolutionary pathways and relationships among organisms.