- Define and explain Classification and Phylogeny in your own words
- Use key terms such as species accurately
- Apply what you have learned to new examples and questions
- Avoid the common mistakes learners make with this topic
This lesson focuses on Classification and Phylogeny: use the taxonomic hierarchy and DNA data to build evolutionary trees.
Use the taxonomic hierarchy and DNA data to build evolutionary trees.
Key ideas
Speciation and classification
Speciation often begins with geographical isolation: a barrier splits a population so the groups cannot interbreed. Different mutations and selection pressures accumulate in each group until they can no longer produce fertile offspring together — they are separate species. Classification reflects these relationships: organisms are grouped into kingdom, phylum, class, order, family, genus and species, and modern phylogeny uses DNA evidence to build evolutionary trees showing who diverged from whom.
Natural selection
Natural selection needs four ingredients: variation within a population, competition for limited resources, survival of the best-adapted individuals (survival of the fittest), and inheritance of the advantageous alleles by offspring. Over generations, the advantageous allele becomes more common. Antibiotic resistance shows it in action: a rare resistant bacterium survives treatment, reproduces, and its descendants dominate the population.
Key term — species: A group of organisms that can interbreed to produce fertile offspring.
Describe how geographical isolation can lead to speciation.
A barrier (e.g. a river or mountain range) splits a population so the groups cannot interbreed. Different mutations and selection pressures build up in each group until they can no longer produce fertile offspring together, forming two species.
Answer: A barrier (e.g. a river or mountain range) splits a population so the groups cannot interbreed. Different mutations and selection pressures build up in each group until they can no longer produce fertile offspring together, forming two species.
- Treating 'theory' as a guess In science, a theory is a well-tested explanation supported by extensive evidence. Evolutionary theory is supported by fossils, anatomy, embryology and DNA.
- Saying organisms evolve because they need to Individuals do not choose to evolve. Mutations create variation randomly; selection then favours the variants that happen to survive and reproduce better.
Practice
Kingdom → phylum → class → order → family → genus → species.
Variation within the population → competition for resources → survival and reproduction of the best adapted → inheritance of advantageous alleles by offspring.
Antibiotics kill non-resistant bacteria, leaving resistant ones alive to reproduce. Their offspring inherit resistance, so the resistant allele spreads through the population.
Structures with the same basic bone arrangement but different functions, e.g. a human arm, bat wing and whale flipper. They suggest the species evolved from a common ancestor.
Quick check
Which of these best defines "species"?
Give two pieces of evidence for evolution besides fossils.
- Classification and Phylogeny: use the taxonomic hierarchy and DNA data to build evolutionary trees.
- Speciation and classification: Speciation often begins with geographical isolation: a barrier splits a population so the groups cannot interbreed.
- fossil: The preserved remains or traces of an organism that lived long ago, providing evidence of how life has changed.
- Watch out for: treating 'theory' as a guess