- Define and explain How Speciation Happens in your own words
- Use key terms such as speciation accurately
- Apply what you have learned to new examples and questions
- Avoid the common mistakes learners make with this topic
This lesson focuses on How Speciation Happens: show how isolation and selection split one species into two.
Show how isolation and selection split one species into two.
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 — speciation: The formation of a new species when populations become reproductively isolated and diverge.
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.
- 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.
- Claiming humans evolved from chimpanzees Humans and chimpanzees share a common ancestor that lived millions of years ago; neither is descended from the other.
Practice
Variation within the population → competition for resources → survival and reproduction of the best adapted → inheritance of advantageous alleles by offspring.
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.
Any two of: homologous structures; similar early embryos in vertebrates; DNA sequence comparisons showing closer relatives share more DNA.
Kingdom → phylum → class → order → family → genus → species.
Quick check
Which of these best defines "speciation"?
Explain why antibiotic-resistant bacteria become more common after antibiotic use.
- How Speciation Happens: show how isolation and selection split one species into two.
- Speciation and classification: Speciation often begins with geographical isolation: a barrier splits a population so the groups cannot interbreed.
- species: A group of organisms that can interbreed to produce fertile offspring.
- Watch out for: saying organisms evolve because they need to