- Define and explain Evidence for Evolution in your own words
- Use key terms such as fossil accurately
- Apply what you have learned to new examples and questions
- Avoid the common mistakes learners make with this topic
This lesson focuses on Evidence for Evolution: weigh the fossil, anatomical, embryological and DNA evidence for common ancestry.
Weigh the fossil, anatomical, embryological and DNA evidence for common ancestry.
Key ideas
Evidence for evolution
Fossils show transitional forms, such as Archaeopteryx with both reptile and bird features. Homologous structures reveal common ancestry beneath different functions. Embryos of different vertebrates look strikingly similar in early stages. Most powerfully, DNA comparisons show that closely related species share more of their genetic code — humans and chimpanzees share the vast majority of their DNA, exactly as common ancestry predicts.
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.
Key term — fossil: The preserved remains or traces of an organism that lived long ago, providing evidence of how life has changed.
Give two pieces of evidence for evolution besides fossils.
Any two of: homologous structures; similar early embryos in vertebrates; DNA sequence comparisons showing closer relatives share more DNA.
Answer: Any two of: homologous structures; similar early embryos in vertebrates; DNA sequence comparisons showing closer relatives share more DNA.
- 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.
- 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
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.
Variation within the population → competition for resources → survival and reproduction of the best adapted → inheritance of advantageous alleles by offspring.
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.
Quick check
Which of these best defines "fossil"?
Put these taxonomic groups in order from largest to smallest: genus, kingdom, species, class, phylum, family, order.
- Evidence for Evolution: weigh the fossil, anatomical, embryological and DNA evidence for common ancestry.
- Evidence for evolution: Fossils show transitional forms, such as Archaeopteryx with both reptile and bird features.
- homologous structures: Body parts with the same basic structure but different functions, such as a human arm and a whale flipper, indicating common ancestry.
- Watch out for: treating 'theory' as a guess