Pseudogenes — non-functional, mutated copies of once-working genes — are found at identical genomic locations in humans and chimpanzees. What does this pattern most strongly indicate?
ABoth species independently evolved the same gene and then independently lost it, a coincidence explained by shared environmental pressures
BViruses regularly insert non-functional gene copies at random genomic locations in multiple species
CHumans and chimpanzees share a common ancestor in which the original functional gene was inactivated, and both lineages inherited the inactivated copy
DPseudogenes are structural regions that all mammals require for chromosomal stability, so they appear in the same locations across species
Shared pseudogenes at identical genomic locations are among the most compelling molecular evidence for common ancestry. The probability of the same gene being inactivated by the same mutation and inserted at the exact same chromosomal location twice, independently, is vanishingly small. The parsimonious explanation is that the gene was inactivated once in a shared ancestor, and both descendant lineages inherited the broken copy. This is the same logic as homologous structures: shared 'mistakes' inherited from a common ancestor are far better explained by descent than by independent design.
Question 2 Multiple Choice
Bird wings and bat wings both allow flight and look superficially similar. Which statement best describes their evolutionary relationship?
AThey are homologous structures — both descended from the same ancestral forelimb bones and evolved flight independently
BThey are analogous structures — they perform the same function but evolved flight independently from different structural starting points
CThey are homologous structures because they perform the same function, demonstrating shared ancestry for flight
DThey are analogous structures because bird and bat DNA shows low sequence similarity
This is a subtler case. Bird wings and bat wings ARE built from homologous bones (the same humerus, radius, ulna, carpals, etc. inherited from a shared tetrapod ancestor), but flight itself evolved independently — making the flight adaptation analogous (convergent), while the underlying skeletal structure is homologous. Contrast this with insect wings, which have a completely different structural origin (not derived from vertebrate forelimb bones) — those are both structurally and functionally analogous to bird wings. The question of homology vs. analogy must be evaluated separately for structure and function.
Question 3 True / False
Molecular phylogenies built solely from DNA sequence comparisons frequently contradict evolutionary trees built from fossils and anatomical features, demonstrating that different lines of evidence support different evolutionary histories.
TTrue
FFalse
Answer: False
The opposite is true — this is one of the most powerful aspects of the case for evolution. Molecular phylogenies built from DNA sequence data consistently match trees built from morphology and the fossil record, even though these methods use completely independent data. When entirely different lines of evidence converge on the same tree topology, it provides strong corroborating support. Cases where molecular and morphological trees initially disagreed have generally been resolved by identifying convergent evolution in morphology (e.g., whale morphology initially obscured their relationship to hippos, confirmed by molecular data and later fossil discoveries).
Question 4 True / False
The discovery of Tiktaalik — a transitional form between fish and tetrapods — in rock strata of exactly the age and location predicted by evolutionary theory is evidence that evolution makes testable predictions.
TTrue
FFalse
Answer: True
A key strength of evolutionary theory is that it makes specific, falsifiable predictions about what should be found in the fossil record. Paleontologists predicted that a fish-tetrapod transitional form should exist in Late Devonian rocks (~375 million years ago) and searched for it in arctic Canada where Devonian-age rocks were exposed. Finding Tiktaalik with exactly the expected features (limb-like fins, flexible neck, flat skull) in exactly the predicted rock age demonstrates that evolution functions as a predictive scientific theory, not merely a post-hoc narrative. Failing to find such forms, or finding them in the wrong rock layers, would have been evidence against the theory.
Question 5 Short Answer
Why is the convergence of multiple independent lines of evidence — fossils, comparative anatomy, molecular data, and direct observation — more compelling than any single line of evidence taken alone?
Think about your answer, then reveal below.
Model answer: Each line of evidence uses completely different methods and data, so they carry different potential sources of error. A single line could in principle be misleading due to artifacts of the method, sampling bias, or misinterpretation. But when independent methods — which could easily disagree with each other — all point to the same conclusion, the probability that all of them are systematically wrong in exactly the same direction becomes vanishingly small. The convergence is the signature of a true underlying pattern.
This is the logic of consilience. Fossils tell us about change over time; anatomy reveals structural relationships across living species; molecular data measures genetic similarity quantitatively; direct observation shows evolution happening in real time. Each could theoretically have been inconsistent with common descent. The fact that they all independently support the same evolutionary relationships — and the same tree of life — is far more powerful evidence than any single source could provide. Scientists would be very surprised if evolution were false yet all these independent methods produced consistent, mutually reinforcing results by coincidence.