Why would a similarity in genes indicate a shared evolutionary history?

Explanation:

Homologous structures provide evidence for common ancestry, while analogous structures show that similar selective pressures can produce similar adaptations (beneficial features). Similarities and differences among biological molecules (e.g., in the DNA sequence of genes) can be used to determine species' relatedness.

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a: the sheep and waste material both release carbon into the atmosphere.

meteorologists would compare a new weather map with one 24 h old to see how fast a front is moving.