Describe the lines of evidence for evolution (fossils, comparative anatomy, embryology and molecular/DNA evidence) and explain how each supports common ancestry (NYSSLS LS4, patterns; structure and function).

What this topic is asking

NYSSLS LS4 wants you to know the lines of evidence that show species have evolved from common ancestors, and to explain how each one supports that conclusion. On the Life Science: Biology Regents this often comes as a cluster using homologous structures (such as forelimbs) or molecular comparisons (echoing the Relationships and Biodiversity lab). The crosscutting concepts are patterns and structure and function.

The fossil record

Fossils show that the kinds of organisms on Earth have changed over time: older rock layers contain simpler or different forms, and newer layers contain forms more like modern species. Transitional fossils show intermediate features between older and newer groups, supporting the idea that one form gave rise to another. The fossil record is a direct record of change through time.

Comparative anatomy and homologous structures

This is a powerful pattern: there is no design reason for a swimming flipper and a flying wing to share the same bones, unless they were inherited from a shared ancestor and modified. Comparative anatomy thus points to common ancestry.

Embryology

The embryos of related species often look very similar in their early stages, even when the adults are very different. These shared early features suggest the species inherited a common developmental plan from a shared ancestor. Embryological similarity is another pattern consistent with common descent.

Molecular evidence

The strongest modern evidence is molecular. Because DNA codes for proteins and is inherited, the DNA and protein sequences of different species can be compared directly. The more similar two species' DNA or proteins are, the more recently they are likely to have shared a common ancestor. For example, species we judge to be closely related on other grounds also turn out to have very similar DNA. This is exactly what the Relationships and Biodiversity investigation explores, comparing structural and molecular features to infer relatedness.

Putting the evidence together

No single line of evidence stands alone; their strength is that they agree. Fossils, anatomy, embryology and molecules independently point to the same family tree of life, with species linked by common ancestry (developed further in common ancestry and phylogeny). When the exam asks for evidence, give a line and explain how it supports a shared ancestor.

Try this

Q1. Define a homologous structure and give an example. [2]

• Cue. A body part with the same basic plan but a different function in different species; for example the forelimb of a human, whale and bat.

Q2. Explain why similar DNA between two species is evidence that they are closely related. [2]

• Cue. DNA is inherited; the more similar two species' DNA, the more recently they likely shared a common ancestor, so molecular similarity indicates relatedness.