VMBO Year 3 · Inheritance and evolution · Section 3.7

Evolutionary relationships

What fossils tell us about evolution

Fossils are preserved remains, impressions or traces of organisms from the past. They show that organisms have appeared, changed and become extinct over time. Together with other evidence, they support evolution. Evolution branches into many lineages; it is not a fixed ladder leading from simple to increasingly complex or better organisms.

Recognising relationships between species

Species sharing a common ancestor are related. Biologists investigate how closely they are related by comparing organ structure, cellular processes and molecules in cells, including DNA and proteins.

Similarities in organs

A human arm, a bird's wing and a walrus's flipper have a similar underlying arrangement of bones, despite different functions. These homologous structures are inherited from a common ancestor.

Vestigial structures

Some structures are reduced remnants of features that had a different or more prominent function in ancestors. Examples include pelvic or hind-limb remnants in whales and the human tailbone. Such vestigial structures can still have functions; they provide evidence about ancestry.

Same function, different structure

Similar functions do not always indicate a close evolutionary relationship. Butterfly wings and bat wings both enable flight but evolved independently as wings and have very different structures. They are analogous in their flight function. All life is related at some level; the point is that these wings do not show a recent shared origin of flight.

Similarities in cells

All organisms consist of cells. Many basic processes, including aspects of cell division and energy release, share important features. DNA and proteins can also be compared. Greater similarity in appropriate inherited features often points to a more recent common ancestor.

Evolutionary trees

Scientists use DNA and other evidence to construct evolutionary trees, diagrams of relationships. Two species are more closely related if their most recent common ancestor is more recent. The position of their names on a page does not itself establish relatedness; the branching pattern does.