Describe the evidence for human evolution from fossils, stone tools and the pentadactyl limb, and how genetic analysis led to the three-domain classification rather than the five kingdoms.

What this dot point is asking

Edexcel statements 4.4 to 4.7 want you to describe the evidence for human evolution from fossils and stone tools, explain how the pentadactyl limb (4.6B is Biology only) gives evidence for evolution, and describe how genetic analysis led to the three-domain classification replacing the older five-kingdom system.

Fossil evidence for human evolution

Stone-tool evidence

The stone tools made by human ancestors also form a record. By dating the rock layers in which tools are found, scientists can put them in order. Over time the tools become more complex and more finely made, from simple sharpened stones to detailed cutting and hunting tools. This matches the fossil evidence of increasing brain size, supporting the idea that human ancestors became more intelligent and skilled as they evolved.

The pentadactyl limb (Biology only)

Although these limbs do very different jobs, a human arm for manipulation, a bat wing for flight, a whale flipper for swimming and a horse leg for running, they share the same underlying bone pattern. The most likely explanation is that all these animals inherited the limb from a common ancestor and then evolved modified versions for their own way of life. A shared structure used for different functions is strong evidence of common ancestry.

Classification: from five kingdoms to three domains

Organisms were once sorted into five kingdoms (animals, plants, fungi, protists and prokaryotes), based mainly on features you can see. As technology improved, scientists could compare the internal structures of cells and the sequences of molecules such as RNA. This genetic analysis revealed that the prokaryotes are really two very different groups.

So Carl Woese proposed the three domains:

• Archaea: primitive bacteria, often living in extreme conditions such as hot springs.
• Bacteria: the true bacteria found widely, including those that cause disease.
• Eukarya: all organisms with eukaryotic cells (animals, plants, fungi and protists).

This shows how new evidence (here, molecular and genetic data) can change a scientific classification.

Try this

Q1. State one feature that changed over time in human ancestors, shown by fossils. [1 mark]

• Cue. Brain size increased (or the skeleton became better adapted to walking upright).

Q2. Name the three domains of life. [1 mark]

• Cue. Archaea, Bacteria and Eukarya.