4.4 - 4.5 - Evidence for human evolution
Use the dated fossils of Ardi, Lucy and Richard Leakey’s team, together with stone tools, to reconstruct evidence for human evolution. Distinguish what is observed from what can reasonably be inferred.
4.4 — Reading evolutionary evidence
Evolution is change in the inherited characteristics of populations over many generations. Evolution is ongoing, but the ancient human-lineage changes examined here happened long before anyone could observe them directly, so scientists reconstruct those changes from evidence left in fossils, rocks, artefacts and genes.
Fossil
A fossil is a preserved remnant or trace of an organism that lived in the past, such as a bone, tooth or footprint.
A piece of evidence becomes useful when an observation supports an inference. For example, the shape and arrangement of leg and pelvis bones can be observed in a fossil. Scientists can then use knowledge of joints and movement to infer whether that organism could walk upright.
The fossil record is incomplete because most organisms do not become fossils, some fossils are destroyed, and many have not been found. It also shows a branching family tree rather than a ladder in which one species inevitably turns into the next. The named fossils in this lesson are therefore dated snapshots of anatomical change; they are not proof that each individual was the direct ancestor of the next.
Both fossil and stone-tool evidence are studied at Foundation and Higher tier.
4.4 — Human evolution in three fossil snapshots
Human evolution can be investigated by placing fossils in time and comparing their anatomy. The important reasoning is not simply that an old skeleton exists; it is that particular structures reveal how an organism moved and how its body differed from older or more recent finds.
| Required fossil evidence | Anatomical observation | What the observation suggests |
|---|---|---|
| Ardi, 4.4 million years ago | Ardi was a partial skeleton of Ardipithecus ramidus. Her short, broad pelvis and other features support some bipedal walking, but her grasping big toe and limbs also retained adaptations for climbing. | Upright walking had begun to evolve while effective movement in trees was still important. Ardi did not walk exactly like a modern human. |
| Lucy, 3.2 million years ago | Lucy was a partial Australopithecus afarensis skeleton. Her pelvis, spine, knee and leg arrangement support regular upright walking. Her species still had a small braincase and climbing-related features such as relatively long arms and curved fingers. | Habitual bipedalism was established by this time, although the body still combined human-like and ape-like features. |
| Richard Leakey's team's fossils, 1.6 million years ago | The best-known example is the Homo erectus skeleton Turkana Boy, first spotted by Kamoya Kimeu during work by Richard Leakey's team. It had long legs, more human-like body proportions and a larger braincase than the much older examples. | The body was more fully suited to efficient upright travel, and the fossil record shows change in body proportions and brain size over time. |
Together, the fossils support a broad pattern: adaptations for regular bipedal movement became more human-like, and brain size generally increased. The evidence is a mosaic because different features changed at different rates. Ardi could combine a pelvis associated with bipedalism with a grasping big toe, while Lucy could walk upright but retained other climbing features.
Worked example: turning anatomy into evidence
Suppose a response says, "Ardi proves humans came from apes because she was old." This does not identify an anatomical observation or explain the inference. A stronger response is: "Ardi's short, broad pelvis suggests that she could walk on two legs, but her grasping big toe was suited to climbing. This mixture of features in a 4.4-million-year-old fossil supports gradual evolutionary change in the human lineage."
Continue this lesson.
You’re previewing NovaLearn without an account. Create a free account to read the rest.
Create free account