11C PP - The Human Fossil Record

Why is the human fossil record important?

The human fossil record provides evidence that allows scientists to make inferences about when hominins lived, how they moved and what they looked like. These conclusions are based on available evidence rather than direct observation.

Why is the human fossil record incomplete?

The fossil record is incomplete because:

• Not all organisms fossilise.

• Rock layers and fossils can erode over time.

• Some fossil-bearing rock layers have not been discovered or accessed.

How does an incomplete fossil record affect scientific conclusions?

Because the evidence is incomplete, interpretations can be challenged, refined or replaced when new evidence is discovered. Scientists may disagree about how fossils should be classified.

Why can human classification change over time?

New fossil discoveries and DNA evidence can lead scientists to re-evaluate evolutionary relationships and classification schemes

What does 'putative species' mean?

A putative species is a species that is generally accepted based on the evidence currently available, but may be revised if new evidence emerges.

Examples of recently identified Homo species

• Homo denisova

• Homo luzonensis

• Homo naledi

These classifications were inferred from fossil evidence and/or DNA evidence.

What evidence suggests humans and Neanderthals were related?

mtDNA comparisons indicate that Homo sapiens and Homo neanderthalensis were different species that shared a common ancestor about 400,000 years ago

What fossil evidence suggests interbreeding was possible?

Fossil evidence shows that H. sapiens and H. neanderthalensis lived in the same regions of Europe and Asia between about 40,000 and 100,000 years ago

What nuclear DNA evidence supports interbreeding with Neanderthals?

Between 1-4% of the genomes of non-African modern humans is identical to Neanderthal DNA.

This similarity is absent in sub-Saharan African populations.

What can be inferred from the 1-4% Neanderthal DNA in modern humans?

Interbreeding likely occurred after humans migrated out of Africa, probably in the Middle East.

What evidence suggests a second interbreeding event with Neanderthals?

100,000-year-old Neanderthal DNA from Siberia contained ancient human DNA not found in other Neanderthal populations.

This suggests another interbreeding event may have occurred

How were Denisovans discovered?

In 2010, bone fragments dating to about 40,000 years ago were discovered in Denisova Cave in Siberia

Why were Denisovans classified as a new species?

Nuclear DNA showed strong similarities to Neanderthals but enough differences to classify them as a separate species

How are Denisovans related to Neanderthals?

Both fossil and mtDNA evidence suggest Denisovans and Neanderthals are closely related species that diverged after the lineage leading to modern humans separated

What evidence suggests Denisovans interbred with modern humans?

Modern Melanesian populations share approximately 4-6% of their DNA with Denisovans, whereas other modern populations do not

When did Denisovan-human interbreeding likely occur?

The evidence suggests interbreeding occurred approximately 44,000 years ago in south-east Asia

What is an important lesson from the Denisovan evidence?

As more ancient DNA and fossils are discovered, our understanding of human evolution and gene flow continues to be re-evaluated.

How was Homo luzonensis discovered?

Between 2007 onwards, 13 bones were discovered in Callao Cave on Luzon in the Philippines, dating to about 67,000 years ago

Why was Homo luzonensis classified as a new species?

The fossils displayed a unique combination of features not seen in other species, including characteristics of both Homo sapiens and australopithecines.

What do Homo luzonensis fossils suggest about human evolution?

They show that human evolution is more complex than once thought and that new fossil discoveries can change classification schemes

How was Homo naledi discovered?

In 2013, fossils of an unknown hominin were discovered in a cave in South Africa

Why is Homo naledi significant?

The fossils showed a mixture of traits associated with both modern humans and Australopithecus

What interpretation has been suggested for Homo naledi?

Some scientists have proposed that Homo naledi may represent a transitional fossil between Australopithecus and Homo.

What is Homo floresiensis?

Homo floresiensis was a small-bodied hominin discovered on the Indonesian island of Flores in 2003 and nicknamed "the hobbit".

What is island dwarfism?

Island dwarfism is an evolutionary process where long-term isolation, limited resources and few predators favour smaller body size. This may explain the small size of Homo floresiensis.

Exam summary: What does the human fossil record show?

• The fossil record is incomplete.

• Human classification is continually revised.

• New fossil and DNA evidence can change evolutionary trees.

• Humans interbred with Neanderthals and Denisovans.

• Recently discovered species such as Homo denisova, Homo luzonensis and Homo naledi demonstrate that human evolution is complex and branching rather than linear.