Practical Biology

A collection of experiments that demonstrate biological concepts and processes.

Mapping change over time


Scientific study of the Earth suggests that living things have changed over the long periods of time since the Earth was formed. The scientific evidence for change comes from careful observation and analysis of fossils in sedimentary rock, and observation and comparative studies of living things today – including behaviour, detailed anatomy, biochemistry, and DNA sequences. Observing change over short periods of time also allows for extrapolation to longer periods of time.

Lesson organisation

Over half a term, build a time line on the wall, adding one or two pieces of information in starters or plenary sessions each week. Discuss issues of scale (liaise with Maths department), as there is much more information about the last million years than the preceding 4500 million. Place pictures of organisms on the timeline, with information about scientific evidence for the position of the organism on the timeline.

Discuss the fact that all living things are considered successful if they survive in their environment, but that some organisms have not survived major changes in their habitats. List organisms that have become extinct for different reasons in the last two hundred years.

Ethical issues

In this procedure you are building a scientific view of how the world has changed over 4500 million years. Students may hold other views. Be sensitive to their concerns, but maintain a focus on scientific evidence. Discussion of the debate around evolution and creation is beyond the scope of this website.

Health & Safety and Technical notes


SAFETY: There are no health and safety issues with this practical.

a Devise a scale for your timeline, and place key time markers around the walls of the teaching room.

b For each organism placed on the timeline, describe the evidence for its form and its position on the timeline.

Teaching notes

Getting to grips with the timescale of change is one of the most difficult factors in understanding evolution by natural selection. It is particularly difficult to display timescales linearly. We have so much more evidence for recent events, including recent and extant lifeforms, than we have for more distant events and extinct lifeforms.

Most textbooks and many websites will have diagrammatic representations of the timescales involved. It might be interesting to compare and contrast these to see which style of presentation students find easiest to understand.

Evidence from the fossil record is patchy and often difficult to interpret. Current molecular biology analyses (of protein and DNA) are used as evidence of relationships within and between groups of living things. From this evidence of relationship, scientists can build a timeline indicating when ancestral groups diverged.

Health & Safety checked, August 2010