In any one species1, there is a large amount of genetic variation2. The survival of a species is often linked with the extent of genetic variation within that species. This variation can be between individuals and between populations3. Population4 genetics5 can tell a story of population change. Population genetics is also the unit of evolution6.
Old Blue, the story of the black robin
New Zealand’s black robin is an amazing story of how a species on the brink of extinction, with one breeding pair left, has now recovered to approximately 250 individuals. All of these individuals are descended from one female called Old Blue.
The gene pool of these individuals tells a story of the species population dynamics.
Photo of Old Blue courtesy Don Merton, Department of Conservation, and photo of plaque courtesy of Katie Labarbera
Evolution by natural selection
Charles Darwin was a great observer. He voyaged around the globe observing the natural world. He noted that there was individual variation in populations, that offspring looked like their parents more than they looked like unrelated individuals of the same population and that, when there is overpopulation, there is competition.
He inferred from these observations that unequal reproductive7 success occurs – individuals with particular traits8 (and therefore genetics) are more likely to reproduce young that will themselves go on to reproduce and so on. He called this natural selection9 – or survival of the fittest (where fitness = reproductive success).
I have called this principle, by which each slight variation, if useful, is preserved, by the term of Natural Selection.
Charles Darwin
The evolution of populations can be explained by considering the changes in the traits of organisms over time from a process of natural selection.
Gene pools
Allele frequencies10 in the gene pool11 of a population change by natural selection and mutation12. When there is a small population, one-off chance events that impact a number of individuals can cause significant changes in allele13 frequencies. This is called genetic drift14.
A population will experience a genetic15 bottleneck when numbers become so low and the few surviving individuals only carry a proportion of the variation from the original gene16 pool. New Zealand populations of takahē17 and the Chatham Islands black robin have experienced a genetic bottleneck.
New genetic research using palaeogenetic techniques has shed new light on another iconic18 species – the takahē. It has not only uncovered the significant impact of humans and past climate change19 on the takahē but has also led to new theories on their evolutionary history.
ZEALANDIA resources for teachers and students
Urban ecosanctuary ZEALANDIA has produced a comprehensive set of teaching resources designed to support Biology Achievement Standard 91158. The interactive Planning pathways using takahē resources has links to the student task information and aquestion bank, and the article Takahē – a context for learning has ideas and links to other useful resources. Many of the materials can be used as stand-alone resources for learning about takahē biology20, evolutionary history, ecological niche, threats and conservation.
Nature of science
Observation is one of the most important skills of any scientist. Take the time to look closely at the world around you, take notice of how things interact and of any changes you observe both long and short term. Be curious about why these changes occur, experiment with ideas. This is science.
Related content
Learn more about the basic concepts of evolution.
Find out more about genotype and phenotype.
Find out about the bottleneck effect21 in little spotted kiwi.
Read about the famous rediscovery of takahē and the huge effort that has gone into boosting the takahē population in the article Takahē conservation efforts.
New technologies can extend our scientific understanding. They can also mean we have to throw out earlier ideas. Learn more about changing ideas, new technologies and insights in the evolutionary story of us.
Discover how genetics analysis helped inform our understanding about ferns in the article A tale of two ferns.
Useful links
Below are some more examples of how extreme changes in population size have impacted New Zealand endemic22 species:
- From the brink of extinction23 – find out more about the black robin.
- Kākāpō is another species that is critically endangered24. Its recovery combines the efforts of scientists, rangers, volunteers and donors. Find out more about the plan for kākāpō recovery and kākāpō gene sequencing.
- species: (Abbreviation sp. or spp.) A division used in the Linnean system of classification or taxonomy. A group of living organisms that can interbreed to produce viable offspring.
- genetic variation: Slightly different sequences in the genetic code of different individuals from the same species. This is important for species adaptation to occur.
- population: In biology, a population is a group of organisms of a species that live in the same place at a same time and that can interbreed.
- population: In biology, a population is a group of organisms of a species that live in the same place at a same time and that can interbreed.
- genetics: The study of heredity and variation in living organisms.
- evolution: In biology, the change in the genetic material and/or the behaviour of a population of organisms over time.
- reproductive system: The system in an organism that aids in the production of new individuals.
- trait: Characteristic, usually a physical characteristic of a living organism, such as the height of a plant or the hair colour of a mammal.
- natural selection: An evolutionary process where heritable traits that arise through mutation give an organism a higher chance of survival in their environment and become more common in a population as these organisms have a higher likelihood of reproducing.
- allele frequency: The percentage of a particular allele in a population.
- gene pool: The variety of genes in a population.
- mutation: Occurs when the DNA is damaged or changed in such a way that it alters the genetic message carried by that gene.
- allele: An alternative form of the same gene that occupies the same location on a chromosome.
- genetic drift: The chance disappearance of particular alleles in a population when individuals die or don't reproduce.
- genetic: Of, relating to, or determined by genes.
- genes: A segment of a DNA molecule that carries the information needed to make a specific protein. Genes determine the traits (phenotype) of the individual.
- takahē: A flightless bird indigenous to New Zealand New Zealand, also known as the South Island takahē (Porphyrio hochstetteri). It was thought to be extinct, but was rediscovered in Fiordland in 1948.
- icon: Representative symbol.
- climate change: The large-scale, long-term increase in the Earth’s average temperatures, with associated changes in weather patterns. There is significant scientific evidence that warming is due to increased quantities of greenhouse gases in the atmosphere, with most of the rise due to human activity.
- biology: The science of living things.
- bottleneck effect: An evolutionary pattern where the loss of a large proportion of the population, often due to a natural disaster, changes the allele frequencies and consequently the allele frequencies of future generations.
- endemic: Native to only one location. For example, species endemic to New Zealand naturally occur only in New Zealand but may have been introduced elsewhere in the world.
- extinction: In biology, the death of the last remaining individual of a species.
- critically endangered: Extremely high risk of extinction in the wild (International Union for Conservation of Nature ranking).
