Unpredictable Evolution in a 30-Year Study of Darwin's Finches

  title={Unpredictable Evolution in a 30-Year Study of Darwin's Finches},
  author={Peter R. Grant and Barbara Rosemary Grant},
  pages={707 - 711}
Evolution can be predicted in the short term from a knowledge of selection and inheritance. However, in the long term evolution is unpredictable because environments, which determine the directions and magnitudes of selection coefficients, fluctuate unpredictably. These two features of evolution, the predictable and unpredictable, are demonstrated in a study of two populations of Darwin's finches on the Galápagos island of Daphne Major. From 1972 to 2001,Geospiza fortis (medium ground finch… 

Evolution in Darwin's finches: a review of a study on Isla Daphne Major in the Galápagos archipelago.

  • B. Grant
  • Environmental Science, Biology
  • 2003
This paper reviews research pertaining to the problem of speciation of the finches on the Galápagos archipelago and considers the nature of the reproductive barrier to gene flow between closely related species.

Evolution of Character Displacement in Darwin's Finches

It is reported that a Darwin's finch species on an undisturbed Galápagos island diverged in beak size from a competitor species 22 years after the competitor's arrival, when they jointly and severely depleted the food supply.

4000 Years of Phenotypic Change in an Island Bird: Heterogeneity of Selection Over Three Microevolutionary Timescales

Some of the first empirical evidence is provided for a scenario of divergence proposed for species colonizing a new environment, involving directional selection with a rapid shift to a new optimum and subsequent stabilization, using morphological data from three timescales in an island bird.

Fission and fusion of Darwin's finches populations

  • B. GrantP. Grant
  • Biology
    Philosophical Transactions of the Royal Society B: Biological Sciences
  • 2008
It is proposed that introgression has the largest effect on the evolution of interbreeding species after they have diverged in morphology, but before the point is reached when genetic incompatibilities incur a severe fitness cost.

Natural selection and the predictability of evolution in Timema stick insects

Study of the evolution of cryptic body coloration and pattern in a stick insect using 25 years of field data, experiments, and genomics found that evolution is more difficult to predict when it involves a balance between multiple selective factors and uncertainty in environmental conditions than when it involved feedback loops that cause consistent back-and-forth fluctuations.

Natural selection and age-related variation in morphology of a colonial bird

Unusual climatic events often lead to intense natural selection on organisms. Whether episodic selection events result in permanent microevolutionary changes or are reversed by opposing selection


A combination of introgressive hybridization and selection jointly provide the best explanation of convergence in morphology and genetic constitution under the changed ecological conditions following a major El Niño event in 1983.

Sisyphean evolution in Darwin's finches

It is argued that the six putative ground finch species of the Galápagos Islands represent a dramatic example of Sisyphean evolution that has been confused with the standard model of speciation, and the pattern of morphological, behavioural and genetic variation supports recognition of a single species of Geospiza, which is suggested should be recognized as Darwin's groundfinch.

Disruptive selection in a bimodal population of Darwin's finches

Analysis of patterns of selection in the medium ground finch of El Garrapatero, Santa Cruz Island, Galápagos suggests a dynamic tug of war among factors such as selection and assortative mating, which may alternatively promote or constrain divergence during adaptive radiation.

Reproductive isolation of sympatric morphs in a population of Darwin's finches

It is demonstrated that the two morphs show strong positive assortative pairing, a pattern that holds over three breeding seasons and during both dry and wet conditions, and provides strong support for the central role of ecology during the early stages of adaptive radiation.



Oscillating selection on Darwin's finches

A reversal in the direction of selection following the opposite climatic extreme is documented, and the connection between oscillating selection and fluctuations in food supply is demonstrated.

Recurrent patterns of natural selection in a population of Darwin's finches

It is shown that in two subsequent periods of moderate to high adult mortality (1980 and 1982), the population was subject to the same selection as before, and beak depth and body weight were commonly under direct selection to increase but, surprisingly, beak width was directly selected to decrease.


The demographic features that enable the finch species to persist in the face of extreme environmental stochasticity are a high maximum life-span, a generally high adult survival under the stressful conditions of drought, a flexible period of maturity, and a high reproductive rate.

Non–random fitness variation in two populations of Darwin's finches

  • P. GrantB. Grant
  • Biology
    Proceedings of the Royal Society of London. Series B: Biological Sciences
  • 2000
It is suggested that the most important determinant of fitness is the ability of an individual to survive to breed in many years, under fluctuating environmental conditions.

Hybridization of Darwin's Finches on Isla Daphne Major, Galapagos

The demonstration of natural hybridization shows that introgression of genes could be a small factor contributing to the interm ediate appearance of G. fortis on Daphne Major and raises questions about how species of Darwin’s finches should be defined and recognized.


  • P. GrantB. Grant
  • Biology
    Evolution; international journal of organic evolution
  • 1994
The Darwin's finch data suggest that these constraints become stronger when species with similar proportions hybridize, but some become weaker when the interbreeding species have different allometries, which facilitates evolutionary change in a new direction.


It appears that few genetically pure parental plants remain in the hybrid population and the average phenotype has shifted from an initial bias toward Helianthus bolanderi to a predominance of H. annuus‐like plants, suggesting that selection pressures in the two halves differ.

Selection often overrides the effects of random processes in island populations of Philaenus spumarius (Homoptera)

The influence of various evolutionary factors on the populations of the colour polymorphic meadow spittlebug, Philaenus spumarius, was investigated on islands in the Gulf of Finland, and it is highly probable that the factor operating is meadow-specific selection.

Warmer springs lead to mistimed reproduction in great tits (Parus major)

This work believes that this is the first documented case of an adaptive response being hampered because a changing abiotic factor affects the environment in which a reproductive decision is made differently from the environments in which selection occurs.

Strength and tempo of directional selection in the wild

Viability selection that was measured over short periods (days) was typically stronger than selection measured over longer periods (months and years), but the strength of sexual selection did not vary with duration of selection episodes; as a result, sexual selection was stronger than viability selection over longer time scales, but not over short time scales.