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Genetic variations accumulating within populations over generations give rise to biological evolution. Evolutionary changes can result in the formation of novel varieties and entire new species. These changes are responsible for the diverse forms of life inhabiting the planet. The evidence for evolution suggests that all living organisms descended from common ancestors.
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While every living organism has a genome of some kind (be it RNA, or DNA), there is considerable variation in the sizes of these blueprints. One major factor that impacts genome size is whether the organism is prokaryotic or eukaryotic. In prokaryotes, the genome contains little to no non-coding sequence, such that genes are tightly clustered in groups or operons sequentially along the chromosome. Conversely, the genes in eukaryotes are punctuated by long stretches of non-coding sequence.
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Related Experiment Video

Updated: Mar 7, 2026

Experimental Manipulation of Body Size to Estimate Morphological Scaling Relationships in Drosophila
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A new explanation for unexpected evolution in body size.

Loeske E B Kruuk1

  • 1Research School of Biology, The Australian National University, Canberra, Australia.

Plos Biology
|February 23, 2017
PubMed
Summary

Wild animals don't evolve to be larger due to a paradox of stasis. Snow voles show larger body mass increases survival, but genetic factors favor smaller size, balancing evolution.

Area of Science:

  • Evolutionary biology
  • Animal ecology

Background:

  • Body size is heritable and often linked to fitness.
  • Wild populations paradoxically do not consistently evolve towards larger body sizes.

Purpose of the Study:

  • To investigate the "paradox of stasis" in body size evolution.
  • To identify selection pressures on body mass in wild snow vole populations.

Main Methods:

  • Analysis of body mass, survival rates, and heritability in Swiss Alps snow voles.
  • Statistical modeling to disentangle phenotypic and genetic selection components.

Main Results:

  • Larger body mass was associated with higher survival rates in snow voles.
  • Heritability of body mass was detected, but a genetic decline in body mass was also indicated.

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  • Positive phenotypic selection on mass was attributed to age-related measurement bias, masking negative genetic selection linked to development time.

    • Conclusions:

    • The "paradox of stasis" in body size may be explained by negative genetic selection on mass due to longer development times.
    • Genes for larger body mass are not evolutionarily advantageous if they increase the risk of failing to complete development before winter.
    • Environmental factors may mask the underlying genetic trends in body size at the phenotypic level.