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Updated: Apr 15, 2026

Experimental Manipulation of Body Size to Estimate Morphological Scaling Relationships in Drosophila

Experimental Manipulation of Body Size to Estimate Morphological Scaling Relationships in Drosophila

Published on: October 1, 2011

Adaptive evolution toward larger size in mammals.

Joanna Baker¹, Andrew Meade¹, Mark Pagel²

¹School of Biological Sciences, University of Reading, Reading, RG6 6BX, United Kingdom; and.

Proceedings of the National Academy of Sciences of the United States of America

|April 8, 2015

Summary

This summary is machine-generated.

Mammals show a long-term evolutionary trend toward increasing body size, driven by faster rates of growth than shrinkage. This finding supports Cope

Keywords:

Cope’s rule adaptive evolution ancestral state reconstruction evolutionary trends macroevolution

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Area of Science:

Evolutionary Biology
Paleontology
Phylogenetics

Background:

The long-standing debate on whether larger body size provides an intrinsic advantage to species.
Previous observations of body size increase through time in the mammalian fossil record (Cope's rule).

Purpose of the Study:

To investigate long-term evolutionary trends in mammalian body size using extant species data.
To test for a directional bias toward increasing body size and its compatibility with Cope's rule.

Main Methods:

Employed a phylogenetic statistical approach to analyze body size evolution across mammal phylogeny.
Allowed for variable rates of evolution across different lineages.
Compared rates of size increase versus decrease on a branch-by-branch basis.

Main Results:

Identified a significant long-term directional bias toward increasing body size in mammals.
This pattern was consistent across 10 of 11 mammalian orders studied.
Increases in body size were over twice as likely as decreases, indicating a persistent trend.

Conclusions:

The study provides the first evidence from extant species supporting Cope's rule.
The observed trend is unlikely to be due to nonadaptive mechanisms and likely reflects adaptive responses to environmental pressures.
Phylogenetic statistical models can reveal ancient evolutionary trends, complementing paleontological data.