Evolution drives many plants and animals to be bigger, faster

Mar 07, 2011

For the vast majority of plants and animals, the 'bigger is better' view of evolution may not be far off the mark, says a new broad-scale study of natural selection. Organisms with bigger bodies or faster growth rates tend to live longer, mate more and produce more offspring, whether they are deer or damselflies, the authors report.

Researchers working at the National Center compiled and reviewed nearly 150 published estimates of natural selection, representing more than 100 species of birds, lizards, snakes, insects and . The results confirm that for most plants and , larger body size and earlier seasonal timing — such as earlier breeding, blooming or hatching —confer significant survival advantages.

"It's a very widespread pattern," said co-author Joel Kingsolver of the University of North Carolina at Chapel Hill.

What's puzzling, the authors say, is not why the 'bigger is better' model of evolution is so common, but why the 'Goldilocks' model is so rare: If organisms are supposedly well-adapted to their particular circumstances, then why is it so seldom the case that the individuals that survive and reproduce the best are the ones that are not too small, nor too big, but just right?

A classic example is human birth weight. Newborns of intermediate size are more likely to survive than newborns that are extremely large or extremely small. In lieu of driving organisms to be bigger and faster over time, the 'Goldilocks' model — also known as stabilizing selection — favors moderation, the authors explained. But for the vast majority of organismal traits, this pattern is the exception, not the rule. "Rarely is it the case that the individuals that survive and reproduce the best are the ones in the middle," Kingsolver said.

The result is puzzling because the conventional wisdom is that most creatures are well adapted to the environments in which they live. "When we look at nature, we see all these amazing ways species are well-adapted to their lifestyles and habitats," Kingsolver said. "Yet the organisms that are bigger, faster, still do the best in terms of survival and reproduction. Why aren't they already just the right size or speed, or pretty close to it?" he asked.

The authors explored three possible explanations. One possibility, they explained, is that evolving to be bigger, faster, or flashier comes at a cost. "A trait that's good for reproduction or fertility may be bad for survival — there may be a tradeoff," Kingsolver said. "In guppies, for example, brightly colored males have greater mating success, but they're also more likely to be eaten by predators," said co-author Sarah Diamond, currently a postdoctoral researcher at North Carolina State University.

Another possibility is that environments simply change from one season to the next, such that the traits that confer the greatest advantage change over time. "In Darwin's finches, for example, there are years where large-beaked birds have an advantage because large seeds are more abundant, and years where smaller-beaked birds do better because small seeds are more abundant," Diamond said.

A third possibility is that drives one trait in one direction, while simultaneously driving another, genetically correlated trait in the opposite direction. "For example it may be good for flying insects to evolve larger wings and smaller bodies for more efficient flight," Kingsolver said, "but if insects with larger wings also have larger bodies, they can't evolve both."

The third explanation frequently limits the of body size, the authors found, but not traits related to timing, or body shape, or coloration. "Size is the one case where correlated selection is important," Kingsolver said.

The findings appear in the March 2011 issue of American Naturalist.

Explore further: Human sense of fairness evolved to favor long-term cooperation

More information: Kingsolver, J. and S. Diamond (2011). "Phenotypic selection in natural populations: what limits directional selection?" American Naturalist 177(3): 346-357. doi:10.1086/658341

Study data are available in the Dryad Digital Repository at datadryad.org/handle/10255/dryad.7997

Provided by National Evolutionary Synthesis Center (NESCent)

3.5 /5 (4 votes)

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User comments : 8

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Djincss
not rated yet Mar 07, 2011
"When we look at nature, we see all these amazing ways species are well-adapted to their lifestyles and habitats," Kingsolver said. "Yet the organisms that are bigger, faster, still do the best in terms of survival and reproduction. Why aren't they already just the right size or speed, or pretty close to it?" he asked.

This is king of question that a school boy will ask, not a real scientist.
The most right question here is that what stop the advance in the species growth is the environmental factors, mostly food(bigger you are more food you need to enpower your body, if there is not such available the chance to die from hunger is greater compared with smaller individ), and with animals great numbers of individs die from hunger.
Djincss
not rated yet Mar 07, 2011
Also the individs that are bigger, mostly dont have genes for bigger body, but have had more food, and they got bigger due to better nutrition(but not always, sometimes it is genetics indeed, but then this doesnt mean they cope better with life-it wont be wise for squirrel to be bigger), also to be faster is one from the 1000 000 strategies for survival, and how exactly this article explained that faster are not better(when the strategy is speed, faster is better always, but in most of the cases it is not that simple)?
Djincss
not rated yet Mar 07, 2011
"In guppies, for example, brightly colored males have greater mating success, but they're also more likely to be eaten by predators,"
So here, they use this to explain this question:
Why aren't they already just the right size or speed, or pretty close to it?"
I wont comment this!!!
In this case nature is not stupid again, lots of animals have this- more vivid you are then you are better, often this is used in animals that are prey, when you are prey and you are colorful and you are alive, then there are 2 options you are really lucky, or you have some quolities to be alive despite the fact you are easyer to spot.
Moebius
3 / 5 (1) Mar 07, 2011
Evolution seems to choose smaller is better. Mostly everything in the prehistoric ages was really big and that trend seems to have reversed ever since.
DamienS
5 / 5 (3) Mar 08, 2011
Evolution seems to choose smaller is better.

That is not a rule. Sometimes it does, sometimes it does not.
Mostly everything in the prehistoric ages was really big and that trend seems to have reversed ever since.

There are a number of reasons for this, including size as a form of self defense, the increase in vegetation availability due to higher CO2 levels and higher temps and due to reptile cold-bloodedness where large size would be advantageous for homeothermy.

In the modern age, species have declined in size because of predation mostly by humans. Look at fish stocks and average sizes. The big fish get taken, leaving the smaller behind, which drives selection pressure for smaller fish.

Dwarfism also occurs on small islands where resources are limited and in other environments where similar restrictions apply.
jmcanoy1860
not rated yet Mar 08, 2011
Alt unghi al problemei: daca ai supracrescut poti sa dai inapoi? Cum poti sa te micsorezi? Cum poti deveni din nou mic?


Yo mama
antialias
5 / 5 (1) Mar 08, 2011
Yet the organisms that are bigger, faster, still do the best in terms of survival and reproduction. Why aren't they already just the right size or speed, or pretty close to it?

Because animals don't live in a static environment? They _themselves_ are a factor that is driving their evolution because the species that is most keenly competeing for your particular set of resources is your own. So even if a species were the only species alive and all external factors were constant it would _still_ be under evolutionary pressure.

It seems rather obvious that small changes in an individual will always be beneficial (and when the mutual arms race drives the entire species into a corner then suddenly a large mutation will be beneficial). So I'd expect a dynamic/undulating form of evolutionary change (and animal history of changing fang strength, armor, speed, size seems to bear me out in this)
Gawad
not rated yet Mar 23, 2011
Alt unghi al problemei: daca ai supra crescut poti sa dai inapoi? Cum poti sa te micsorezi? Cum poti deveni din nou mic?
It's actually not that hard. Once evolved, many genes (such as for increased size) don't need to to be deleted for the species to revert to an earlier state. Mechanisms to switch genes on an off may also evolve and come into play. So when selective pressure to revert a trait come occurs it may actually be easier to "go back" than to evolve the original gene in the first place.