E-mail updates
Follow on Twitter
Subscribe to RSS
Oxford Scientific / Getty Images Stock
Researchers found that it was easy to breed guppies with bigger brains, but the fish had smaller guts and also produced fewer progeny. The results serve as experimental evidence of evolutionary trade-offs.
Scientists have long suspected that big brains come with an evolutionary price — but now they've published the first experimental evidence to support that suspicion, based on their efforts to breed big-brained fish.
A Swedish team found it relatively easy to select and interbreed common guppies to produce bigger (or smaller) brains — as much as 9.3 percent bigger, to be precise. But the bigger-brained fish also tended to have smaller guts and produce fewer babies.
This finding is consistent with what's known as the "expensive-tissue hypothesis" — the idea that there's a trade-off between the demands of the brain and the demands of other organs. For example, we humans have bigger brains than other primates, relative to body size. About 20 percent of the energy we take in is used up by the brain, which represents just 2 percent fo our body mass. But the amount of energy devoted to digestion is smaller, relatively speaking.
Some evolutionary biologists have speculated that when our distant ancestors shifted to an easier-to-digest diet, that freed up the energy for bigger brains. But that speculation has been based primarily on comparative studies of brain size and gut size as they are in present-day species. And some of the recent studies on the subject have been interpreted as refuting the expensive-tissue hypothesis.
Niclas Kolm and his colleagues at Uppsala University used artificial evolution — that is, selective breeding — to show the tissue trade-off in action. Their results were published online today by the journal Current Biology.
The experiment put 48 of the guppies through an underwater arithmetic test to see whether better cognitive abilities came with the bigger brains. It turned out that the brainier fish were better at learning to recognize how many geometric symbols were on a door in order to get to the food on the other side (at least if there were up to four symbols).
But in the gut-size department, the bigger-brained fish, especially the males, came up short (20 percent smaller for males, 8 percent for females). What's more, the big-brained fish had 19 percent fewer offspring than the small-brained fish. That result suggests that bigger brains are somehow associated with smaller broods — a phenomenon that researchers have noticed with regard to primates as well as cetaceans.
Although the raw numbers seem to support the expensive-tissue hypothesis, Kolm and his colleagues weren't able to tease out the genetic mechanism for the trade-off. Thus, it's not fully clear which comes first: smaller guts or bigger brains.
"Our results on the guppies demonstrate that the order of evolutionary transitions is starting with a change in brain size, followed by a decrease in gut size," Kolm told NBC News in an email. "At the same time, this does not automatically mean that the opposite response is not also possible. To test this would of course require further experiments. Currently, our cautious conclusion is that we have identified a new possible direction of events in that selection for increased brain size may indeed have 'forced' a reduction in gut size."
The same caveat goes for the findings on reproduction. Kolm said he and his colleagues interpret their results as supporting the view that reduced reproductive capacity is one of the evolutionary costs associated with bigger brains.
"This would seemingly suggest a lower fitness in large-brained individuals, which would not be intuitively 'possible' from an evolutionary point of view," Kolm acknowledged. "Here it is important to remember that in our selective set-up, we have no additional selection pressures from avoiding predators, finding food, competing for mates, etc., that would occur in the natural environment. Hence, there might still be an overall fitness benefit from increased brain size in the wild, at least in certain environments/situations, that would allow selection for increased brain size despite the lowered fecundity."
The Swedish researchers are planning a new round of experiments to see how big-brained (and small-brained) guppies handle a more realistic evolutionary environment.
"Watch this space," Kolm said.
More about brains and evolution:
- How diet affected human evolution
- Theory says humans are losing intelligence
- Flash interactive: Take a tour of your brain
- Gallery: The 10 smartest animals
In addition to Kolm, the authors of "Artificial Selection on Relative Brain Size in the Guppy Reveals Costs and Benefits of Evolving a Larger Brain" include Alexander Kotrschal, Björn Rogell, Andreas Bundsen, Beatrice Svensson, Susanne Zajitschek, Ioana Brännström, Simone Immler and Alexei Maklakov.
Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.
Leave a Comment:
From reading this I can conclude that Fat people have smaller brains.
And morons propagate like mad. Seems about right to me....
I have noticed that the dumber the person, the more determined they are to reproduce. Or maybe it's just that it doesn't take a whole lot of brain to reproduce.
No it's parents with many children!
In terms of long term (geologic scale) the utility of the human big brain adaptation has yet to be proven.
Well, we're soon going to prove that we were fully capable of making the planet uninhabitable. Then we'll turn it over to the cockroaches who'll eventually evolve into species that are less destructive.
"Don't you tell us what to evolve into!"- The Cockroaches
The roaches will probably have bases on the Moon and Mars long before humans.
Roaches to planet Earth: "We are already on the MOON!"
the key is not just the number of progeny, but their ability to survive and procreate. if smarter fish have higher survival it compensates for reduced fecundity and evolution goes that way. It seems to me that with humans, the adoption of a higher energy diet would have coincided with the increased intelligence necessary to procure it.
Exactly right. Why do we as humans have brains that are good enough to produce satellites, when recently our ancestors were hunter/scavengers on the East African plains? Why would we need a brain THAT big? If I could tell exactly I'd be Nobel bait, but I'm not there yet...
Building a satellite makes you more attractive to mates. At least it does on-line and in 1950's movies.
Actually Tetrapoda raises an extremely good point. It is my opinion, as someone who studies the brains of animals, that a feat like building a satellite does not require a comparatively greater amount of brain power compared to hunting and scavenging for food.
If you think about what is required to hunt an animal efficiently - problem solve on the fly in de novo situations, predict an animal's movements, and the very most useful capability of all: possess a theory of mind, which allows you to understand your prey to a much greater degree; this requires tremendous neural complexity. But, our brain hasn't evolved since our hunter-gatherer days. We have become more knowledgeable, in the sense that cultural knowledge, science, and technology continues to improve - but biologically speaking we are not more intelligent.
Our brain, from the start, had the potential to do calculus, build satellites, solve the mysteries of the universe. But what these feats require is understanding - understanding passed down and improved over generations. The neural capacity to understand, however, is far more biologically and evolutionarily significant.
I, for one, welcome our new guppy overlords.
Stereotypes often contain grains of truth. One stereotype that exists is the belief that less intelligent people tend to have large families and tend to be over weight. Now we have a study on fish that supports the stereotype, at least as it applies to fish.
I'd love to see a study that compares brain size with the intelligence of humans and the number of offspring they have. I bet the results would be very interesting.
"One stereotype that exists is the belief that less intelligent people tend to have large families and tend to be over weight."
I don't know about family sizes but you don't know the same academics I do hehe.
Ideocracy (2006)
The movie...maybe it was not just a silly science fiction movie...maybe its foreshadowing the future...scientists just proved the smarter you are the less brood you have...conversely, the dumber you are, the more you breed...oh well...its the electrolytes that will help us grow....
..it's what plants crave.
You have been sentenced to one night rehabilitation. Rumor has it Beef Supreme himself will be there.
Why are you trying to read those words? Are you f*gs?
And many thought genetic engineering would solve the problem, but the greatest minds on the planet were focused on finding cures for baldness and erectile dysfunction.
Human nerds also have evolved bigger brains at the cost of not being able to produce offspring. (or find someone to produce offspring with :| )
And yet, they still manage to breed and make millions of dollars.
more brawns == less brain
these were proven by all the highschool jocks and the cheerleadery types from the time they invented high schools.
you know it then, you know it now, you were not wrong.
I'd like to see them try this experiment with humans.
Wonder if the bigger brained guppies might have less offspring, but increased lifespan, less offspring than forces those bigger brained guppies to focus more on preserving their offpspring, Probably not, suspect its not that much of a advantage, but perhaps if they would be isolated from other guppies this would eventually happen.
Lifespan and brain size do not necessarily go together. The longest lived vertebrates are the giant tortoises. They are certainly not very brainy. Another experiment that the researchers could try is the survival rate between big brained guppies and small brained guppies during a prolonged fast (starvation). The logical (predicted) result would be greater survival in the small brained guppies.
Big brains are metabolically expensive. As a result, vertebrates with low basal metabolic rates (fish, amphibians, reptiles) have small brains compared with those with high basal metabolic rates (mammals, birds). Further, it is a common observation that predators are almost universally smarter (bigger brained) than their prey. The evidence is such, that the expensive-tissue hypothesis is really a pretty well documented theory rather than a hypothesis.
If they were allowed to mingle, the big brained group might start eating the small brained ones.
Or, they might produce reality guppy shows to get the small brained guppy dollars.
seems to prove what I've long suspected -- smarter beings have the intelligence not to reproduce beyond their means ... ;)
then again, guppies eat their own young, so how smart can they be? hmmm "food" for thought ...
sorry.
Swedish Fish
These sort of articles really frustrate me. The world starts drawing all sorts of conclusions, we use this to confirm whatever theories we want to believe anyway, but it's actually just bad science. What is not mentioned in the article is that because of the techniques used it is not only possible, but nearly certain that there is significant linkage between the gene or genes that cause larger brain mass and other genes. Thus, they may have shown a revealing glimpse into a fundamental biological principle.....or they just discovered that a gene affecting gut size is located somewhat near a gene affecting brain size. In fact, isn't this exactly the type of experiment that was done to get gene maps? They only used 2 generations of fish so linkage is pretty much a certainty. Scientists make claims like this, and then think anyone who doubts them is stupid. Now, I'm not saying that a larger brain won't cause a smaller gut or less progeny. I'm just saying that this paper, which somehow got published after being reviewed by other respectable scientists, and then found worthy of being shared with the world by a respectable news organization, in no way proves the claims they are making and is a pretty good example of bad science.
Good observation, and spot-on.
The experiment is interesting- but the speculation is unjustified without a far stronger empirical foundation.
To back up the claim of a causal relationship between brain size and digestive capacity, you'd need to see what transpired across several unrelated species when they were selectively bred for larger brains.
Even then you'd want a close study of the gene sites involved- because one common ancestor far enough back (the first chordate, for example) could pass a characteristic up the line to influence the result over thousands of species.
I'd also prefer to involve, say, predatory arthropods (larger arachnids or mantids might do) and molluscs (like octopi, squid or cuttlefish) as well- just to avert that possibility.
For completeness, they should breed small brained guppies for study and a future career in politics.
Stupid people having more children than smart people will drive America to a famine. It's sad, but we don't have a eugenics program anymore.
Eugenics is too influenced by what the current leadership regards as a desirable set of characteristics for the ideal citizen.
The crucible of predation has always been the refining fire which burned the dross of random evolutionary drift from any gene pool- and we've extinguished everything which might effectively serve us in that venue.
Even sociopaths can only kill so many of the lethally afflicted- so the downwards trend you describe so succinctly may very well continue until true sapience is altogether lost.
I suspect this is why the stars are silent, and not ablaze with signals from intelligent civilizations: no species which attains our current pinnacle of self-awareness lasts long enough to brag about it for very long...
This exactly proves that the theory of evolution is just that a theory. It took intelligent scientists using labs under controlled condition to get a desired outcome. Yet they want to have us believe that the same intelligent brain that developed the labs for this test, just came about by an evolutionary process. Losers.
Well, Mother Nature conducts experiments over millions of years. Most of these scientists don't live long enough to see million year long experiments show results, whereas Mother Nature has all the time she wants.
The losers remain those who won't learn enough to find the flaws in such an experiment- and who subsequently decry the entire process of scientific investigation as inferior to superstition.
fish in aquariums don't always act as they do in the wild. They adapt to the environment they are in and that would be based on when the "scientists" show up to feed them.Their day and night would be based on when the lights are turned on or off.Some people with aquariums don't realize fish need light and dark cues and wonder why they can't keep fish alive.
Morons. Experimental Evidence will be looked at as if fact to give evidence to what? To your belief that through a big BANG it all happened and the stew became organized and the organized is actually disorganized going through changes. So, it became a fish ? Great work there morons. Put your efforts to something useful.
Some people have problems seeing changes over weeks. Billions of years are beyond their comprehension.
Lute, the information in this article was written by a human, concerning empirical evidence studied in great detail by other humans, and you call them all morons. Yet on the other hand you take information written in your good book by other humans, and accept it without question as being fact. Without doing anything more than reading those words and listening to others who lecture you about those words. Who's the real moron?
You know, every cult in the world lectures their followers that believing without seeing is the path to salvation.
Some people say it's not the size that matters, it's what you do with it.
That's what I keep saying about my beer gut.
Hey, girth is what really turns the ladies on!
There's no evolution here. Why? Despite the fact that there's bigger brained fish, small fish, Gold Fish, Guppies, Minnows, Trout....all different types of fish..nothing evolved because THEIR STILL FISH!! The bigger brained fish did not 'evolve' into a German Shepard, No?
Thea are still FISH!! Nice try though.
Yer Pal Always,
Thee Ox & Friends
A German Shepherd starts out as a lil sperm, No? Just like a Human Evo-denier, No? And a lil sperm is just a microscopic fish, No? Lil swimmer, No? So everything evolves from fish, No?
See, I run rings around you, logically!
Though he brings up a good point. Someone should selectively breed fish until they can walk and breath out of water.
Ok, as long as they don't start barking all day, I hate that.
"It is only a theory" Well, yes it is a scientific theory meaning it is based upon facts, complies with all known scientific laws and is repeatable. It can be changed if additional data is obtained that changes it. Fish do not become dogs or whatever. Scientists noticed a group of flowers that were hybrids of two other flowers. The hybrids could reproduce among themselves but not with either of the parent flowers. New species. Sorry creationists you are idiots. Also, scientists have been able to reverse evolution with chickens to produce chickens with teeth and tails. The attempt to produce a reptile ancestor of modern birds. Likely will happen within the next 5 years.
Harry, how did the first single cell life form start, and work perfectly right from the start (have instruction code (DNA), made to live, ways to take in energy and excrete waste, capability to reproduce)? It would If any of things don't exist in the the life-form, it dies. How did the universe come to be since matter does not spontaneously come into existence, if so, we notice that I think. Sure I have heard of the big bang, but where did the energy come from, energy had to come somewhere (energy is neither create or destroyed, just changes forms). And what about that nasty law of entropy that would life impossible. How fast would the earth be spinning billions of years ago?
That book you speak of has many predictions, tell me which ones were wrong? When archeologists use it to find digs, it has ALWAYS been correct. Why is it so accurate, even today?
wsmcke, if it is hard to understand how life started without being divinely created, then try to understand what created the Creator. If life is too complex to have worked right from the start without someone looking over it and creating it, then consider how complex the thing that created the Creator must be.
If life too complex to be here without a Creator, then the Creator must be even more complex and must have an even more complex Creator Creator, and the Creator Creator must have an even more complex Creator-Creator Creator, which must have an even more complex......
Evolution. lol
Truth be told people. Yehovah created the heavens and the Earth in six days as we know it. He created Man in one of those days from the dust of the Earth. Man did not evolve. Science does not support it. Everything to do with evolution is theory. The fool says in his heart that there is no God, but one day coming soon we will all stand before Him to give account. Blessed be the name of Yehovah.
I'm not saying there's no God, I'm saying it makes no sense that the Universe was created in six days. The evidence says otherwise.