Wednesday, March 9, 2011

Being Bigger is Better and Faster

The researches working at the National Evolutionary Synthesis Center conducted a study where they reviewed the national selections of hundreds of species of birds, lizards, snakes, insects and plants. They found that the larger body size and earlier seasonal timing including breeding, blooming or hatching have a larger effect in their survival.

However, the puzzling part is that why the concept of “bigger is better” is so common in evolution study. The authors studied “Goldilocks” model known as stabilizing selection, where they argued the idea of having rare cases of being intermediate size that survive and reproduce better. For example, human birth weight: newborns of intermediate size are more likely to survive than newborns that are extremely large or small, but it is rare case. The reasons for why it’s so puzzling concept is because most creatures are well adapted to the environment in which they live.

The authors presented three possible explanations for this puzzling concept. One possibility is that evolving to be bigger and faster comes at cost meaning there can be a trade off between their survivals and reproducing. Another possibility is that the environments changes from seasons to seasons, in which the trait that has greater advantage changes over time such as in Darwin’s finches’ example, where large-beaked and small-beaked birds were favored due to availability of seeds. The third possibility is that natural selection drives one trait in one direction. For example, it can be advantage for flying insects to evolve larger wings and smaller bodies for more efficient flight; however, insects with larger wings having larger bodies cannot evolve.

From these explanations, the authors concluded that the third explanation limits the evolution of body size. However, the traits related to timing and/or body shape does not correlate with the idea of “Goldilocks” model.

Posted by Arpita Patel


  1. I feel that the first explanation seems most reasonable. I feel there is a strong correlation between the size of the organism and its ability to reproduce. Of course, there are benefits and costs to being large. A larger organism could be more easily identified meaning they are predated more often than their smaller peers. On the other hand, they could have the upper hand when it comes to competition among their own species. Overall, I feel that an average size is probably the best size since you get the best of both worlds.

    Kevin McLaughlin

  2. It makes sense that an intermediately sized offspring would be more successful. If the offspring is two small it probably did not get enough nourishment during development and will have a lesser chance of survival upon birth. A larger offspring will have to struggle to find enough food when they are born to accommodate the bigger size. If the offspring is intermediate size they will not have to face these problems.
    I also feel like the authors first and last explanations are almost the same thing. They are both saying that animals who are unsuccessful in terms of survival or reproduction will not evolve.

    -Jessica Kusmirek

  3. Arpita,

    The evolution of the size of organisms, or the size of parts of organisms as in the case of Darwin's finches, take all of these things into account. You mention stabilizing selection, but that is a far too narrow-minded theory. You need to also take into account both directional and disruptive selection. For example, directional selection comes into play in ponds where the smallest fish survive because they are more able to escape the bigger species of fish by swimming between tiny spaces in rocks and such. And, of course, if this fish were very big instead, the bigger species of fish may not bother it, in which case this would be disruptive selection. And yes, clutch size and individual egg sizes are inverses of each other. The more energy inputed into a single egg, the bigger and more likely it will survive. Amphibians typically lay thousands of very small eggs (r-selection), while we humans have one of so at a time, excluding Octomom. We practice k-selection. And as for natural selection driving evolution and body size, that is a no-brainer; of course it does.

    Posted by Derek Melzar

  4. I feel the size of the organism definitely has to do with the rate of reproduction. Also sexual selection could have a big part in it. Also, when the organism is big the chances of its predators finding it are large. Intermediate offsprings are the best I would think because they are not too big and would be able to hide more often. The big ones would be good because they could potentially be the predators. But the middle sized ones I think would have the best chance of survival since they r in the middle. I don't know I think I have to look more into this subject to fully understand it!

    Cleopatra Duque

  5. Last semester I took a marine vertebrates class where we learned a general trend that the lower in latitude or the colder the climate, the larger the average body size of animals. This study reminded me of this trend. It could be that larger body sizes has an advantage in a more variable climate due to global climate change. This is the same concept that those species that are evolved to survive in high temperature climates have a lower tolerance for global temperature increase.

    -Posted by Marlena Grasso

  6. The problem with insects especially ones that are large is that they have a small surface-area-to-body-size ratio making it difficult to get oxygen to muscles such as the ones involved in flight, so being larger as you implied is a disadvantage. On a response for a question on one of my posts, I mentioned that larger insects overcome the size issue by having more air sacs to make their air intake more efficient. In this case, more and bigger air sacs is better.

    Posted by: Nelson Milano

  7. Larger individuals are typically better fit. There are plenty of biological exceptions, such as human babies. They are most healthy within a certain body weight range. Larger or smaller than the ideal weight results in complications with the childbirth or complications with the mother after. Although, bigger can be better.

    Reed Allen

  8. Kevin,
    I agree with you on the first explanation. Bigger size organisms have some benefits as they can compete more easily for food and some disadvantages as they are predated, however, they can also attempt to defeat themselves from predator as being large. I would definitely agree that intermediate size benefits better.

    I feel the same way about medium sized offspring would survive better without facing problems like small and bigger sized offspring would do. Also, first and third explanations say same thing as one benefits and other one doesn’t. But the author also believes that medium sized offspring are rare cases to be found than other sized offspring, which are common, especially larger sized, which are capable of surviving in seasonal changes.

    I see that the author only uses the idea of stabilizing selection while they can take the ideas of directional and disruptive selections into account to overcome their explanations into more details. So they can differentiate among sizes and their benefits and explain the “Goldilocks” model as in why there are fewer cases of the intermediate sized organisms. Sizes do matter for survival and reproduction.

    I definitely agree on the idea of predation among medium and bigger sizes of organisms. Bigger would have low survival due to being exposed to predators more than medium sizes but they would also survive because they can defeat themselves as they are larger in size and be predator themselves. However, medium size would benefit more in all terms.

    It’s good that you made connection from your other course. I do agree on the concept of environmental changes. Organisms have their own optimal temperatures for survival. As the climate is changing day by day, more species are dying because of their optimal temperature is no longer there.

    Having small surface-area-to-body-size ratio does make sense as having disadvantage in flight. Larger size insects can be incapable of lifting their weight or incapable to slow down or speed up during flight. However, they might have advantages in mating or protection. Also, as you mentioned about having more air sacs in large size, it would benefit them in better oxygen supply and assist them in flight by lowering the specific gravity.

    Posted by Arpita Patel

  9. The authors first and last explanations are almost similar. They are both saying that animals who are unsuccessful in terms of survival or reproduction will not evolve.
    If the offspring is two small it probably did not get enough food during development and will have a lower possibility of surviving during birth. -Jean Fedna