Query: what is the evolutionism for scale? Why are animals different sizes?

[Gottservant]

I'm smarter than to start by venturing my own thoughts here, but I am grateful that there are many who believe in their status as experts enough to help me out.

Again, don't try to put prejudice on me, I haven't stated an opinion at all.

 

[BrainHertz]

I don't purport to be an expert by any means, but if I understand your question correctly, evolution does not suggest any particular "ideal" for size. Rather, the most fit size can only be evaluated in terms of the particular ecological niche to which that particular species is adapted.

Did that answer your question?

 

[anonymous1515]

I'm smarter than to start by venturing my own thoughts here, but I am grateful that there are many who believe in their status as experts enough to help me out.

Again, don't try to put prejudice on me, I haven't stated an opinion at all.

Well, as far as I understand it, there are many explanations for why certain creatures are the size they are. In general though, evolution tends to favour larger body sizes. Larger organisms tend to dominate smaller organisms in interspecific agression (i.e. fighting each other). Also, in the higher latitudes, mammals tend to be larger. This is likely because, as you go further north it gets much colder. Larger animals are better at maintaining homeostasis (keeping their body temperature constant).

Those are a few of the hypotheses explaining evolution of larger body sizes.

 

[anonymous1515]

I don't purport to be an expert by any means, but if I understand your question correctly, evolution does not suggest any particular "ideal" for size. Rather, the most fit size can only be evaluated in terms of the particular ecological niche to which that particular species is adapted.

Did that answer your question?

Yes, that is also true. Body size is very dependent on the ecological niche of the organism. It is also dependent upon evolutionary constraints (sometimes organisms just can't get larger for certain reasons), and sometimes it is actually beneficial for certain organisms to be smaller. It all depends on the selection pressure.

 

[Morcova]

oh gottservant's back.... this guy makes speakout look educated.

 

[Gottservant]

I don't purport to be an expert by any means, but if I understand your question correctly, evolution does not suggest any particular "ideal" for size. Rather, the most fit size can only be evaluated in terms of the particular ecological niche to which that particular species is adapted.

Did that answer your question?

I heard "I don't care what size something is, all something has to do is survive regardless of what size it is."

Have I heard you correctly?

If I have then "no", you have not answered my question, you have stated that you do not want to.

 

[Patashu]

Speaking in the most general terms, animals will evolve to be the optimal size for their niche given their environment. Animals who are taking to being top-level carnivores, your lion et cetera. will want to be big, but not big to the point where they can't gather enough resources to keep their body going. (The bigger you are the more weight each limb will have to hold up, and the weight increases faster than the surface area does) Something small, on the other hand, doesn't need as much to survive but at the same time can't exert nearly as much force against the potential threats of other creatures. Small creatures can also reproduce faster and more often, since there's less to make. The main tradeoff is thus between big, powerful and resource-hungry and small, diminutive but more efficient and more numerous.

 

[coyoteBR]

Indeed, things find a quick balance in nature. As Patashu said, you grow to the size that gives you an edge to find food/escape from perils.
The quantity of resources also plays a determinant role on this. The ocean has enough to suppoort creatures like the Great White Whale and the Colossal Squid; on the other hand, in land creatures are adapting to the human enviroment, made of "islands" of florests, surrounded by cities and roads. This creates a tendency of creatures getting smaller in size.

 

[Gottservant]

No, there is something you don't get: what actually makes scale changeable from creature to creature. You would say "a mutation" wouldn't you?

Let's assume you would say "mutation" if you could, ok, so how is it that one mutation leads to so many different sizes? Is it more than one mutation, like a different mutation for every different size? If it is the one mutation that subsequently leads to all the changes, how does the mutation suddenly work?

I'll check back to see what you say.

 

[BVZ]

No, there is something you don't get: what actually makes scale changeable from creature to creature. You would say "a mutation" wouldn't you?

Let's assume you would say "mutation" if you could, ok, so how is it that one mutation leads to so many different sizes?

It is not one mutation. The size of a creature (ignoring environmental effects) is determined by THOUSANDS of genes. A mutation in any one of these could increase or decrease the total size of a creature.

Is it more than one mutation, like a different mutation for every different size?

Not quite.

You can see genes as building plans for building a creature. A specific part of the plan might control the size of the vertebrae. A mutation in THIS part of the gene can change the vertebrae to be slightly larger. Another gene controls the length of the femur. A mutation in THIS gene might increase the length of the femur. Another gene controls the growth hormones. A mutation in this gene might cause too much of a certain hormone to be released/produced, causing the creature to grow to an abnormal size.

Another possibility are genes that INHIBIT growth. If this gene becomes damaged by a mutation, growth is no longer inhibited, and the creature grows larger than normal. (We see this in ligers.)

The conclusion is that the size of a creature is a result of thousands of genes, and a mutation in any one of these genes has an effect on the resulting creatures size.

If it is the one mutation that subsequently leads to all the changes, how does the mutation suddenly work?

Good question.

The mutation does not have a purpose in mind, it just happens.

Like others have said, the environment the creature finds itself in plays a very important role.

In any environment there will be a 'sweet spot' where you want to be. You want to be bigger and harder to catch by predators. Or perhaps you want to be smaller so that you can hide from predators more easily. Depending on your environment and survival strategy, there is a certain size that is optimal.

Any mutation that moves you TOWARDS that optimal state will be selected FOR, and any mutation that moves you AWAY from that optimal state will be selected against.

Your question is what makes the mutation 'work'. Not all mutations 'work'. Some make the resulting creature unable to survive. But the few mutations that results in a living creature, that is BETTER suited to its environment, will be selected for by natural selection, and the mutation will spread until it becomes the norm, rather than the exception.

I'll check back to see what you say.

Please do.

 

[BrainHertz]

I heard "I don't care what size something is, all something has to do is survive regardless of what size it is."

Have I heard you correctly?

If I have then "no", you have not answered my question, you have stated that you do not want to.

That wasn't quite what I was saying; what I was saying is that the reason difference species are different sizes is because they are adapted to different ecological niches.

Referring back to my earlier response, if I didn't respond to the right question, then it's because I didn't know what it was. Could you better clarify what your question is in that case?

 

[BrainHertz]

No, there is something you don't get: what actually makes scale changeable from creature to creature. You would say "a mutation" wouldn't you?

Let's assume you would say "mutation" if you could, ok, so how is it that one mutation leads to so many different sizes? Is it more than one mutation, like a different mutation for every different size? If it is the one mutation that subsequently leads to all the changes, how does the mutation suddenly work?

I'll check back to see what you say.

Uh, ok. So what you're asking for is the mechanism by which the variation occurs?

Look at it like this: if you have a population of one variant of a particular species (say a particular breed of dogs, for the sake of argument), there will be a distribution of heights within that population. That is, there will be some distribution with some mean value.

If, for some reason, there is selection pressure applied which causes either larger or smaller to be favored in terms of reproduction, the distribution will begin to drift in one direction or another. This is not an effect applied to a particular individual or blood line of individuals, but a shift in the statistics of the population as a whole.

Over some large number of generations, you will find that the mean value of that parameter has drifted in a direction which makes the population a better fit for that particular selction pressure.

 

[ChordatesLegacy]

I'm smarter than to start by venturing my own thoughts here, but I am grateful that there are many who believe in their status as experts enough to help me out.

Again, don't try to put prejudice on me, I haven't stated an opinion at all.

There are many reasons for size change in a specific population, the most obvious is food availability, and there have been studies into this on the English Channel Islands of Jersey, Guernsey, Alderney and Sark. Basically the findings show that during the war years when these islands were under German occupation children grew up to be significantly shorter than children either side of the war and this as been put down to food shortages during that time period.

From an evolutionary position this situation probably suited children who were genetically predisposed to being short, as they would have been under less stress that children predisposed to being tall. If this situation had continued over generations then shorter people would have been fitter (evolutionary speaking) than taller people, leading to an overall shortening of the islands human population


Quote from this link


Following the fall of France in June 1940, the Channel Islands (Jersey, Guernsey, Alderney, and Sark) were demilitarized, and 30,000 civilians (including more than 5,000 schoolchildren, most of them from Guernsey) were evacuated to the mainland (Read 1995). The German occupation of the Channel Islands began at the end of that month (June 30, 1940), and food restrictions were formally introduced the following year when bread was first rationed (Bunting 1995). As the occupation progressed, the range of foodstuffs and other household goods (such as fuel and soap) subject to rationing gradually increased while the amounts officially allocated, and those actually available, gradually declined (McKinstry 1946; Symons 1946). Conditions on the Channel Islands deteriorated rapidly following the successful D-Day landings in June 1944 and the subsequent liberation of Cherbourg, St. Malo, and Grouville. These were the principal French ports supplying the German garrison and civilian population of the Channel Islands, and the islands were effectively under siege until the German garrison surrendered on May 9, 1945. By the end of 1944 conditions on the islands had deteriorated to such an extent that the civilian authorities negotiated with the International Committee of the Red Cross to send emergency supplies for the beleaguered population.

At the end of the war a series of studies were published that examined the impact of the occupation on the health of Channel Islanders (e.g., Banks and Magee 1945). These studies included reports produced by the medical officers of health in Guernsey (Symons 1945) and Jersey (McKinstry 1946), the latter containing weight and height measurements of Jersey schoolchildren recorded before, during, and after the occupation. Notwithstanding the changes in schooling policy that occurred during the occupation (when children started school at a younger age and left a year older), McKinstry (1946) concluded that children in comparable age classes were lighter and shorter during the German occupation. This has been confirmed by multivariate statistical analyses (Kelly and Ellison 2002), which found significant short-term declines in weight and body mass index [weight/(height) (2); BMI] and a significant longer term reduction in height.

 

[Gottservant]

It is not one mutation. The size of a creature (ignoring environmental effects) is determined by THOUSANDS of genes.

And somehow that happens by chance?

(don't worry I read everything else you wrote)

Like... you accidentally get giraffes of the right size over time and then all of a sudden they are always the right size.

 

[Gottservant]

If, for some reason, there is selection pressure applied which causes either larger or smaller to be favored in terms of reproduction, the distribution will begin to drift in one direction or another. This is not an effect applied to a particular individual or blood line of individuals, but a shift in the statistics of the population as a whole.

Ok and you are saying that

• it stays that way by chance
• it doesn't mutate out of control
• none of the animals choose to breed against it

is there an evolutionism for why these three are also the case?

 

[Patashu]

And somehow that happens by chance?

(don't worry I read everything else you wrote)

Like... you accidentally get giraffes of the right size over time and then all of a sudden they are always the right size.

It's not so much a 'right' size for a giraffe to be as an 'optimal' size for a giraffe. Given a population of giraffe, the ones with a size closer to the optimal than those who don't will be slightly more likely to survive and reproduce. Repeat over many generations and you'll see a drift towards optimality for the environment the giraffes are in.

 

[Gottservant]

It's not so much a 'right' size for a giraffe to be as an 'optimal' size for a giraffe. Given a population of giraffe, the ones with a size closer to the optimal than those who don't will be slightly more likely to survive and reproduce. Repeat over many generations and you'll see a drift towards optimality for the environment the giraffes are in.

This is interesting, to me, because you have taken this massive drive to change from amoeba (or whatever it is evolution says life started with) to all the life we have today and you are saying that it comes to a standstill with only "slight" changes all because that is what the selection pressures portend... but you offer no test by which a species will be satisfied by that standstill: that something survives is somehow "enough".

How did survival become "enough" (for any creature) ?

 

[Patashu]

Evolution will come to a standstill if the species is already filling its niche perfectly and the environment around it is not changing significantly enough to warrant change. If no benefitial mutations emerge that provide an impressive degree of reproductive success and manage to take root in the population then the population will remain static. Evolution can be fast but it can also be slow.

What do you mean about survival being 'enough'? If a creature survives long enough to reproduce and ensures that its offspring similarly survive, then its genes are surviving and thus becoming more emergent in the population relative to genes that die out, no?

 

[Gottservant]

Evolution will come to a standstill if the species is already filling its niche perfectly and the environment around it is not changing significantly enough to warrant change. If no benefitial mutations emerge that provide an impressive degree of reproductive success and manage to take root in the population then the population will remain static. Evolution can be fast but it can also be slow.

Are you saying mutations are regulated now? My understanding was that mutations were perpetually random. If it is true that mutations are perpetually random, there can be no stand still. Either mutations are weaker than selection pressures or they are stronger, are they not?

If mutations are weaker than selection pressures, how do they ever work? If they are stronger how do they ever stop?

What do you mean about survival being 'enough'? If a creature survives long enough to reproduce and ensures that its offspring similarly survive, then its genes are surviving and thus becoming more emergent in the population relative to genes that die out, no?

Let me describe a particular creature in a particular situation as an example: the grasshopper. Did you know that the grasshopper, if trapped, automatically dies? If a grasshopper dies, it does not pass on its genes, naturally; so this is a situation in which survival is not enough. People suicide as well. One must ask "how is it that survival ceases to be enough for the grasshopper, if it is evolved to survive" don't you think? After all, it may be trapped merely temporarily!

I realise at this point that the issue of how a mutation becomes a controlling factor has split into two issues: how does it lead to the right responses to the environment and how are those responses recognised as right. As you can see I am able to learn from this.

 

[Patashu]

Mutations are random, yes, but if they are all either neutral or detrimental (because the species has already reached the top of a fitness 'mountain' and can't improve unless the environment changes or a slightly higher area can be found) then the species will remain more or less the same. It's kind of like a chemical system in equilibrium; even while you have tons of molecules reacting in both ways, the net effect cancels out so there is lots of movement and yet no movement.

Asking whether mutations are stronger then selective pressures or not is meaningless. Selective pressures act[/i] on mutations. It's like asking whether x is stronger or weaker than f(x).

As for the grasshopper, detrimental traits can be kept in the genome if they are detrimental but not quite detrimental enough to be weeded out. An example would be cancer in humans; it's the biggest killer today, but only because so many humans grow to old age when it becomes prominent. In the past this would rarely have been a problem. In addition, most cancer will occur well after the human in question has reproduced, if he plans to, thus not effecting reproductive success. You could also consider a trait that is detrimental but can't be removed by mutation without upsetting some other benefitial trait (for example, the way the optic nerve is arranged in the human eye creates a blind spot, but to fix it and move it the right way around is impossible; you'd have to travel through intermediate stages where the eyes do not work for millions of years, a clear disadvantage)