I have argued for the first time that each animal or plant that has a stronger blood/ fluid circulatory system could have a larger bulk (Fig 1a); that animals with no circula- tory system such as nematodes and plant’s mites , have a tiny body size. Animals that have an open circulatory system (without arteries, without veins, without capillar- ies) – such as insects and some mollusks– have small body size. Animals owing a semi-open circulatory system (Comprise some veins and arteries, without capillaries) – such as crustaceans and some mollusks (bivalve) – have average body size. A closed circulatory system (Comprise arteries, veins and capillaries) is associ- ated to animals – such as some mollusks (Octopus), Annelid worms (earthworms) and vertebrates (fish, amphibians, reptiles, birds and mammals) – having a large body size.
Zoologists put all animals in the three groups: no circulatory system, open circulatory system and closed circulatory system. But for the first time, I use the term "semi-open circulatory system" and put the animals in four groups: no circulatory system, open circulatory system, semi-open circulatory system and closed circulatory system.
I begin with an analogy. Let us consider a city and its population. Each individual lives in a large or a small house depending on his/her financial condition. This means that if someone is well-to- do, he probably would live in a spacious house, whereas someone less well-off is not able to afford a roomy house and therefore is constrained to live in a cramped one. It is common sense and everyone accepts this easily. Similarly, during my inquiry I found out that animals and plants having a stronger heart or fluid circulatory system could afford larger body masses (Figs. 1a,1b).
Fig. 1. Reasoning about animal’s sizes (see the text for a longer discussion). – a) Animals that have a stronger blood circulatory system could have larger size. – b) Plants that have a stronger fluid circulatory system could have larger size. – c) If an animal’s/plant’s blood/fluid circulatory system is weak, it definitely has a small size. – d) If an animal’s/plant’s size is large, it definitely has a powerful blood/fluid circulatory system. – e) But if its blood/fluid circulatory system is powerful, its body is not necessarily large! – f) And if its bulk is small, its blood/fluid circulatory system is not necessarily weak!
This is because their strong system enables them to better overcome gravity and to pump fluids to greater distances and to higher levels. It is a matter of logic, that everyone can understand and accept. But if this is so obvious, why are scientists not aware of it ? What is the obstacle to find out the relation? Why is it that this simple relation between the power of blood/fluid circulatory system and bulk size of animals and plants has been overlooked? Where lies the problem? To find this out, let us go back to our example and ask ourselves some questions. Do people who are in a poor financial state live in small houses? The answer is "Yes", because no one who disposes of few money is able to buy a large house. Do all people who are well-to-do live in large houses? The answer is "No"! This is because some who have a lot of money live in small houses for whatever reason. It means that some of the rich may live in large houses, while others inhabit a small house, without any restriction to them. So, when we look at the houses of a city and see large houses among them, we can def- initely say that their owners are rich. But when we see a small house, we cannot say that their owners are poor. Because they may be rich!
In the biological world things are simi- lar. If the blood/fluid system of a living organism is weak, it is forced to have a small body (Fig. 1c). However, if its blood/fluid system is powerful, the body must not necessarily be large! It may be large or small, depending on different other factors (Fig.1e). But if it is large, it means that the cir- culatory system is strong (Fig. 1d). We can thus conclude that small animals or plants may have weak or strong blood/fluid systems (Fig. 1f). This confusing fact is the issue that has caused scientists not to find the relation between the power of blood/fluid circulatory system and bulk size of animals and plants.
To solve the problem, we should at first classify animals and plants according to their power of blood/fluid circulatory systems, then choose the largest species of each group and made the comparison among them. We should not involve animals having strong heart/small size in our consideration and compare only between animals having weak heart/small bulk and animals having strong heart/large bulk. By proceeding this way, the direct relation between the power of blood/fluid circulatory system and animals/plants bulk size will become evident.
Now, what about those "rich people living in a small house" – the animals that have strong hearts but small sizes? We should find a reason for their existence. We should ask ourselves what is the factor preventing them to live in larger houses. The animal has strong heart but small size. What is the factor preventing it to get larger? Scientists, instead of following the causal chain of the process, facing the difficoulty of the job, become disappointed and discouraged to find the sulution and do not ask to themselves the following correct questions:
A) Why have some of the animals and plants small sizes while they have strong blood/fluid circulatory systems? What is the factor preventing them to get larger?
B) Why the nature, have put such a factor inside the body of animals and plants so that their bulk sizes remain small despite of having strong circulatory system? Why the nature needs such animals (strong heart and small bulk)?
These two questions have been discussed and answered in two chapters of the book (Mardfar, 2000) and are two of the most important chapters of my book. It is impossible to create a logical and simple relation between blood/fluid circulatory system and body size of animals and plants without finding the answers of these two question and that why scientists previous to me were not able to find the relation.