One of my many hats at work is flagging wetlands and identifying 'protected species'.
So I use morphological indicators to identify the extent of inundation and saturation (plant adaptations for anaerobic conditions).
It is not a huge leap to imagine that plants that survive at the fringe and spread uphill and down hill from the shore might adapt over time until they diverge as two related but distinct species.
So I get micro-evolution.
Where I struggle is the bigger change like from cold-blooded to warm-blooded.
At one point, there were no warn-blooded animals.
At some point there were both cold and warm blooded animals.
How does that happen slowly?
Where are all of the 'tepid-blooded' fossils?
I do not claim that these transitions do not exist ... I simply claim ignorance on the topic.
Now if you want to talk Newtonian Physics, then I am your man.
The circulatory system is complicated, but it its wrong to assume there is a distinction between warm-blooded animals and cold-blooded animals that can't be crossed. Consider:
"A
poikilotherm is an
organism whose internal temperature varies considerably. It is the opposite of a
homeotherm, an organism which maintains
thermal homeostasis. Usually the variation is a consequence of variation in the
ambient environmental temperature. Many terrestrial
ectotherms are poikilothermic.
[1] However some ectotherms remain in temperature-constant environments to the point that they are actually able to maintain a constant internal temperature (i.e. are
homeothermic). It is this distinction that often makes the term "poikilotherm" more useful than the vernacular "cold-blooded", which is sometimes used to refer to
ectotherms more generally.
Poikilothermic animals include types of vertebrate animals, specifically fish, amphibians, and reptiles, as well as a large number of
invertebrate animals. The
naked mole-rat is the only mammal that is currently thought to be poikilothermic.
[2][3]"
http://en.wikipedia.org/wiki/Poikilothermy
As far as how natural selection allows for increasing complex system, I can give you some materials for food of thought:
The circulatory systems of all
vertebrates, as well as of
annelids (for example,
earthworms) and
cephalopods (
squids,
octopuses and relatives) are
closed, just as in humans. Still, the systems of
fish,
amphibians,
reptiles, and
birds show various stages of the
evolution of the circulatory system.
In fish, the system has only one circuit, with the blood being pumped through the capillaries of the
gills and on to the capillaries of the body tissues. This is known as
single cycle circulation. The heart of fish is, therefore, only a single pump (consisting of two chambers).
In amphibians and most reptiles, a
double circulatory system is used, but the heart is not always completely separated into two pumps. Amphibians have a three-chambered heart.
In reptiles, the
ventricular septum of the heart is incomplete and the
pulmonary artery is equipped with a
sphincter muscle. This allows a second possible route of blood flow. Instead of blood flowing through the pulmonary artery to the lungs, the sphincter may be contracted to divert this blood flow through the incomplete ventricular septum into the
left ventricle and out through the
aorta. This means the blood flows from the capillaries to the heart and back to the capillaries instead of to the lungs. This process is useful to
ectothermic (cold-blooded) animals in the regulation of their body temperature.
Birds and mammals show complete separation of the heart into two pumps, for a total of four heart chambers.
Circulatory system - Wikipedia, the free encyclopedia
And:
The term
warm-blooded is a colloquial term to describe
animal species that have a relatively high blood temperature when compared with ectothermic ones, and maintain thermal
homeostasis primarily through internal
metabolic processes. These are characteristics of
mammals and
birds.
Both the terms "warm-blooded" and "
cold-blooded" have fallen out of favour with scientists because of the vagueness of the terms and an increased understanding of the field. Body
temperature types are not discrete categories. Each term may be replaced with one or more variants (see the next section for examples). Body temperature maintenance (
thermoregulation) incorporates a wide range of different techniques that result in a body temperature continuum.
Contents
Characteristics of warm-bloodedness
In general, warm-bloodedness refers to three separate aspects of
thermoregulation.
- Endothermy is the ability of some creatures to control their body temperatures through internal means such as muscle shivering or increasing their metabolism (Greek: endon = "within", thermē = "heat"). Some writers[who?] restrict the meaning of endothermy to mechanisms that directly raise the animal's metabolic rate in order to produce heat. The opposite of endothermy is ectothermy.
- Homeothermy is thermoregulation that maintains a stable internal body temperature regardless of external influence. This temperature is often, though not necessarily, higher than the immediate environment (Greek: homoios = "similar", thermē = "heat"). The opposite is poikilothermy.
- Tachymetabolism is the kind of thermoregulation used by creatures that maintain a high "resting" metabolism (Greek: tachys/tachus = "fast, swift", metabolēn = "throw beyond"). In essence, tachymetabolic creatures are "on" all the time. Though their resting metabolism is still many times slower than their active metabolism, the difference is often not as large as that seen in bradymetabolic creatures. Tachymetabolic creatures have greater difficulty dealing with a scarcity of food.
Reasons for term falling into disuse
A large proportion of the creatures traditionally called "warm-blooded", such as
mammals and
birds, fit all three of these categories (i.e., they are endothermic, homeothermic,
and tachymetabolic). However, over the past 30 years, studies in the field of animal thermophysiology have revealed many species belonging to these two groups that do not fit all these criteria. For example, many
bats and small birds are
poikilothermic and
bradymetabolic when they sleep for the night (or, in nocturnal species, for the day). For these creatures, the term
heterothermy was coined.
Further studies on animals that were traditionally assumed to be
cold-blooded have shown that most creatures incorporate different variations of the three terms defined above, along with their counterparts (
ectothermy,
poikilothermy, and
bradymetabolism), thus creating a broad spectrum of body temperature types. Even some
fish have warm-blooded characteristics.
Swordfish and some
sharks have
circulatory mechanisms that keep their
brains and
eyes above ambient temperatures, and thus increase their ability to detect and react to
prey.
[1][2][3] Tunas and some sharks have similar mechanisms in their muscles, improving their stamina when swimming at high speed.
[4]
Heat generation
Body "heat" is
generated by the
metabolism. This refers to the chemical reactions
cells use to break down
glucose into water and
carbon dioxide and, in so doing, generate ATP (
adenosine triphosphate), a high-energy compound used to power other cellular processes.
All organisms metabolize food and other inputs, but some make better use of the output than others. Like all energy conversions, metabolism is rather inefficient, and around 60% of the available energy is converted to heat rather than to ATP. In most organisms, this heat is simply lost to the environment. However, endothermic
homeotherms (the animals generally characterized as "warm-blooded") both produce more heat and have better ways to retain and regulate it than other animals. They have a higher basal metabolic rate, and also a greater capacity to increase their metabolic rate when engaged in strenuous activity. They usually have well-developed insulation in order to retain body heat, fur in the case of mammals and
feathers in birds. When this insulation is insufficient to maintain body temperature, they may resort to
shivering — rapid muscle contractions that quickly use up ATP, thus stimulating cellular metabolism to replace it and consequently produce more heat. In general, in hot environments, they use evaporative cooling to shed excess heat, either by
sweating (some mammals) or by panting (many mammals and all birds) — in general, mechanisms not present in poikilotherms.
Defence against fungi
It has been hypothesized that mammals and birds evolved warm-bloodedness as a defence against fungal infections. Very few fungi can survive the body temperatures of warm-blooded animals. By comparison, insects, reptiles, and amphibians are plagued by fungal infections.
[5]
Warm-blooded - Wikipedia, the free encyclopedia
Maybe I can find some relevant lecture material.
