A D MACKAY © All Rights Reserved


Over the last 180 million years the land masses have been drifting over the surface of the planet, changing their latitude and climatic conditions. Land animals have been constantly challenged and these challenges have required intelligent opportunism. Many of those animals which were unable to adapt to changing conditions became extinct. Arduous conditions often naturally select for intelligent behavioural repertoires. Large rivers and deep lakes are perhaps the most consistent habitats on land and this could account for the evolutionary stasis of the crocodile. Crocodiles have always been able to conceal themselves in rivers and avoid predation by predators like Tyrannosaurus rex and a river habitat offers a constant source of prey animals which need to either cross the river in migration or just drink from it. The crocodile’s ability to ambush animals, drag them under water and drown them, ensures their constant supply of food. They can endure long periods of starvation by living on fat reserves stored in their tails. Crocodiles have been in their present form for at least 180 million years and the break up of the Super-continent Gondwana and the drift of its fragments, has dispersed these animals as far afield as Australia, on one side of the Earth, and America

on the other.




Evolutionary Trimming and Vestigial-ism


Each species organism is constantly being ‘tuned’ for survivability. When a species pioneers a new habitat - certain attributes required in the old habitat may be surplus to requirements in the new one.


Fish which have chosen to live in dark caves, for example, no longer need vision and so their eyes are reduced to a minimal presence. They become vestigial. Why possess a functional pair of eyes when organs are, from an energy point of view, expensive to run?


Snakes have vestigial pectoral and pelvic girdles. We have sinus tubes which appear to be the vestiges of a very elaborate olfactory system. We, like other apes, have vestigial tails. We also have vestigial third eyelids (nicticating membranes). Functioning third eyelids are found in many birds and reptiles.


We also have many vestigial muscles systems like those that can move the scalp or the ear lobes. We also have an organ in our digestive system known as the appendix and this is the vestige of a large caecum found in other animals. Basically, vestigial organs are comprised of cells which are constantly suppressed in their development. From time to time these organs re-appear in full form and  if the circumstances of the environment have changed the animals with them may be selected for again.


One may ask why do mammals have tails anyway? Tails do serve many purposes. In rats and mice, for example, they are used for counterpoise when walking along and reaching out from narrow branches. Kangaroos use them for balance when hopping along on their back legs. Beavers, otters and platypuses use their tails as paddles when swimming. Some monkey tails are prehensile while others are used for balance or braking when swinging through the trees. Many animals use their tails as whisks for removing flies from their rear quarters.




The predominant factor which drives evolution is the adaptation of the animal to a new environment. The characteristics of the animal are then fashioned by this new environment.

An analogy of this process is the wide range of vehicles which now exist. The basic concept of a motor vehicle with four wheels, a chassis, and an engine has ‘evolved’ into several variants and it is the ‘environment’ which has determined their shape and size. Racing cars are like they are because they need to be powerful and go round corners at high speed. Road cars need to carry passengers safely as possible and be economical to run. Trucks need to be huge in order to carry heavy loads. Tractors need to be able to pull machinery over boggy fields. The result is that all these different forms of vehicles are variations on a basic theme. In a similar manner, animals of a particular group have a wide range of species which exploit or specialise different niches within environments. This specialisation was first observed by Darwin when he visited the Galapagos Islands and noted that the finches there had a variety of beak forms and each species had adapted to a different niche within the Galapagos eco-system.

Taking the above analogy further, vehicles ‘evolve on’ and change their shape or style over time; Veteran cars, for example, could be classed as extinct and can be seen as no longer suitable for present day road environments. Competition from more dynamic and efficient models has forced their demise.

Adaptation to a new environment or habitat may be by the slow selection for traits which better suit the new environment. This change is incremental throughout subsequent generations of a species population.

Page 86
Page 83
Page 88
Evolution of the horse
Evolution of whales
Vestigial wings
Vestigial organs