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
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
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
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.