Biology:
Implicating Continental Drift in Speciation:

The displacement and rearrangement of land masses over geologic time has
helped to create biological diversity on our planet. Without the profound effects
created by geological reconfiguration life on earth might have been very different
from the way that it is now.

Continental drift is the movement of land masses due to the effects of plate
tectonics. Originally all of the world’s surface land was located in one region on
the globe, Pangea. This supercontinent supposedly began to separate late in the
Triassic Period (245 to 208 million years ago) into a southern landmass,
Gondwanaland, and the northern landmass Laurasia. Gondwanaland was
composed of the modern day continents of India, Africa, Australia, Antarctica and
South America. These continents began to break up and head towards their
present day locations only some 130 million years ago. Because these two land
masses were the only two continents on the face of the earth for about 520 million
years they are perhaps two of the most important geological structures of the last
billion years. Our modern understanding of continental drift, and the structures that
it has produced, has inexorably impacted our understanding of the fossil record
and has given us detailed information about the evolutionary history of animal
species.

The earth is populated by tens, perhaps hundreds of millions of animal species.
We can attribute this fantastic diversity, in part, to an evolutionary trend called
speciation. Speciation is a phenomenon that normally takes place when a group
of animals of the same species find themselves isolated from one another. They
can be isolated geographically by great distances, rising mountains or large
bodies of water.

They can also be isolated by biological or behavioral barriers. One species is
distinguished from another by their inability to create viable offspring together,
and this is the precise effect that isolation can have on an animal species. Once
a group of animals of the same species becomes split apart or isolated, they
begin to be changed, molded and fashioned by the hand of natural selection to
more properly fit in with their surroundings. After a period of time these two
groups begin to be so different anatomically and genetically that soon it becomes
impossible for them to procreate. This inability for two animals, that were once
the same species, to create viable offspring is called speciation.

Before 130 million B.C. the land mass of Gondwanaland was the home to many
types of mammals. Thanks to plate tectonics it was split in two to create modern
day South America and Australia. Many mammals called Gondwanaland their
home and after it split, two very different types of mammals emerged. One order
of mammal began to both thrive in Australia and die out in South America. These
were marsupials, or pouched mammals, and they evolved into modern day
kangaroos, koalas, wallabies, wombats and tasmanian devils. Infant mammals
that leave the mother’s stomach and finish off their gestation period in a warm,
nutrient providing pouch are marsupials. The only type of marsupial species able
to survive in the South American continent after the break up of Gondwanaland
was the opossum. On the other hand, on the isolated continent of Australia,
almost all of the indigenous mammals are in fact marsupials.

Very soon placential mammals, (the order that we belong to) and marsupials
were on opposite sides of the globe. Today marsupials cannot mate with
placential mammals. Their genetic and anatomical differences created
unsurmountable barriers, making them sexually incompatible. The story of the
order marsupialia is perhaps one of the most dramatic demonstrations of the
effects of continental drift on speciation.

The different types of primates with whom humans were able to mate have long
since died out. At one time we were very similar anatomically and genetically to
some of the other species of primates on the planet. Humans and Neanderthals
were sexually compatible, meaning that functionally we were not two different
species. Because of behavioral differences, probably due to discrepancies in
socialization and intellect we simply did not mate with their kind very much at all.

Animal speciation can be caused by geographical barriers, sexual barriers,
behavioral barriers -and this example makes it obvious that social barriers can
prove causal as well. If some of these barriers had not existed, and if our
geographical configurations were not in constant flux then humans may never
have evolved the way that they did, or may never have evolved at all.

Evolution: noun
Change in the genetic composition of a population during successive
generations. The development of species resulting from the way natural selection
acts on the genetic variation among individuals.

Gondwanaland: noun
The hypothetical protocontinent of the Southern Hemisphere that, according to
the theory of plate tectonics, broke up into India, Australia, Antarctica, Africa, and
South America.

Neanderthal: noun
An extinct human species (Homo neanderthalensis) or subspecies (Homo
sapiens neanderthalensis) living during the late Pleistocene Epoch throughout
most of Europe and parts of Asia and northern Africa and associated with Middle
Paleolithic tools.

Order: noun
Biology. A taxonomic category of organisms ranking above a family and below a
class.

Pangea: noun
A hypothetical supercontinent that included all the landmasses of the earth.  
Before the Triassic Period Pangaea broke up into Laurasia and Gondwanaland.

Speciation: noun
The evolutionary formation of new biological species, usually by the division of a
single species into two or more genetically distinct ones.

Triassic Period: noun
The period from 190 million to 230 million years ago. Marked by dinosaurs,
marine reptiles; volcanic activity
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