FREE ESSAY ON THE CATCHER IN THE RYE

THE CATCHER IN THE RYE

Our species has been so successful in spreading over the world and changing it, sometimes
more
to our liking, that it is difficult to see ourselves in relation to other forms of life,
to see ourselves
in nature. We have made ourselves different and set ourselves apart from the rest of the
natural
world. Perhaps for that reason alone, among many others, it is useful and instructive to
try to
understand our origins and to reconstruct our relationship to other life on the planet.
Since the great task of classifying the world's life forms according to their anatomical
similarities
got well under way during the late 18th century, the affinities between humans and the
great apes
have been recognized and pondered. In the mid nineteenth century, Charles Darwin
postulated
that apes and humans had a common ancestor. Until recently, however, we classified the
apes as
very distant cousins of human beings. The living great ape species include (from left to
right) the
gibbon; the orangutan; the gorrilla; the chimpanzee; the pigmy chimp or bonobo.
The pigmy chimp was only identified as a separate species in the 1930's.
More recently, genetic evidence from comparing our DNA with that of apes has led to new
views
of our degrees of relatedness. Asian apes--gibbons and orangutans--are, according to this
line of
evidence, not closely related to us or to the African apes. But human DNA is surprisingly
similar
to, and almost identical with, the DNA of chimps and gorillas; both ape species have 48
chromosomes, we have 46. Chimpanzees even share the same ABO blood types with humans,
and
thus appear to be very close kin to us.
As we approach the end of the twentieth century, new discoveries continually force us to
re-examine our origins, and to search for clues about our own nature, and what we share
with
other forms of lifeIntroduction
The mechanisms that led to the evolution of the huge diversity of species living today
are believed
to be identical to those that led to the evolution of our own species (Homo sapiens).
Whilst the above is true in general, there are details of the evolution of humans which
are still the
subject of much research and sometimes much controversy.
It is generally accepted that humans share a common ancestor with the other primates, and
many
lines of evidence support this. Most textbooks will have a diagram showing the most
likely
relationships between primates. Some of the animals on this diagram survive today, others
have
long been extinct.
*censored*Picture*censored*Look at the pictures of primates here, look at other primate
pictures in your textbook,
visit the Primate Gallery Web site, or best of all, take a trip to the Zoo and look at
the primates
there. 
You will see that all of these animals (including our own species), share many common
structural,
functional and behavioural characteristics, that is, there are many similarities in our
phenotypes,
including:
?Rounded faces with reduced snouts. Eyes protected by bony ridges. ?Relatively large
brains, with
a small area for smell, a larger area for vision. ?Large eyes point forward, giving
binocular 3D
vision. Colour vision present. ?Variation in tooth size and shape. A varied, omnivorous,
diet is
possible. ?Collarbones present, enabling brachiation (swinging by arms). ?Mobile limb
joints,
giving a wide range of limb movement. ?Five digits on hands and feet. Nails, not claws.
Opposable
thumbs enable grasping. ?Many quadrapedal, but most sit upright. Some bipedal, freeing
hands for
other activity. ?Internal fertilisation, long gestation. Long period of parental care.
?Social groups
usually well developed. Heirarchies common. Communication evident. 
This seems too much of a coincidence to blame on convergent evolution. When the
biochemical
evidence, based on similarity of DNA sequence for selected, common genes, is examined, it
is
clear that all of these animals are closely related.
Does this similarity between ourselves and our primate relatives mean that we came from
monkeys, or that monkeys evolved from humans?
Certainly not! 
This is merely another example of divergent evolution from a common ancestor. Somewhere
back
in evolutionary history the first primate ancestor appeared. Then, over time, mutations
occurred in
some populations of that animal, natural selection acted to favour the best adapted
individuals for
the particular environments, and slowly new species evolved. This evolution continued and
the
'branches' of the primate tree sprouted. Some branches flourished, some died, but what we
are left
with is a variety of similar but significantly different species. All are primates, all
came from that
common ancestor, but they are each the products of the environments that shaped their
present
forms.
that exist on the Earth with us.