A species is defined as a group of similar animals that can breed
together to produce fertile offspring.
Taxonomy is the scientific name for the classification of living things by
humans. A species is the ‘narrowest’ form of
classification, despite its common use among the non-scientific community. Carl
Linnaeus first developed the taxonomy hierarchy in the 18th century.
As you can see below, there are seven ‘layers’ to classification. The
example given is for the domestic cat. A helpful way to remember this is the acronym Keep Ponds Clean Or Frogs Get Sick.
In the past, species were categorised according to their morphology
(body shape) and common features. However, this method is not accurate
to today's standard. We now know that evolution has resulted in
animals evolving structures with similar functions separately, multiple times
(known as analogous features). For example, wings in birds and bats. Simply
sharing this feature, does not mean that bats and birds closely related.
Species are constantly being re-named and re-categorised, largely due to
the new technology available to taxonomists today. DNA analysis can be used to
work out the tree of life of modern species and their ancestors (the
phylogeny). This technology has led to many species being re-classified, such
as the mammal the pangolin. These creatures were once thought to be closely related
to anteaters and sloths (Order: Xenarthra) to form the toothless group of
mammals named the Edentata. However, DNA
analysis has resulted in pangolins being re-classified into their own Order,
the Pholidota . The analysis of
their genes has determined pangolin's closest living relatives are actually
carnivores!
DNA technology has discovered that many animals, previously thought of
as a species, are actually two or more sub-species meaning that they are
distinctly different from each other. This is the case in the tuatara reptiles
(genus Sphenodon) on different islands near New Zealand. This
knowledge strongly affects the conservation of these reptiles, as they must be
managed as different species. Management aims to
avoid the dilution of their rare and unique genes, amongst the more common
sub-species caused when two sub-species mate.
A species is actually just name created to classify nature into
categories. There is a debate regarding how to define a discrete ‘species’ and
whether individual species actually exist. Darwin and many others argue that
species are just a belief by humans, and that a species is not a 'natural
category', but more of a continuum. This debate has
been occurring for the last 150 years. Living organisms
are constantly under the influence of evolution and selection influecnes the
population. Under intense natural selection or over long time periods species
change and become new species. The issue is, how do we declare one species has
become another? And when do we decide this?
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