Transcript Variation Within Species

Variation Within Species
Individual Variation

This is more obvious in some species
than is others.

E.g. in humans it is obvious, we are all
unique, with different fingerprints etc, but if
we looked at a jar of flies, it is doubtful if we
could tell the difference between them.
(although the flies probably could.)
Geographic Variation
Generally this occurs on a larger scale
than individual variation.
 The different races of humans are mostly
due to the geographical area in which
each race evolved.


Dark skin is an advantage in regions of
intense sunshine, e.g. the equatorial belt.
(India, Africa, Northern Australia, Polynesia)
Geographic Variation
Dark skin in high (cold) lattitudes prevents
the formation of vitamin D in the skin, so in
those areas pale skin has evolved.
 Along with this is a loss of pigment in the
hair and eyes, giving blonde hair and blue
eyes.

Geographic Variation
Among other animals the geographical
variation is not so obvious, but birds and
mammals living in high altitudes are
generally larger, and have shorter ears,
tails and limbs to reduce heat loss.
 In hot areas, long extremities and small
body size increase heat loss.

Arctic Fox – small pinna
European Fox –
medium pinna
African Fox – Large pinna
A Cline

If we move in a particular direction
through a range of a species, and find
that there is a continuous increase or
decrease in some characteristics
between adjacent populations, this
pattern is called a Cline.
A Cline
The NZ Tomtit shows a clinal variation in
the length of the tail and wing.
 North Island tomtits have shorter tails
and wings than their South Island
counterparts, and this reaches all the
way down to the Chathams, the Snares
and the Aukland Islands.

A Cline
The Snares Island sub-species is
actually an exception as it has a longer
wing than the more southern Auckland
Island sub-species.
 This is probably due to random variation
in the gene frequencies in a small
population on the Snares.

A Ring Species
When 2 apparently different species are
joined by a series of geographical and
structural intermediate types.
 This is called a Ring Species.
 E.g. in Britain and NW Europe – the
herring gull and the black-backed gull.
 These don’t interbreed in the wild, so
they act as 2 species.

A Ring Species
If you go east, there are initially only
black-backed gulls; the further east you
go, the more herring gull traits start to
appear.
 If you go west, there are only herring
gulls to start with; but as you continue
west, the birds start to show some blackbacked gull characteristics.
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A Ring Species

So you can form a circle around the
Arctic polar region with this ring of
different birds, emerging into 2 distinct
species.