The koala is found in coastal regions of eastern and southern Australia, from Adelaide to the southern part of Cape York Peninsula. Populations also extend for considerable distances inland in regions with enough moisture to support suitable woodlands.
Koalas have been divided into three subspecies and as a matter of rule individuals from southern cooler climates are larger.
A typical Victorian koala (formerly P. cinereus victor) has longer, thicker fur; is a darker, softer grey, often with chocolate-brown highlights on the back and forearms; and has a more prominently light-colored ventral side and fluffy white ear tufts. Typical and New South Wales koala weights are 12 kg (26 lb) for males and 8.5 kg (19 lb) for females.
The other extreme are Koalas in tropical and sub-tropical Queensland. In Queensland the koala is smaller (at around 6.5 kg (14 lb) for an average male and just over 5 kg (11 lb) for an average female); a lighter often rather scruffy grey in colour; and has shorter, thinner fur. In Queensland, the koala was previously classified as the subspecies P. cinereus adustus.
Intermediate forms are found in New South Wales named as P. cinereus cinereus.
A fourth variation, though not technically a subspecies, is the "golden koala", which has a slight golden tinge to the fur as a result of an absence of the melanin pigment that produces albinism in most other mammalian species.
The variation from one form to another is continuous. There are substantial differences between individual koalas in any given region such as hair colour. Koalas may also have white fur in rare cases due to a recessive gene.
Koala fossils are quite rare, but some have been found in northern Australia dating to 20 million years ago. During this time, the northern half of Australia was rainforest. The fossil record indicates that before 50,000 years ago, giant koalas inhabited the southern regions of Australia. The koala fills the same ecological role as the sloths of South America.
Koala lives almost entirely on Eucalyptus leaves. It has firm preferences for particular varieties of eucalypt and these preferences vary from one region to another: in the south Manna Gum, Tasmanian Blue Gum, and Swamp Gum are favoured; Grey Gum and Tallowwood are important in the north, and the ubiquitous River Red Gum of the isolated seasonal swamps and watercourses that meander across the dry inland plains allows the koala to live in surprisingly arid areas. Many factors determine which of the 680 species of eucalypt trees the koala eats.
From the above account of geography related variations in Koala size; fur color, length and texture; preference for different species of Eucalyptus trees in different regions it is obvious that 20 million years of existence of Koala in Australia have been insufficient to eliminate those variations. This is true despite there being no isolation and ample opportunities for dispersal and migration. These observations are in accordance with conclusions of J.C. Willis that dispersibility as an aid to invasion of unoccupied grounds is rarely significant for the purpose of evolution and the most cosmopolitan genera lacked such dispersion adaptations.
Darwinism says that evolution advances by accumulation of selected random variations and species come into being by dispersion of ancestral species followed by isolation of various populations followed by evolution of different populations into individual species by further accumulation of variations along divergent lines ultimately leading to origin of species.
However in the case of Koala bear we find:-
1. Variations are not random, rather they are geography related. Even Darwin admitted that flora and fauna on Galapagos Islands varied according to some geographical rule.
2. 20 million years of existence of Koala bear are neither able to eliminate those differences nor evolve different subspecies into species despite geographical continuity or lack of geographical isolation or absence of any barrier to dispersion.
3. Variations as well as species identity have been maintained despite geographical continuity.
Hence Darwinism can’t be reconciled with geography related variations in Australian Koala. Therefore Darwinism is not the final word about mechanism of evolution.