"Reproductive strategies for the human species have basically remained unaltered since Homo sapiens first appeared, probably in the valleys of Africa: males have always attempted to pass their genes to the largest feasible number of females, selecting those females capable of providing the best quality of oocytes; females invariably have sought a male capable of providing the best means of survival for herself and her offspring. This meant that human sexuality has been essentially conceptive, although it is reasonable to suppose that it began to lose this 'exclusive' connotation early in the cultural evolution of the species. Then, during the 20th century, major revolutions occurred: first, with the advent of contraception, sex without reproduction became a reality; then, with assisted reproduction technology, humans devised reproduction without sex; finally, very recently, women have begun to reproduce even in menopause. Additional strategies will, no doubt, soon be available, although we cannot as yet clearly see whether, or when, reproduction without sex and gametes, or in-vitro gestations will become available." from http://www.ncbi.nlm.nih.gov/pubmed/12470340

Reproductive strategies of Australian Marsupials: http://www.adelaide.edu.au/ANZCCART/publications/AustMarsupials_21.pdf


"Considerable interchange of mammals between South America and Australasia occurred during the first half of the Tertiary, including the presence of placental mammals in Australia. This challenges the old assumption that the marsupial radiation in Australia was made possible by the absence of placental competition, and suggests that two properties of marsupial organization may have favoured their survival in the increasingly arid climates that developed after the separation of Australasia from Antarctica. The basal metabolic rates of marsupials are about 70% of equivalent placentals, so their maintenance requirements for energy, nitrogen and water are lower, whereas their field metabolic rates are about the same, which means that they have a greater metabolic scope to call on when active. This may have given marsupials an advantage in semi-arid environments. The lengthy and complex lactation of marsupials enables the female to exploit limited resources over an extended period without compromising the survival of the young. Both these properties of marsupials enabled them to survive the double constraints of low fertility soils and the uncertain climate of Australia throughout the Tertiary. The arrival of people was followed first by the extinction of the large marsupials and, much later, by the wholesale decline or extinction of the small-to-medium sized species. The common factor in both extinctions may have been the constraints of marsupial reproduction." from http://www.publish.csiro.au/paper/RD01079.htm