Michael A Woodley suggests that what was going on was much more likely to be mutation accumulation with deleterious (but not-individually-fatal) mutated genes incrementally accumulating with each generation and generating a wide range of increasingly maladaptive behavioural pathologies this process rapidly overwhelming and destroying the population before any beneficial mutations could emerge to 'save' the colony from extinction. The suppression of breeding happened very quickly, and never recovered even after the population declined rapidly and crowding was reduced, and 3. The mouse population never actually became crowded, 2. But this seems, very obviously – I would have thought – an incorrect explanation because 1. The Mouse Utopia experiment is usually interpreted in terms of social stresses related to 'over-population' that crowding generated pathological behaviours and a loss of the will to reproduce. This was a very surprising outcome, biologically and implies that some very major factor about the basic requirements or behaviour of the mice was neglected. The main fact about Mouse Utopia, was that despite everything possible being done to create ideal biological conditions the mouse colony rapidly declined and became entirely extinct. To summarise – when four breeding pairs of mice were allowed to reproduce under ideal ‘utopian’ conditions, the colony entirely ceased to breed after three years, and then went extinct. The last conception was about day 920, after which there were no more births, all females were menopausal, the colony aged and all of them died. Terminal Phase E - population declining to zero. Emergence of many pathological behaviours. Phase D - days 560-920 population stagnant with births just matching deaths. Phase C - from day 315-560 population growth abruptly slowed to a doubling time of 145 days. Phase B - up to day 315 - exponential population growth doubling every 55 days. Phase A - 104 days - establishment of the mice in their new environment, then the first litters were born. What happened was described by the author in terms of five phases: establishment, exponential growth, growth slowing, breeding ceases and population stagnant, population decline and extinction: The so-called ‘Mouse Utopia’ experiment was conducted from 1968 by John B Calhounįour healthy breeding pairs of mice were allowed to reproduce freely in a 'utopian' environment with ample food and water, no predators, no disease, comfortable temperature – a near as possible ideal conditions and space. Note: for convenience in referencing - this essay is cross-posted in a dedicated blog: A microcosm of what went wrong with the industrial revolution: Calhoun’s Mouse Utopia experiment
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