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Era of 'Biological Annihilation' Is Underway, Scientists Warn (theguardian.com)
Tatiana Schlossberg reports via The New York Times (Warning: source may be paywalled, alternate source): From the common barn swallow to the exotic giraffe, thousands of animal species are in precipitous decline, a sign that an irreversible era of mass extinction is underway, new research finds. The study, published Monday in the Proceedings of the National Academy of Sciences, calls the current decline in animal populations a "global epidemic" and part of the "ongoing sixth mass extinction" caused in large measure by human destruction of animal habitats. The previous five extinctions were caused by natural phenomena. Dr. Ceballos emphasized that he and his co-authors, Paul R. Ehrlich and Rodolfo Dirzo, both professors at Stanford University, are not alarmists, but are using scientific data to back up their assertions that significant population decline and possible mass extinction of species all over the world may be imminent, and that both have been underestimated by many other scientists. The study's authors looked at reductions in a species' range -- a result of factors like habitat degradation, pollution and climate change, among others -- and extrapolated from that how many populations have been lost or are in decline, a method that they said is used by the International Union for Conservation of Nature. They found that about 30 percent of all land vertebrates -- mammals, birds, reptiles and amphibians -- are experiencing declines and local population losses. In most parts of the world, mammal populations are losing 70 percent of their members because of habitat loss.
Since this is all about habitat loss, which is mainly caused by people clearing land to make way for farmland, we already have a well known proven effective solution to minimize the need for all of that: GMO. Unfortunately, groups like Greenpeace and pretty much every European government have dashed all hopes of that ever seeing global adoption, and the Democrats in the US figure it would be awesome if we made agriculture even less efficient and more wasteful than what we have now by pushing for everybody to go all organic under the (totally false) notion that it is healthier. But you know, because Monsanto exists, obviously we need to throw out GMO technology and never use it again.
Any ancestors we had with 4-color vision were probably before we became mammals. Most mammals have 2-color vision; only some primates (including humans) have 3-color vision, due to duplication and later mutation of one of the genes that support 2-color vision.
While we can't say for sure why mammals went down to 2-color vision, the standard explanation is that nocturnal animals do not need the extra color channel, and may be helped if they lose it (e.g. by having more space for rod cells). This explanation is supported by studies of modern mammals, and how one of the two common mammalian cone cells are absent or non-functional in strongly nocturnal mammals. If mammals did not have such a long small-nocturnal-animal phase, we would probably have retained more capacity for color vision.