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The ancestors of modern humans interbred with Neanderthals and another extinct line of humans known as the Denisovans at least four times in the course of prehistory, according to an analysis of global genomes published on Thursday in the journal Science. The interbreeding may have given modern humans genes that bolstered immunity to pathogens, the authors concluded. “This is yet another genetic nail in the coffin of our over-simplistic models of human evolution,” said Carles Lalueza-Fox, a research scientist at the Institute of Evolutionary Biology in Barcelona who was not involved in the study. The new study expands on a series of findings in recent years showing that the ancestors of modern humans once shared the planet with a surprising number of near relatives — lineages like the Neanderthals and Denisovans that became extinct tens of thousands of years ago. Before disappearing, however, they interbred with our forebears on at least several occasions, and toda...

Gender is determined genetically by two sex chromosomes. In mammals these are the X and Y chromosomes, with males having XY chromosomes and females having XX. In a mating, the parents each contribute one sex chromosome. As a result, it is the male that, genetically, determines the gender of the offspring. In birds, however, the sex chromosomes are referred to as Z and W, with females having ZW chromosomes and males having ZZ. In birds, therefore, it is the female that determines the gender of the offspring. In addition to determining gender, sex chromosomes carry genes that can affect other traits, such as plumage color. These characteristics have been used in sex-linked crosses and can be used to determine the gender of the offspring. Sex-linked crosses can only be produced with male and female chickens of differing breeds in specific combinations. For example, a Delaware female mated to a New Hampshire or Rhode Island Red male results in male offspring that will grow up t...

Water is a critical, but often overlooked, nutrient. Animals can survive longer without food than they can without water. Water is involved in every aspect of animal metabolism. It plays an important role in regulating body temperature, digesting food, and eliminating wastes. At normal temperatures, chickens typically consume twice as much water as feed. During periods of high temperature, water consumption can double or quadruple. To remain healthy, poultry flocks require water of adequate quality and quantity.  Several factors influence water quality, including the color, taste, and odor of water, as well as the presence of bacteria or other microbes, the levels of minerals, and other chemical and physical factors. Color, Taste, and Odor It is important that drinking water be clear, tasteless, odorless, and colorless. Water that is contaminated exhibits different characteristics depending on the contaminants. The presence of particles such as clay, silt, or organic mater...