Natural Selection In Animals

According to Zimmer and Douglas 2013, evolution is a species changing over time. Zimmer also stated that since “nature” produces more individual with more variation. Thus, it appoints natural selection as one of the main mechanism for evolution. Thomas Malthus, who was an English cleric that dabbled in the areas of demography and economy, wrote about the “struggle for existence” in relationship to there being a limited food supply, however, if permitted through no external forces, species will continue to breed until the ratio of them is higher than available food. At which point, completion for the depleting resources will arise. Malthus directed this thought to humans; but this theory got Darwin thinking about natural selection in animals

Some of these parental behaviors included feeding, grooming, “babysitting”, and protecting the territory. Cooperative breeding can be found in avian and mammals where adult “relinquish” breeding rights and tend to other’s offspring’s in an effort to raise the young. Cooperative breeding has been noted to exist in more than 150 species of birds and nearly 25 species of mammals (ranging from rodents to elephants (Jennions and MacDonald 1994), and as more studies are conducted the number marked animals that cooperative breed is on the rise (Elmen 1982). One example of cooperative breeding in avian species is the acorn woodpecker. They have one of the most bizarre mating systems of any bird in the world. They are cooperative breeders that live in subunits composed of sometimes six co-breeding males (brothers and/or fathers and their sons competing for mates), three joint-nested females (who are sisters or a mother and her daughter who lay their eggs together), and nonbreeding helpers of both sexes (Koenig 1998). Thus, proving co-breeding can be different between different

In these groups, the one adult male reproduces with genetically similar females. Due to close-nit coteries, black-tailed prairie dogs undergo inbreeding often. Inbreeding illustrates a decrease of the offspring’s overall fitness, due to the limited variation; however, studies have shown no evidence to support this claim (Jennions and MacDonald 1994). Its main purpose that the author (John L. Hoogland) is trying to convey is evidence to support his earlier work, called Analysis of the Mating System in the Black-Tailed Prairie Dog (AMSBTPD), on prairie dogs. These prairie dogs exist where some females and pups (yearlings) within the “town” usually do not breed. However, they behave parentally towards non-offspring. Another article states that about 90% of the yearling black-tailed prairie dogs females do not breed. Most females do not disperse whereas yearling males, during the breeding season, disperse (Blumstein 1999). In addition, the Hoogland classified these black-tailed prairie dogs as cooperative breeders, although "do not assist breeders to the same degree as most bird cooperative breeding groups” (Hoogland 1981, pg. 285), in 1983, two years after his 1981