Developmental homeostasis is a process in which animals develop more or less normally, despite defective genes and deficient environments. It is an organism's ability to overcome certain circumstances in order to develop normally. This can be either a physical or mental circumstance that interferes with either a physical or mental trait. Many species have a specific norm, where those who fit that norm prosper while those who don't are killed or find it difficult to thrive. It is important that the animal be able to interact with the other group members effectively. Animals must learn their species' norms early to live a normal, successful life for that species.
Developmental homeostasis determines how a species adapts to live a normal life. Therefore, it has been the focus of many experiments. These experiments are geared and designed to test the threshold for certain species to overcome and prosper despite certain circumstances.
Due to the fact that survival of the species is based on the ability to interact with their own in a normal manner, these experiments—which usually interfere with that—walk a fine line for animal rights and what is acceptable. The rhesus monkey experiments show how the young monkey needs the physical contact with other monkeys to learn the social behaviors and interact with each other effectively. This is one of the ways mental developmental homeostasis has been researched. One way physical developmental homeostasis was tested was in the facial symmetry experiment where people were asked to rate which of the faces they saw as better looking. This experiment resulted in the pictures with more symmetrical faces being called better looking. This is not just found in humans but other experiments such as the brush-legged wolf spider and the barn swallow birds. Favored traits give the bearer an advantage in attracting high quality mates.
In species that value developmental homeostasis, both physically and mentally, the ability of one to adapt to social norms seems to increase the likelihood of having a reproductive advantage being able to attract mates and leave offspring.
Developmental homeostasis: isolation of monkeys
Developmental homeostasis attributes to the way many animals develop. This contains the way they develop normally or abnormally despite faulty genes and an insufficient environment. This property of development reduces the variation around a mean value for a phenotype, and reflects the ability of developmental processes to suppress some outcomes in order to generate an adaptive phenotype more reliably.
Effects of social isolation in rhesus monkeys
The effects of developmental homeostasis were demonstrated in an experiment conducted in 1966 by Margaret and Harry Harlow. They wanted to test what the consequences of infant rhesus monkeys would be from being separated from their mothers and having little interaction with other monkeys. First, they were separated from their mothers for six to twelve hours after birth and placed with a human made mechanical substitute in which they called the "surrogate mother." These surrogates were made either of a wire cylinder structure or a terry cloth structure and were placed with the babies is a cage. The terry cloth structure was also placed with a nursing bottle. The monkeys preferred and clung to the cloth surrogate mother. In a short period of time the monkeys took on side effects of weight loss and not abnormal physical development. Once the monkeys reached an age where they could eat solid foods, they were separated from their cloth mothers for three days. When they were reunited with their mothers, they clung to them and did not wander off. Young rhesus monkeys in their natural habitat normally explore and venture off. Harlow concluded from this that the need for contact comfort was stronger than the need to explore. Being isolated from social interaction also caused negative outcomes later in their life. The surrogate-raised monkeys exhibited depression and aggressive behavior as they would clutch to themselves, rock constantly back and forth, and avoid interaction with others. Not only affecting their social behavior, it also impacted them interacting sexually. The monkeys underwent little if any sexual posturing or reproduction in their lifetime.