Mammals_Concept_8
Mammalian Lifecycles
Mammalian Lifecycles
The key feature that sets mammals apart from other animals is the combination of live birth and initial feeding of the young from maternal mammary glands. The first stage of the life cycle of a mammal can be said to take place within the womb or uterus. All of the food and oxygen needs of the unborn foetus are supplied directly by the mother through the placenta: the foetus absorbs nourishment directly from the mother's blood supply
Due to this relatively lengthy pre-birth growing period, mammals are born fully formed — though some require a long period of parental care before they can be left to fend for themselves. Depending on the environment that they are normally born into, a mammal may be capable of running with its parent to avoid predators within thirty minutes of birth, or be helpless (perhaps even blind) and dependent on the mother for anything from a few days up to several months,
In this infant stage, a mammal will depend entirely on the mother for nourishment in the form of milk. The number of mammary (milk-producing) glands on the adult female is usually closely linked to the number of infants likely to be born at any one time — if there are any more infants than that number, some are likely to die due to lack of access to food. Over a period of time, the infant will be weaned off the milk (usually to make way for another birth group) and will begin to accept a more adult diet. The extended period that mammals spend in family groups of this kind allows the young to learn from the adults. They will learn survival skills such as predator avoidance, food gathering and possibly social behaviours. During adolescence, most mammals become more independent; in some species, they will move (or be driven) away from their family groups entirely.
When a mammal reaches maturity, which could be weeks or years after birth depending on the species (the larger mammals usually take longer to mature), they will often establish their own family groups. This helps to prevent inbreeding, which (for genetic reasons) would be bad for the health of the group.
While in the mature (adult)reproductive phase of their life cycle, most mammals change relatively little. The weakness brought about by old age will often result in the end of 'reproduction rights' and a change in lifestyle — but this depends on the social nature of the particular species. Some mammals support the elderly members of their family group for as long as possible, whereas others drive them away. There is still debate as to which of these categories humans fall into!
Most placental mammals progress through very similar developments within their life cycles. The level of parental care varies from species to species, but the initial maternal link is consistent. Most children will be aware of the stages of human development from their own experience, and can be encouraged to look for similarities and differences with other mammals. The life cycle of a non-placental mammal is discussed in another section.
Adolescent — an immature adutt stage in which reproductive capability and other adult characteristics are developing.
Adult — the stage of development in which the individual is fully capable of reproduction.
Infant — the stage of development immediately following birth, when there is still a high dependence on the mother or family group for nourishment
Some species of rat breed up to 1 3 times a year, with a maximum of 22 young in each litter. That's up to 286 young per mother in one year.
A baby blue whale grows at a rate of 90kg per day.
Elephants develop in the womb for almost 22 months, humans for nine months, and hamsters for 20 days.
For some common misconceptions and questions relating to the human life cycle .
Those children with mammalian pets can be encouraged to keep records of their development (including photographs or videos) and to share these with the rest of the class,
An excellent range of wildlife videos are available that focus on a single family group of a particular species of mammal. This will give the children the opportunity, within a single lesson, to observe the yearly cycle of such a group. The children could go on to collect information about other mammal species, using books, CD-ROMs or the internet.