How are mammals born? How do mammals give birth?
The miracle of childbirth is an universal phenomenon that occurs in many different ways throughout the animal kingdom. The process of birth is fascinating for us humans as well as our pets and wild animals. Understanding the birth of mammals reveals an incredible story of parental care and biological adaptation. It also reveals fundamental traits that tie our entire group of animals together. This article will explore the journey from conception through to delivery and the various reproductive strategies that help ensure the survival of future generations. It also addresses the query “how are mammals born”.
What is the defining feature of a mammal?
It’s important to know what makes a mammal before we can understand the birth process. The most important trait for birthing mammals is the presence of mammary glands in females. These glands are responsible for producing milk, which is the only source of nutrition in the early days of life of newborn mammals. The need for milk is what drives mammalian reproduction, parental care and the birthing process.
Mammalian birth is rooted in two main reproductive strategies, which have evolved to achieve different benefits.
The two paths to mammalian birth: viviparity and exceptional oviparity
Viviparity is a term used to describe the birth of live young by nearly all mammals. There is one remarkable exception to the rule.
1. Viviparity is the birth of a child.
In viviparous mammal species, the embryo is developed inside the mother’s body. This occurs in a special organ called the “uterus” (or “womb”). This provides a protected, temperature-controlled environment where the developing offspring, connected via the placenta, receives oxygen and nutrients directly from the mother’s bloodstream while also having waste products removed.
This internal development offers superior protection against predators and other environmental hazards, compared with eggs that are left unattended. The level of development is used to divide viviparity into two distinct categories.
2. Monotremes are Egg-Laying Mammals.
A small group of monotremes, a subgroup of mammal species, lay eggs. It is called oviparity. Monotremes include the platypus, two species of echidna and other animals.
The process: After a brief gestation inside the mother’s body, she lays an egg that is similar to the egg of a reptile.
The “Birth:” She incubates an egg for a certain period of time (e.g. ten days or so for a platypus).
The Mammalian Connection: When the egg hatches and the underdeveloped baby is born, it becomes a mammal. It is blind and hairless. It’s completely dependent on the mother’s milk.
Monotremes are a link in evolution between reptiles, other mammals and reptiles. They represent a primitive mammalian form of reproduction.
The stages of viviparous mammalian birth
The vast majority of mammals including humans, cats and dogs, whales and elephants follow a viviparous birth path. This process can easily be divided into three stages.
Stage 1: Gestation (The Internal Development)
The gestation period is the time between conception, and delivery. During this period, the fertilized ovary implants into the uterine walls and develops to a fetus. The length of gestation is highly variable between species and closely related to the size of the animal and the level of development required by the newborn.
Short Gestation:Small rodents such as mice have a pregnancy of around 20 days. They have large litters with many altricial (underdeveloped young).
This category includes humans (9 month), dogs (2 month), and cats.
Long Gestation: Large animals require more time. The elephant’s pregnancy lasts 22 months, the longest gestation period of any land mammal. A calf born after this time can walk in just a few hours.
The placenta provides a vital link between mother and child during the entire gestation.
Stage 2: Parturition and Labor (The Birth Process).
The act or process of giving childbirth is called parturition. Typically, it is divided into three stages:
1.Dilation: Hormonal fluctuations trigger contractions in the uterine muscle. The opening of the uterus (cervix) starts to dilate to allow for the passage of the fetus. This stage is usually the longest of all.
2.Expulsion:The fetus is pushed through the birth canal by rhythmic, strong contractions. During this phase, the mother will often actively push. Most babies are born with their heads first, but breech births, or feet-first, are not uncommon.
3. Afterbirth: After the baby is born, the placenta, fetal membranes and other tissues are expelled by further contractions. This is collectively known as the afterbirth.
Stage 3: The First Moments
Birth is not the end for viviparous mammal development. Survival depends on the first hours and minutes of life.
Breathing:The change from a fluid-filled uterus into a world that breathes air is dramatic. Passing through the birth canal causes the fluid in the lungs to be cleared by the physical pressure. A change in temperature or environment can trigger the newborn’s first breath.
The Umbilical Cord. The cord that connected the fetus with the placenta is normally severed by either the mother by chewing or by a professional. The remnant falls off and dries, leaving only the navel.
The first meal: A newborn’s instinct is to drink its mother’s breast milk. The first milk is called colostrum and it contains a lot of antibodies and nutrients. It provides passive immunity as well as essential nutrition. Nursing strengthens the relationship between mother and child.
The Spectrum of Newborn Development – Precocial vs. Altricial
Not all newborn mammals are equal. The level of development they have at birth is on a scale:
Young Altricial: These newborns have no hair, are blind, deaf and helpless. These newborns are completely dependent on their mothers for warmth, nutrition, and protection. Humans, cats, and dogs are examples. They are usually born in litters, and they develop safely within a nest or den.
Precocial young:These newborns arrive in a more advanced condition. These newborns are often covered in fur and have open eyes. They can also stand, walk and run within hours of being born. It is vital for animals such as horses, deer and wildebeest, which live in open areas and must avoid predators instantly. Calves, lambs, and foals are examples.
This is an evolutionary trade-off that forces you to choose between investing in a long pregnancy (precocial), or in intensive postnatal care.
The Unified Journey to Nourishment & Care
How do mammals get their start? Answer: a complex web of biological processes. The journey ends in the same crucial, defining moment, whether it is the egg-laying platypus, or the live birthing whale calf. The mammary is responsible for this act of nursing. This ensures that a newborn, whether it is a helpless baby or a galloping horse, receives nourishment and protection to thrive. It continues the amazing cycle of life which defines the class Mammalia.