1.0 Introduction
Human beings, as organisms, are subject to these facts of life, but uniquely in the living world, we are also able to rationalise and to moralize. We can readily understand that the basic instinct for life is present in other people too, and appreciate that we have a moral duty to protect that instinct in them. This has been termed the presumption in favour of life. Reproduction in mammals is a critical biological process that ensures the survival and continuity of species. It involves a complex interplay of physiological, genetic, and environmental factors that together drive the reproductive strategies and behaviors observed across diverse mammalian taxa.
Mammalian reproduction is characterized by internal fertilization, with most species exhibiting viviparity, where offspring develop inside the mother's body and are born live (Perry et al., 2004). Reproduction is the single most distinguishing characteristic of life. It is the driving force of evolution, which itself is responsible for the diversity of plant and animal species on Earth.
We humans are living organisms and these forces act on us just as any other species with which we share the Earth. We feel the urge to reproduce at a very powerful biological level at various times in our lives. It is not surprising therefore, that over the course of history all aspects of human reproduction have been the subjects of intense moral and ethical debate.
1.1 Background of Study
The study of reproduction is a relatively new specialty, and developed in large part from a focus on body politics during second wave feminism in the 1970s. It was also in the 70s, that the first IVF baby was born, making “infertility,” more of a chronic condition as opposed to barrenness or sterility. As new technological advances made it possible for increasing numbers of infertile couples to conceive biological children, more people came forward to seek assistance with reproduction (Angela, 2011)
Reproduction in humans and others mammals is the process by which sperm and egg cells are produced, brought together, join and develop into a new individual. Reproduction is the key to the continued existence of our species. Mammals reproduce by uniting sperm and egg internally in the female body by a process called internal fertilization.
Many mammals reproduce only during particular seasons of the year; not so with humans. Men produce sperm more or less continuously and women ovulate (produce an egg) about once a month. The male reproductive tract consists of the paired gonads (organs that produce sex cells), the testes, where sperm are produced, plus accessory structures that store the sperm, produce secretions to activate them and finally conduct them to the inside of the female reproductive tract.( Richard, 2000).
Reproduction in mammals is a foundational aspect of their biology, pivotal for the perpetuation and evolution of species. This reproductive process encompasses a wide array of strategies and mechanisms tailored to maximize reproductive success and ensure the survival of offspring under varying ecological conditions. The study of mammalian reproduction integrates knowledge from genetics, endocrinology, behavior, and ecology, offering a comprehensive understanding of how mammals adapt to their environments and maintain population viability.
The complexity of mammalian reproduction can be traced back to the evolutionary transition from external to internal fertilization, a hallmark of vertebrate evolution that provided significant reproductive advantages. Internal fertilization protects the developing embryo from environmental hazards and predation, a critical advancement that facilitated the success of terrestrial vertebrates (Perry et al., 2004). Among mammals, the development of viviparity, where the embryo develops within the mother’s body and is nourished through the placenta, represents a significant evolutionary milestone. The placenta not only facilitates nutrient and waste exchange but also acts as a selective barrier, protecting the developing fetus from harmful substances (Cross et al., 1994).
The earliest mammals appeared approximately 200 million years ago during the Mesozoic era. These early mammals were small, nocturnal creatures that likely laid eggs, similar to modern monotremes such as the platypus and echidna (Lillegraven et al., 1979). The evolution of viviparity, where offspring develop inside the mother’s body and are born live, marked a significant shift in reproductive strategies. This transition provided several advantages, including enhanced protection of the developing embryo from environmental hazards and predators, and greater control over the timing and conditions of birth (Perry et al., 2004).
The development of the placenta was another crucial evolutionary advancement. The placenta facilitates nutrient and waste exchange between the mother and the developing fetus, supporting more complex and prolonged embryonic development. This feature is particularly well-developed in eutherian mammals (placental mammals), which include the vast majority of modern mammal species (Cross et al., 1994). The evolution of the placenta allowed for longer gestation periods and the birth of more developed and viable offspring.
The diversification of mammalian reproductive strategies has been driven by ecological pressures and the need to optimize reproductive success in varying environments. For instance, the evolution of seasonal breeding patterns in many temperate species allows them to synchronize reproduction with periods of resource abundance, thereby increasing the likelihood of offspring survival (Bronson, 1989). Social structures and mating systems also evolved to maximize reproductive efficiency, with some species adopting monogamous pairings while others developed polygamous systems with complex hierarchies and competition for mates (Clutton-Brock, 1989).
Sexual selection has played a significant role in shaping reproductive traits in mammals. The differential investment in offspring by males and females has led to the evolution of secondary sexual characteristics, such as antlers in deer and elaborate courtship displays in birds and mammals. These traits are often used by males to attract females and compete with other males, driving the evolution of reproductive behaviors and physical characteristics (Andersson, 1994).
Human understanding of mammalian reproduction has advanced significantly over the past few centuries. Early studies were primarily descriptive, focusing on the anatomy and behavior of reproductive systems. With the advent of microscopy in the 17th century, scientists began to observe sperm and egg cells, leading to the discovery of fertilization and early embryonic development (Farley, 1981).
The 20th century saw major advancements in reproductive biology and technology. The discovery of hormones and their roles in regulating reproductive cycles revolutionized the field, leading to the development of contraceptives and fertility treatments (Greep & Astwood, 1975). The advent of assisted reproductive technologies (ART), such as artificial insemination and in vitro fertilization, has had profound implications for both human medicine and animal breeding. These technologies have enabled the manipulation of reproductive processes, facilitating genetic research, conservation efforts, and the treatment of infertility (Trounson & Mohr, 1983).
The role of sexual selection in shaping reproductive traits is well-documented, driving the evolution of characteristics such as elaborate courtship displays, secondary sexual traits, and competitive behaviors among males. These traits often result from the differential reproductive investment between males and females, with females typically investing more in offspring production and care, thereby becoming choosier in mate selection (Andersson, 1994). This dynamic creates a powerful selective pressure on males to develop traits that enhance their attractiveness or competitive ability.
1.2 Statement of Problems
Fertility changes with age. Both male and females become fertile in their teens following puberty. For girls, the beginning of their reproductive years is marked by the onset of ovulation and menstruation. It is commonly understood that after menopause, women are no longer able to become pregnant. Generally, reproductive potential decreases as women get older, and fertility can be expected to end 5 to 10 years before menopause. In today's society age-related infertility is becoming more common because, for a variety of reasons, many women wait until their 30s to begin their families.
Even though women today are healthier and taking better care of themselves than ever before, improved health in their in later life does not offset the natural age-related infertility. It is important to understand that fertility declines as a woman's ages due to the natural age-related decrease in the number of eggs that remain in the ovaries. This decline may take place much sooner that most women expect and thus hinder their chances of reproduction.
1.3 Hypothesis of the Study
The hypothesis of this study is stated in the null as;
- H0:Not every pregnant woman knows what to do if her labour starts early.
- H1:Every pregnant woman knows what to do if her labour starts early.
1.4 Aim and Objectives of the Study
The aim of this study is to outline the concept of reproduction in man and the challenges faced overtime. Some of the objectives include but not limited to;
- Give an insightful introduction to the concept of reproduction.
- Give an insight into some challenges of reproduction and how they can be managed.
1.5 Scope of Study
This study, as the title implies, has used man as a case study, hence all attempt to make the subject of reproduction clearer has been duly focused on man. Some of the areas covered include pregnancy and child birth.
1.6 Definition of Terms
The following definition of terms has been provided to ensure uniformity throughout the study.
Reproduction: The biological process by which new individual organisms are produced from their "parents." In mammals, reproduction typically involves sexual reproduction, where male and female gametes (sperm and egg cells) combine to form a new organism (Perry et al., 2004).
Viviparity: A mode of reproduction in which the embryo develops inside the body of the mother, leading to live birth rather than hatching from an egg. This is characteristic of most mammals, providing protection and a stable environment for the developing young (Cross et al., 1994).
Placenta: An organ that develops in the uterus during pregnancy in most mammals. It facilitates the exchange of nutrients, waste products, and gases between the mother and the developing fetus. The placenta also produces hormones that support pregnancy (Moffett & Loke, 2006).
Gestation: The period of time during which an embryo develops inside the mother’s body, from fertilization to birth. The length of gestation varies widely among mammalian species (Carter & Mess, 2007).
Fertilization: The process by which male and female gametes (sperm and egg) unite to form a zygote, initiating the development of a new individual. In mammals, fertilization typically occurs within the female reproductive tract (Yanagimachi, 1994).
Zygote: The cell formed by the union of a sperm and an egg. It contains genetic material from both parents and undergoes multiple divisions to develop into an embryo (Gilbert, 2000).
Embryo: The early stage of development in mammals, following fertilization and zygote formation, but before becoming a fetus. This stage involves critical processes of cell division, differentiation, and organ formation (Sadler, 2012).
Fetus: The developmental stage following the embryo in mammals. This stage is characterized by the growth and maturation of organs and systems, preparing the organism for birth (Sadler, 2012).
Sexual selection: A mode of natural selection in which individuals with certain inherited characteristics are more likely than others to obtain mates. This can lead to the development of traits that improve mating success, such as elaborate courtship behaviors or physical characteristics (Darwin, 1871).
Monotremes: A group of egg-laying mammals, including the platypus and echidna. Monotremes are distinguished from other mammals by their reproductive mode, which involves laying eggs rather than live birth (Lillegraven et al., 1979).
Marsupials: A group of mammals characterized by giving birth to relatively undeveloped young, which typically complete their development in a pouch on the mother’s belly. Examples include kangaroos and opossums (Renfree, 1983).
Eutherian (Placental) Mammals: Mammals that give birth to well-developed young after a prolonged gestation period supported by a complex placenta. This group includes the vast majority of modern mammal species (Cross et al., 1994).
Parental Investment: The time and resources that parents provide to their offspring to enhance their survival and reproductive success. In mammals, this often includes gestation, lactation, and postnatal care (Trivers, 1972).
Lactation: The production and secretion of milk by the mammary glands of female mammals, which provides essential nutrients and immune protection to the newborn (Neville et al., 2001).
Estrous Cycle: The reproductive cycle in female mammals, characterized by periods of sexual receptivity (estrus) and non-receptivity. Hormonal changes regulate this cycle, which prepares the female for mating and potential pregnancy (Ferin et al., 1993).
Artificial Insemination: A reproductive technology involving the manual introduction of sperm into a female’s reproductive tract to achieve fertilization without natural mating. This technique is used in both animal breeding and human fertility treatments (Foote, 2002).
In Vitro Fertilization (IVF): A reproductive technology in which an egg is fertilized by sperm outside the body, and the resulting embryo is implanted into the uterus. IVF is a common treatment for infertility (Trounson & Mohr, 1983).
Embryo Transfer: A reproductive technique where an embryo created through IVF or naturally is transferred to the uterus of a female, enabling pregnancy. This method is used in both human medicine and animal breeding programs (Betteridge, 1981).
Mating System: The social structures and strategies related to reproduction within a species. Common mating systems in mammals include monogamy, polygyny, and promiscuity (Clutton-Brock, 1989).
Photoperiod: The length of day and night, which can influence the reproductive cycles of many mammals, especially those in temperate regions. Changes in photoperiod signal seasonal breeding times (Bronson, 1989).
Endocrinology: The study of hormones and their effects on the body. in the context of reproduction, endocrinology focuses on how hormones regulate reproductive processes such as the estrous cycle, pregnancy, and lactation (Greep & Astwood, 1975).
Sexual Dimorphism: The differences in size, appearance, and behavior between males and females of the same species, often driven by sexual selection. These differences can include traits like body size, coloration, and secondary sexual characteristics (Andersson, 1994).
Gametes: The reproductive cells (sperm and eggs) that unite during fertilization to form a zygote. Gametes are haploid, meaning they contain half the genetic material of a normal body cell (Gilbert, 2000).
Oogenesis: The process by which female gametes (eggs) are produced in the ovaries. Oogenesis involves the maturation of ovarian follicles and the release of a mature egg during ovulation (Sadler, 2012).
