It was Robert Trivers who first described the concept of a parent investing in one of their children at the expense of their potential to do the same for their other children’s future well-being (either current siblings or future ones). When it comes to evolution and psychology, any parental expenditure (such as time, energy, or resources) that helps offspring is considered a form of parental investment Males and females (biparental care) or only females (exclusive maternal care)
Can make financial contributions to their children’s upbringing (exclusive paternal care). Prenatal (e.g., egg protection and incubation in birds, placental nutrition in mammals) and postnatal (e.g., neonatal care) care can be provided at any point of the child’s existence (e.g. food provisioning and protection of offspring).
According to Robert Trivers’ Parental Investment Theory, a phrase coined in 1972, parents that invest more in their progeny tend to be more selective in their mating choices, whereas less-investing parents face intrasexual rivalry. Throughout the animal kingdom and in humans, this idea has been influential in explaining sex differences in sexual selection and choice.
On the Origin of Species was written by Charles Darwin in 1859.
Natural selection and associated theories like sexual selection were brought to the world as a result of this. First-time evolution has been used to explain why women are “coy” and men are “ardent” and compete with each other for the attention of women. It was in this book, published in 1930, that Ronald Fisher created the contemporary concept of parental investment, and introduced the sexy son theory. He reasoned that because female gametes are more expensive to create than male gametes,
The reproductive success of females was limited by their ability to produce ovum, while the reproductive success of males was limited by their access to females in 1948.  In 1972, Trivers proposed the parental investment theory, which explains how parental investment influences sexual behaviour. When it comes to mating, he finds that sexes with the higher parental investment will be more selective, whereas those with the lower investment will compete intrasexual.
A Parent’s Love
Topic: Child and Adolescent Care
The theory of life history and parental investment are closely related. Before Fisher’s work in 1930 on natural selection’s genetic theory of natural selection, parents’ investments in their kids were first discussed in The Genetical Theory of Natural Selection. Expanding on the concept of parental investment, Clutton-Brock added any other expense to parental fitness. The males of a polyandrous or polygynandrous system are unlikely to distinguish between their own young and those of a competing sire. It is an excellent predictor of paternity for males to feed their offspring by their access to the female during the mating season, which they use to maximise their reproductive success.  Male red lip blennies also show this indiscriminate parental care.
A Basement Spider Takes a Stand to Protect Her Young
A nuptial gift is a sort of male paternal investment in some insects. Spermatophore comprising nutrition, sperm, and anti-toxin molecules is given to ornate moth females by the male during copulation. An investment of up to 10% of a male’s body mass constitutes the male’s entire parental contribution.
It is common for young animals to be unable to support themselves for an extended period after birth, such as humans and many birds. As a result, males in these species place a higher value on their kids than male parents in precocial animals do.
Territoriality, Parenting, and the Art of the Home
In Animal Behavior (Second Edition), 2016 by Janice Moore and Michael D. Breed
There are several ways in which parents invest in their offspring, from providing gametes and young to building nests and protecting their territories. Chapter 11 discusses the relationship between patterns of sexual selection and patterns of parental investment, particularly in terms of whether parent invests the most or all of their resources in their children.
Conditions such as the certainty of motherhood or paternity, the value of childbirth and the cost of missed opportunities with other partners all affect how uniparental and biparental care is provided. The conflict between parents and their children is common, and infanticide is often the result of male-male competition or the lack of resources needed to raise a child.
Competition for parental attention can lead to conflict among siblings. Aggressive behaviour can have a variety of causes, and this leads to a consideration of that topic. As a result, the focus of this chapter returns to nesting and territorial defence.
Why Do Women Tend to Take on More of the Responsibility for Raising Their Children?
So, why do women take better care of others? Another aspect, according to the researchers, is critical: investing in being sexy, and so mating sooner, maybe at odds with the ability to offer healthcare effectively. Evolution favours the more-caring sex over the less-caring sex because of this balancing act.
Sociable Monogamy and Biparental Parental Care
Mammalian social monogamy is unusual (3–9% of species; Kleiman, 1977; Lukas and Clutton-Brock, 2013); even less common is paternal engagement in relationships between partners (Wright, 1990; Pleck, 1997). Sexual tension may be to blame for this rarity, as it prevents the development of a simple cooperative system of biparental care. Both parents reap the rewards of their joint efforts in raising children, but parents who invest may incur an opportunity cost or see their survival chances drop.
The Theory of Parental Investment and Sexual Selection as a Tool Module
When discussing natural selection, sexual selection is sometimes referred to as a different mechanism. In species where the sexes are highly separated and individuals compete to attract members of the opposite sex, this phenomenon is commonplace.
As in natural selection, the individual’s immediate life is not at issue in sexual selection, but rather the ability to leave more or fewer offspring. Secondary sexual characteristics, such as the flamboyant plumage of some birds, are frequently favoured by sexual selection.
The peacock’s tail piqued Darwin’s interest. “How could natural selection alone have resulted in an enormous tail that threatens the bird’s survival?” he asked himself. According to Darwin, this tail might have been the outcome of the females’ preference for male partners who demonstrated the most strength and vigour. In Darwin’s time, the tail of the male peacock has been regarded as a symbol of sexual selection.
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