Parental Investment

  • parental investment refers to the investment per individual offspring
  • females most often have a higher parental investment than males
  • we differentiate between a qualitative and quantitative reproductive strategy
  • qualitative strategy: few descendants with a lot of care each
  • quantitative strategy: many descendants with little care each
Topics overview:
From water to land
The asymmetric parental investment
Qualitative versus quantitative reproductive strategy
Parental investment explains them all

From water to land

About half a billion years ago, our ancestors moved from water to land. Before then, spawning in water came with little effort. Only sometimes it was necessary to fan oxygenated water to or to protect the spawn. Since the male would be the last at the clutch, it took over these tasks.

Now on land and until a hundred million years ago, our ancestors probably laid eggs. In humans, inactive remnants of the egg yolk genes were discovered. Originally, milk production only served to moisten the eggs. The additional food from the casein genes for the offspring probably was the reason why the egg could be replaced1.

The asymmetric parental investment

Parental investment is the cost that a parent incurs for the production of a single offspring compared to potential offspring2.

The internal fertilization forced an unequal distribution of the effort for descendants between the sexes, which is referred to as an asymmetric parental investment. The extent of inequality varies greatly between species. However, females that can produce comparatively few offspring generally have very high investment costs. We assume an average potential of offspring per female of ten. In principle, a single male has the possibility to produce significantly more. We assume a potential of 1,000 descendants. But because the number of males and females is almost equally distributed, males do not have the possibility to use their potential for lack of partners. Here lies the reason for competition among males.

Another question is efficiency. In order to use their full potential, the males would have to leave their investment per offspring at mere fertilization. There would be no time for more. Such behaviour could, however, result in the own offspring having a much lower chance of survival than those where the male helps with the care. To succeed from an evolutionary perspective, it is not even enough to survive and reproduce. The offspring must also be equipped to generate their own offspring, which in turn are equipped to generate offspring, which generate offspring, which …

🙋: „Thank you, I get that.“

👩‍💼: „Generate offspring, generate offspring, … sorry“

🙋: „So it’s not just about generating offspring, but about generating offspring that is prepared for life and competition, so that the genetic material can be passed on over many, many generations.“

👩‍💼: „Right! In other words, it’s about efficient propagation.“

Qualitative versus quantitative reproductive strategy

The degree of parental investment determines the reproductive strategy which can be qualitative or quantitative. If I simply put a lot of offspring into the world and trust the statistics that a certain proportion of them will make it, I am following the quantitative strategy. By contrast, if I help the statistics and increase the survival and reproductive probability of my offspring and offer brood, I follow a qualitative strategy. It follows from this that I can generate only fewer offspring, because I invest more of my resources per descendant. Which strategy has been genetically implemented differs according to species, life circumstances and, of course, gender.


… are less flexible in their choice, as there can be no offspring without a significant investment by mammal females. Their potential for offspring is therefore comparatively low and their motivation higher to ensure successful brood care. The goal is to maximize the chances of survival of each individual offspring and to create the optimal environment. In mammals, the qualitative strategy has even manifested itself anatomically through the mammary glands.


… among primitive creatures tend towards the quantitative strategy and also males in species in which the females can look after their offspring very well on their own are in good hands with this strategy. Even if the males invested more time in brood care, they would not be able to provide any relevant added value. In elephants, for example, females can feed and defend their young on their own. Male penguins, however, make an indispensable contribution to the nutrition of the young animals. Only if females and males take care of the offspring together will the species survive.

High versus low parental investment of males:

high parental investmentlow parental investment
competitive behaviourbarelyhigh
contribution breedinghighbarely
demands on partner & situationhighlow
optical differences to femalesbarelyhigh
reproductive strategyqualitativequantitative

Parental investment explains them all

Asymmetrical parental investment explains from the evolution perspective all gender differences of humans. In the following chapters we´ll go through the topics step by step! Why? In order to overwrite today´s stereotypes, we must learn where actual differences are.

» next topic:

Mating motivation and advertising strategies

Learn the influence the reproductive strategy has on mating motivation »

sex on the beach - mating motivation - Happy Jona


  1. Bischof-Köhler 1979
  2. Bischof-Köhler “Von Natur aus anders” 2006

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