The Nature of Male and Female Sexuality

NOTE: This is an excerpt of a concept discussed in my book Ramayana 3000. Ramayana 3000 is a Futuristic Dystopian Science Fiction Book that combines Evolutionary Theories with Hindu Religious Philosophy. You can read my book online directly in your browser (Mobile/ Desktop) here.

The evolution of sexual reproduction

The primary advantage sexual reproduction has over asexual reproduction is that beneficial mutations can be combined easily to improve the overall genetic health of the species. Suppose there are two beneficial mutations, A and B, which have occurred in two separate individuals. Both mutations are beneficial and as a result, the individuals containing such mutations will enjoy a reproductive advantage over others who don’t.

Suppose this species reproduced asexually – both those individuals may clone themselves to produce others possessing either mutation A or B. But, an individual possessing both mutations A and B cannot occur. Such an occurrence would be statistically improbable. On the other hand, suppose that same species reproduced sexually. Now, it is probable, inevitable even, that soon all progeny of that species will have both mutations A and B together. Therefore, species that reproduce sexually enjoy a selective advantage over species that reproduce asexually.

The evolution of sexual dimorphism

Once a species started reproducing sexually, it soon becomes advantageous for some individuals (say Type A) within that species to produce high-quality gametes that are larger and rich in nutrition, with the trade-off being that only a smaller quantity of such gametes could be produced. Such nutritiously rich gametes would improve the odds of success of their offspring; hence, individuals capable of producing such gametes would be highly sought after for mating purposes. Alternatively, it also becomes advantageous for individuals (say Type B) within that species to produce a higher quantity of gametes that are smaller but more mobile. Type B individuals could potentially target the high quality, nutrient rich gametes produced by Type A individuals with greater odds of reproductive success.

Over time, under certain conditions, the species would be dominated by individuals exhibiting Type A (high quality, nutrient rich gametes) or Type B (high quantity of small, mobile gametes) specialization. Individuals that did not specialize in Type A or Type B strategies would die out. This is how anisogamy (females specializing in producing small numbers of high-quality, nutrient-rich eggs and males specializing in producing large numbers of smaller, mobile sperms) became the dominant pattern among sexually reproducing organisms on Earth.

The evolution of polygamous mating in mammals

Among female mammals, the cost of childbirth is significantly greater than just egg production. Female mammals, like females of other classes like reptiles and amphibians, have to produce nutrient-rich eggs. However, female mammals also have an additional cost – they provide milk to their offspring from specialized mammary glands and help rear them during the early stages of their life. These additional costs imply that females should be extremely choosy with their mating decisions: Only males that have proven their worth would typically be allowed to mate with them. The basic nature of female sexuality is hypergamous (i.e.) female members of a species want to select the best possible males to mate with them to secure the best genes for their offspring.

Males, on the other hand, are biologically wired to compete so that they can get to the top of the male hierarchy and be chosen for mating by multiple female partners. The basic nature of male sexuality is polygynous (i.e.) male members of a species want to spread their sperm and mate with as many different female members of that species as possible.

The combined interactions of basic natures of male and female sexualities result in the polygamous pattern of mating illustrated below:

Males compete with each other to prove their sexual worth and the winners – say the top 20% – are selected for mating by the females. The male competition to be selected happens via different mechanisms in different species – lions fight, elk lock antlers, peacocks strut their feathers etc.

The impact of sexual selection on mammalian reproduction

When you think of natural selection, you naturally think of predator-prey relationships (if the gazelle can survive being hunted, it increases its odds of reproductive success; if the tiger can hunt successfully, it can increase its odds of reproductive success) or resource races (if the tree can grow tall enough to get sunlight and block out other trees, it can increase odds of reproductive success).

But, the greatest force of natural selection among polygamous mammals is sexual selection (i.e.) convincing a partner to select you for mating. Sexual selection does not act upon females – generally, 80% of all females successfully manage to reproduce. Sexual selection, however, applies great pressure on males – Only about 20-40% of the males get to reproduce, creating a winner-take-all scenario among male mammals.

Life in the pre-civilized world >>

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Ramayana 3000 is a Futuristic Dystopian Science Fiction Book that combines Evolutionary Theories with Hindu Mythology. You can read my book online directly in your browser (Mobile/ Desktop) here.

You can purchase your paperback copy of Ramayana 3000 here.

You can read my book online directly in your browser (Mobile/ Desktop) here.

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