Charles Darwin went against traditional learning and values in order to bring forth another idea of how natural selection takes place throughout the world (Boyd & Silk, 2015). He was expected to take the route of a clergyman or a doctor, but instead revolutionized how people came to think about the world around them. Through three postulates Darwin generated a process by which people began to realize how species change through time.
Those three postulates are: 1) A population’s ability to expand is infinite, but environmental resources are finite, 2) A species’ characteristics can define how well they survive and reproduce, and 3) Those characteristics are passed from parents to their offspring. Where natural selection is primarily seen to produce adaptation, sexual selection, while still a natural form, comes from the success of differential mating in a single gender (Boyd & Silk, 2015). Natural selection revolves around three important postulates, those being limited resources, the various ways in which creatures survive and continue their species, and survival traits that are capable of being handed down from parents to offspring (Silk & Boyd, 2015). In this manner natural selection is more about adaptation of a species than sexual selection, which is about the process of successfully selecting a mate.
In natural selection it is more important that the three traits mentioned above be present in order to continue a species. The lack of proper resources or even the lack of a mate can stunt natural selection as it creates a deficit that cannot be overcome. Without resources a female cannot feed, and therefore cannot feed their young. Also, without a viable mate to be found there can be no young to begin with. Sexual selection has the same requirements in needing resources for both adults and young, but it is different in that it is more the process of finding a suitable mate.
Intrasexual selection is the process by which males find success in selecting a mate by constant and continual competitions for a female’s attention. This is commonly seen in mammals and can even help to weed out any unwanted traits as the strongest typically are seen to endure in most cases. Intersexual selection occurs when circumstances and adaptation contrive to make the male the more attractive of the species (Boyd & Silk, 2015), thereby leading the female to choose a mate. No matter which mode of selection is used, the cost of reproduction to the female is generally that she still needs to acquire resources that are not only adequate for herself, but also for her offspring.
Considering that many male parents within the animal kingdom have limited to no parental involvement with their offspring, the female of the species must take it upon themselves to assess and understand the costs to their own welfare that must be considered. To explain further this means that females of warm-blooded species have only two options, those being less offspring or to mate, give birth, and let the newborns fend for themselves as they go and mate again and again in order to continue the numerical advantage that will allow their species to continue. As is seen with many species the male has little if any real involvement with offspring, though with some there is a family dynamic that sees the male care for and even help raise the young. Many females of many species however are quite capable of raising their young without help.
Parental investment in offspring is usually seen to be stronger in mammals and often associated with animals that bear fewer offspring. For instance, elephants are seen to be far more invested in their young than pigs. While there is still investment, the involvement of the males is far more pronounced in animals with less offspring more often. In other creatures such as insects, reptiles, fish, and various other species, the numbers of offspring are much greater in an effort to insure that the species will survive. In this manner however traits that are considered weaker and less useful are just as prevalent as those that are most desired.
In regards to human beings, natural selection and sexual selection both take a very large
role in the survival of the species. Unlike many animals however human beings introduce abstract thinking into the process of adaptation and how genetics work. Mankind is always seeking a way to weed out the most undesirable traits amongst its own ranks, and unlike nature the methods used are often anything but natural. According to Darwin nature will seek to pass along traits and effect change through the process of adaptation and the survival of the strongest.
Boyd, R. & Silk, J.B. (2015). How Humans Evolved. New York, NY: W.W. Norton & Co.