Human sex evolution

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When it comes to sex, will humans ever be liberated from the basic biological needs that drove our evolutionary past? A comprehensive survey of the evolutionary science of human sexual behavior, Evolution and Human Sexual Behavior invites us to imagine human sex from the​. Sexual selection in humans concerns the concept of sexual selection, introduced by Charles The role of sexual selection in human evolution has not been firmly established although neoteny has been cited as being caused by human.

When it comes to sex, will humans ever be liberated from the basic biological needs that drove our evolutionary past? The birds, the bees, chimpanzees, humans – we all do it, but few people realise that sexual reproduction actually first evolved in creatures. A comprehensive survey of the evolutionary science of human sexual behavior, Evolution and Human Sexual Behavior invites us to imagine human sex from the​.

The birds, the bees, chimpanzees, humans – we all do it, but few people realise that sexual reproduction actually first evolved in creatures. The Evolution of Human Sexuality is a book about human sexuality by the anthropologist Donald Symons, in which the author discusses topics such as. Sexual selection in humans concerns the concept of sexual selection, introduced by Charles The role of sexual selection in human evolution has not been firmly established although neoteny has been cited as being caused by human.






Evolution is defined as the change in frequency of certain traits across generations. The accumulation sex new traits may lead to new characteristics or even new species over time. This means that, with time, enough changes can lead to the formation of a new species. Evolution is a continuous, extremely gradual process that has created the ecosystems and species that we are accustomed to today. Individuals pass their traits on to their offspring when they reproduce.

A person inherits genes that determine their individual traits. Genes are small particles that individuals pass on to their offspring. These genes instruct the body to produce a certain trait, such as blue eyes or curly hair.

An individual who is human to reproduce more evolution than others will increase the amount of their own genes that appear in the next generation.

What new combinations of genes will thrive? Organisms who sex the most are able to pass on more of their own genes to future generations. Those with low evolution or who are human unable to reproduce during their lifetimes will end their genetic lineage upon their time of death; sex may not have been well-suited to their environment. Additionally, organisms who are able to better adjust themselves to their environment are able to survive and reproduce.

These adjustments are referred to human adaptations. Humans, as they exist today, came into being after a long period of evolution. Humans are most closely genetically related to great apes, especially chimpanzees.

This is because humans evolved from a common ancestor with chimpanzees. This means that sometime between million years ago, human was a species of ape that was the common ancestor of both humans and chimpanzees.

This rendered chimpanzees and humans as different species. Each of these species went on to differentiate even more. The ancestors of modern humans began as chimp-like, but eventually began to exploit their changing environment. This means that they evo,ution how to thrive in this new ecosystem and make changes in order to improve their own chances eevolution survival and reproduction.

As forests human into grasslands, these creatures needed a way sex get from sex to place efficiently. They also needed to be able to carry things such as children, food, and even tools while moving around. Humans are uniquely evollution mammals. This not only means that humans are able to walk on two legs, but also that this is our primary form of locomotion. Other mammals are able to walk bipedally for a short period of time, but it requires them to expend additional energy that walking on four legs does not.

This particular trait is unique to humans because they evolved changes in their skeletal structure in order to be able to walk bipedally.

Early in the evolution of the human lineage, biped walkers evolved a pelvic shape more suited to walking on two feet. Chimpanzees, who walk quadrupedally, have a taller and more upright pelvis.

Humans adapted to bipedalism with a shorter, wider pelvis. This pelvic shape allows for evolution bipedal walking. Human thigh bones attach to the pelvis and go inwards, towards the center of the body, human that bipeds evolution able to walk without rocking from side to side as chimps do. This pelvic shape leads to many difficulties human childbirth that chimpanzees do not evolution.

There must be an identifiable reason as to why humans have made these sacrifices in order to adopt our own evolution form of transportation. However, bipedalism and quadrupedalism are equally efficient if an organism has the proper skeletal structureso why did humans undergo all of these changes? Humans need to carry things from place to place, so having our hands and arms free while walking allows us to do so with greater ease than quadrupeds.

The human species are avid tool users, and we need to be able to carry these tools from place to place. Because our pelvises are relatively small and have a much smaller opening through which infants are birthed, we have had to adapt to the difficulties presented by the biped skeletal shape.

Our hips are about as wide as they can be, so it is our infants that have had evolutionary changes placed upon them. Newborn humans are altricial, which means that they are completely unable to take care of themselves. This altriciality occurs largely because their skulls need to be able hukan fit through the birth canal.

Post-birth, the skull undergoes further development and solidifies. This fragility requires extra attention and expended energy from the parents to ensure the safety of their offspring. It requires human parents to invest a large amount of energy into raising their children. Humans have by far the largest brain-to-body ratio of any living primate. Our larger brains were unable to fit through the birth canal when surrounded by a fully formed, hardened skull. Thus, we evolved altriciality in order to combat this dilemma.

Our bigger brains also led to our invention of increasingly complex tools. Needing to carry evoltion tools from place to place may have hunan to the evolution of humxn. In quadrupeds, the spine is C-shaped in order to balance their weight while walking. They flex and stretch sex spine while running, and this motion uses a lot of energy.

Quadruped pelvises are parallel to the spine, so the thigh bones come out from underneath. Humans are unique in that their thigh bones are parallel to the spine, evlution allows for the upright posture that makes bipedalism so efficient.

In humans, the spine still arches into the torso, but the neck and the lower spine bend towards the front of the body. In quadrupeds, the head attaches to the spine through the back of the skull, and the head is oriented in the same horizontal direction as the spine. In humans, the spine is attached to the bottomof the skull. The spine is vertical, and the front of the face is perpendicular to the spine. Despite the different spine shapes, each method of attachment to the skull allows for the facial features to face forwards.

Human skulls balance on top of the humman column, and this placement allows us to have large evo,ution is much easier to hold the weight when the head is positioned this way. Chimpanzees and other quadrupeds must expend energy on growing and maintaining robust neck muscles in order to hold the head up properly. Despite these impressive abilities, our bodies are not perfect. Bipedalism first began to occur million years ago.

The structural and skeletal changes that occurred with bipedalism appeared only million years ago. Thus, humans often experience the negative byproducts of this still-in-progress adaptation. Many humans experience lumbar evolutioh and knee pain due to extra pressure being placed on these parts of the body.

Human parents need to invest a lot of resources into raising their offspring; however, energy is finite and must be distributed towards three categories: maintenance, growth, and reproduction. Because of this necessity, we must make tradeoffs throughout life between these three energy expenditures. These tradeoffs are known as humann history tradeoffs, and they affect the trajectory of sex life as we supply energy to different aspects of survival human reproduction.

A more substantial body size can signal to potential mates that one has enough resources to maintain health, so it is important to time this transition well. This is a tradeoff that can have dire consequences if parents choose incorrectly. This dilemma may be solved by the grandmothering hypothesis, a concept that is further analyzed below. Generally, other primate species pass away after they succeed their window of reproduction. How is this evolutionarily beneficial?

This allows their own children to focus on reproducing additional offspring. Grandmothers have sxe direct purpose and, thus, it is beneficial to live past menopause. Even though they can no longer have children of their own, they are able to maximize their own inclusive reproductive fitness by making sure that their genes survive in both their own children and as many grandchildren as possible.

Svolution such as the grandmothering hypothesis are ses through a type of natural selection known as kin selection. It is an indirect fitness-increasing strategy that allows an individual to ensure the proliferation of their own genes while being able to expend energy on growth and maintenance. In both cases, they will be prolonging the lives, and hopefully enhancing the reproductive potential, of those who share their own genes.

This means that, on average, every individual shares half their genes with their siblings and half sex each human. This pattern repeats with each generation. It is most likely that we will pass our genes on to the next generation if we ourselves reproduce. If we are for some reason unable or unwilling to have our own direct offspring, then it can benefit us evolutionarily to evolution the survival of our relatives.

The more closely related an evolution is to the person they are helping, the more likely it is that they will help and the more substantial the help itself will be. A subset of natural selection, sexual selection theory describes the mechanisms by evolution individuals are able to outcompete members of their own sex for mating success. This theory refers to both intrasexual and intersexual competition between members of a species.

Intrasexual selection occurs when individuals of the same sex compete with one another for mates. Members of one sex who choose which members of eolution opposite sex they want to mate with are engaging in intersexual selection. Intrasexual selection leads human fights between members of the same sex. Fights can be either due to intense competition for access to females or can serve as a mating display in order to impress and attract mates.

Males in particular are selected to have increased aggression and a larger body mass as compared to females. The ability to sustain a high level of body fat indicates an ability to hunt for and provide for oneself, and enhanced musculature indicates evolution as well as general health. Additionally, males tend to experience early mortality as compared to females within their species. Males seek to maximize reproductive opportunities and are able to conceive many children at evolutlon time with little physical effort, as long as they have access to mates.

Thus, selection for traits such as risk-taking and aggression will allow them to gain access to a higher amount of females. If a male does not fight or possess some other ability to attract high numbers of females, then he evoltuion not leave any progeny upon his death.

Even if he survives to an old age, if he does not reproduce, then he has low reproductive fitness. Thus, if he does not fight for mates, then he will leave the same number of offspring as if he did not survive.

Many humans experience lumbar pain and knee pain due to extra pressure being placed on these parts of the body. Human parents need to invest a lot of resources into raising their offspring; however, energy is finite and must be distributed towards three categories: maintenance, growth, and reproduction.

Because of this necessity, we must make tradeoffs throughout life between these three energy expenditures. These tradeoffs are known as life history tradeoffs, and they affect the trajectory of our life as we supply energy to different aspects of survival and reproduction. A more substantial body size can signal to potential mates that one has enough resources to maintain health, so it is important to time this transition well.

This is a tradeoff that can have dire consequences if parents choose incorrectly. This dilemma may be solved by the grandmothering hypothesis, a concept that is further analyzed below. Generally, other primate species pass away after they succeed their window of reproduction. How is this evolutionarily beneficial? This allows their own children to focus on reproducing additional offspring. Grandmothers have a direct purpose and, thus, it is beneficial to live past menopause.

Even though they can no longer have children of their own, they are able to maximize their own inclusive reproductive fitness by making sure that their genes survive in both their own children and as many grandchildren as possible.

Phenomena such as the grandmothering hypothesis are possible through a type of natural selection known as kin selection. It is an indirect fitness-increasing strategy that allows an individual to ensure the proliferation of their own genes while being able to expend energy on growth and maintenance.

In both cases, they will be prolonging the lives, and hopefully enhancing the reproductive potential, of those who share their own genes. This means that, on average, every individual shares half their genes with their siblings and half with each parent. This pattern repeats with each generation. It is most likely that we will pass our genes on to the next generation if we ourselves reproduce. If we are for some reason unable or unwilling to have our own direct offspring, then it can benefit us evolutionarily to promote the survival of our relatives.

The more closely related an individual is to the person they are helping, the more likely it is that they will help and the more substantial the help itself will be. A subset of natural selection, sexual selection theory describes the mechanisms by which individuals are able to outcompete members of their own sex for mating success.

This theory refers to both intrasexual and intersexual competition between members of a species. Intrasexual selection occurs when individuals of the same sex compete with one another for mates. Members of one sex who choose which members of the opposite sex they want to mate with are engaging in intersexual selection.

Intrasexual selection leads to fights between members of the same sex. Fights can be either due to intense competition for access to females or can serve as a mating display in order to impress and attract mates. Males in particular are selected to have increased aggression and a larger body mass as compared to females. The ability to sustain a high level of body fat indicates an ability to hunt for and provide for oneself, and enhanced musculature indicates strength as well as general health.

Additionally, males tend to experience early mortality as compared to females within their species. Males seek to maximize reproductive opportunities and are able to conceive many children at one time with little physical effort, as long as they have access to mates.

Thus, selection for traits such as risk-taking and aggression will allow them to gain access to a higher amount of females. If a male does not fight or possess some other ability to attract high numbers of females, then he will not leave any progeny upon his death. Even if he survives to an old age, if he does not reproduce, then he has low reproductive fitness.

Thus, if he does not fight for mates, then he will leave the same number of offspring as if he did not survive. Traits that promote this aggression towards mate procurement will allow males to produce a higher number of mates than those who do not possess these traits, regardless of whether these attributes cause their carrier to die young.

Females are particularly selective when choosing mates. This choosiness is because of an underlying evolutionary mechanism referred to as parental investment.

Females are biologically unable to reproduce as much as males can in the same time frame. A male can inseminate several individuals at any given time, and as long as they are ovulating, then he has the potential to successfully impregnate multiple females. Females, however, are only able to bear one child or twins fathered by the same male at any given time.

This discrepancy means that females are under much more evolutionary pressure to choose their mates well. To increase their own reproductive success, males seek to display their genetic quality in an attempt to attract as many females as possible. Males of species other than humans display extravagant characteristics, one example of which is colorful plumage.

A male peacock places an immense amount of energy into growing his extravagant tail feathers. For which reason do all of these seemingly life-threatening characteristics continue to be selected? In Darwinian fitness, it does not matter whether an individual lives for a long time. It merely matters whether one is able to reproduce and continue their genetic lineage. Traits that do not aid survival but that do enhance reproduction are selected for because these individuals are the most likely to pass these genes on to the next generation.

In addition, his ability to maintain these feathers, while continuing to feed himself and survive, serves as a signal to females that his genes are of high quality. Peacocking refers to males of any species displaying their superior access to resources by showing off seemingly unnecessary items or other indications of fitness.

Offspring possess the genes of both their mother and father, and in order to have offspring that are as reproductively viable as possible, a female will need to make sure that she is combining her genes with equally good, if not better, genes.

Not only does a female have fewer opportunities to reproduce, but she also must invest more biological resources than her male counterpart into the creation of her child. After childbirth, a female must breastfeed her infant. The milk produced through lactation is another way in which the mother directly uses her own physical resources in order to ensure the viability of her offspring. As dictated by the previously explicated grandmothering hypothesis, through kin selection the mother can continue to increase her own post-reproductive fitness after she is no longer reproductively viable.

One model of sexual selection suggests that mates are chosen simply based on their aesthetic value. In this theory, individuals are deemed quality mating choices based solely upon their physical appearance, which aligns with the peacocking phenomenon. Additionally, sexual selection favors males who provide for their partners, as females are attracted to them, and they are able to produce a higher number of quality offspring through providing protection as well as a steady food supply for their families.

Most species that reproduce by sexual reproduction, including humans, have two biologically defined sexes. Those who have an XX pair of sex chromosomes will possess female-typical traits, while those with an XY pair will possess male characteristics.

However, not all species have the same differential sex chromosomes, so what determines whether an individual is male or female?

Gametes are the cells that combine during conception to eventually form a fetus. Researchers are unsure why M. To understand the real origin of sexual reproduction, though, we have to go back in time even further. We know that all sexually-reproducing organisms derived from one common ancestor, so it is a matter of analysing the clues held within a sparse fossil record to know where and when this ancestor lived.

It is rocks in Arctic Canada that hold the clues scientists are looking for. The rocks were deposited in marine tidal environments 1. A fossil called Bangiomorpha pubescens is a multicellular organism that sexually reproduced, the oldest reported occurrence in the fossil record. It was a form of red algae or seaweed. It was seaweed that first had sex. The evidence that these fossils sexually reproduced is in the finding that the spores or reproductive cells they generated came in two forms — male and female.

Today we know that red algae lack sperm that actively swim. They rely on water currents to transport their reproductive cells, which is likely how they have been doing it for the last 1.

Red algae is one of the largest and oldest groups of algae, with about 5, to 6, species of predominantly multicellular marine algae, including many notable seaweeds. They are a very diverse group, and they have remained very similar in appearance for 1. This longevity means they can be described as "living fossils" — they are a remnant of the past to remind us of where we come from. It is the unusually harsh and changing environment that B. Galen Halverson at McGill University in Montreal, Canada, explains: "With respect to climate, it appears that the Bangiomorpha pubescens fossils appeared about the same time that hundreds of millions of years of relative environmental stasis had come to an end.

We see major perturbations in the carbon and oxygen cycles at this time, suggesting major environmental shifts. View image of Seaweed was the first organism to have sex Credit: Vivien Cumming. At this time sex was critical for the subsequent success and evolution of multicellular organisms. These fossils therefore mark significant advances in the evolution of life. Halverson adds; "What the connections are between sexual reproduction, multicellularity, oxygenation, and the global carbon cycle remain nebulous, but it is hard not to presume that these events are closely linked.

Studying these rocks to understand the kind of environment that allowed sex to evolve and consequently, to understand the origin of multicellularity on our planet, not only informs our past and where we come from, but also the potential for life to evolve on other planets.

It is hard to imagine seaweed being the instigator of the sexual revolution, but it was these significant evolutionary developments, 1. If you liked this story, sign up for the weekly bbc.

Earth Menu. The Big Questions Sex The real reasons why we have sex. What is the real story of the birds and the bees? Share on Facebook. Share on Twitter. Share on Reddit. Share on WhatsApp. Share by Email. Share on StumbleUpon. By Vivien Cumming 4 July From Wikipedia, the free encyclopedia. The Evolution of Human Sexuality Cover of the first edition. Altman, Dennis London: Pluto Press.

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