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Orb-Weaving Spiders, Elephant Seals, Men, and Women: A Biological Survey and Theological Reflection on Sexual Dimorphism

June 8, 2021
By Craig M. Kline, MD FACS

Editor’s note: The following essay appears in the Spring 2021 issue of Eikon.


We seldom appreciate the biologic diversity and complexity of our world. Our lives, and even much of the biblical narrative itself, grow upon a lattice of biology. A survey of this fascinating biological framework allows for reflection on the specific ways God ordered living things and how this shapes our understanding of the universe, reality, and even the Godhead itself. In considering the diverse processes in which life survives, interacts, and reproduces, we realize the ways in which life can do these things are quite broad. In judging mankind’s place in this diversity, men and women seem more specific, peculiar, and interesting. Why did God create life exactly the way he did? Why did God create humans as male and female and not in other forms? Why did he create these genders specifically as we find men and women, and not something different altogether?

After a brief survey of the biology of reproduction and gender, we will consider humanity’s place within this biological spectrum, the specific nature of sexual dimorphism[1] in humans, and reflect theologically on the peculiar nature in which men and women are created, how they relate, and how this dimorphism reflects the image of God.

Life Created to Reproduce

Before considering the ways life reproduces, it is fascinating to consider at a more fundamental level that God intended life to replicate. Surely, the need for reproduction stemmed from a desire to fill an earth devoid of life, and to replace organisms that would pass away through events proceeding from the Fall (e.g., disease, trauma, aging, and even being consumed by other organisms for food). Beyond this, however, the biological cycle of reproduction, growth, and death is essential to understanding the nature of God and his redemption of mankind. When we witness new life created, we are amazed at the complexity of life that could only proceed from a Creator. Death reminds humans of ultimate judgment for sin. Our biological constraints are in sharp contrast to a God who never suffers change or death. Our very conception contrasts with a God who was never created. Biology provides the language for Paul to refer to our unregenerate state as being “dead in the trespasses and sins” in which we walked (Eph. 2:1) and allows for Jesus to describe our regeneration as being “born again” (John 3:3). Indeed, it would be impossible for us to understand the theological canvas of the substitutionary death of Jesus on our behalf and our resurrection from death to everlasting life, without the pre-existing biological “paint strokes” of life and death, procreation and passing, conception and expiration. Biology provides a lens that allows us to comprehend the nature and revelation of God, consequences of sin, and our redemption to a new creation through Jesus Christ. It seems impossible for us to comprehend God without the language of biology.

Asexual Reproduction

Male and female forms do not exist in all living things. Most prokaryotic organisms (i.e., those without an organized nucleus, such as bacteria) reproduce without the uniting of two different sexual cells (gametes) such as an egg or sperm. The organism doubles its genetic information and divides into two similar organisms, each an exact genetic replica of the original. This has contemporary application in the field of medicine. If a surgeon obtains a bacterial sample from a diseased organ, this small culture can be analyzed for resistance to different antibiotics. Antibiotics can be chosen based upon this analysis. It is assumed that any remaining bacteria will have similar resistance patterns because the bacteria have reproduced asexually. A single colony of bacteria will have a more homogeneous genetic pool than, for example, a single flock of turkeys. Interestingly, through a process known as conjugation, even prokaryotic cells may still share genetic information by sharing genes through structures on their surfaces known as pili. All prokaryotic organisms reproduce in this manner, as well as some eukaryotic organisms (i.e., those with an organized cell nucleus) such as some types of fungi.

Beyond bacteria, multicellular life (such as invertebrates) can also reproduce asexually. Budding is a process where smaller offspring may grow from larger “parent” organisms. These offspring may detach from their parent organism or remain attached and form large colonies, common with species of coral. In a process known as fission, a larger animal may split down the middle into two separate, similarly-sized organisms with the same genetic makeup. Sea anemones (e.g., Anthopleura elegantissima) reproduce in this manner. Fragmentation is still a different method whereby an animal broken or cut into pieces may regenerate portions of its body, and thus under certain circumstances produce multiple new individuals. Certain species of worms and starfish can reproduce by fragmentation.[2]

Asexual and Sexual Reproduction

Before considering the more familiar biology of sexual reproduction, incredibly, some organisms can produce in both asexual and sexual manners.

Chlamydomonas is a green algae which can reproduce in an asexual manner in absence of biological stress. However, in harsh conditions such as a lack of nutrients or adequate water, the algae will form two identical gametes and undergo sexual reproduction. When reproducing sexually, the two identical gametes fuse to form a new organism which can develop a durable coat, protecting the organism from harsh conditions. This coat does not develop when the organism reproduces asexually.[3]


In a process known as parthenogenesis (παρθένος, “virgin” + γένεσις, “creation”), offspring may develop from an egg that has not been fertilized by sperm. Some invertebrates such as the small freshwater crustacean Daphnia produce two types of eggs, one which may be fertilized by sperm and another which may produce offspring without fertilization. Different eggs may be produced depending on the season or occur during different times of stress, with asexual reproduction more common in stable conditions and sexual reproduction dominating during times of environmental stress. Adults produced from parthenogenesis may be haploid (containing only one full set of chromosomes), or diploid (two full sets of chromosomes, where the egg combines with a polar body or another nucleus).[4]

Parthenogenesis is essential in forming the hierarchical structure of social insects such as bees, wasps, and ants. Male honey bees develop via parthenogenesis from unfertilized eggs, while both female “worker” bees and queens develop from fertilized eggs. Thus, males carry only one set of genes, and females carry two sets, similar to humans. Females that are fed a special food known as “royal jelly” will become queens.

Certain species of whiptail lizards of the genus Cnemidophorus reproduce only through parthenogenesis. All members of these species are female, and though offspring grow from unfertilized eggs, members of the species still imitate courtship and mating with some lizards adopting a “male role.” Females with higher levels of estrogen during ovulation will be mounted by lizards with lower levels of estrogen. Mimicking lizards who reproduce sexually, this stimuli seems essential for reproductive success, as isolated lizards lay fewer eggs than those who engage in this role playing behavior.[5]

Finally, some animals which do not usually reproduce through parthenogenesis may be seen to do so in circumstances where they are isolated from a mate. Termed “facultative parthenogenesis,” this phenomenon has been seen in some species of sharks, Komodo dragons, and various other species, with some famous examples in zoos where females had given birth to offspring despite having been isolated from males of their species for an extended period of time.[6]

Sexual Reproduction

Most eukaryotic[7] organisms reproduce exclusively through sexual reproduction, which occurs when two specialized sex cells (or gametes) containing half of the genetic information within an organism’s genome combine to give a full complement of genetic material to the offspring.

Some types of sexual reproduction can involve the fusion of two gametes that are identical. This is termed isogamy, as opposed to the much more common (and familiar) anisogamy where the two gametes are different, such as with sperm and ova. Isogamy can be found in unicellular organisms such as the green alga Chlamydomonas, mentioned earlier.[8]


Though a survey of plant reproduction is beyond this article, plants are an example of how sexual reproduction can occur without copulation and without separate male and female organisms. The fact that plants cannot move and find mates has not prevented them from reproducing sexually! Most plants contain both “male” and “female” organs, the “male” parts producing pollen that fertilizes female organs of other plants.[9] In other plants known as dioecious plants, the plants exist in both male and female forms. For example, date palms are dioecious plants, and male plants have flowers with only stamen which produce pollen, and female plants have flowers that contain only carpel organs that then bear fruit.[10] The biology of plant life is incredibly diverse, genetically fascinating, and is interwoven with the animal kingdom in manners of seed dispersal, pollination by insects, and fruit production.[11]


Interestingly, some animals reproduce sexually, yet without distinct male or female sexes. Hermaphroditism[12] is a condition where one organism will contain both male and female functional genitalia. Most land gastropods (snails and slugs) are hermaphrodites. Most hermaphrodite species must still mate with another organism, with each animal simultaneously serving male and female roles, donating and receiving sperm, fertilizing and being fertilized. In this manner, each organism will bear offspring, potentially doubling the number of progeny. In some species, self-fertilization is possible.

Some species demonstrate mixtures of hermaphrodite genders and males and/or females. Gynodioecy is a term used to describe organisms where both female and hermaphroditic organisms exist in a population. Gynodioecy is found in certain flowering plants. Androdioecy describes species that exhibit male and hermaphrodite organisms, common in roundworms and some shrimp. Some roundworms from the genus Rhabditis exhibit trioecy, where all three forms (hermaphrodites, males, and females) exist. Males seem to prefer mating with females, possibly explaining why the hermaphrodite form does not predominate.[13]

Another incredible process is sequential hermaphroditism, in which an organism can change sex during its lifespan. In some species, the individual lives as a female before it becomes a male (protogynous) and in others, may live as a male before it becomes a female (protandrous). In yet other species, such as wrasse species living among coral reefs in the Caribbean, sex may be determined by size. The largest female wrasse in the group will transform into a male fish in as little time as one week. If this male fish dies, the next largest female will undergo transformation to a male.[14] Many will remember a scene from the movie Jurassic Park when the chaos-theorist Ian Malcom (played by actor Jeff Goldblum), was asked how a population of female dinosaurs isolated on an island could breed. He humorously quipped, “Life, uh . . .finds a way.” When newly laid eggs are later found on the island, moviegoers are reminded that the damaged dinosaur DNA was repaired in the movie with DNA from West African frogs, which according to the movie exhibit sequential hermaphroditism, thus explaining how some dinosaurs became male in an all-female environment.[15]

Internal and External Fertilization

Mechanisms of fertilization in sexual reproduction include both external fertilization, where eggs are released by the female and fertilized outside the body by sperm released by the male, and internal fertilization, where sperm deposited in or near the female reproductive tract will fertilize an egg within the tract itself. As external fertilization requires an environment suitable for egg survival, it occurs almost exclusively in aquatic or moist habitats. Internal fertilization requires cooperative sexual behavior, specialized genitalia to deliver and accept sperm, and organs to allow fertilized eggs to develop.[16]

Though technically still classified as occurring via external fertilization, the male seahorse receives eggs from the female through an ovipositor into a brood pouch in the male, where the eggs are fertilized by the sperm and develop in the pouch until they are released into the external environment. Thus, the male of the species carries the fertilized eggs until they are released, not the female!

It may be worth mentioning that we do not have examples of more than two sexes contributing to reproduction of life on earth. Even in the example of roundworms that exist in male, female, and hermaphrodite forms (trioecy), only one or two of the genders are involved in reproduction. One might assume that it would be impossible for anything other than one or two sexes to contribute in reproduction because the genomes we are most familiar with (our own) contain two sets of every gene, usually one set from each parent. However, some plants have genomes that are triploid, quatraploid, or hexaploid, with three, four, or six copies of each gene. It would thus be biologically possible for three or more sexes to contribute in reproduction, but we do not know of any such organisms. Biological reasons for having only two sexes could relate to the biological simplicity of only two forms of an organism, and the increased difficulty of mating if more than two organisms were needed to create offspring.

The diversity of ways in which life can reproduce, adapt to times of stress, and survive is truly astonishing, as we continue to explore in organisms found in two familiar forms: male and female.

Male and Female: Sexual Dimorphism within the Animal Kingdom

The presence of two different genders is almost ubiquitous in multicellular organisms. The biological definition of sex is based upon the different anisogamous sexual cells, the sperm and the egg. In other words, the definition of male and female is not based upon size, external genitalia, presence of secondary sexual organs (e.g., breasts), care for young, etc. The male is instead defined as producing the smaller (often motile) sperm, and the female producing the larger and most commonly immotile ovum, or egg.[17] Biologists have written extensively about why this difference in gametes may be beneficial to organisms, and it is exciting to know that research will continue to discover more nuances to this design. This difference in gamete production is, however, accompanied by many other differences, forming the basis of the sexual dimorphism which will be considered in the following sections.

Difference in Size

One of the most obvious ways that dimorphism is recognized is size. Female-biased sexual size dimorphism, where females are larger than males in a given species, is more common in the animal kingdom. Among birds and mammals, however, more species demonstrate male-biased sexual size dimorphism, where males are larger than females. Some notable exceptions among birds and mammals include bats (Chiroptera), rabbits and hares (Lagomorpha and the familyLeporidae), baleen whales (Mysticeti), raptors (Falconiformes) and owls (Strigiformes), where females tend to be larger than males.[18] Extremes of male-biased sexual size dimorphism can be found in the southern elephant seal (Mirounga leonine), where males weighing over 7,500 pounds can be up to seven times larger than females. Male cichlid fish from Lake Tanganyika can be twelve times larger than females.[19] However, even greater extremes can be found in female-biased species. The female orb-weaving spider Argiope aurantia is hundreds of times larger than male spiders, who die shortly after mating (if they are not eaten first by the female). The most extreme example of dimorphism in the animal kingdom occurs in the blanket octopus (Tremoctopus violaceous), where females are 100 times longer, and up to 40,000 times heavier, than males.[20] In some species with such extreme female-biased sexual size dimorphism, the males tend to be nothing more than parasitic sperm donors, permanently attached to females.

In looking over the difference between sexes in the animal kingdom, some general observations emerge regarding size. Aquatic environments tend to demonstrate the most extreme differences between male and female sizes. In warm-blooded mammals, the vast majority of species exhibit males that are on average approximately 1.2x larger than females.[21]

Other Differences in Appearance

Of course, dimorphism between the sexes of the animal kingdom is not constrained to differences of overall body size. The Hercules beetle Dynastes hercules is famous for the large horn found only on male beetles which can approach four inches in length, making this the longest insect in the world; females lack this horn. Fiddler crabs of the family Ocypodidae are famous for their sexually dimorphic claws, with males having a major claw many times larger than their minor claw, with females having claws of the same size. Variations of color are common in the plumage of many birds, with male birds often displaying more colorful or ornate plumage (the peacock serving as one famous example). The males of some birds will have other differences beyond plumage, such as the male turkey (Meleagris gallopavo) which has a fleshy organ known as the waddle or snood which hangs from the origin of the beak. All male turkeys will have a large beard on their chest, whereas females will have a small beard or none at all. In some species, such as bighorn sheep (Ovis canadensis), both male and female sheep grow horns, but the horns of the males are larger and more curved. In other species, such as the white-tailed deer (Odocoileus virginians), only male deer grow antlers. Both African bush and African forest elephants grow tusks, but only male Asian elephants grow large tusks, with females growing short tusks or none at all. The male lion famously displays a mane of fur, which the female lion lacks. Mature male orangutans and gorillas can be distinguished not only by size from females but also by their cheek flanges and silver backs, respectively.

It is interesting to consider that most animals who reproduce sexually will display some kind of sexual dimorphism. In other words, the sexes are distinguishable by their morphology apart from differences in genitalia. We also see a pattern emerge as we study this spectrum of biology: as organisms become more complex, there is a distinct trend towards sexual reproduction with sexually dimorphic (but comparatively similar) sexes with male-biased sexual size dimorphism, and with fertilization occurring internally as opposed to externally in the environment.

Human Sexual Dimorphism

Beyond the differences in genitalia, men and women have many biological differences that distinguish one sex from the other. Differences in genitalia and breast development are obvious, but secondary sexual characteristics are permeating.


At birth, newborn boys and girls are distinguished by their genitalia. However, other differences already exist. Male newborns are, on average, heavier than females,[22] although this difference is not so great that the sex of a newborn can be differentiated on weight alone. Different growth curves exist for male and female children as they mature. Upon reaching adulthood, men are on average 7% taller than females,[23] and also weigh more on average than women. Men possess a denser bone structure and more muscle mass on average, and women have a higher proportion of subcutaneous adipose tissue on average. Of course, there is significant overlap of the sexes, such that many women may be taller, have more muscle mass, and have greater body mass than any given man.


Recent studies have lessened the degree to which men’s and women’s brains were thought to be physically dimorphic. Males, on average, have 11% more volume of brain when controlled for body size. This size increase provides no increase in intelligence. Females have traditionally had a slightly higher ratio of grey matter to white matter and have a higher ratio of connections between cerebral hemispheres, versus within each hemisphere. Newer research states that some of these differences are not related to dimorphism but are related to the size of the brain alone. Some small differences still remain, such as the amygdala (involved in social-emotional behaviors) being 1% larger in men than in women.[24] Earlier research had suggested more widespread differences such as in the caudate, cingulate, hippocampus, parietal, and occipital regions.[25]

However, even if men and women have brains more structurally similar than previously thought, major differences remain between the function of these brains. In a recent Stanford Medical journal article reviewing these differences, Dr. Nirao Shah remarked,

Women excel in several measures of verbal ability — pretty much all of them, except for verbal analogies. Women’s reading comprehension and writing ability consistently exceed that of men, on average. They outperform men in tests of fine-motor coordination and perceptual speed. They’re more adept at retrieving information from long-term memory. Men, on average, can more easily juggle items in working memory. They have superior visuospatial skills: They’re better at visualizing what happens when a complicated two- or three-dimensional shape is rotated in space, at correctly determining angles from the horizontal, at tracking moving objects and at aiming projectiles.[26]

There are significant emotional and mental differences between men and women. When shown videos of different emotional states, men and women react differently to videos of anger, amusement, pleasure, and sadness, but more similarly in terms of horror, disgust, or surprise.[27] Other studies have supported that women are more emotionally expressive, can more easily recognize emotions, and more easily express emotion through facial expression, but men show greater responses to dominant, violent, or aggressive cues. Androgen exposure during development of males has permanent effects on neuronal connections and survival.[28]

Musculoskeletal Structure

The bone structure of men and women differs both in bone density and structure. The greatest difference is in the shape of the pelvis, with the female pelvis being wider to allow for childbirth. The male pelvis is heavier, thicker, and has more prominent bone markings.[29] The width of the pelvis also affects the Quadriceps angle, or Q-angle, relating to the angle at which the femur and thus quadriceps tendon align with the knee and patellar tendon. Women also have a greater carrying angle at the elbow compared to men. Men have greater bone density (up to 50% more density) and have differences in the skeletal structure of bones of the hand. Males have 45–50% of their body weight in muscle, compared to 30–35% for women. A study evaluating the volume of muscles using MRI scans on over 460 individuals over a wide range of ages revealed that, on average, men have 60% more upper body muscle than women, and 50% more lower body muscle.[30] Hand-grip strength is an interesting comparison, as one recent study found that 90% of females produced less force than 95% of males.[31]


On average, men speak at a frequency of 125 Hz, while women speak at a higher frequency of 200 Hz. When exposed to higher levels of testosterone during puberty, the vocal cords of men irreversibly lengthen and become thicker (16 mm average for men and 10 mm average for women). Beyond differences in fundamental frequency, there are important vocal characteristics that also differentiate men and women. Men have less complex overtones in speech than women during speaking and screaming. Though obviously affected by language and culture, men seem to raise the volume of their speech for emphasis, and women raise the pitch of their voice.[32]

Hair Distribution

Men and women have obvious differences in hair distribution. Androgen levels affect the growth of terminal hair on the face, chest, abdomen, legs, arms, and feet. Women develop some hair on the legs, arms, feet, and near the areola, but the hair growth in these areas is significantly decreased when compared to males. Among terrestrial mammals, the lack of hair in humans is surprising, which highlights the sexually dimorphic hair distribution among males and females.

Athletic Performance

Men and women have different abilities in athletic performance. At the outset, it is important to realize how much overlap exists between the sexes. Any man who has run a 5K road race can usually find women finishing ahead of him. Men and women can enjoy many sporting events together, and many athletic women will outperform their male peers. In elite athletes, the difference between men and women for running events is 10–12%, while in jumping events is 19%.[33]

Flexibility is also an important aspect of athletic performance. Some studies have supported that women are measurably more flexible on average than men in both a deep trunk flexion test[34] as well as other joints such as the ankle.[35]Many athletic events and hobbies depend as much on flexibility as strength or endurance.


Though most physiology between men and women is similar, one glaring exception is in the female gender’s ability to support the conception, development, and birth of another human life within her body. Males are physically and physiologically incapable of this amazing biologic feat. The physiology associated with pregnancy and childbirth finds no corollary in the male gender, and includes several physiologic processes (such as positive feedback loops) that are uncommon elsewhere in human physiology.

Incidence of Disease

Gender plays an important role in the incidence of disease in humans.[36] Beyond sex-specific cancers such as testicular and ovarian cancer, men and women display vastly different rates of cancers in almost all cancer types. In all age ranges (even in childhood), males have a higher incidence and worse prognosis for cancer than females. Second malignancies are more common in boys who have survived cancer. Many common cancers have a high male-to-female ratio, such as colorectal cancer (1.35), lung and bronchus (1.52), and urinary bladder (4.0). Kaposi’s sarcoma is 28 times as likely to affect men than women. Some cancers showing a female bias include gallbladder, anus, and thyroid cancers.[37] Though both men and women have breast tissue, 99% of all breast cancer is in females. Beyond neoplastic diseases, other medical conditions show a strong disposition towards one gender. Autoimmune diseases are more common in females, as are symptomatic gallstone disease, while gout more commonly affects men.[38] These differences are mediated both through genetic factors and differences in environmental exposure to food, alcohol, tobacco, and other environmental exposures.


Newborn girls are more likely than boys to survive to their first birthday. Incredibly, females actually demonstrate decreased mortality across all age ranges. Though some of this may be attributable to differences in risk-taking behavior, alcohol and tobacco use, and participation in armed conflicts, there is nonetheless a biological advantage to being female in terms of longevity. Women outlive males on average by six to eight years.[39]

A Theological Reflection on Sexual Dimorphism

Mankind occupies a unique place within the biology of created life. Mankind is biologically unique but also theologically distinctive as the only organism created in God’s image. After a brief survey of the biology of reproduction and sexual dimorphism on earth, we realize the diversity of what is biologically possible with reproduction and gender. Life can multiply asexually, with combinations of asexual and sexual replication, sexually but without copulation, without two genders, and with extremes of sexual dimorphism.

To start, when one considers created beings with moral judgement and high intelligence,[40] humans are distinct from angelic beings in that we have the ability to reproduce.[41] Only humans marry and bear children that resemble us physically and emotionally.[42] This gives humans a unique and firsthand perspective on the relation between a parent and child. When we refer to God as “Father,” or when we read that God cared for the Israelites during the Exodus “as a man carries his son” (Deut. 1:30–31), we can thank God from a perspective that angels cannot experience firsthand. If all humans were created at once (as angels likely were), biblical language using parents and children as metaphors would lose their power. We would have no personal concept of a human child and would not understand Jesus well when he said, “whoever does not receive the kingdom of God like a child shall not enter it” (Mark 10:15), or Peter when he spoke of longing for “pure spiritual milk” like newborn infants (1 Pet. 2:2). When we celebrate Mother’s Day and Father’s Day, we celebrate a unique grace withheld from angels, but given to men and women alone.

Why did God create mankind to reproduce sexually? Like many other life forms, we could have reproduced by budding offspring from our limbs, or fissuring our bodies down the middle in two. Yet God desired that children would have a mother and father, with traits from each parent passed down to the child. The miracle of the virgin birth would not have been miraculous if we reproduced asexually, or had been capable of parthenogenesis. Our sexual biology allowed the appearance of Christ to be seen as an incarnation, allowing him to enter the world through human gestation and birth and yet for his divinity to be displayed through his providential conception by the Holy Spirit.

As childhood friends have grown up, it is wonderful to see their physical features and personality traits passed down to their sons and daughters. It is incredible to think that DNA molecules too small to see can give the shape to the eyes of the child that recalls his mother, or a way of walking that mimics her father, or a smile that can be traced to a grandparent. Paul referred to Timothy as “my true child in the faith” (1 Tim. 1:2) and spoke to the Corinthian church reminding them that he was not just their spiritual guide, but father in the faith (1 Cor. 4:15). We know that things are passed down from a parent to a child because we see this displayed through the genetics of our sexual reproduction.

Moreover, sexual reproduction, and the timespan that human children take to mature, help to form and reinforce the social ties of a family. It would be hard to imagine the concept of family if humans were fertilized from eggs and sperm in an outside environment, never knowing our mother nor father personally.[43] This is why it was so striking when Jesus himself remarked, “For whoever does the will of my Father in heaven is my brother and sister and mother” (Matt. 12:50), and when the writer of Hebrews states that Jesus “is not ashamed to call (us) brothers” (Heb. 2:11). As Jesus welcomes us into his family as brothers and sisters, we can be grateful for such intimacy with our Savior.

We can also reflect on why God made sex such an intimate act between two human beings. We could imagine a sexual act that occurred without copulation or that did not involve the intimacy that we find in human sexual expression. Not only is the act intimate, the act’s exclusivity was prescribed by God to be within the bounds of marriage (Matt. 19:5–6), something never reproduced throughout the rest of creation.[44] Though humans reproduce through sexual means, human children are not conceived in the manner of plants or even amphibians with gametes randomly combining with others in the environment. Instead, human fertilization occurs internally, through copulation.[45] God describes the sexual act as the man and woman becoming “one flesh” (Gen. 2:24). Human reproduction is no dispassionate biological process, and God uses the metaphor of marriage and intimacy to describe not only his own desire for intimacy with his people (Hos. 2:20), but also uses the language of promiscuity to describe the Israelites when they chased after other gods (Hos. 1:2).

We could also imagine a universe in which God created us as sexual creatures, reproducing through an intimate sexual act, yet created only one gender. Other organisms are hermaphroditic, and it is not biologically impossible for us to imagine that the case could be so with mankind. Yet, God stated in Genesis 2:18 that it was not good for man to be alone, and created a “helper fit for him.” Thus, the male gender was specifically created with a deficiency that it could not fill by another male. As a gender, man needed another kind of human, which would be taken from, and named from, his own body.

Even if sexually dimorphic, we could imagine God creating men and women with different genitals and reproductive tracts, but otherwise having identical stature, physique, brain function, voice, and other characteristics. We could even imagine both sexes having functional breasts to nurse young. When we meet Eve (woman) in Scripture and in life, we find this is not the case! We see in Genesis 1:27 that God created both male and female in his image. We can infer from this statement that without both genders, something of this imago Dei would be lost. The reflection of the character of God was best served through both women and men. God in his wisdom created men and women with pervasive biological differences, and pronounced that both men and women were made in his image (Gen. 1:27). Why did God create men and women in this way?

First, as we have seen in some extreme examples of dimorphism from the animal kingdom, we should remark at how similar men and women actually are. When we consider the average size of men and women, we certainly see a variety of different sizes and shapes, and yet set against the wide backdrop of biology, we find that men and women are in fact quite similar sizes. No doubt, this helps to remind us that both men and women were created in the image of God, but it also helps us to enjoy life with one another. Men are not dwarfed by women many times larger as with an orb-weaving spider. Women are not dwarfed by men many times larger than them as the elephant seal. We can ride in the same cars, sit together in the pews of a church, enjoy many different activities together, and can care for and serve one another. We can play basketball together, run together, and enjoy many other activities as friends, couples, and family. Adam could truly say that Eve was “bone of my bones, and flesh of my flesh” (Gen. 2:23), instantly recognizing her form as his equal human companion. The voices of men and women are distinct, and yet we still communicate in similar frequencies of sound and tone. Bass, baritone, tenor, alto, and soprano voices complement one another in song. The strengths and nature of each sex have in some ways woven the two sexes together in mutual dependance.

There is much to our sexual dimorphism — our masculinity and femininity — which cannot be captured in biological analysis. The arts better convey the reality of the romantic attraction found between the two genders, which surpasses all other living things in its complexity, intensity, and expression. No other organism listens to songs or reads books out of the need to find expression to romantic love. No other form of life travels thousands of miles to interact with one specific individual when other suitable mates are closer.[46] No other species feels the pain of a broken relationship, or grieves like humans when a spouse dies.[47] This attraction between the sexes is used by God to describe his love and care for the church, and to display his horror when men and women are not faithful to him (see Ezek. 16 or Hosea 1–2).

Finally, the New Testament states that marriage has the power to display the love of Christ for his bride the church, as men lead and care for their wives as Christ would nurture and cherish the church (Eph. 5:22–33). The highest calling of marriage is to display this mystery to the world as we await the marriage between the body of the church and her head, Jesus Christ. We would do well to reflect upon the differences between men and women and celebrate these distinctions. We should also celebrate the union that we enjoy as equal partners in our redemption through the cross of Jesus Christ (Gal. 3:28). God is glorified not only in our distinctions as men and women, but also our friendships, family relations, and marriages. We should be humbled by the wisdom of God who designed not only the incredible diversity of life on earth but also our particular biological and theological place within it. As biblical wisdom describes the roles of men and women, we should seek to understand, obey, and glorify God through our embodiment of our gender and personhood. This preserves not only healthy ideas about men and women, but also the biblical narratives that are predicated upon them as we await a wedding supper with our bridegroom, who promises to love us and care for us in his family without end.

Craig M. Kline, MD FACS, General Surgeon, Southwestern Medical Clinic, St. Joseph, MI

[1] Sexual dimorphism will be defined as the presence of two forms of an organism — male and female — differentiated based upon their secondary sexual characteristics (i.e. differences beyond their genitalia and reproductive tracts).

[2] Neil Campbell, Jane Reece, and Lawrence Mitchell. Biology, 5th edition. (Melo Park: Benjamin/Cummings, 1999), 913–14.

[3] Campbell et al., Biology, 5th edition, 541.

[4] Campbell et al., Biology, 5th edition, 914.

[5] Campbell et al., Biology, 5th edition, 914.

[6] see for example Phillip Yam, “Strange but True: Komodo Dragons Show that ‘Virgin Births’ Are Possible”, Scientific American , accessed 3/16/2021,

[7] I.e. organisms with membrane-enclosed organelles and nucleus in their cells. All multicellular plants and organisms in the animal kingdom are eukaryotic.

[8] Instead of identifying these gametes as male (♂) and female (♀), they are referred to as “+” and “-“ gametes.

[9] As a teenager, I worked in the cornfields of southwest Michigan, where a common summer job involved “detasseling.” In order to cross different strains of corn, four rows of one variety of corn were planted between one row of a second variety. By detasseling, or removing the “male” portions of the corn stalk that produced pollen (the tassel), one could ensure that the “female” corn could only be pollinated by the “male” corn, thus ensuring that the two species of corn would be crossed, and that no self-pollination would occur. The middle rows of female corn would then be harvested, leaving the male corn standing in the field after the harvest.

[10] Campbell et al., Biology, 5th edition, 732.

[11] One interesting example is the bee orchid Ophrys apifera, whose flower looks like a resting bee. Male bees attempt to “mate” with this portion of the flower, facilitating pollination.

[12] Some medical conditions in humans where portions of both male and female reproductive tracts are present were once referred to using this term, but the term “intersex” is now preferred, and there are important differences between intersex conditions in humans and the biology of hermaphrodite animals.

[13] Jyotiska Chaudhuri, Neelanjan Bose, Sophie Tandonnet et al. “Mating Dynamics in a Nematode with Three Sexes and its Evolutionary Implications.” Scientific Reports 5:17676 (2015): 1–11.

[14] Campbell et al., Biology, 5th edition, 915–16.

[15] Though some species of African frogs have exhibited sequential hermaphroditism in captivity, this has not been demonstrated to occur in amphibians in the wild.

[16] Campbell et al., Biology, 5th edition, 916.

[17] Campbell et al., Biology, 5th edition, 913.

[18] Daphne J. Fairburn et al. Sex, Size, and Gender Roles: Evolutionary Studies of Sexual Size Dimorphism. (Oxford: Oxford University Press, 2007), 3.

[19] Fairburn et al. Sex, Size, and Gender Roles, 2–3.

[20] Fairburn et al. Sex, Size, and Gender Roles, 3.

[21] Fairburn et al. Sex, Size, and Gender Roles, 25.

[22] From “Physical Growth of Newborns,”, accessed 3/24/2021

[23] Anders Gustafsson et al. “Human Size Evolution: No Evolutionary Allometric Relationship Between Males and Females,” Journal of Human Evolution 47 (2004): 253–66.

[24] Lise Eliot, Adnan Ahmed, Hiba Khan et al. “Dump the “Dimorphism”: Comprehensive Synthesis of Human Brain Studies Reveals Few Male-Female Differences Beyond Size,” Neuroscience & Behavioral Reviews, 125 (2021): 667–97.

[25] Kret, M. E., & de Gelder, B. “A Review on Sex Differences in Processing Emotional Signals”. Neuropsychologia, 50(7) (2012): 1211–21.

[26] Bruce Goldman, “Two Minds: The Cognitive Differences between Men and Women”, Stanford Medicine, volume 34 no.2 (2017): 12–17.

[27] Yaling Deng, Lei Chang, Meng Yang et al. “Gender Differences in Emotional Response: Inconsistency between Experience and Expressivity”, PLoS ONE 11(6): e0158666.

[28] Kret et al., “A Review on Sex Differences in Processing Emotional Signals,” 1211–21.

[29] Keith L. Moore and Arthur F. Dalley. Clinically Oriented Anatomy, 4th edition (Baltimore: Lippincott, Williams, & Wilkens, 1999), 336–37.

[30] Ian Janssen, Steven B. Heymsfield, ZiMian Wang et al. “Skeletal Muscle Mass and Distribution in 468 Men and Women Aged 18–88 yr”. Journal of Applied Physiology , 89:1 (2000): 81–88.

[31] Leyk, D., et al. “Hand-Grip Strength of Young Men, Women and Highly Trained Female Athletes.” European Journal of Applied Physiology 99.4 (2007): 415–21.

[32] Voice-over and voice recording services have studied some of these tendencies. One example can be found at, accessed on 5/27/21.

[33] Espen Tønnessen , Ida Siobhan Svendsen, Inge Christoffer Olsen et al. “Performance Development in Adolescent Track and Field Athletes According to Age, Sex and Sport Discipline”. PLoS ONE 10(6): e0129014,

[34] Olga Delgado Valdiaia, María Angustias Martín Cañada, Félix Zurita Ortega et al. “Changes in flexibility according to gender and educational stage”. Apunts Med Esport. 161 (2009):10–17.

[35] Katherine M Hoge, Eric D Ryan, Pablo B Costa et al. “Gender Differences in Musculotendinous Stiffness and Range of Motion after an Acute Bout of Stretching”. Journal of Strength and Conditioning Research , 24 (2010):2618–26.

[36] In my own practice as a surgeon, there are gender distinctions in almost every condition I treat. A cholecystectomy (gallbladder removal) is similar in men and women, yet gallstones form more frequently in women due to interactions between cholesterol and estrogens. The anatomy of an inguinal hernia is different in men and women. Perforated appendicitis rates differ between boys and girls. Even colonoscopies can demonstrate subtle differences in the curvature of the sigmoid colon due to the wider pelvic inlet found in females.

[37] M. Tevfik Dorak and Ebru Karpuzoglu. “Gender Differences in Cancer Susceptibility: An Inadequately Addressed Issue”. Frontiers in Genetics no. 3 (2012): 268.

[38] A. Glücksmann. Sexual Dimorphism in Human and Mammalian Biology and Pathology. (London: Academic Press, 1981), v.

[39] Data from the World Health Organization, available at, accessed 3/27/21.

[40] Wayne Grudem, Systematic Theology (Grand Rapids: Zondervan, 1994), 397.

[41] It is unlikely that the Biblical account of the Nephilim refers to angels that had relations with human women. See Grudem, Systematic Theology, 413–14.

[42] See Matt. 22:30 and Luke 20:34–36

[43] This of course does not diminish those who did not personally know their father and mother, and were raised by other means, such as adoption. The point is that our very concept of family is dependent upon our peculiar reproductive biology.

[44] Even in animals that are thought to “mate for life,” they display social monogamy by mating and raising young together, but do not demonstrate sexual monogamy.

[45] Reproductive technologies have allowed other methods such as in vitro fertilization, yet this is not the way the vast majority of humans were conceived.

[46] Many animals migrate long distances to mate, but are not seeking out a specific individual to court or mate.

[47] Some animals are capable of grieving (the most famous example being elephants), yet there is no argument that human expressions of grief in the context of romance and relationships are significantly more intense, prolonged, and complex.

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