Flashy feathers, hulking heft, amazing antlers—why do the males and females of some species look different?
When you see a peacock strutting his stuff for a peahen, you may be surprised that a drab brown bird is the object of his affection. There are obvious differences between the appearances of male and female peafowl. Many other animals also exhibit radically different traits between genders, a phenomenon known as sexual dimorphism. Secular theory claims sexual dimorphism is a result of evolutionary forces that drove males and females down separate paths for reproductive success, but is there a biblical explanation for why male and female animals aren’t always identical?
Contrasts between male and female animals fall into two main categories: ornamentation and size. We often see flashy colors, elaborate dances, and exaggerated body features used by males to attract mates, whereas females are often understated in appearance. Peacocks are vibrantly colored and have elegant rear feathers called trains with striking eye feathers. They display their tails for peahens, and females select mates based on the length of their trains and the number of flamboyant eye feathers.
Male birds of paradise are brilliantly colored and perform choreographed dances to attract mates. Females select males with the best dances and prettiest feathers.
Size difference is another common form of sexual dimorphism. Males are often larger than females, sometimes to an extreme. Male southern elephant seals can weigh a whopping 8,800 pounds (~4000 kg), while females weigh less than 1,800 pounds (~820 kg).
However, males are not always bigger. Female black widow spiders are exponentially larger than males. While females can grow up to 0.5 inch (1.3 cm) in length, males are often as small as 0.1 inch (0.25 cm).
Some animals are sexually dimorphic in both ornamentation and size. The long manes and large size of male lions make them the most sexually dimorphic members of the cat kind.
Mandrills are the most sexually dimorphic primates. Male mandrills have brightly colored faces and backsides and are also three times larger than females.
Males of most species of deer grow beautiful antlers despite the cost to their fitness, since antlers must be shed and regrown yearly and present a risk of entanglement. Bucks can also weigh up to twice as much as does.
How do Christians explain sexual dimorphism in animals? Genesis 1 shows how God created a perfect universe in six 24-hour days 6,000 years ago. He made the animals according to their kinds and commanded them to multiply and fill the earth.
After humans disobeyed God and the world was cursed (Genesis 3), animals struggled to survive and reproduce in an earth affected by sin. Those original kinds would have undergone a great deal of natural selection (and other mechanisms), resulting in species that best survive in today’s habitats.
Although natural selection and evolution are often falsely equated, natural selection is the opposite of evolution. Natural selection is simply survival of the fittest. Organisms with the most favorable traits for a given environment survive, and organisms with unfavorable traits are reduced or eliminated. However, true evolution would require changing from one kind to another by the gain of new structures and functions, a process which has never been observed. When God created animals, he gave them all vast genetic potential, including the genetic programming for all their sexually dimorphic features. The sexual dimorphism we see today has been driven by thousands of years of natural selection (and other mechanisms) within animal kinds to best suit their needs in their environments.
Ornamentation, such as in male peafowl and birds of paradise, seems counterintuitive to survival. Wouldn’t bright colors and amplified features make these creatures obvious to predators? Absolutely, but features needed to attract mates outweigh the need for camouflage. Females of these species likely see these fancy displays as proof of health and vitality, characteristics that, by God’s design, they instinctually want to pass on to their offspring. Since females consistently choose to reproduce with the flashiest males, those showy traits carry on to future generations. In contrast, since females don’t have to attract mates but do have to safely raise their young, the appearances of females may have been naturally selected for camouflage rather than display.
Natural selection is also at work when we see drastic size differences between males and females. Since male elephant seals are responsible for protecting their immense harems of females and offspring, their enormous size makes them more successful guardians.
However, black widow females are considerably larger because producing hundreds of eggs, spinning egg sacs, and guarding them requires a lot of energy. Conversely, it behooves black widow males to be small. Since the females can be cannibalistic in our fallen world, the males need to make quick getaways.
Some animals have been naturally selected for both ornamentation and size differences. Studies show that lionesses prefer thicker, darker manes on male lions. However, these manes can take physical tolls on males by raising their body temperatures. Consequently, male lions in warmer regions tend to have thinner manes, but those in cooler regions tend to have thicker manes. Also, heavier male lions are more capable of protecting their prides.
Male mandrills are three times larger than females and boast brighter colors.
The more testosterone male mandrills have, the brighter their colors, which advertises their overall fitness to females. Additionally, the largest males have the best chances of winning in the intense competition for dominance and mates.
In male deer, the bigger the size and the more elaborate the antlers, the more dominant they are and the greater chance they have of reproducing and defending themselves from threats. Therefore, females choose the largest bucks with the most decorative antlers, ensuring that their offspring inherit the best traits for survival.
Sexual dimorphism does not require a complicated evolutionary explanation. When we look at beautiful peacocks, enormous elephant seals, and magnificent mandrills from a biblical perspective, we see clear evidence of created design and natural selection of favorable traits to best suit them for survival in our fallen world.