Examples of Homologous & Analogous Traits as Seen in Nature

The following is a breakdown of an example of a homologous trait:

Species chosen: Venus Flytrap, Cactus

Homologous trait identified: Leaves

Venus Flytrap

A brief background: A Venus Flytrap (scientific name: Dionaea Muscipula) is one of almost a thousand different types of carnivorous plants. While most species of plants rely solely on photosynthesis as their primary means of nutrient intake, the Venus Flytrap also captures insects as prey for food. This plant is native to the Eastern United States, most commonly found in North and South Carolina. A cactus (scientific name: Cactaceae) is a more succulent plant that lacks “typical” plant-like leaves and is instead characterized by pointy spikes that cover its surface. Cacti are usually found in dry, arid regions or in homes as houseplants and decor.

Cactus

Explanation of the trait: In the case of the Venus Flytrap, the leaves are kidney-shaped and hinged, allowing them to open and close. They are lined with short, stiff hairs that alert the plant to insects who may land on it, serving as food to the plant. When an insect triggers one or more of these hairs, the trap immediately closes shut, trapping whatever insect may be inside. The plant is then able to form an air-tight seal around its captured prey and digestion ensues. Venus Flytraps actually developed these leaves as an adaptation due to the nutrient-poor soil they originated in. Since they couldn’t get enough nutrients from the soil and photosynthesis alone, having a means to obtain those nutrients another way was important. When we look at the cactus, we see that it doesn’t have leaves but rather pointy spikes that cover its surface. But wait! Those pointy spikes are indeed leaves! Having spines as opposed to traditional leaves allow the cactus to better retain water without losing it all through the transpiration process. Cacti also grow in areas where the environment has not always met the needs of the plant. Since cacti grow in severely dry areas, the ability to absorb and retain water for large periods of time is important. Having spikes for leaves not only protect the cacti from herbivores, but also provide a means to trap water inside of them and use it as necessary over long periods of time. The leaves of the Venus Flytrap are significantly different than those of a cactus, however, the trait of having leaves in general ultimately came from a shared common ancestor. The Venus Flytrap adapted and changed over time to use its leaves as a mean for food intake while the cactus used its leaves (or spines) as a means for protection and water retainment. While the appearance and function of this trait is different for each species of plant, it is a homologous trait because it has been continued on and passed down from an originating ancestor. 

Tracheophyta

How we know this is homologous (common ancestor): Figuring out the common ancestor of these two plants is tricky as our botanical history of this planet goes back a bit further than our animal history. However, leaves did not appear on plants until vascular plants formed sometime in the Silurian Period (425 million years ago). So, I would say the common ancestor of a cactus and a Venus Flytrap would have to be a plant belonging to the Tracheophyta family. I know that members of this family possessed leaves as a trait because there is fossil evidence confirming this. Preserved fossils from this period of time clearly show imprints of plants containing lateral appendages, later to be identified as leaves. 

The following is a breakdown of an example of an analogous trait:

Species chosen: Hummingbird, Bumblebee 

Analogous trait identified: Wings

Hummingbird

A brief background: A hummingbird (scientific name: Trochilidae) is one of the smallest existing species of birds. To give you an idea of just how small these birds are, they are often measured in centimeters and weighed in grams. Hummingbirds are native to North and South America and live primarily off a diet of flower nectar and insects. The wings of a hummingbird are very small but move so quickly they are often just a blur to those observing them. A bumblebee (scientific name: Bombus) is a large, hairy bee that typically lives in underground colonies. These bees are typically black with orange or yellow colored stripes and have a distinct hum or buzz. Bumblebees are a crucial contributor to the food source of thousands of other species. Without the pollination of bumblebees, our food sources would be seriously depleted and overtime, cease to exist. The wings of bumblebees are small and transparent and allow them to fly and hover over flowers when pollinating. 

Bumblebee

Explanation of the trait: As said before, the wings of a hummingbird are small and move very quickly, similar to those of the bumblebee. Both species’ wings allow them to fly and hover over flowers, giving them the ability to eat and pollinate. Both the hummingbird’s wings and the bumblebee’s wings are very thin and operate in a similar manner, either moving up and down or- more commonly- forward and backward depending on the situation. 

How we know this is analogous: The common ancestor of these two species could not have possessed this trait or this would be a homologous trait as opposed to an analogous one. By definition we know an analogous trait is one in which a common environmental stress of some sort causes two species to develop a similar adaptation. In this case, both the hummingbird and the bumblebee use their wings to fly as well as to pollinate and to consume nectar. Because the appearance and function of their wings is similar, we can infer that the driving force behind both species developing these types of wings was a shared previous environmental stress that resulted in both species needing to adapt to meet their needs. Hence, we have two unrelated species with similar traits even though they are not the direct offspring of the same parent species. It is because the common ancestor did not possess this trait that we know this trait is not genetically related from common decent, but indeed the shared result of an environmental pressure.