Homology/Analogy Blog Post

1.      Homologous trait shared between Whales and Chimpanzees

a.       Whale is a generic name for a group of marine mammal, including dolphins, porpoises, sperm whale, killer whale, pilot whale, and beluga whale, to name a few. Whales are decedents of land-living mammals from the Aritodactyl order. Whales evolved from Ambulectus going fully aquatic about 5-10 million years ago. Whales, like mammals, are warm blooded; they nurse their young, have hair, and have lungs which breathe air.

Chimpanzees are members of the Hominidae family, along with humans. Chimps live on land and walk upright on two legs when carrying things. They are covered in black hair with a bare face, fingers, toes, and have palms on hands and feet. They have strong family bonds and wean infants by about three years old, maintaining a close relationship with their children. They reach puberty around 10 and generally live to around 50 years old. Chimpanzees live in West and Central Africa and are currently, sadly, on the endangered species list.

b.      Homologous trait: One aquatic and one land living:

The homologous trait between the two species is their forelimbs. Whales and Chimpanzees, along with humans, birds, and reptiles, all share a common four-legged ancestor, the tetrapod. Having lived over 365 million years ago the tetrepod is a common ancestor that is responsible for the forelimbs found in the listed groups, including whales and chimpanzees. Whales’ forelimbs are structured as flippers. They are a flat broad limb adapted for swimming. Whale flippers differ slightly between each sub-category of whales. For instance killer whales have Pectoral flippers with a skeleton of forelimb land mammals.  Their flippers are rounded and paddle like, used for steering and stopping. They have a thick cartilage that pads the bones. Humpback whales have flippers with bumpy edges, yet provide the whale the ability to channel flow and increase aerodynamic efficiency. The structure of the whales forelimbs are greatly different to that of the chimpanzees in that the skeletal structure is padded by a cartilage and rough, rigid surface forming a rounded shape. The function is different because whales use their forelimbs to help them swim and maneuver through water. Chimpanzee’s forelimbs are structured the same in that they have the same skeleton structure humerus, ulna, radius, carpals and phalanges, but they are housed differently which accounts for the different functions.  Chimpanzees’ forelimb skeletal structure is housed in muscle, flesh and fur. The phalanges are detached allowing for fingers on the palmed hand. The elbow joint moves too, just as a human. These structural differences allow for the difference in function. Chimpanzees use their forelimbs for climbing trees, carrying things or babies, and for walking.

c.       Whales and Chimpanzees are ancestors from a four-legged animal called the tetrapod, which produced the forelimb homologous trait found in these species. A tetrapod are vertevrate animals with four limbs, so I know that the tetrapod had that trait.  

     d. Pictures

Killer Whale

Humpback Whale

Chimpanzee

    

2.      Analogous trait shared between Sugar Gliders and Flying Squirrels

a.       A Sugar Glider is a small gliding possum and originates from the marsupial family, like kangaroos. They live in the eastern and northern mainland of Australia as well as New Guinea. They have a squirrel-like body with a long tail. They have five digits on each foot, equipped with claws. They have large eyes and the females have a marsupium, (pouch) for carrying their babies because marsupial species give birth to babies who are not fully developed.  

The name, Flying Squirrel, can be misleading as they are not capable of actual mechanical flight like birds, but they are capable of gliding. They live in North America and are part of the placental family. They bare a strong physical appearance to Sugar Gliders in that they have a tail and five-digit feet with large eyes. They do not have a pouch however because mammals in the placental family give birth to fully developed babies.

b.      Analogous trait: Both gliders, yet not from the same family.

The analogous trait shared by Sugar Gliders and Flying Squirrels is the thin piece of skin that stretches from their feet to their hands, allowing the small fur balls to glide from tree to tree. The trait of “wings” evolved in each species independently as a product of their environment. Both species are tree dwellers who adapted the paper-like wings to allow a gliding movement from on tree to another. Flying squirrel produce more lift and less drag with their wings than Sugar Gliders and they have a well-developed propatagium in the structure of their forewing. Sugar Gliders have this as well but it is smaller. Regardless of size and performance, both the Sugar Glider and the Flying Squirrel have this trait which allows them to glide in their environment.

c.       Sugar Gliders, from the marsupials family, and Flying Squirrels, from placental, are thought to have come from a common ancestor over 100 million years ago and independently evolved ever since.  The group was mammal which diverged into the two groups, placental and marsupials. According to a website at UC Berkley “Since sugar gliders and flying squirrels are very distantly related [100 mya], it seems very unlikely that their common ancestor had flaps of skin stretched between its legs…. Instead, each lineage probably evolved the trait independently as adaptations for gliding and tree-living” (evolution.berkley.edu). The quote basically explains that because these mammals lived so far apart and branched off from their common ancestor over 100 mya, than the probability of having an ancestor possessing the “paper-wing” trait is highly unlikely. It is more likely that the Sugar Glider and the Flying Squirrel, through parallel evolution, evolved with “wings” to be more “fit” for their environment.  

d.       Pictures

Sugar Glider

Flying Squirrel