Two species that possess the homologus trait are humans and monkeys. Humans are bipedal primate mammals that are considered to be one of the smartest species to ever live. Humans are "us", we are currently defined as the Homo sapiens species. Monkeys are non-hominoid simians, which consist of 260 known living species. Monkeys generally possess tails and live in or by trees. Monkeys come in all different shapes and sizes just like humans do. Monkeys and humans share many similar characteristics like being extensively social in their own environment, and they share many differences like humans habituating all parts of the world and monkeys usually only habituating forest regions where lots of tree coverage is available. 
The homologus trait between monkeys and humans are that they have tails, which is an extension of
the torso. The tails that monkeys possess are called prehensile tails which act as an extra limb for the monkeys. This "limb" allows the monkey to grasp objects, swing from branches, hold onto things, and ward off insects. Humans possess a very similar feature known as the coxxyx or the tailbone. The coxxyx was thought to have once been a fully formed tail. The human tailbone is an extension of the torso and is made of "rudimentary vertebrae" and is often called a vestigial structure. The coxxyx does not have the same function as the monkey's tail. The human tailbone serves as a muscle attachment for our lower limbs as well as helps in balance and support for when a person sits. The obvious difference in these structures are size, the human tailbone generally measures less than one inch in length while generally monkeys tail bones could measure from 2 inches all the way to 23 inches. Monkeys tails display a series of tail vertebrae while humans tailbone is loosely fused bones that are attached to the sacrum. These homologus traits exhibit differences between humans and monkeys mainly because of environmental factors. Monkeys have made use for the tails due to their environment, using it to grasp and hold onto branches as well as for climbing and agility. Humans, on the other hand, did not need much use for this longer tail because of the environment, they became bipedal and probably had no use for a tail anymore.
Paleontologist's working in Tanzania have discovered the oldest known fossils from two major primate groups — Old World monkeys and apes which include humans. This study recovered a lone tooth and jaw fragment with three teeth from a site in Rukwa in southwestern Tanzania. They dated geological nearby rocks and found out that the fossils are 25.2 million years old, which is older than any other example from either primate group. This fossil trove “fills in a roughly 10-million-year gap in primate evolution,” says John Fleagle, an anthropologist at Stony Brook University in New York. This discovery also confirms the fossil record analyses of mutations in DNA that can be traced back to estimate how long ago two species diverged, which suggests that old world monkeys and apes split from their common ancestor 25 million to 30 million years ago. This discovery proves that approximately 30 million years ago monkeys and human ancestors the "apes" split from their common ancestor, which was generally said to resemble a primate-like mammal species that possessed a tail of some sort. With this evidence it would seem that this unknown common ancestor possessed the homologus trait but then due to many factors this species diverged into two new species carrying with them this homologus trait but with different structures and functions.
Two different species that possess the analogus trait is a dolphin and a horse. Dolphins are aquatic mammals that have teeth. There are 39 species of oceanic dolphins classified in four genus, but these numbers continue changing with new discoveries. There are even small amounts of dolphins that inhabit freshwater rivers. Dolphins have smooth, rubbery skin that usually is a mixture of black, white, and gray. They have two flippers or fins on their sides, a triangular fin on the back, and a large layer of blubber beneath their skin. On the other hand, Horses are odd-toed ungulate mammals belonging to the taxonomic family Equidae. Their average height is 4 ft. to 6ft. and their average weight is 840lbs to 2,200lbs. They have long tails, short hair, muscular torsos, long thick necks and elongated heads. Due to domestication they are found all over the world.
The analogus trait of each species is their limbs. A dolphins flipper or limb measures 11-19 inches and are curved back. A horse's limbs are made of dozens of bones, ligaments, muscles, and tendons that support the weight of the body. Both a horse and dolphin possess similarities in their structure, for example, they both contain a humerus, radius, ulna, carpals, metacarpals, and phalanges. They have complete difference in size and shape, but are used for the same function and motion
whether it be in water or land. This similar function is for moving and steering. Both horses and dolphins use their limbs for moving, steering, and even balancing across the ocean for the dolphin or land for the horse. This analogus trait between these species exhibit similarities because both are needed for them to be able to move around areas properly and thrive. The common ancestor of these two species could definitely have had possessed this analogus trait. Scientists believe that the earliest ancestors of dolphins were not marine creatures but were terrestrial animals. The evidence is that dolphins have to come to the surface of water to get air. Since ancestors of the horse were terrestrial maybe this analogus trait was possessed by the common ancestor o these two species because they were in similar environments and those certain bones were needed for different functions and many survival. The function of these limbs are ultimately to move and steer which in any environment seems helpful. We know these traits are analogus because they have the same function but belong to a different class of vertebrates so that must mean their evolutionary line must be different.
Very good opening description of your homologous species pairing.
ReplyDeleteExcellent discussion on the homologous trait comparison. I just want to point out one issue:
"Humans, on the other hand, did not need much use for this longer tail because of the environment, they became bipedal and probably had no use for a tail anymore."
Yes, but the tail was lost long, long before humans became bipedal. The absence of a true tail is a trait of apes, not just humans. So if we want to understand why the tail was lost in humans, we actually need to ask why it was lost in early apes, who were still arboreal.
Good discussion on ancestry, but you do talk about apes losing their tails, which makes me wonder about your earlier claim about the loss of tails due to bipedalism?
RE: Analogous traits.
Good opening description.
Let's back up here and take a look at what you are comparing here. We have two mammals with two distinctly different limbs, in both structure and function. Since they are both mammals, we can confirm from the fossil record that they arose from a common ancestral mammal that possessed the primitive form of this limb and then passed it onto these two descendent species. That means they shared a common genetic origin.
So, a common genetic origin with differences in traits arising due to different environmental pressures. That describes homologous traits, not analogous.
"Since ancestors of the horse were terrestrial maybe this analogus trait was possessed by the common ancestor o these two species"
That should have raised alarm bells. Yes, the common ancestor did have the generalized mammalian limb and passed it onto these two species. That means these CAN'T be analogs.
"We know these traits are analogus because they have the same function but belong to a different class of vertebrates so that must mean their evolutionary line must be different. "
That is not how you define analogy. E.g., the tiny ear ossicles in humans are homologous with the branchial arches of ancient fish. Really. So genetic difference tells us nothing about analogous status. You can't make that assumption.
Good images.
Hey Origins,
ReplyDeleteI found your comparison in the similarity of function between the horse and the dolphin one that I would not have otherwise found myself. I also used the dolphin for my analagous trait section, so it was interesting to see another student use that same animal from a different point of view. Well done!
Hi origins,
ReplyDeleteI thought your homologus trait example was very interesting. I never thought about humans having a tail, even though we have a tail-bone! I really liked how you described your comparison in an easy way and that you gave a lot of background information.