Cats and humans are both mammals that have hair, give live birth and produce milk. Another trait that the both share, a homologous trait is the structure of their limbs. Humans and cats share the same bone structure in the arms. Though most of the bone structure is strikingly similar with the exception of size, the cats upper humerus bone became curved for ease of walking on all fours. Humans learned to walk straight and developed apposable thumbs allowing them to grip things but no longer walk on their hands. Whereas cats developed paws and claws for walking, climbing, and catching prey. These differences in the paw and hands and curvature of the humerus occurred because of the different functional needs applied to the animals in the form of environmental pressures.
According to National Geographic Researchers who studied the skeletons of 86 different species and over 4,500 anatomical homologous traits, the common ancestor of all cats, humans, bats, whales and mice looked like the image below, called the Ancestral Placental Mammal.
Analogous Traits
Bats and insects may have the common trait of wings however this is analogous trait because the two species did not have a common ancestor that passed down this trait to them. Instead this, like a paw and hand example, is a result of evolution in that environmental pressures cause the forelimbs of these two animals to develop in to flight capable wings. This trait is also analogous because the function is the same but the structures are quite different. Bats have bones similar in structure to humans underneath the skin however insects have veins that make up the frame of the wings and membrane that covers each cell created between the veins.
If we went far enough back for these two species however this ancestor would not posses the trait of wings because the wing trait was a result of later environmental pressures.
I first want say that you did a great job with your blog and species used to describe homologous, I knew that we had a lot in common with cats. I found that I had a better understanding of the information after reading your blog. Again great job on the blog.
ReplyDeleteRachel Parker
Good choice of homologous trait and very good explanation of the structural/functional differences and why they arose.
ReplyDeleteOn the issue of ancestry, since all organisms share some common ancestor, simply identifying a common ancestor is not sufficient for confirming that they are homologous. I do see from the image that the possible common ancestor possessed forelimbs, but it needed to be part of the discussion. More generally, you needed to explain that since both humans and cats are mammals, their common ancestor was an archais mammals, who did possess the ancestral forelimb structure. This is what we needed to know to confirm that these traits are indeed homologous.
Good description of the analogous traits. You make a good start of offering two pieces of evidence (phylogenetic and anatomical) that these traits are analogous, but simply stating that the "two species did not have a common ancestor that passed down this trait to them" isn't sufficient... namely because the common ancestor might well have had wings! This common ancestor lived a very, very long time ago (hundreds of millions of years) which makes it difficult to use this information to confirm analogous status. The common ancestor might well have had wings and passed the trait onto modern insects. The question is, did it also pass the trait on to modern bats? Well, we know quite a bit about the evolution of bats and this helps us confirm that these traits are indeed analogous. Bats are mammals and arose from a non-winged, tetrapedal mammalian ancestor. That confirms that the winged trait in bats arose independently from that common ancestor (long, long ago) and that these traits are indeed analogs.
Good images.