The Primate Order: Homologies vs Analogies and derived traits

I am a Supplemental Instruction Leader for Physical Anthropology at Long Beach City College, and in this week’s blog post I will be covering a lesson on the Order primates and the concept of homologous and analogous structures.

Analogies vs Homologies, what’s the difference? 

-Both birds and butterfly’s have wings

-The humerus of a bat and a human

Both instances above are examples of each of the terms. Can you guess which ones? Just because both birds and butterfly’s have wings does not mean their wings share a common ancestor, so they are analogous in structure. Likewise, the humerus of a bat and human, though different in function, do share a common ancestor, thus they are homologous in structure.


Homologous structures among the order primates 

The word “primate” is an umbrella term to classify a certain group of mammals that are defined by certain characteristics that separate them from other mammals. By definition, all primates share key homologous structures because they all share a common ancestor. Examples of these structures are opposable thumbs, prehensile hands and feet, and five digits on each of these appendages to name a few. Many shared behavioral aspects also define the primate order which will get to at a later section. main-qimg-2d191cdc2c09be02e3e5a392438daa49-c

Breaking it down even further… down the primate rabbit hole. 

You are walking on top a dirt field and you are getting ready to dig a hole. You are going to need a shovel. I want you to think of this shovel as a metaphor for the term derived traits. You are looking for the skeletal remains of your great great ancestor so you are determined to dig until you find them. You start digging, and shortly thereafter you come across skeletal remains of something that looks very vaguely like it could be your ancestor, but there are many traits missing. You keep digging, and you come across another skeletal remain that looks more like it could be your ancestor, but not quite enough. You keep digging and digging, each time coming across remains that look more and more like your ancestor until finally you have dug a hole so deep that you come across what you’ve been looking for.

Derived traits are homologous structures that can be modified to the point where it pertains to the particular species in question. In this case, when we say derived traits we are referring to humans. Every time you encountered a skeletal remain as you dug deeper, the traits were more and more derived until you eventually came across your human ancestor. In regards to the primate order, the primate classification is the very top of the dirt field you are about to dig. In other words, it is less specific, or less derived to humans.

Now we are going to start digging into the primate rabbit hole, and see what we find. Grab your shovel, start digging, and soon you will encounter the primate suborder.famtree

Suborder: Strepsirhini and Haplorhini

Strepsirhini is a group of primates that have a rhinarium, or “wet nose” (along with the basic characteristics of all primates: opposable thumbs, five digits, etc…)

Haplorhini is a group of primates that lack a rhinarium, or “dry nose” (along with the basic characteristics of all primates: opposable thumbs, five digits, etc…)

Already we can tell which trait is more derived to humans. Just think, do we have a rhinarium or not? Clearly we do not, so therefore we belong under the suborder Haplorhini.

As you are shoveling, you quickly notice that the path down the Strepsirhini does not lead to your ancestor, so you move down the one that does: Haplorhini.

Following this logic, each time you dig deeper you will eventually see that there are more similarities to humans. In the next lesson we will cover the infraorder Catarrhini.



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