Determining How Species are Related- A closer look at phylogeny

What is the goal of modern classification?To assign species into taxa so that their classification reflects both morphological similarities among organisms, as well as hypotheses about their phylogeny.If two species share a similar evolutionary history, it means they have a fairly recent common ancestor (an organism from which other groups of organisms are descended).

How do we know if there is evidence of a shared common ancestor amongst species?Anatomy branch of biology that deals with structure and form, including internal systems

Physiology branch of biology dealing with physical & chemical functions of organisms, including internal processes.

DNA Evidence

Anatomical Evidence from FossilsTake a look at the oviraptor (top) and New Guinean cassowary (below). Do you think theyre related? Why? Why not?ANSWER = YES!They are closely related because: both have bones with hollow spaces the arrangement of bones in the hip, leg, wrist, & shoulder are very similar

Anatomical Evidence from Living SpeciesCompare the bones of the different species below. These are homologous structures (similar anatomical structure, but different functions that have a common evolutionary origin). Over millions of years, the bones have been modified for specialized purposes, such as swimming, flying, running, & grasping.

Physiological EvidenceDo you think horseshoe crabs are more closely related to other crabs or spiders?Biochemistry the study of chemical processes in living organisms (not always limited to living matter).

Proteins made inside the bodies of species (i.e. Digestive enzymes, cell organelles, tissues) allow us to see the degree of genetic similarity among different species.?? Blood proteins in horseshoe crabs show that they are indeed more closely related to spiders than crabs.

DNA EvidenceExamine the diagram above. What does it show? Does this surprise you?

DNA EvidenceMajor technological advances have made it more possible to determine the sequence of nucleotides of specific genes (sections of DNA).

DNA can then be compared between different species giving us yet another tool to classify organisms.

In some cases, this new evidence has meant that prior classifications had to be completely changed (i.e. Turkey vultures are more closely related to storks than the similar looking vultures from Asia & Africa.

How do you read a phylogenetic tree?A phylogenetic tree is a branching diagram that shows the evolutionary history of a group of organisms.Common AncestorThe roots or base of the tree represent the oldest ancestral speciesForks in each branch are points in the past at which an ancestral species split into two new speciesUpper ends represent modern-day speciesHas general characteristics shared by all the species that evolved from it.

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