Phylogeny

Phylogeny is the study of the evolutionary origins of an organism or, in the case of behavioral biology, of a behavior. Biologists following the model of Tinbergen's four questions attempt to identify the roots of the behavior in question in the ancestors of the animal expressing it in hopes of developing a better understanding of what caused it to appear within the population, and ultimately spread through out it.

Modern cetaceans (the group containing whales, dolphins and porpoises) are clearly distinguished from land mammals by the loss of hind limbs, which began approximately 41 million years ago, and was accelerated about 34 million years ago by the decline and ultimate cessation of production of the hormone Sonic hedgehog (Ssh) at the hind limb bud. (J. G. M. Thewissen et. al. 2006)

This process, among others, produced the lineage ending in modern whales, as displayed in the image below, taken from the paper “What Is a Whale?” by Annalisa Berta (1994). The two extant families of whales, Odontoceti (toothed whales) and Mysticeti (baleen whales) are shown at the bottom of the tree, with more ancient families above.

 

Source: "What is a Whale?"

Image Source: "What is a Whale?"

In “The Origins of Vocal Learning,” (1972), Fernando Nottebohm raises the observation, first made by Darwin, that in mammals, unlike in birds and reptiles, there is little or no distinct difference in vocal apparatus between males and females of the same species. So while males of some other orders evolved their vocalizations as a mechanism of winning a female's attention, this is not necessarily the case in most mammalian species. Whales, or at least humpbacks, the most studied species, are an exception to this rule. Additionally, in a case of convergent evolution, bearded seals, Erignathus barbatus, also display a pattern of male underwater vocalization with the intent of attracting females. Taken together, these facts reveal that singing developed sometime after 42 million years ago, and likely after 34 million years ago, still well before the appearance of the major modern families of cetaceans. Also, its value can be attested to by the fact that it developed in parallel in at least one other species of marine mammal.