- Email: [email protected]
Social Evolution: The Force of the Market
Current Biology
Dispatches Social Evolution: The Force of the Market Shane J. Macfarlan Department of Anthropology, University of Utah, 270 S. 1400 E., Salt Lake City, UT 84112, USA Correspondence: [email protected] http://dx.doi.org/10.1016/j.cub.2016.07.041
Biological market forces shape patterns of cooperation typical of small-scale human societies that are organized by division of labor based on age and gender. Labor specialization promotes trade, while supply and demand affect the amount individuals exchange for commodities.
When people think about markets and the trade that occurs within them, they probably imagine something like the New York stock exchange or their local farmers market. Despite their vastly different size, these two examples are similar because they both are made up of individuals trying to exchange commodities (i.e. goods and services) in order to maximize individually beneficial outcomes. However, market trade is not restricted to our modern, large-scale human societies. Instead, markets may be a common feature of the biological world and could explain the evolution of cooperation [1,2]. Markets exist anytime commodities are unevenly distributed in a population and individuals who produce one type of commodity can choose exchange partners to obtain other commodities. Choice over whom to trade with induces competition between individuals to be chosen as exchange partners. The exchange value of commodities is then determined by supply and demand. Under these contexts, specialization and division of labor promote gains through trade and therefore cooperation between individuals whose exchange relationships can range from one-shot encounters to long-term reciprocal exchanges. Ronald Noe¨ and Peter Hammerstein [3,4] brought these insights to the attention of biologists in the early 1990s to clarify questions about the evolution of cooperation between non-kin that could not be addressed under the paradigm of reciprocal altruism, which relies on rewarding cooperative behavior and punishing non-cooperative behavior [5,6]. Instead, Noe¨ and Hammerstein [3,4] sought to understand how partner choice and partner switching could
affect who exchanges with whom and how individuals modulate investment in partners. Building on neoclassical economic theory — such as the law of supply and demand — they made a convincing case that trade does exist in nature and that reciprocity — long-term statistical associations between individuals who give to one another — could be due to mechanisms other than reciprocal altruism. The biological market paradigm led to a number of important findings on the role markets play in inter-specific mutualisms, intra-specific cooperation and inter-sexual selection [7,8]. However, research on biological markets was often limited in scope, explaining in a piecemeal fashion particular aspects of trait evolution or cooperative exchanges across one or two commodity classes. Furthermore, it remained unclear whether biological market theory was capable of explaining aspects of organismal biology, including holistic perspectives on a species ecological niche? A new study by Adrian Jaeggi and colleagues [9] in this issue of Current Biology sheds light on these issues in the context of human social evolution through an examination of commodity exchanges in a small-scale human society, the Tsimane’. The Tsimane’ (pronounced: CHI-ma-nay) are a population of approximately 15000 Amerindians from lowland Bolivia who live in communities of 50–500 people (Figure 1). Anthropologists have been working intensively with them since 2001, when Hillard Kaplan and Michael Gurven instituted the Tsimane’ Health and Life History Project to examine the evolutionary ecology of human life history [10]. Tsimane’
R756 Current Biology 26, R756–R777, August 22, 2016 ª 2016 Elsevier Ltd.
economy relies on subsistence farming, hunting, and fishing [11]. Typical of most small-scale human societies, they are only weakly integrated into the larger Bolivian political-economic system, resulting in minimal access to formal institutions, such as police forces and impartial judiciaries. Thus, the nature of market transactions in Tsimane’ society is conceivably more similar to those found in biological contexts. A key difference between biological markets and markets found in large-scale, competitive market economies is that interdependence and common interest rather than formal institutions enforce contracts [2,12,13]. Humans are recognized for unusually high levels of cooperation. Our long lives, needy children and occasional illnesses necessitate assistance from others. The skills necessary to rear offspring, care for the sick and obtain food are difficult to learn and often are dependent on age and gender [11,14]. Task specialization leads to divisions of labor and promotes individuals and groups to engage in mutually beneficial exchanges for goods and services in which they themselves do not specialize. The biological market paradigm predicts that these exchanges should produce a complex web of social interactions that are guided by market forces of supply and demand. To investigate how biological market forces pattern social organization in Tsimane’ society, Jaeggi and colleagues [9] analyzed five years of ethnographic data on exchanges across five commodity classes: meat, garden produce, garden labor, childcare and sickcare. While not all commodities
Current Biology
Dispatches were exchanged for one another directly, the exchange economy was fully connected — a person could conceivably use one commodity type to obtain any other using appropriate intermediate transactions. In general, commodities that represented similar forms of wealth — material capital, such as meat and garden produce, versus social capital, such as garden labor, childcare, and sickcare — were traded for one another more often. For example, meat was exchanged more often for meat and for garden produce, but not for garden labor, childcare, or sickcare, while childcare was exchanged for garden labor, childcare, and sickcare, but not meat. These analyses suggest that most trade is patterned by labor specializations occurring within wealth classes: material capital for material capital and social capital for social capital. These specializations are also based on divisions of labor based on age and gender: adult males dedicate more effort to meat production and garden labor than females, while adult females spend more time harvesting garden produce and caring for the infirm than males, and adolescent females allocate proportionally more time to childcare than adolescent males [15,16]. Furthermore, Jaeggi and colleagues [9] found that the prices individuals are willing to pay for items, such as meat and garden produce, were related to supply and demand. Meat is more difficult to obtain relative to garden produce. This is partly due to local ecology, which determines where meat can be found, but also because a more sophisticated toolkit and greater cultural learning are required to acquire game [14]. Meat is also in higher demand. Consistent with the forces of supply and demand, meat is more valuable than garden produce (for every 100 kilocalories of meat given, approximately 300 kilocalories of garden produce are returned). However, when meat is in high supply, the exchange rate falls, resulting in fewer calories of garden produce exchanged for meat. These results suggest human social organization is made possible through a biological marketplace that leverages
Figure 1. A typical Tsimane’ family. Humans are cooperative breeders who live in a skill-intensive foraging niche that requires individuals and groups to cooperate in child care, sick care, and resource provisioning. Market forces pattern some of this cooperation. Naturally occurring individual differences promote individuals to specialize their skillsets and exchange with others whether it be meat for garden produce or garden labor for child care. Photo: Adrian Jaeggi.
naturally occurring individual differences based on age and gender into task specialization. This in turn promotes mutually beneficial divisions of labor and leads to exchanges that solve problems related to needy children, infirm elderly and resource shortfalls. The terms of these exchanges are affected by the supply and demand of commodities. These findings are no small feat, as some social scientists have debated whether individuals from small-scale societies do at all employ economizing principles towards transactions in daily life. While trade in biological markets is stabilized by common interest, trade in large-scale, human market economies is stabilized by explicit contracts and formal institutions [2,13]. Trade in small-scale human societies, such as the Tsimane’, may be regulated by a mix of both. For example, reputation promotes common interest and trade throughout all small-scale societies [17–19]. However, all humans can make use of language to discuss the terms of trade, thereby creating conditions necessary for more complete contracts, without formal institutions. As such, trade in small-scale human societies may represent an intermediate
state between the markets found in biological contexts and large-scale economies. The evolutionary processes driving shifts between these three states are unresolved; however, it is fertile ground for understanding the biological roots of human sociality and is particularly pertinent as many of the world’s small-scale societies become integrated into the global market. REFERENCES 1. Barclay, P. (2013). Strategies for cooperation in biological markets, especially for humans. Evol. Hum. Behav. 34, 164–175. 2. Hammerstein, P., and Noe¨, R. (2016). Biological trade and markets. Phil. Trans. R. Soc. B. 371, 20150101. 3. Noe¨, R., and Hammerstein, P. (1994). Biological markets: Supply and demand determine the effect of partner choice in cooperation, mutualism, and mating. Behav. Ecol. Sociobiol. 35, 1–11. 4. Noe¨, R., and Hammerstein, P. (1995). Biological markets. Trends. Ecol. Evol. 10, 336–339. 5. Trivers, R.L. (1971). The evolution of reciprocal altruism. Q. Rev. Biol. 46, 35–57. 6. Axelrod, R., and Hamilton, W.D. (1981). The evolution of cooperation. Science 211, 1390–1396.
Current Biology 26, R756–R777, August 22, 2016 R757
Current Biology
Dispatches 7. Bshary, R., and Noe¨, R. (2003). Biological markets: The ubiquitous influence of partner choice on the dynamics of cleaner fish-client fish interactions. In Genetic and Cultural Evolution of Cooperation, P. Hammerstein, ed. (Cambridge: MIT Press), pp. 167–184. 8. Gomes, C.M., and Boesch, C. (2011). Reciprocity and trades in wild West African chimpanzees. Behav. Ecol. Sociobiol. 65, 2183–2196. 9. Jaeggi, A.V., Hooper, P.L., Beheim, B.A., Kaplan, H., and Gurven, M. (2016). Reciprocal exchange patterned by market forces helps explain cooperation in a small-scale society. Curr. Biol. 26, 2180– 2187. 10. Shenk, M.K., Hooper, P.L., Gurven, M., and Kaplan, H. (2006). The Tsimane’ life history project. Anthropol. News 47, 52–53.
11. Hooper, P.L., Demps, K., Gurven, M., Gerkey, D., and Kaplan, H.S. (2015). Skills, division of labor, and economies of scale among Amazonian hunters and South Indian honey collectors. Phil. Trans. R. Soc. B. 370, 20150008. 12. Leimar, O., and Hammerstein, P. (2010). Cooperation for direct fitness benefits. Phil Trans. R. Soc. B. 365, 2619–2626. 13. Bowles, S., and Hammerstein, P. (2003). Does market theory apply to biology? In Genetic and Cultural Evolution of Cooperation, P. Hammerstein, ed. (Cambridge: MIT Press), pp. 153–165. 14. Kaplan, H.S., Hooper, P.L., and Gurven, M. (2009). The evolutionary and ecological roots of human social organization. Phil. Trans. R. Soc. B. 364, 3289–3299. 15. Steiglitz, J., Gurven, M., Kaplan, H., and Hooper, P.L. (2013). Household task delegation among high-fertility forager-
horticulturalists of lowland Bolivia. Curr. Anthropol. 54, 232–241. 16. Hooper, P.L. (2011). The structure of energy production and redistribution among Tsimane’ forager-horticulturalists. (PhD. Dissertation: University of New Mexico). 17. Macfarlan, S.J., Remiker, M., and Quinlan, R.J. (2012). Competitive altruism explains labor exchange variation in a Dominican village. Curr. Anthropol. 35, 118–124. 18. Macfarlan, S.J., Quinlan, R.J., and Remiker, M. (2013). Cooperative behaviour and prosocial reputation dynamics in a Dominican village. Proc. Biol. Soc. 280, 20130557. 19. Macfarlan, S.J., and Lyle, H.F. (2016). Multiple reputation domains and cooperation behavior in two Latin American communities. Phil. Trans. R. Soc. B. 370, 20150009.
Evolution: Fossil Ears and Underwater Sonar Olivier Lambert D.O. Terre et Histoire de la Vie, Institut Royal des Sciences Naturelles de Belgique, 29 rue Vautier, Brussels, 1000, Belgium Correspondence: [email protected] http://dx.doi.org/10.1016/j.cub.2016.06.021
A key innovation in the history of whales was the evolution of a sonar system together with high-frequency hearing. Fossils of an archaic toothed whale’s inner ear bones provide clues for a stepwise emergence of underwater echolocation ability.
Whales are one of the most impressive examples of a radical evolutionary transition to a new environment. Starting with a terrestrial ancestor, more than 55 million years ago, the ancestors of whales and dolphins progressively invaded aquatic habitats. This invasion was accompanied by countless changes, impacting underwater locomotion, predation techniques and sensory organs [1]. Among these acquisitions, the emergence of an echolocation system in the toothed whales, the odontocetes, undoubtedly played a major role in the evolutionary success of the group, allowing beaked whales, dolphins, porpoises and sperm whales to venture into low visibility waters, such as great oceanic depths or turbid rivers. However, the evolution of the underwater sonar has been relatively
poorly studied from a deep time perspective. Although echolocation ability was experimentally demonstrated in only a few extant species, anatomical correlates for the production (phonic lips in the forehead), transmission (through the melon giving the dolphins’ forehead its typical outline) and reception (via a fat pad in the mandible) of ultrasonic sounds are found in all modern odontocetes (Figure 1) [2–5]. Ultrasound production distinguishes the odontocetes from the non-echolocating mysticetes. The mysticetes possess a specialized filtering device themselves: baleen — keratin plates and bristles hanging from the upper jaw, allowing the simultaneous capture of a large amount of small prey. Moving back in time, the external cranial morphology of many fossil odontocetes
R758 Current Biology 26, R756–R777, August 22, 2016 ª 2016 Elsevier Ltd.
suggests that at least part of the soft tissue structures involved in sound production and propagation were present in many extinct odontocetes, including early Oligocene (34–28 million years ago) taxa [6,7]. However, until now only a few studies have focused on the hearing abilities of archaic whales (archaeocetes) and early odontocetes [8–11], providing only a limited amount of data for deciphering the first steps of the evolution of the high-frequency sensitive ears required for an efficient sonar system. In a paper in this issue of Current Biology, Morgan Churchill and colleagues [12] describe a new archaic odontocete from late Oligocene (27–24 million years ago) marine deposits of South Carolina and compare its inner ear morphology to a broad range
Dispatches Social Evolution: The Force of the Market Shane J. Macfarlan Department of Anthropology, University of Utah, 270 S. 1400 E., Salt Lake City, UT 84112, USA Correspondence: [email protected] http://dx.doi.org/10.1016/j.cub.2016.07.041
Biological market forces shape patterns of cooperation typical of small-scale human societies that are organized by division of labor based on age and gender. Labor specialization promotes trade, while supply and demand affect the amount individuals exchange for commodities.
When people think about markets and the trade that occurs within them, they probably imagine something like the New York stock exchange or their local farmers market. Despite their vastly different size, these two examples are similar because they both are made up of individuals trying to exchange commodities (i.e. goods and services) in order to maximize individually beneficial outcomes. However, market trade is not restricted to our modern, large-scale human societies. Instead, markets may be a common feature of the biological world and could explain the evolution of cooperation [1,2]. Markets exist anytime commodities are unevenly distributed in a population and individuals who produce one type of commodity can choose exchange partners to obtain other commodities. Choice over whom to trade with induces competition between individuals to be chosen as exchange partners. The exchange value of commodities is then determined by supply and demand. Under these contexts, specialization and division of labor promote gains through trade and therefore cooperation between individuals whose exchange relationships can range from one-shot encounters to long-term reciprocal exchanges. Ronald Noe¨ and Peter Hammerstein [3,4] brought these insights to the attention of biologists in the early 1990s to clarify questions about the evolution of cooperation between non-kin that could not be addressed under the paradigm of reciprocal altruism, which relies on rewarding cooperative behavior and punishing non-cooperative behavior [5,6]. Instead, Noe¨ and Hammerstein [3,4] sought to understand how partner choice and partner switching could
affect who exchanges with whom and how individuals modulate investment in partners. Building on neoclassical economic theory — such as the law of supply and demand — they made a convincing case that trade does exist in nature and that reciprocity — long-term statistical associations between individuals who give to one another — could be due to mechanisms other than reciprocal altruism. The biological market paradigm led to a number of important findings on the role markets play in inter-specific mutualisms, intra-specific cooperation and inter-sexual selection [7,8]. However, research on biological markets was often limited in scope, explaining in a piecemeal fashion particular aspects of trait evolution or cooperative exchanges across one or two commodity classes. Furthermore, it remained unclear whether biological market theory was capable of explaining aspects of organismal biology, including holistic perspectives on a species ecological niche? A new study by Adrian Jaeggi and colleagues [9] in this issue of Current Biology sheds light on these issues in the context of human social evolution through an examination of commodity exchanges in a small-scale human society, the Tsimane’. The Tsimane’ (pronounced: CHI-ma-nay) are a population of approximately 15000 Amerindians from lowland Bolivia who live in communities of 50–500 people (Figure 1). Anthropologists have been working intensively with them since 2001, when Hillard Kaplan and Michael Gurven instituted the Tsimane’ Health and Life History Project to examine the evolutionary ecology of human life history [10]. Tsimane’
R756 Current Biology 26, R756–R777, August 22, 2016 ª 2016 Elsevier Ltd.
economy relies on subsistence farming, hunting, and fishing [11]. Typical of most small-scale human societies, they are only weakly integrated into the larger Bolivian political-economic system, resulting in minimal access to formal institutions, such as police forces and impartial judiciaries. Thus, the nature of market transactions in Tsimane’ society is conceivably more similar to those found in biological contexts. A key difference between biological markets and markets found in large-scale, competitive market economies is that interdependence and common interest rather than formal institutions enforce contracts [2,12,13]. Humans are recognized for unusually high levels of cooperation. Our long lives, needy children and occasional illnesses necessitate assistance from others. The skills necessary to rear offspring, care for the sick and obtain food are difficult to learn and often are dependent on age and gender [11,14]. Task specialization leads to divisions of labor and promotes individuals and groups to engage in mutually beneficial exchanges for goods and services in which they themselves do not specialize. The biological market paradigm predicts that these exchanges should produce a complex web of social interactions that are guided by market forces of supply and demand. To investigate how biological market forces pattern social organization in Tsimane’ society, Jaeggi and colleagues [9] analyzed five years of ethnographic data on exchanges across five commodity classes: meat, garden produce, garden labor, childcare and sickcare. While not all commodities
Current Biology
Dispatches were exchanged for one another directly, the exchange economy was fully connected — a person could conceivably use one commodity type to obtain any other using appropriate intermediate transactions. In general, commodities that represented similar forms of wealth — material capital, such as meat and garden produce, versus social capital, such as garden labor, childcare, and sickcare — were traded for one another more often. For example, meat was exchanged more often for meat and for garden produce, but not for garden labor, childcare, or sickcare, while childcare was exchanged for garden labor, childcare, and sickcare, but not meat. These analyses suggest that most trade is patterned by labor specializations occurring within wealth classes: material capital for material capital and social capital for social capital. These specializations are also based on divisions of labor based on age and gender: adult males dedicate more effort to meat production and garden labor than females, while adult females spend more time harvesting garden produce and caring for the infirm than males, and adolescent females allocate proportionally more time to childcare than adolescent males [15,16]. Furthermore, Jaeggi and colleagues [9] found that the prices individuals are willing to pay for items, such as meat and garden produce, were related to supply and demand. Meat is more difficult to obtain relative to garden produce. This is partly due to local ecology, which determines where meat can be found, but also because a more sophisticated toolkit and greater cultural learning are required to acquire game [14]. Meat is also in higher demand. Consistent with the forces of supply and demand, meat is more valuable than garden produce (for every 100 kilocalories of meat given, approximately 300 kilocalories of garden produce are returned). However, when meat is in high supply, the exchange rate falls, resulting in fewer calories of garden produce exchanged for meat. These results suggest human social organization is made possible through a biological marketplace that leverages
Figure 1. A typical Tsimane’ family. Humans are cooperative breeders who live in a skill-intensive foraging niche that requires individuals and groups to cooperate in child care, sick care, and resource provisioning. Market forces pattern some of this cooperation. Naturally occurring individual differences promote individuals to specialize their skillsets and exchange with others whether it be meat for garden produce or garden labor for child care. Photo: Adrian Jaeggi.
naturally occurring individual differences based on age and gender into task specialization. This in turn promotes mutually beneficial divisions of labor and leads to exchanges that solve problems related to needy children, infirm elderly and resource shortfalls. The terms of these exchanges are affected by the supply and demand of commodities. These findings are no small feat, as some social scientists have debated whether individuals from small-scale societies do at all employ economizing principles towards transactions in daily life. While trade in biological markets is stabilized by common interest, trade in large-scale, human market economies is stabilized by explicit contracts and formal institutions [2,13]. Trade in small-scale human societies, such as the Tsimane’, may be regulated by a mix of both. For example, reputation promotes common interest and trade throughout all small-scale societies [17–19]. However, all humans can make use of language to discuss the terms of trade, thereby creating conditions necessary for more complete contracts, without formal institutions. As such, trade in small-scale human societies may represent an intermediate
state between the markets found in biological contexts and large-scale economies. The evolutionary processes driving shifts between these three states are unresolved; however, it is fertile ground for understanding the biological roots of human sociality and is particularly pertinent as many of the world’s small-scale societies become integrated into the global market. REFERENCES 1. Barclay, P. (2013). Strategies for cooperation in biological markets, especially for humans. Evol. Hum. Behav. 34, 164–175. 2. Hammerstein, P., and Noe¨, R. (2016). Biological trade and markets. Phil. Trans. R. Soc. B. 371, 20150101. 3. Noe¨, R., and Hammerstein, P. (1994). Biological markets: Supply and demand determine the effect of partner choice in cooperation, mutualism, and mating. Behav. Ecol. Sociobiol. 35, 1–11. 4. Noe¨, R., and Hammerstein, P. (1995). Biological markets. Trends. Ecol. Evol. 10, 336–339. 5. Trivers, R.L. (1971). The evolution of reciprocal altruism. Q. Rev. Biol. 46, 35–57. 6. Axelrod, R., and Hamilton, W.D. (1981). The evolution of cooperation. Science 211, 1390–1396.
Current Biology 26, R756–R777, August 22, 2016 R757
Current Biology
Dispatches 7. Bshary, R., and Noe¨, R. (2003). Biological markets: The ubiquitous influence of partner choice on the dynamics of cleaner fish-client fish interactions. In Genetic and Cultural Evolution of Cooperation, P. Hammerstein, ed. (Cambridge: MIT Press), pp. 167–184. 8. Gomes, C.M., and Boesch, C. (2011). Reciprocity and trades in wild West African chimpanzees. Behav. Ecol. Sociobiol. 65, 2183–2196. 9. Jaeggi, A.V., Hooper, P.L., Beheim, B.A., Kaplan, H., and Gurven, M. (2016). Reciprocal exchange patterned by market forces helps explain cooperation in a small-scale society. Curr. Biol. 26, 2180– 2187. 10. Shenk, M.K., Hooper, P.L., Gurven, M., and Kaplan, H. (2006). The Tsimane’ life history project. Anthropol. News 47, 52–53.
11. Hooper, P.L., Demps, K., Gurven, M., Gerkey, D., and Kaplan, H.S. (2015). Skills, division of labor, and economies of scale among Amazonian hunters and South Indian honey collectors. Phil. Trans. R. Soc. B. 370, 20150008. 12. Leimar, O., and Hammerstein, P. (2010). Cooperation for direct fitness benefits. Phil Trans. R. Soc. B. 365, 2619–2626. 13. Bowles, S., and Hammerstein, P. (2003). Does market theory apply to biology? In Genetic and Cultural Evolution of Cooperation, P. Hammerstein, ed. (Cambridge: MIT Press), pp. 153–165. 14. Kaplan, H.S., Hooper, P.L., and Gurven, M. (2009). The evolutionary and ecological roots of human social organization. Phil. Trans. R. Soc. B. 364, 3289–3299. 15. Steiglitz, J., Gurven, M., Kaplan, H., and Hooper, P.L. (2013). Household task delegation among high-fertility forager-
horticulturalists of lowland Bolivia. Curr. Anthropol. 54, 232–241. 16. Hooper, P.L. (2011). The structure of energy production and redistribution among Tsimane’ forager-horticulturalists. (PhD. Dissertation: University of New Mexico). 17. Macfarlan, S.J., Remiker, M., and Quinlan, R.J. (2012). Competitive altruism explains labor exchange variation in a Dominican village. Curr. Anthropol. 35, 118–124. 18. Macfarlan, S.J., Quinlan, R.J., and Remiker, M. (2013). Cooperative behaviour and prosocial reputation dynamics in a Dominican village. Proc. Biol. Soc. 280, 20130557. 19. Macfarlan, S.J., and Lyle, H.F. (2016). Multiple reputation domains and cooperation behavior in two Latin American communities. Phil. Trans. R. Soc. B. 370, 20150009.
Evolution: Fossil Ears and Underwater Sonar Olivier Lambert D.O. Terre et Histoire de la Vie, Institut Royal des Sciences Naturelles de Belgique, 29 rue Vautier, Brussels, 1000, Belgium Correspondence: [email protected] http://dx.doi.org/10.1016/j.cub.2016.06.021
A key innovation in the history of whales was the evolution of a sonar system together with high-frequency hearing. Fossils of an archaic toothed whale’s inner ear bones provide clues for a stepwise emergence of underwater echolocation ability.
Whales are one of the most impressive examples of a radical evolutionary transition to a new environment. Starting with a terrestrial ancestor, more than 55 million years ago, the ancestors of whales and dolphins progressively invaded aquatic habitats. This invasion was accompanied by countless changes, impacting underwater locomotion, predation techniques and sensory organs [1]. Among these acquisitions, the emergence of an echolocation system in the toothed whales, the odontocetes, undoubtedly played a major role in the evolutionary success of the group, allowing beaked whales, dolphins, porpoises and sperm whales to venture into low visibility waters, such as great oceanic depths or turbid rivers. However, the evolution of the underwater sonar has been relatively
poorly studied from a deep time perspective. Although echolocation ability was experimentally demonstrated in only a few extant species, anatomical correlates for the production (phonic lips in the forehead), transmission (through the melon giving the dolphins’ forehead its typical outline) and reception (via a fat pad in the mandible) of ultrasonic sounds are found in all modern odontocetes (Figure 1) [2–5]. Ultrasound production distinguishes the odontocetes from the non-echolocating mysticetes. The mysticetes possess a specialized filtering device themselves: baleen — keratin plates and bristles hanging from the upper jaw, allowing the simultaneous capture of a large amount of small prey. Moving back in time, the external cranial morphology of many fossil odontocetes
R758 Current Biology 26, R756–R777, August 22, 2016 ª 2016 Elsevier Ltd.
suggests that at least part of the soft tissue structures involved in sound production and propagation were present in many extinct odontocetes, including early Oligocene (34–28 million years ago) taxa [6,7]. However, until now only a few studies have focused on the hearing abilities of archaic whales (archaeocetes) and early odontocetes [8–11], providing only a limited amount of data for deciphering the first steps of the evolution of the high-frequency sensitive ears required for an efficient sonar system. In a paper in this issue of Current Biology, Morgan Churchill and colleagues [12] describe a new archaic odontocete from late Oligocene (27–24 million years ago) marine deposits of South Carolina and compare its inner ear morphology to a broad range