Evolutionary origin of human traits

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Evolutionary origin of human traits is a variable page about the topic. For a survey study looking at researchers' opinions about this topic, see How scientists perceive the evolutionary origin of human traits: results of a survey study

Question

Why and how did humans become so different from other apes?

Answer

Rationale

Hypotheses

There are conflicting hypotheses to explain why the traits that so clearly distinguish humans from other primates originally evolved. One idea is that the ancestors of humans came to live in a different kind of environment than the ancestors of chimpanzees and gorillas, and hence experienced different selection pressures and obtained a suite of unique traits as adaptations to the new environment. What that new environment was and which selection pressures were most important has been debated, however, and a number of hypotheses based on ideas other than environmental adaptation have also been proposed. To date, general discussion on the topic seems mostly to have focused on finding merit or flaws in one hypothesis at a time. The purpose of this page is to provide a structured forum for the general evaluation and comparison of the different hypotheses on human origins.

Below you can find a list of hypotheses explaining different traits that separate humans from other great apes. They were a part of a survey done on people's understanding about the reasons behind human traits, answered by paleontologist, biologists, medical professionals, and other people with professional understanding about evolution (human or in general) or how human bodies work. Some analysis done on the survey answers can be found below. Some hypotheses much discussed in literature in the last years are missing from the survey (and thus he list below), such as the postural feeding hypothesis, stating bipedalism originally arose as a feeding posture and not as a way of locomotion, and the expensive tissue hypothesis, which suggests the energy needed for building a big brain came from reducing some other expensive tissue in our body, namely the gut. A literary review was done on the same hypotheses asked about in the survey to find out whether the understanding about human evolution the answerers had was the same that could be gotten from scientific literature published in the last decades. Some analysis on the literary review results is found on this page.

The short version of the hypotheses in the list below are the ones used to refer to them in the analysis.

**Hypotheses and their shorter versions**
For short	Hypothesis
Bipedalism
Energy efficiency	When covering long distances on the ground, walking or running erect on two legs is energetically more efficient than walking or running on four legs.
Thinner branches	In the canopy, walking erect facilitates using multiple supports (as in orangutans) and hence makes it possible to move on thinner branches than when brachiating or moving quadrupedally.
Wading	In a littoral habitat, walking erect allows wading in deeper water with the nostrils above the surface (apes cross water bodies bipedally), and the same posture increases streamlining when swimming and diving for food (as in penguins).
Thermoregulation-b	Walking erect helps in thermoregulation in the savanna by exposing less skin to the midday sun and more skin to cooling wind.
Better view	Walking erect makes it possible to see above the savanna grass and hence spot danger from further away.
Foraging	Walking erect makes foraging more efficient, because hands are not needed for locomotion.
Carrying food	Walking erect makes it easier for a male to carry high-quality food such as meat to the female and infants.
Carrying baby	Walking erect makes it possible for a female to carry its offspring in its arms.
Tool use	Walking erect makes it easier to use tools and weapons.
Genitals	Walking erect is favored by sexual selection, as it makes the genitals more visible.
Big brain
Meat	A shift in diet towards eating more meat triggers encephalization, because meat is rich in energy.
Fish	A shift in diet towards eating more fish and other seafood triggers encephalization, because seafood is rich in both energy and the omega-3 fatty acids that are an essential component of brain tissue.
Cooking	The use of fire triggers encephalization, because cooking increases the nutritional value of plant foods.
Social	Complex social organization causes pressure for greater intelligence and hence triggers encephalization.
Collaborative hunting	Collaborative hunting causes pressure for greater intelligence and hence triggers encephalization.
Language	Spoken language causes pressure for greater intelligence and hence triggers encephalization.
Warfare	Warfare causes pressure for greater intelligence and hence triggers encephalization.
Neoteny	Encephalization is a secondary effect of neoteny (the retention of juvenile features into adulthood), which is advantageous when specialized adult morphology adapted to one environment has become maladaptive in a new environment.
Bipedalism-b	Encephalization is triggered by bipedalism, which changes the blood circulation and provides a cooling mechanism for the larger brain.
Nakedness	Encephalization is triggered by nakedness, which provides a cooling mechanism for the larger brain.
Nakedness
Skin contact baby	Direct skin-to-skin contact strengthens the emotional bond between a female and its nursing offspring.
Skin contact sex	Direct skin-to-skin contact makes sex more enjoyable, and is favored by sexual selection.
Cleanliness	In animals that feed messily on carrion, naked skin stays cleaner than hairy skin (or feather-covered skin as in vultures).
Ectoparasites	In mammals that live in permanent nests, naked skin helps to avoid a high ectoparasite load.
Drag	In mammals that live partly or entirely entirely in water, fur is often lost because it causes drag when swimming but fails to provide efficient insulation when wet (e.g. walrus, hippopotamuses, dolphins).
Thermoregulation-h	In mammals that hunt on the savanna, naked skin dissipates heat more efficiently and reduces the risk of becoming overheated.
Large mammal	Large mammals can regulate their body temperature without investing in hair, and humans are relatively large compared to other primates.
Clothes	Once the use of clothes has become common, fur becomes unnecessary.
Subcutaneous fat
Energy supply	In conditions of variable food supply, subcutaneous fat can store energy for times of food scarcity, and in infants it secures the development of the large brain.
Insulation	In wet conditions, subcutaneous fat provides more efficient insulation than hair does, and it makes swimming easier by increasing buoyancy and streamlining of the body.
Savannah thermoregulation	Subcutaneous fat is an adaptation to thermoregulation in the savanna, together with nakedness and sweating.
Body shape	Subcutaneous fat defines the body shape and its evolution is driven by sexual selection.
Descended larynx
Articulation	Articulate speech requires a descended larynx, because this makes it possible to produce a wider variety of sounds.
Impressive voice	A descended larynx makes the voice stronger and more impressive, and can evolve through sexual selection (as in the males of some deer).
Diving-l	A descended larynx can evolve as an adaptation to diving (as in some aquatic mammals), because it makes it possible to close the air passages when under water and to inhale rapidly through the mouth when surfacing.
Speech
Larynx	Speech is triggered by the descended larynx, which allows making a wider variety of sounds.
Diving-s	Speech requires voluntary breath control, which can evolve as an adaptation to diving. In water, visual and olfactory cues are inadequate and therefore liable to be replaced by vocal communication (as in whales).
Bipedalism-s	Speech requires voluntary breath control, which can evolve after bipedalism frees breathing from the constraint posed by the mechanics of locomotion.
Reassurance	Speech provides a means for females to reassure their offspring who have to be put down while foraging.
Sociality	Social pressure for more elaborate communication triggers evolution of speech.
Hunting	Collective hunting requires a means of effective communication and therefore triggers evolution of speech.
Culture	Transmitting cultural tradition (e.g., how to cope with unusually severe droughts) from one generation to the next requires a means of effective communication and therefore triggers evolution of speech.
Other traits that could be explained by an aquatic phase in human evolution
Baby swimming	Human babies can be taken for a swim long before they can walk. They are comfortable in water and capable of holding their breath when submerged.
Nose	Unlike apes, humans have an arched nose and flexible nostrils. These help prevent water from entering the respiratory tract when diving.
Smell	Humans have a relatively weak sense of smell, as aquatic mammals often do.
Webbing	Humans have partial webbing between their fingers and toes. Webbed feet are common among semi-aquatic animals (such as otters and ducks), but are not found in non-human primates.
Eccrine glands	Cooling sweat is excreted from eccrine glands in humans but from apocrine glands in other primates. Apocrine glands could have lost their thermoregulatory function in human ancestors during a period when dip-cooling replaced sweat-cooling.
Sweating	Humans sweat more profusely than any other primate. Since this can lead to fatal loss of water and electrolytes in a few hours, the trait probably evolved in conditions of abundant water and salt supply.
Diving-o	Compared to other primates, humans are stronger swimmers and can dive both deeper and further.
Apnea	The diving reflex (slowing down of heartbeat and oxygen usage in water) increases the resistance of the brain to apnea, and its magnitude in human divers is comparable to that in semi-aquatic mammals such as otters and beavers.
Fond of water	Compared to other primates, humans are unusually fond of immersing themselves in water. This is manifested in the popularity of beach holidays, swimming and bathing.

The answerers' opinions should be used as continuous [0,1] variables in such a way that each answer is transformed into its quantile of all answers to that question. Then neural networks, Bayesian belief network analyzers (such as B-source), or other statistical tools can be applied.

For single answer analyses, multinomial regression models should be applied.

In the following sections, we will present results about support to different hypotheses explaining the traits studied. We have two sources of information and three graphs for each hypothesis: Survey to authors of relevant journals, with ca. 1200 responses; and authors of articles about human evolution and the traits of interest (272 individual authors). The survey graphs on the left show the repondents' views on how likely each hypothesis is. The middle graphs show the same information separated by the expertise of the respondent (and for visibility, we assumed the X axis to be continous so that we could draw probability densities). The graphs on the right show the support from article authors in the literature review. Each hypothesis has one row of graphs, and they are ordered by the trait the hypotheses explain.

Bipedalism

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Brain

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Nakedness

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Subcutaneous fat

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Larynx

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Speech

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Other traits

**Other traits that could be explained by a waterside hypothesis**
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Survey

The graph above shows the results for correlations done from the survey answers between all different hypotheses. In most cases the correlations were quite small, and almost always positive. There are only a few negative correlations in these answers, and in them the correlations are very small, -0.14 being the strongest negative correlation. The most notable correlations are between the hypotheses that suggest a semi-aquatic ancestor. If one believes in one, then all the water-relates hypotheses seem likely, and if one doesn't, they seem unlikely. Interestingly, eating of fish and other sea food enabling brain growth does not correlate with the rest of the water-related hypotheses, even though if fish was needed for brain growth, it indicades humans lived on shores, fishing and wading, thus probably spending a significant time in water, which is also the basis for all the other waterside hypotheses. The fish hypothesis does however have a correlation with eating meat being a major step toward bigger brains, as well as cooking the food, which makes it possible to get more energy from it.

The graph below shows the results for principal components analysis done on the survey data. All the water-related hypotheses (except eating fish) are at the top right corner, and the rest are at the bottom. This means those people who have an opinion about one water-related hypothesis are more or less the same opinion about the rest of them. What people thought about the water-related hypotheses doesn't seem to have much of a connection to their opinions about the rest of the hypotheses.

For other hypotheses it seems that the idea that brain developed as a response to hairlessness convinces the same people as the hypotheses of hairlessness evolving to enhance skin contact and bipedalism to show off genitals. Completely different people were the people who found it convincing that the brain developed to enable speaking or hunting and that the subcutaneous fat layer developed as an energy supply.

The sizes for the dots tell about how likely the hypothesis was found to explain the trait in the survey. The bigger the dot, the more likely people thought it was. The numbers from the scaling were gotten by calculating the average answer (1 being very likely and 5 being very unlikely), and subtracting that from 5 (to get the likeliest ones with the highest values instead of the lowest).

Literary review

Hidden below you can find a summary of the articles found in a literary review on the evolution of human traits done in the summer 2016 to find out, which hypothesis on which human traits are currently discussed in scientific articles, and which according to them seem the most likely ways the human traits have evolved. F, A and N in the last column stand for For, Against and Neutral, according to which point of view is argued in the article about the hypothesis in question.

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Literary review summary(-)
Obs	Article	Year	Type	Hypothesis	Trait	For Against Neutral
1	Ko 2015-1	2015	Review article	Better view	Bipedalism	A
2	Videan & McGrew 2002	2002	Research article	Better view	Bipedalism	A
3	Bender et al. 2007	2007	Review article	Better view	Bipedalism	A
4	Sutou 2012	2012	Essay	Carrying baby	Bipedalism	F
5	Watson et al. 2008	2008	Research article	Carrying baby	Bipedalism	A
6	David-Barret & Dunbar 2016	2016	Research article	Carrying food	Bipedalism	A
7	Ko 2015-1	2015	Review article	Carrying food	Bipedalism	F
8	Videan & McGrew 2002	2002	Research article	Carrying food	Bipedalism	F
9	Carvalho et al. 2012	2012	Comment	Carrying food	Bipedalism	F
10	Sutou 2012	2012	Essay	Carrying food	Bipedalism	F
11	Lieberman 2011	2011	Essay	Energy efficiency	Bipedalism	F
12	Rodman & McHenry 1980	1980	Research article	Energy efficiency	Bipedalism	F
13	David-Barret & Dunbar 2016	2016	Research article	Energy efficiency	Bipedalism	N
14	Sockol et al. 2007	2007	Research article	Energy efficiency	Bipedalism	F
15	Leonard & Robertson 1995	1995	Comment	Energy efficiency	Bipedalism	F
16	Leonard & Robertson 2001	2001	Comment	Energy efficiency	Bipedalism	F
17	Isbell & Young 1996	1996	Review article	Energy efficiency	Bipedalism	F
18	Pontzer et al. 2009	2009	Research article	Energy efficiency	Bipedalism	F
19	Pickford 2002	2002	Review article	Energy efficiency	Bipedalism	F
20	Halsey & White 2012	2012	Research article	Energy efficiency	Bipedalism	A
21	Wang et al. 2003	2003	Research article	Energy efficiency	Bipedalism	A
22	Steudel 1996	1996	Research article	Energy efficiency	Bipedalism	A
23	Taylor & Rowntree 1973	1973	Comment	Energy efficiency	Bipedalism	A
24	Steudel-Numbers 2003	2003	Research article	Energy efficiency	Bipedalism	A
25	Crompton et al. 1998	1998	Research article	Energy efficiency	Bipedalism	A
26	Wheeler 1984	1984	Review article	Energy efficiency	Bipedalism	N
27	Carey & Crompton 2005	2005	Research article	Energy efficiency	Bipedalism	N
28	Videan & McGrew 2002	2002	Research article	Foraging	Bipedalism	F
29	David-Barret & Dunbar 2016	2016	Research article	Thermoregulation-b	Bipedalism	N
30	Wheeler 1984	1984	Review article	Thermoregulation-b	Bipedalism	F
31	Morgan 1993	1993	Review article	Thermoregulation-b	Bipedalism	A
32	Porter 1993	1993	Comment	Thermoregulation-b	Bipedalism	F
33	Wheeler 1994	1994	Comment	Thermoregulation-b	Bipedalism	F
34	Wheeler 1991-1	1991	Research article	Thermoregulation-b	Bipedalism	F
35	Wheeler 1991-2	1991	Research article	Thermoregulation-b	Bipedalism	F
36	Ruxton & Wilkinson 2011	2011	Research article	Thermoregulation-b	Bipedalism	A
37	Ko 2015-1	2015	Review article	Thermoregulation-b	Bipedalism	A
38	Chaplin et al. 1994	1994	Research article	Thermoregulation-b	Bipedalism	A
39	Bender et al. 2007	2007	Review article	Thermoregulation-b	Bipedalism	A
40	Roberts & Thorpe 2014	2014	Review article	Thinner branches	Bipedalism	F
41	Stanford 2006	2006	Research article	Thinner branches	Bipedalism	F
42	Crompton et al. 2010	2010	Review article	Thinner branches	Bipedalism	F
43	Sigmon 1971	1971	Research article	Thinner branches	Bipedalism	F
44	Stanford 2002	2002	Brief communication	Thinner branches	Bipedalism	F
45	Senut 2006	2006	Book section	Thinner branches	Bipedalism	F
46	Thorpe 2009	2009	Research article	Thinner branches	Bipedalism	F
47	Tuttle 1981	1981		Thinner branches	Bipedalism	F
48	Preuschoft 2004	2004	Review article	Thinner branches	Bipedalism	F
49	Thorpe et al. 2007-1	2007	Report	Thinner branches	Bipedalism	F
50	Thorpe et al. 2014	2014	Debate	Thinner branches	Bipedalism	F
51	Crompton et al. 2003	2003		Thinner branches	Bipedalism	F
52	Gebo 1996	1996	Research article	Thinner branches	Bipedalism	A
53	Begun et al. 2007	2007	Comment	Thinner branches	Bipedalism	A
54	Thorpe et al. 2007-2	2007	Comment	Thinner branches	Bipedalism	F
55	Wheeler 1984	1984	Review article	Tool use	Bipedalism	A
56	Harcourt‐Smith 2007	2007	Book section	Tool use	Bipedalism	A
57	Bender et al. 1997	1997		Wading	Bipedalism	F
58	Morgan 1993	1993	Review article	Wading	Bipedalism	F
59	Wrangham et al. 2009	2009	Research article	Wading	Bipedalism	F
60	Niemitz 2010	2010	Review article	Wading	Bipedalism	F
61	Kuliukas 2002	2002	Research article	Wading	Bipedalism	F
62	Kuliukas 2009	2009	Review article	Wading	Bipedalism	F
63	Kuliukas et al. 2009	2009	Research article	Wading	Bipedalism	F
64	Bender et al. 2007	2007	Review article	Wading	Bipedalism	F
65	Isler & van Schaik 2014	2014	Review article	Collaborative hunting	Brain	F
66	Carmody & Wrangham 2009	2009	Research article	Cooking	Brain	N
67	Joordens et al. 2014	2014	Research article	Fish	Brain	F
68	Broadhurst et al. 2002	2002	Review article	Fish	Brain	F
69	Broadhurst et al. 1998	1998	Review article	Fish	Brain	F
70	Cunnane 2007	2007	Comment	Fish	Brain	F
71	Cunnane et al. 2007	2007	Short report	Fish	Brain	F
72	Cunnane & Crawford 2003	2003	Review article	Fish	Brain	F
73	Cunnane et al. 1993	1993	Research article	Fish	Brain	F
74	Cunnane & Crawford 2014	2014	Research article	Fish	Brain	F
75	Verhaegen 1995	1995	Brief communication	Fish	Brain	F
76	Braun et al. 2010	2010	Research article	Fish	Brain	F
77	Carlson & Kingston 2007-1	2007	Research article	Fish	Brain	A
78	Carlson & Kingston 2007-2	2007	Comment	Fish	Brain	A
79	Langdon 2006	2006	Review article	Fish	Brain	A
80	Lakatos & Janka 2008	2008		Language	Brain	F
81	Brown & Greenhood 1991	1991	Review article	Language	Brain	F
82	Falk 1980	1980	Review article	Language	Brain	F
83	Previc 2002	2002	Brief communication	Meat	Brain	F
84	Speth 1989	1989	Research article	Meat	Brain	A
85	Ibraimov 2007	2007	Review article	Nakedness	Brain	N
86	Shea 1989	1989	Review article	Neoteny	Brain	A
87	Sandel et al. 2016	2016	Research article	Social	Brain	F
88	Shultz & Dunbar 2010	2010	Research article	Social	Brain	F
89	Shultz & Dunbar 2007	2007	Review article	Social	Brain	F
90	Navarrete et al. 2011	2011	Letter	Social	Brain	F
91	Dunbar 1992	1992	Research article	Social	Brain	F
92	Dunbar 1998	1998	Research article	Social	Brain	F
93	Dunbar 2003	2003	Review article	Social	Brain	F
94	Allman 1999	1999	Book section	Social	Brain	A
95	Falk 1980	1980	Review article	Warfare	Brain	A
96	Pitt 1978	1978	Review article	Warfare	Brain	F
97	Pawlowski 1999	1999		Body shape	Fat	N
98	Cunnane & Crawford 2003	2003	Review article	Energy supply	Fat	F
99	Wells 2006	2006	Research article	Energy supply	Fat	F
100	Correia et al. 2004	2004	Research article	Energy supply	Fat	F
101	Rebora 2010	2010	Review article	Insulation	Fat	A
102	Wheeler 1984	1984	Review article	Savannah thermoregulation	Fat	F
103	Pawlowski 1998	1998		Savannah thermoregulation	Fat	F
104	Pawlowski 1999	1999		Savannah thermoregulation	Fat	F
105	Rantala 2007	2007	Review article	Clothes	Hairlessness	A
106	Pagel & Bomder 2003	2003	Letter	Clothes	Hairlessness	N
107	Pagel & Bomder 2004	2004	Book section	Clothes	Hairlessness	N
108	Rebora 2010	2010	Review article	Clothes	Hairlessness	A
109	Kushlan 1985	1985	Review article	Clothes	Hairlessness	N
110	Glass 1966	1966	Letter	Clothes	Hairlessness	F
111	Hershkovitz 1966	1966	Letter	Clothes	Hairlessness	A
112	Brace et al. 1966	1966	Letter	Clothes	Hairlessness	A
113	Rantala 2007	2007	Review article	Drag	Hairlessness	A
114	Pagel & Bomder 2003	2003	Letter	Drag	Hairlessness	A
115	Rebora 2010	2010	Review article	Drag	Hairlessness	A
116	Wheeler 1985	1985	Review article	Drag	Hairlessness	A
117	Rantala 2007	2007	Review article	Ectoparasites	Hairlessness	F
118	Pagel & Bomder 2003	2003	Letter	Ectoparasites	Hairlessness	F
119	Rantala 1999	1999	Discussion	Ectoparasites	Hairlessness	F
120	Dean & Siva-Jothy 2012	2012	Letter	Ectoparasites	Hairlessness	F
121	Pagel & Bomder 2004	2004	Book section	Ectoparasites	Hairlessness	F
122	Dunn 1966	1966	Comment	Ectoparasites	Hairlessness	A
123	Rebora 2010	2010	Review article	Ectoparasites	Hairlessness	A
124	Giles 2011	2011	Review article	Skin contact baby	Hairlessness	F
125	Giles 2011	2011	Review article	Skin contact sex	Hairlessness	F
126	Rantala 2007	2007	Review article	Skin contact sex	Hairlessness	A
127	Wheeler 1984	1984	Review article	Thermoregulation-h	Hairlessness	F
128	Ruxton & Wilkinson 2011	2011	Research article	Thermoregulation-h	Hairlessness	F
129	Ibraimov 2007	2007	Review article	Thermoregulation-h	Hairlessness	F
130	Rantala 2007	2007	Review article	Thermoregulation-h	Hairlessness	A
131	Pagel & Bomder 2003	2003	Letter	Thermoregulation-h	Hairlessness	A
132	Rebora 2010	2010	Review article	Thermoregulation-h	Hairlessness	A
133	Wheeler 1985	1985	Review article	Thermoregulation-h	Hairlessness	F
134	Schwarts & Rosenblum 2005	2005	Research article	Thermoregulation-h	Hairlessness	F
135	Lupi 2008	2008	Review article	Thermoregulation-h	Hairlessness	F
136	Wheeler 1996	1996	Comment	Thermoregulation-h	Hairlessness	F
137	Wheeler 1992	1992	Research article	Thermoregulation-h	Hairlessness	F
138	Ebling 1985	1985	Review article	Thermoregulation-h	Hairlessness	F
139	Kushlan 1985	1985	Review article	Thermoregulation-h	Hairlessness	F
140	Brace et al. 1966	1966	Letter	Thermoregulation-h	Hairlessness	F
141	Amaral 1996	1966	Review article	Thermoregulation-h	Hairlessness	N
142	Davidson 2003	2003	Review article	Articulation	Larynx	F
143	Shprintzen 2003	2003	Comment	Articulation	Larynx	A
144	Nishimura et al. 2006	2006	Research article	Articulation	Larynx	A
145	Frey et al. 2011	2011		Impressive voice	Larynx	F
146	Frey et al. 2015	2015	Research article	Impressive voice	Larynx	F
147	Hombert 2010	2010	Book section	Impressive voice	Larynx	F
148	Fitch & Reby 2001	2001	Research article	Impressive voice	Larynx	F
149	Fitch 2002	2002	Review article	Impressive voice	Larynx	F
150	Apicella & Feinberg 2009	2009	Research article	Impressive voice	Larynx	N
151	Apicella et al. 2007	2007	Letter	Impressive voice	Larynx	N
152	Falhman & Schagatey 2014	2014	Review article	Diving-o	Other	F
153	Schagatey 2011	2011	Book section	Diving-o	Other	F
154	Verhaegen 1993	2013	Review article	Nose	Other	F
155	Mladina et al. 2009	2009	Review article	Nose	Other	N
156	Verhaegen 1995	1995	Brief communication	Smell	Other	F
157	Verhaegen et al. 2007	2007	Book section	Smell	Other	F
158	Wheeler 1991-2	1991	Research article	Sweating	Other	A
159	Wheeler 1992	1992	Research article	Sweating	Other	A
160	MacLarnon & Hewitt 1999	1999	Research article	Bipedalism-s	Speech	A
161	Stout & Chaminade 2012	2012	Review article	Culture	Speech	F
162	Corballis 2009	2009	Book section	Culture	Speech	F
163	Verhaegen 1995	1995	Brief communication	Diving-s	Speech	F
164	Verhaegen et al. 2002	2002	Opinion	Diving-s	Speech	F
165	MacLarnon & Hewitt 1999	1999	Research article	Diving-s	Speech	A
166	Lieberman 1973	1973	Review article	Hunting	Speech	N
167	Shprintzen 2003	2003	Comment	Larynx	Speech	A
168	Nishimura et al. 2006	2006	Research article	Larynx	Speech	A
169	Falk 2004	2004	Review article	Reassurance	Speech	F
170	Brown & Greenhood 1991	1991	Review article	Sociality	Speech	F
171	Dunbar 1993	1993		Sociality	Speech	F
172	Hamilton 1974	1974	Review article	Sociality	Speech	F
173	Kurland & Beckerman 1985	1985		Sociality	Speech	F
174	Locke 2001	2001	Review article	Sociality	Speech	F
175	Ko 2015-2	2015	Review article	Sociality	Speech	N

There are may histograms drawn from the review data to show how many of the found articles support or argue against all of the different hypotheses. They also show which hypotheses are the most talked about in the literature. Another set of histograms were drawn from the amount of authors writing the articles about each of the hypotheses. For this, all the authors for all articles were listed and plotted the same way as he articles, being for, against or writing something neural about the hypothesis. Before drawing the histograms the data was processed so that one author was counted only once to support or oppose a certain hypothesis, even if they had authored more than one article on the topic. You can see the histograms by trait from the authors below. Green color means supporting, red opposing and blue writing something neutral about the topic. All of the histograms can be found here and here. Note that not all of the hypotheses in the survey were discussed at all in any of the articles in the literature review.

The lower graph above shows relations between writers (small dots) and hypotheses (bubbles), or how the different writers wrote about hypotheses. Green lines mean supporting, red lines mean arguing against, and grey lines mean writing something on the topic, but not being clearly for or against the hypothesis. It shows us which hypotheses are discussed by the same authors, and whether the author supported both, opposed both, or whether they're hypotheses that one person doesn't think likely to both be true.

Several observations can be made from the graph. First, most authors only discussed a single hypothesis. The maximum number of different hypothesis discussed by a single author was six ----#: . CHECK THE DATA --Jouni (talk) 12:48, 4 September 2016 (UTC) (type: truth; paradigms: science: comment), but few authors discussed more than two hypotheses.

Second, some areas, notably nakedness, stimulated many authors to discuss several possible hypotheses. Another similar area was bipedalism, where, interestingly, authors supporting thinner branch hypothesis simultaneously opposed energy efficiency hypothesis. However, in the survey data these two hypotheses were not correlated.

Third, there are some isolated hypotheses such as neoteny, culture, and impressive voice, where the authors of these topics did not discuss any of the other hypotheses, and also none of the other authors discussed these hypotheses.

It can be concluded that there is no single study that would systematically look at the evolution of important human traits and evaluate strengths and weaknesses of related hypotheses.

Student survey

A questionnaire was sent to students to study whether they found the reasoning of each hypothesis convincing.

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Student survey(-)
Obs	Trait	Hypothesis	Reasoning	For Against Neutral
1	Bipedalism	Better view	You see further when on two legs	F
2	Bipedalism	Carrying items	Chimps carry food in hands	F
3	Bipedalism	Carrying items	Females prefer males that can carry food	F
4	Bipedalism	Carrying items	Hairless mothers had to carry babies	F
5	Bipedalism	Carrying items	Carrying baby on either side uses energy	A
6	Bipedalism	Carrying items	First tools date 1.5 M years after bipedalism	A
7	Bipedalism	Energy efficiency	Knuckle walk is least energy efficient	F
8	Bipedalism	Energy efficiency	Bipedalism is at least as efficient as tetrapedalism	F
9	Bipedalism	Energy efficiency	Easy to develop efficient bipedalism	F
10	Bipedalism	Energy efficiency	For chimps bipedalism is less efficient than on knuckles	A
11	Bipedalism	Energy efficiency	Bipedalism is not more efficient than tetrapedalism	A
12	Bipedalism	Energy efficiency	Knees-bent bipedalism is not efficient	A
13	Bipedalism	Foraging	Current primates walk on two legs when eating from bushes	F
14	Bipedalism	Foraging	First apes have structures for forging but not for long-distance walk	F
15	Bipedalism	Foraging	On two legs you can reach higher	F
16	Bipedalism	Foraging	During foraging, bipedalism is efficient	F
17	Bipedalism	Foraging	There was no reason to focus on standing-height foods	A
18	Bipedalism	Thermoregulation-b	Smaller surface area	F
19	Bipedalism	Thermoregulation-b	Longer operation times on savannah	F
20	Bipedalism	Thermoregulation-b	No other savannah animals are bipedalists	A
21	Bipedalism	Thermoregulation-b	There are easier ways to thermoregulate	A
22	Bipedalism	Thermoregulation-b	Humans did not actually develop on savannah	A
23	Bipedalism	Thinner branches	This is how orangutangs walk	F
24	Bipedalism	Thinner branches	Chimps cannot extend their legs like humans and orangutangs	F
25	Bipedalism	Thinner branches	Human scapula resembles that of orangutangs	F
26	Bipedalism	Thinner branches	Chimp climbing is like bipedalism	F
27	Bipedalism	Thinner branches	Many attachment points help moving on thinner branches	F
28	Bipedalism	Thinner branches	First erect humans had thumb-like pollux	F
29	Bipedalism	Thinner branches	Wrist bone association with knuckle walk is false	F
30	Bipedalism	Thinner branches	If gorilla and chimp ancestors walk on knuckles, so did human ancestors	A
31	Bipedalism	Thinner branches	Orangutangs are poor walkers on two legs.	A
32	Bipedalism	Thinner branches	If human-oranguntang ancestors walked on trees, that should be seen in chimps and gorillas	A
33	Bipedalism	Tools use	Bipedalism helps carrying tools around	F
34	Bipedalism	Wading	Apes walk on two legs when wading	F
35	Bipedalism	Wading	Two other primate species waded	F
36	Bipedalism	Wading	Shallow waters offer a lot of food	F
37	Bipedalism	Wading	Boyance helps bipedalism	F
38	Bipedalism	Wading	Bipedalism makes body streamlined for swimming	F
39	Bipedalism	Wading	Primates usually don't go to water	A
40	Bipedalism	Wading	From trees to ground is more parsimonious than trees-water-ground	A

+ Show code - Hide code

library(OpasnetUtils)
library(ggplot2)
library(igraph)
dat <- opbase.data("Op_en5865",subset="Student survey")

#order <- c("F", "N", "A")

#dat$Result <- factor(dat$Result, levels=order)

for(i in 1:ncol(dat)) {dat[[i]] <- as.character(dat[[i]])}

edg <- data.frame(
  from = c(dat$Reasoning, dat$Trait),
  to = rep(dat$Hypothesis, 2),
  Etype = c(rep("If then", nrow(dat)), rep("Makes relevant", nrow(dat))),
  FAN = c(dat$Result, rep("", nrow(dat)))
)
edg <- edg[!duplicated(paste(edg$from, edg$to)) , ]

ver <- data.frame(
    name = c(dat$Reasoning, dat$Trait, dat$Hypothesis),
    Vtype = rep(c("Reasoning", "Trait", "Hypothesis"), each = nrow(dat))
)

ver <- ver[!duplicated(ver$name) , ]

dag <- graph.data.frame(edg, directed = TRUE, vertices = ver)

colo <- c("Red", "Blue", "Pink", "Orange", "Brown", "Yellow", "Purple")

plot(
  dag,
  vertex.label.cex = 0.8,
  vertex.size = ifelse(V(dag)$Vtype == "Hypothesis", 6, 3),
  vertex.label.family = "Helvetica",
  vertex.color = ifelse(V(dag)$Vtype == "Hypothesis", 
                        colo[as.factor(V(dag)$Trait)],
                        "SkyBlue2"
  ),
  vertex.label = V(dag)$name, #ifelse(V(dag)$Vtype == "Hypothesis", V(dag)$name, NA),
  edge.color = c("Gray", "Red", "Green")[as.factor(E(dag)$FAN)],
  edge.arrow.size = 0.3,
  layout = layout.fruchterman.reingold,
  asp = 0.7
)

Calculations

calc1

+ Show code - Hide code

library(OpasnetUtils)
library(ggplot2)

# Creates a sample data a.

a <- data.frame(
	Occupation = rep(c("Biology", "Paleontology"), each = 3), 
	Question = c("A", "B", "C"), 
	Answer = sample(1:5, size = 180, replace = TRUE)
)

# Creates a simple histogram with font size 24. 
# Then makes a grid of these histograms based on different values of Occupation * Question

ggplot(a, aes(x=Answer)) +
	geom_histogram() + 
	theme_grey(base_size = 24) +
	facet_grid(Occupation~Question, scale='free')

Data version 1: raw data in Excel from Webropol: free text columns removed [1]
Data version 2: cleaned with this code [http://en.opasnet.org/en-opwiki/index.php/Special:R-tools?id=

+ Show code - Hide code

library(OpasnetUtils)
library(ggplot2)

# Fetch the stored raw data (requires a password to open it).

objects.get("Gygi7pqJFrngDdbx")

data <- objects.decode(etable, key)

# Print and plot examples of the cleaned data.

titles <- c(
"- ",
"- ",
"- ",
"- ",
"Anthropology or archaeology",
"Biology (animal physiology, anatomy or morphology) ",
"Biology (ecology) ",
"Biology (evolution) ",
"Biology (genetics or molecular biology) ",
"Biology (other, please specify) ",
"Geology ",
"Human cardiovascular or respiratory system ",
"Human musculoskeletal system ",
"Human nervous system ",
"Human nutrition ",
"Other aspects of human biology (please specify) ",
"Paleoanthropology ",
"Paleontology ",
"Other, please specify ",
"Peer reviewed articles in scientific journals ",
"Articles or books targeted at the general public ",
"Peer reviewed articles in scientific journals ",
"Articles or books targeted at the general public ",
"- ",
"- ",
"When covering long distances on the ground, walking or running erect on two legs is energetically more efficient than walking or running on four legs. ",
"In the canopy, walking erect facilitates using multiple supports (as in orangutans) and hence makes it possible to move on thinner branches than when brachiating or moving quadrupedally. ",
"In a littoral habitat, walking erect allows wading in deeper water with the nostrils above the surface (apes cross water bodies bipedally), and the same posture increases streamlining when swimming and diving for food (as in penguins). ",
"Walking erect helps in thermoregulation in the savanna by exposing less skin to the midday sun and more skin to cooling wind. ",
"Walking erect makes it possible to see above the savanna grass and hence spot danger from further away. ",
"Walking erect makes foraging more efficient, because hands are not needed for locomotion. ",
"Walking erect makes it easier for a male to carry high-quality food such as meat to the female and infants. ",
"Walking erect makes it possible for a female to carry its offspring in its arms. ",
"Walking erect makes it easier to use tools and weapons. ",
"Walking erect is favored by sexual selection, as it makes the genitals more visible. ",
"A shift in diet towards eating more meat triggers encephalization, because meat is rich in energy. ",
"A shift in diet towards eating more fish and other seafood triggers encephalization, because seafood is rich in both energy and the omega-3 fatty acids that are an essential component of brain tissue. ",
"The use of fire triggers encephalization, because cooking increases the nutritional value of plant foods. ",
"Complex social organization causes pressure for greater intelligence and hence triggers encephalization. ",
"Collaborative hunting causes pressure for greater intelligence and hence triggers encephalization. ",
"Spoken language causes pressure for greater intelligence and hence triggers encephalization. ",
"Warfare causes pressure for greater intelligence and hence triggers encephalization. ",
"Encephalization is a secondary effect of neoteny (the retention of juvenile features into adulthood), which is advantageous when specialized adult morphology adapted to one environment has become maladaptive in a new environment. ",
"Encephalization is triggered by bipedalism, which changes the blood circulation and provides a cooling mechanism for the larger brain. ",
"Encephalization is triggered by nakedness, which provides a cooling mechanism for the larger brain. ",
"Direct skin-to-skin contact strengthens the emotional bond between a female and its nursing offspring. ",
"Direct skin-to-skin contact makes sex more enjoyable, and is favored by sexual selection. ",
"In animals that feed messily on carrion, naked skin stays cleaner than hairy skin (or feather-covered skin as in vultures). ",
"In mammals that live in permanent nests, naked skin helps to avoid a high ectoparasite load. ",
"In mammals that live partly or entirely in water, fur is often lost because it causes drag when swimming but fails to provide efficient insulation when wet (e.g. walrus, hippopotamuses, dolphins). ",
"In mammals that hunt on the savanna, naked skin dissipates heat more efficiently and reduces the risk of becoming overheated. ",
"Large mammals can regulate their body temperature without investing in hair, and humans are relatively large compared to other primates. ",
"Once the use of clothes has become common, fur becomes unnecessary. ",
"In conditions of variable food supply, subcutaneous fat can store energy for times of food scarcity, and in infants it secures the development of the large brain. ",
"In wet conditions, subcutaneous fat provides more efficient insulation than hair does, and it makes swimming easier by increasing buoyancy and streamlining of the body. ",
"Subcutaneous fat is an adaptation to thermoregulation in the savanna, together with nakedness and sweating. ",
"Subcutaneous fat defines the body shape and its evolution is driven by sexual selection. ",
"Articulate speech requires a descended larynx, because this makes it possible to produce a wider variety of sounds. ",
"A descended larynx makes the voice stronger and more impressive, and can evolve through sexual selection (as in the males of some deer). ",
"A descended larynx can evolve as an adaptation to diving (as in some aquatic mammals), because it makes it possible to close the air passages when under water and to inhale rapidly through the mouth when surfacing. ",
"Speech is triggered by the descended larynx, which allows making a wider variety of sounds. ",
"Speech requires voluntary breath control, which can evolve as an adaptation to diving. In water, visual and olfactory cues are inadequate and therefore liable to be replaced by vocal communication (as in whales). ",
"Speech requires voluntary breath control, which can evolve after bipedalism frees breathing from the constraint posed by the mechanics of locomotion. ",
"Speech provides a means for females to reassure their offspring who have to be put down while foraging. ",
"Social pressure for more elaborate communication triggers evolution of speech. ",
"Collective hunting requires a means of effective communication and therefore triggers evolution of speech. ",
"Transmitting cultural tradition (e.g., how to cope with unusually severe droughts) from one generation to the next requires a means of effective communication and therefore triggers evolution of speech. ",
"Human babies can be taken for a swim long before they can walk. They are comfortable in water and capable of holding their breath when submerged. ",
"Unlike apes, humans have an arched nose and flexible nostrils. These help prevent water from entering the respiratory tract when diving. ",
"Humans have a relatively weak sense of smell, as aquatic mammals often do. ",
"Humans have partial webbing between their fingers and toes. Webbed feet are common among semi-aquatic animals (such as otters and ducks), but are not found in non-human primates. ",
"Cooling sweat is excreted from eccrine glands in humans but from apocrine glands in other primates. Apocrine glands could have lost their thermoregulatory function in human ancestors during a period when dip-cooling replaced sweat-cooling. ",
"Humans sweat more profusely than any other primate. Since this can lead to fatal loss of water and electrolytes in a few hours, the trait probably evolved in conditions of abundant water and salt supply. ",
"Compared to other primates, humans are stronger swimmers and can dive both deeper and further. ",
"The diving reflex (slowing down of heartbeat and oxygen usage in water) increases the resistance of the brain to apnea, and its magnitude in human divers is comparable to that in semi-aquatic mammals such as otters and beavers. ",
"Compared to other primates, humans are unusually fond of immersing themselves in water. This is manifested in the popularity of beach holidays, swimming and bathing. ",
"AAH conflicts with what is known about evolutionary processes in general. ",
"A major problem with AAH is that it is based on extreme environmental determinism. ",
"AAH is not needed, because all human traits can be explained by terrestrial scenarios. ",
"AAH is merely an exercise in comparative anatomy, not a scientific hypothesis. ",
"Not all aquatic mammals have naked skin, so hairlessness cannot be considered an aquatic adaptation. ",
"Humans may be similar to aquatic mammals in some traits, but this is only a coincidence and has no evolutionary relevance. ",
"According to AAH, humans should swim better than apes and have more streamlined bodies, but they do not. ",
"AAH lacks credibility, because the evidence presented in its favor is false. ",
"AAH is not supported by fossil evidence, because this shows no skeletal adaptations to an aquatic environment. ",
"AAH is contradicted by the fossil record, because this suggests a permanently non-aquatic environment. ",
"AAH lacks credibility, because its proponents do not agree on when and where the supposed aquatic phase took place. ",
"There has not been enough time for an aquatic phase. ",
"AAH is too simplistic to be taken seriously. ",
"AAH is less parsimonious than other proposed hypotheses: it has to explain both how human traits evolved in water, and how they were retained after return to land. ",
"AAH is internally less consistent than other proposed hypotheses. ",
"AAH is unscientific, because it cannot make predictions. ",
"AAH is unscientific, because it has been used in feministic argumentation. ",
"AAH can be ignored, because it was not published in a peer reviewed journal, and because it is mostly discussed in forums other than scientific journals. ",
"AAH can be ignored, because its main proponents are not professionals in the field of human evolution. ",
"AAH is pseudoscience comparable to creationism. ",
"- ",
"Articles in scientific journals ",
"Books by Elaine Morgan ",
"Books by other authors ",
"Articles or programs in popular media (press, TV, radio) ",
"University courses on human evolution ",
"Personal communication from someone who knew the hypothesis ",
"Blogs or other personal web pages ",
"Wikipedia ",
"AAH was rejected as implausible. ",
"AAH was mentioned or described, but no opinion on its validity was expressed. ",
"AAH was found more plausible than alternative hypotheses. "
)

# oprint(head(data))

X <- colnames(data)[X]

graph <- function(data, x, fillcol) {

fillname <- colnames(data)[fillcol]
my_title <- wrapper(titles[fillcol], width = 50)

out <- ggplot(data, aes_string(x = x, weight = 1, fill = fillname)) +
geom_bar(position = "fill", na.rm = TRUE) +
theme_grey(base_size = 24) +
labs(title = my_title)

return(out)
}

wrapper <- function(x, ...) paste(strwrap(x, ...), collapse = "\n")

if(is.null(fillcol)) fillcol <- 26:108 # If not defined, show all result columns as graphs.

for(i in fillcol) {
print(graph(data, X, i))
}

Histograms

A code for drawing histograms from the literary review data showing the number of articles and and authors supporting and arguing against different hypotheses. You can see all the histograms by clicking "Run code".

Model run 13.9.2016

+ Show code - Hide code

library(OpasnetUtils)
library(ggplot2)
library(igraph)
summary_data <- opbase.data("Op_en5865",subset="Literary review summary")
authors <- opbase.data("Op_en5865",subset="Literary review authors")


authors_summary <- merge(summary_data, authors,by="Article") # Merged tables

authors_short <- authors_summary[,c("Trait","Hypothesis","Result.x","Result.y")] # Irrelevant columns taken out

authors_uniq <- unique(authors_short) # A list of authors only defending of attacking one hypothesis once.

#ggplot(data=summary_data, aes(summary_data$Result)) + geom_histogram()

#ggplot(summary_data, aes(Result, fill = Hypothesis)) + geom_histogram() # eri hypoteesit eri värillä

#ggplot(summary_data, aes(Hypothesis, fill = Result)) + geom_histogram() # F/A/N eri värillä hypoteeseittain.

hypothesis.order <- c("Tool use","Foraging","Better view","Energy efficiency","Carrying baby","Carrying food","Thermoregulation-b","Wading","Thinner branches","Genitals","Social","Language","Collaborative hunting","Warfare","Meat","Neoteny","Fish","Cooking","Bipedalism-b","Nakedness","Thermoregulation-h","Ectoparasites","Large mammal","Clothes","Drag","Cleanliness","Skin contact sex","Skin contact baby","Energy supply","Savannah thermoregulation","Insulation","Body shape","Articulation","Impressive voice","Diving-l","Sociality","Hunting","Culture","Larynx","Bipedalism-s","Reassurance","Diving-s","Baby swimming","Sweating","Diving-o","Apnea","Nose","Fond of water","Smell","Webbing","Eccrine glands")

authors_uniq$Hypothesis <- factor(authors_uniq$Hypothesis, levels=hypothesis.order)


## histograms per trait in articles

for(i in unique(summary_data$Trait)){
	trait2 <- ggplot(summary_data[summary_data$Trait == i,], aes(Hypothesis, fill = Result)) +
	geom_histogram() +
	labs(x="", y="Count", title= paste(i, "in articles")) + 
	theme_grey(base_size=24)

	print(trait2)

}

## histograms per trait by author

for(i in unique(authors_uniq$Trait)){
	authors2 <- ggplot(authors_uniq[authors_uniq$Trait == i,], aes(Hypothesis, fill = Result.x)) +
	geom_histogram() +
	labs(x="", y="Count", title= paste(i, "by author")) + 
	theme_grey(base_size=24)

	print(authors2)

}

order <- c("F", "N", "A")

authors_uniq$Result.x <- factor(authors_uniq$Result.x, levels=order)
summary_data$Result <- factor(summary_data$Result, levels=order)


## Histograms wrapped by trait in articles

for(i in unique(summary_data$Trait)) {

	trait <- ggplot(summary_data[summary_data$Trait == i,], aes(Result)) + 
	geom_histogram(fill="blue") +
	labs(x = "", y = "count", title = paste(i, " in articles")) +
	theme_grey(base_size=24) + 
	facet_wrap(~Hypothesis)

	print(trait)
}


## Histograms wrapped by trait by authors

for(i in unique(authors_uniq$Trait)) {
	authors <- ggplot(authors_uniq[authors_uniq$Trait == i,], aes(Result.x)) +
	geom_histogram(fill="blue") +
	labs(x="", y="Count", title = paste(i, " by author")) + 
	theme_grey(base_size=24) +
	facet_wrap(~Hypothesis)

	print(authors)

}


###Summary graphs

authors_all <- ggplot(authors_uniq, aes (Hypothesis, fill = Result.x)) + geom_histogram() + labs(x="", y="count") + theme_grey(base_size=20) + theme(axis.text.x=element_text(angle=90,hjust=1,vjust=0.4))

authors_all + facet_wrap(~Trait, ncol=4, scales="free_x")

#all <- ggplot(summary_data, aes(Hypothesis, fill=Result)) + geom_histogram() + labs(x="", y="count")

#all + facet_wrap(~Trait, ncol=4, scales="free_x)


## All hypotheses separately

for(i in unique(authors_uniq$Hypothesis)) {
	authors_uniq$weight <- ifelse(authors_uniq$Hypothesis == i, 1, 0)

	temp <- ggplot(authors_uniq, aes(x=Result.x, weight=weight)) + 
	geom_bar(fill="blue") +
	labs(x = "", y = "count", title = paste(i, " by authors")) +
	theme_grey(base_size=24) +
	coord_cartesian(ylim = c(0, 25))

	print(temp)
}


#oprint(odag)
#?odag
#odag()

#authors_for <- authors_uniq[authors_uniq$Result.x == "F",]

#oprint(authors_for)

#authors_against <- authors_uniq[authors_uniq$Result.x == "A",]

#oprint(authors_against)

edg <- data.frame(
  from = authors_uniq$Result.y, 
  to = authors_uniq$Hypothesis,
  Trait = authors_uniq$Trait,
  FAN = authors_uniq$Result.x
)

ver <- rbind(
  data.frame(
    name = authors_uniq$Result.y,
    Trait = NA
  ),
  data.frame(
    name = authors_uniq$Hypothesis,
    Trait = authors_uniq$Trait
  )
)
ver <- ver[!duplicated(ver$name) , ]
ver$Type <- ifelse(ver$name %in% authors_uniq$Hypothesis, "Hypothesis", "Author")

dag <- graph.data.frame(edg, directed = TRUE, vertices = ver)

colo <- c("Red", "Blue", "Pink", "Orange", "Brown", "Yellow", "Purple")

plot(
  dag,
  vertex.label.cex = 0.4,
  vertex.size = ifelse(V(dag)$Type == "Hypothesis", 6, 3),
  vertex.label.family = "Helvetica",
  vertex.color = ifelse(V(dag)$Type == "Hypothesis", 
                        colo[as.factor(V(dag)$Trait)],
                        "SkyBlue2"
                      ),
  vertex.label = ifelse(V(dag)$Type == "Hypothesis", V(dag)$name, NA),
  edge.color = c("Red", "Green", "Gray")[as.factor(E(dag)$FAN)],
  edge.arrow.size = 0.3,
  layout = layout.fruchterman.reingold,
  asp = 0.7
)

Keywords

Human evolution, Bipedalism, Brain, Hairnessless, Subcutaneous fat, Speech

References

Related files

Evolutionary origin of human traits

Contents

Question

Answer

Rationale

Hypotheses

Bipedalism

Brain

Nakedness

Subcutaneous fat

Larynx

Speech

Other traits

Survey

Literary review

Student survey

Calculations

calc1

Histograms

See also

Keywords

References

Related files

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