# The Genus Homo and the Emergence of Us

## Tracking Genomes: Our Human Story Unfolds


### Learning Objectives

By the end of this section, you will be able to:
1. Describe how mtDNA sheds light on early human migrations and explain the Out of Africa model.
2. Explain how studying the genomes and coevolution of lice can fill current gaps in the human fossil record.
3. Describe the origin of human variation from an evolutionary perspective.

### Mitochondrial Eve

Begun in 1990 and concluding in 2003, the Human Genome Project was an ambitious international effort that sequenced about 99 percent of the human genome with an accuracy of 99.99 percent. Genetics has thus far largely confirmed the Out of Africa theory, which proposes that early humans left Africa around 100,000 years ago and migrated to diverse areas of the world. When early humans left Africa and moved into Europe, they not only lived alongside but also interbred with non-African species such as the Neanderthal, who were already inhabiting the region.
Molecular anthropologists have an interest in determining when living human populations began diverging from one another. This has been difficult to do using nuclear DNA because it mutates much too slowly for measurable accumulations to occur in 200,000 years. Many of the genetic studies that have been conducted are thus based on genetic material carried in the mitochondria (mtDNA), which are passed on maternally. There is no recombination in mtDNA, so unless the mitochondria carries a novel mutation, a child has exactly the same mitochondrial genes as its female genetic contributor (which may be its mother, egg donor, or someone in a similar genetic relationship). The mitochondria of every living person is a copy, modified only by rare mutations, of the mitochondria passed down via matrilineal descent from a population in our ancient past. This population is referred to as Mitochondrial Eve or mtMRCA (mitochondrial most recent common ancestor), believed to have lived in southern Africa 100,000–200,000 years ago.
As discussed in Chapter 4, the longer ago two populations share a common ancestor, the more time there is for mutations to occur and for adaptations and change to take place. Although genetic variation is small among the world’s human populations, it is greatest in Africa. This indicates that the human populations in Africa have the longest established genetic lineage. While multiple hypotheses exist as to human origins and new evidence could change the current views, the consensus is an Out of Africa model traced back to the matrilineal descent of a population living in Africa about 200,000 years ago.

### How the Genome of Lice Can Fill in the Gaps

While perhaps not a pleasant thought, lice have long been a part of human history. Studying the coevolution relationship between humans and lice has shed much light on human story. Dr. David Reed, the Curator of Mammals and Associate Director of Research and Collections at the University of Florida Museum, has been studying the coevolution of humans and lice, an area of research that has developed only within the last 20 years. Reed’s groundbreaking research has the potential to fill in some big gaps in humans’ rather sketchy fossil record and provides important data that might have applications in medicine and biology. Two questions that this research has already begun to ask are when did we become less hairy and when did we start wearing clothes.
 shows three types of lice associated with humans: the head louse (Pediculus humanus capitis), the body louse (Pediculus humanus corporis), and the crab louse or pubic louse (Pthirus pubis). Body lice infest clothing and lay their eggs on fibers in the fabric. Head and pubic lice infest hair, laying their eggs at the base of hair fibers. The human head and body lice (genus Pediculus) share a common ancestor with chimpanzee lice, while crab lice (genus Pthirus) share a common ancestor with gorilla lice. By tracking louse variations, scientists have been able to determine when the head louse and pubic louse diverged, enabling estimates as to when we lost our extra hair and when we started to wear clothes. It is interesting to note that the divergence of the genus Pediculus (head and body lice) correlates with the divergence of the human lineage from chimpanzees about six million years ago. Research on lice also provides further support for the Out of Africa model of human migration. Reed has observed that the genome of African lice shows a higher degree of genetic diversity than that of lice found elsewhere in the world, supporting the hypothesis that both humans and lice existed in Africa first.
Many hypotheses about what may have triggered the loss of hair in humans point to thermoregulation, the need to control body temperature in extreme conditions. Living in the heat of the savanna, humans needed a cooling mechanism to enable them to be better hunters. Other evidence of adaptation to the heat includes the appearance of sweat glands, which are more numerous in humans than in other primates. Another theory about the cause of the loss of hair among humans suggests that it was an adaptation to control parasites on the body. Did people immediately throw on clothes after losing all of that extra body hair? Reed’s research suggests that the wearing of clothes was not something that happened quickly. Humans lost body hair about a million years ago and didn’t start wearing clothes until around 170,000 to 190,000 years ago. That’s about 830,000 years living in their birthday suits! When humans began to wear clothes, the body louse adapted structures that enabled them to attach to clothes instead of hair.

### Natural Selection and Human Variation: Are Humans Still Evolving?

Human variability is attributed to a combination of environmental and genetic factors, including social status, ethnicity, age, nutrition, quality of life, access to healthcare, work and occupation, etc. As mentioned in Chapter 1, anthropology contributes many insights into both the social construct of race and the impacts racial categories have on people’s lives. The focus in this chapter is the role of natural selection in human variation.
A number of changes are associated with the Neolithic era and the rise of agriculture around 10,000 to 8,000 years ago. Many have noted that changes during this time period did not have positive effects on human and environmental health. The evolutionary mismatch hypothesis proposes that our bodies are best suited to the environments we have spent much of our evolutionary history in, which are very different from the environments we inhabit today (Li, van Vugt, and Colarelli 2018).
Humans evolved for one million years as hunter-gatherers. Today, human bodies are still trying to adapt to the largely grain-based diet brought about by agriculture, a diet characterized by less diversity and lower levels of nutrition than that of a typical hunter-gatherer. Incomplete adaptation to this change has made people susceptible to a number of diseases and nutritional deficiencies. Lactose intolerance is a prime example. The domestication of cattle and the drinking of cow’s milk began during the agricultural age, not very long ago in evolutionary history. Currently 65 percent of humans are unable to digest cow’s milk. Dental caries (cavities) are another problem linked to the change in diet associated with agriculture. The grain-based and high-sugar diets associated with agriculture are very different from the diet of hunter-gatherers. Neither our bodies nor the bacteria in our mouths have had time to fully adapt to this change.
Another adaptation that took place during the Neolithic era is related to variation in skin pigmentation. Humans who left Africa and settled in Europe about 40,000 years most likely had dark skin with high levels of melanin, which provides protection against ultraviolet radiation New data confirms that about 8,500 years ago, early hunter-gatherers in Spain, Luxembourg, and Hungary also had darker skin. Skin pigmentation is an adaptation to ultraviolet radiation, with different tones offering different advantages, depending on one’s distance from the equator. As humans migrated to the Northern Hemisphere, they were exposed to less ultraviolet radiation, which also meant less absorption of the Vitamin D needed for strong bones and other important immune functions. In order to compensate for this loss and to allow for greater exposure to ultraviolet radiation, skin pigmentation became lighter.
Another example of human variation as a result of adaptation to the environment can be seen in Indigenous populations in the Andes, Tibet, and the Ethiopian highlands. Each of these three groups faces the same environmental challenge, living in a low-oxygen environment, and they have responded with unique adaptations. Tibetans compensate for low oxygen levels by taking more breaths per minute than people who live at sea level. Those living at high altitudes in the Andes have been found to have higher concentrations of hemoglobin in their blood than other people. Ethiopians living at altitudes of 9,800 to 11,580 feet have neither of these adaptations. The explanation as to how the Ethiopian highlanders thrive in their environment is still a mystery.
This chapter has explored just some of the immense biological and cultural diversity of the genus Homo. This diversity has emerged in response to highly complex and variable environments connected to factors such as exposure to UV radiation, low oxygen levels at high altitude, changes in diet as a result of hunting or agricultural practices, geographic isolation in island populations, and climate variability and temperature. The genus Homo has proven to be resilient and adaptive in response to whatever environment or challenge it has faced. Variation is the key to survival. While scientists recognize that biological and cultural variation has greatly contributed to our human evolution, the human species is now facing a moment in which we must contemplate a difficult question: To what extent has our success as a species jeopardized the survival of other species and the health of the planet we all call home?

### Summary

In this chapter we have explored our human journey as a member of the genus Homo, following a trail of adaptations and change that ultimately led to us. First on the scene were the australopithecines, who were already walking on two feet and paved the way for the evolutionary changes and cultural achievements that were to follow. A colder climate with drastic changes in climate were associated with an increased reliance on cooked meat, which may have contributed to a growing brain. A brain with highly developed cognitive skills gave humans the capacity to solve problems and create tools that enabled better hunting and survival skills. Adaptations provided H. ergaster and H. erectus the ability to walk and run longer distances, to more effectively track and follow game, and to explore nearby continents.
Genetic information provided by mtDNA indicates that all humans shared common ancestors who lived in Africa 200,000 years ago. Studies of genetics shows examples of coevolution and how even small organisms such as lice can shed light on the human story. The rise of agriculture created new challenges for humanity, with evolutionary mismatch still impacting people today. From the earliest toolmakers to the cave art of the Upper Paleolithic to the modern computer age, the predominant theme of human history has always been about change. The ability to adapt to this change is why humans are still here. Humans’ evolutionary story, however, does not end with the emergence of the species. Today humans are faced with numerous challenges as they adapt to an increasingly changing environment as a result of climate change, loss of habitat, and decreasing biodiversity. In 2020, Darwin’s theory of natural selection played out in real time as people began an arms race with a mutating and evolving COVID virus. Evolutionary change is not something that happened to people just in the past—it is very much still happening today, and it will continue to be part of the future.

### Critical Thinking Questions


### References

Ahern, Jim. 2015. “Archaic Homo.” In Basics in Human Evolution, edited by Michael P. Muehlenbein, 163–76. Cambridge, MA: Academic Press. doi:10.1016/B978-0-12-802652-6.00012-8.
Aiello, L., and P. Wheeler. 1995. “The Expensive-Tissue Hypothesis: The Brain and the Digestive System in Human and Primate Evolution.” Current Anthropology 36 (2): 199–221. http://www.jstor.org/stable/2744104.
Akst, Jef. 2019. “Neanderthal DNA in Modern Human Genomes Is Not Silent.” The Scientist, September 1, 2019. https://www.the-scientist.com/features/neanderthal-dna-in-modern-human-genomes-is-not-silent-66299.
Beier, J., N. Anthes, J. Wahl, and K. Harvati. 2018. “Similar Cranial Trauma Prevalence among Neanderthals and Upper Paleolithic Modern Humans.” Nature 563:686–90. https://doi.org/10.1038/s41586-018-0696-8.
Boaz, Noel T., Russell L. Ciochon, Qinqi Xu, and Jinyi Liu. 2004. “Mapping and Taphonomic Analysis of the Homo erectus Loci at Locality 1 Zhoukoudian, China.” Journal of Human Evolution 46 (5): 519–49. doi:10.1016/j.jhevol.2004.01.007.
Bramble, D., and D. Lieberman. 2004. “Endurance Running and the Evolution of Homo.” Nature 432:345–52. https://doi.org/10.1038/nature03052.
Chen, F., F. Welker, C. C. Shen, S. E. Bailey, I. Bergmann, S. Davis, H. Xia et al. 2019. “A Late Middle Pleistocene Denisovan Mandible from the Tibetan Plateau.” Nature 569:409–12. https://doi.org/10.1038/s41586-019-1139-x.
Dirks, Paul HGM, Lee R. Berger, Eric M. Roberts, Jan D. Kramers, John Hawks, Patrick S. Randolph-Quinney, Marina Elliott et al. 2015. “Geological and Taphonomic Context for the New Hominin Species Homo naledi from the Dinaledi Chamber, South Africa.” eLife 4:e09561. doi:10.7554/eLife.0956.
Dorey, Fran. 2020. “Homo erectus.” Australian Museum. https://australian.museum/learn/science/human-evolution/homo-erectus/.
Dorey, Fran. 2019. “Homo naledi.” Australian Museum. https://australian.museum/learn/science/human-evolution/homo-naledi/.
Dunsworth, Holly M. 2010. “Origin of the Genus Homo.” Evolution: Education and Outreach 3:353–66. doi:10.1007/s12052-010-0247-8.
Durvasula, Arun, and Sriram Sankararaman. 2020. “Recovering Signals of Ghost Archaic Introgression in African Populations.” Science Advances 6 (7): eaax5097. doi:10.1126/sciadv.aax5097.
Egeland, Charles P., Manuel Domingues-Rodrigo, Travis R. Pickering, Colin G. Menter, and Jason L. Heaton. 2018. “Hominin Skeletal Part Abundances and Claims of Deliberate Disposal of Corpses in the Middle Pleistocene.” PNAS 115 (18): 4601–06. https://doi.org/10.1073/pnas.1718678115.
Fuentes, Agustin. 2019. Biological Anthropology: Concepts and Connections. 3rd edition. New York: McGraw-Hill Education.
Frayer, David & Clarke, Ronald & Fiore, Ivana & Blumenschine, Robert & Pérez-Pérez,FF Alejandro & Martínez Martínez, Laura & Estebaranz-Sánchez, Ferran & Holloway, Ralph & Bondioli, Luca. (2016). OH-65: The earliest evidence for right-handedness in the fossil record. Journal of Human Evolution. 100. 10.1016/j.jhevol.2016.07.002.
Hawks, John, Marina Elliott, Peter Schmid, Steven E. Churchill, Darryl J. de Ruiter, Eric M. Roberts, Hannah Hilbert-Wolf et al. 2017. “New Fossil Remains of Homo naledi from the Lesedi Chamber, South Africa.” eLife 6:e24232. doi:10.7554/eLife.24232.
Holloway, Ralph L. 2018. The International Encyclopedia of Biological Anthropology. Hoboken, NJ: John Wiley and Sons.
Huber, J. 2018. “Inherited Neanderthal Genes Protect Us Against Viruses, Study Shows.” Scope, October 5, 2018. https://scopeblog.stanford.edu/2018/10/05/inherited-neanderthal-genes-protect-us-against-viruses-study-shows.
Jerison, H. J. 1973. Evolution of Brain and Intelligence. New York: Academic Press.
Ji, Qiang, Wensheng Wu, Yannan Ji, Qiang Li, and Xijun Ni. 2021. “Late Middle Pleistocene Harbin Cranium Represents a New Homo Species.” The Innovation 2 (3): 100132. https://www.cell.com/the-innovation/fulltext/S2666-6758(21)00057-6.
Leakey, L. S., P. V. Tobias, and J. R. Napier. 1964. “A New Species of the Genus Homo from Olduvai Gorge.” Nature 202:7–9. doi:10.1038/202007a0.
Li, Norman P., Mark van Vugt, and Stephen M. Colarelli. 2018. “The Evolutionary Mismatch Hypothesis: Implications for Psychological Science.” Current Directions in Psychological Science 27 (1): 38–44. https://doi.org/10.1177/0963721417731378.
Lieberman, P. 2007. “The Evolution of Human Speech: Its Anatomical and Neural Bases.” Current Anthropology, 48 (1): 39-66. doi:10.1086/509092.
Meyer, Matthias, Juan-Luis Arsuaga, Cesare de Filippo, Sarah Nagel, Ayinuer Aximu-Petri, Birgit Nickel, Ignacio Martínez et al. 2016. “Nuclear DNA Sequences from the Middle Pleistocene Sima de los Huesos Hominins.” Nature 531: 504–07. https://doi.org/10.1038/nature17405.
Monfils, A., J. Allen, B. W. Goodner, and D. Linton. 2020. “Louse and Human Coevolution.” Biodiversity Literacy in Undergraduate Education, QUBES Educational Resources. doi:10.25334/JJBH-SG27.
Mortazavi, S., K. Kaveh-Ahangar, S. Mortazavi, D. Firoozi, and M. Haghani. 2021. “How Our Neanderthal Genes Affect the COVID-19 Mortality: Iran and Mongolia, Two Countries with the Same SARS-CoV-2 Mutation Cluster but Different Mortality Rates.” Journal of Biomedical Physics and Engineering 11 (1): 109–14. https://doi.org/10.31661/jbpe.v0i0.2010-1218.
Nielsen, R., J. Akey, M. Jakobsson, J. Pritchard, S. Tishkoff, and E. Willersley. 2017. “Tracing the Peopling of the World through Genomics.” Nature 541: 302–10. https://doi.org/10.1038/nature21347.
Petr, Martin, Mateja Hajdinjak, Qiaomei Fu, Elena Essel, Hélène Rougier, Isabelle Crevecoeur, Patrick Semal et al. 2020. “The Evolutionary History of Neanderthal and Denisovan Y Chromosomes.” Science 369 (6511): 1653–56. doi: 10.1126/science.abb6460.
Pike, A. W. G., D. L. Hoffmann, M. García-Diez, P. B. Pettitt, J. Alcolea, R. De Balbín, C. González-Sainz, C. De Las Heras, J. A. Lasheras, R. Montes et al. (2012). “U-Series Dating of Paleolithic Art in 11 Caves in Spain.” Science 336 (6087): 1409–13 doi:10.1126/science.1219957.
Schaik, Carel P. V., Triki, Zegni, Bshary, R. Heldstab, S.A., (2021) “Farewell to the Encephalization Quotient: A New Brain Size Measure for Comparative Primate Cognition” Brain Behav Evol 96:1–12 van Schaik/Triki/Bshary/Heldstab DOI: 10.1159/000517013
Toups, M.A. Kitchen, A., Light, J.E. Reed, D.L (2011). “Origin of clothing lice indicates early clothing use by anatomically modern humans in Africa” Molecular Biology and Evolution, Volume 28, Issue 1, January 2011, Pages 29–32, https://doi.org/10.1093/molbev/msq234
Read, Dwight, and Sander van der Leeuw. 2008. “Biology Is Only Part of the Story.” Philosophical Transactions of the Royal Society 363 (1499): 1959–68. doi:10.1098/rstb.2008.0002.
Rogers, A. R., R. J. Bohlender, and C. D. Huff. 2017. “Early History of Neanderthals and Denisovans.” PNAS 114 (37): 9859–63. doi:10.1073/pnas.1706426114.
Roth, G., and U. Dicke. 2012. “Evolution of the Brain and Intelligence in Primates.” Progress in Brain Research 195:413–30. doi:10.1016/B978-0-444-53860-4.00020-9.
Semaw, S., P. Renne, J. W. K. Harris, C. S. Feibel, R. L. Bernor, N. Fesseha, and K. Mowbray. 1997. “2.5-Million-Year-Old Stone Tools from Gona, Ethiopia.” Nature 385:333–6. https://doi.org/10.1038/385333a0.
Slon, Viviane, Fabrizio Mafessoni, Benjamin Vernot, Cesare de Filippo, Steffi Grote, Bence Viola, Mateja Hajdinjak et al. 2018. “The Genome of the Offspring of a Neanderthal Mother and a Denisovan Father. Nature 561:113–6. https://doi.org/10.1038/s41586-018-0455-x.
Snow, Dean. 2013. “Sexual Dimorphism in European Upper Paleolithic Cave Art.” American Antiquity 78 (4): 746–61. doi:10.7183/0002-7316.78.4.746.
Sommer, J. D. 1999. “The Shanidar IV Flower Burial: A Re-evaluation of Neanderthal Burial Ritual.” Cambridge Archaeological Journal 9 (1): 127–9. https://doi.org/10.1017/S0959774300015249.
“Study Finds Earliest Evidence in Fossil Record for Right-Handedness.” 2016. University of Kansas. https://news.ku.edu/2016/07/21/study-finds-earliest-evidence-fossil-record-right-handedness.
Susman, R. 1991. “Who Made the Oldowan Tools? Fossil Evidence for Tool Behavior in Plio-Pleistocene Hominids.” Journal of Anthropological Research, 47 (2), 129–51. http://www.jstor.org/stable/3630322
Xiujie, Wu, Liu Wu, and Christopher J. Norton. 2007. “Endocasts —The Direct Evidence and Recent Advances in the Study of Human Brain Evolution.” Progress in Natural Science 17 (9).
Zeberg, H., and S. Pääbo. 2020. “The Major Genetic Risk Factor for Severe COVID-19 Is Inherited from Neanderthals.” Nature 587:610–2. doi:10.1038/s41586-020-2818-3.

### Additional Resources

Visual timelines and maps
The Atlas of Human Evolution has put together a user friendly interactive map on the development of Homo sapiens.
The Smithsonian Institute's Human Evolution Interactive Timeline provides an interactive overview of major milestones and species ranges.
Coevolution of lice and humans
David Reed, associate curator of mammals at the Florida Museum of Natural History, offers an explanation of his research for a general audience.
The Smithsonian Magazine explores possible causes and benefits of the human loss of hair.