Introduction

Sexual dimorphism (genetic/morphological differences between the sexes) is incredibly common throughout primates, and our ancestors were no exception to this. In primates, especially apes, males are typically much larger than females, along with other differences, such as larger maxillary (upper) canines. At its greatest extent, primates can be up to 50% sexually dimorphic. Modern humans are much less sexually dimorphic as compared to our relatives, and we usually are around 15% sexually dimorphic. Sexual dimorphism likely began decreasing in humans around 2 million years ago, though some earlier hominins, such as Ardipithecus ramidus had low levels of sexual dimorphism at 4.4 million years ago.

Sexual dimorphism in later hominins, in the genus Australopithecus, is controversial. Research on the femora of Australopithecus afarensis and Australopithecus africanus suggests that these species had very high levels of sexual dimorphism, similar to what is seen in modern gorillas and orangutans. If this is accurate, female australopiths may have had different locomotor styles (methods of walking) than males due to their sexual differences. 

Other research suggests that Australopithecus had little levels of sexual dimorphism, closer to what is seen in modern humans. As it stands right now, it appears that Australopithecus did express some levels of sexual dimorphism, though this is subject to change as new evidence comes about. However, no matter how sexually dimorphic our australopith ancestors were, there is one hominin genus that was clearly very sexually dimorphic, and that is Paranthropus.

What is Paranthropus?

Paranthropus is a unique genus of hominin which lived from 2.5-1.4 million years ago. Members of this genus are also commonly known as the ‘robust australopiths’ due to their odd and robust skeletal and cranial morphology. Paranthropus was originally considered to be in the genus Australopithecus, until it was decided that it was unique enough among other australopiths to be placed within its own genus, though some anthropologists still consider it to be in the Australopithecus genus. 

Paranthropus is an off-branching lineage, and is not directly ancestral to modern humans. It likely branched off from Australopithecus afarensis or Australopithecus africanus sometime in the late Pliocene epoch. Paranthropus contains 3 known and recognized species: P. aethiopicus, P. boisei, and P. robustus. The former two lived throughout eastern Africa, while Paranthropus robustus lived in South Africa. 

Perhaps its most unique trait was its diet. Paranthropus was seemingly mostly herbivorous. The eastern species had a diet mostly composed of C4 plants, meaning they were mostly consuming savannah grasses, while Paranthropus robustus had a slightly more varied diet, with a mix of C4 and C3 (forest) plants, and likely changed its diet seasonally. This diet was possibly a fall back diet, where the genus adapted for a more accessible diet, not a preferred diet. 

Because of this unique diet, Paranthropus had some specialized morphology. This genus possessed a pronounced sagittal crest, (a bony crest on the top of the head), large round zygomatic arches (cheek bones), and incredibly large molars and thick tooth enamel, a condition known as post-canine megadontia. 

All these traits gave Paranthropus a very powerful bite, perfect for the tough vegetation it was eating. This gave P. boisei the nickname “nutcracker man”, though analysis of tooth wear on Paranthropus teeth shows it wasn’t eating much tough food. Tougher meats, nuts, and seeds may occasionally have been a part of its diet however. 
Perhaps one of the most interesting things about Paranthropus is their high levels of sexual dimorphism, which makes them stand out even among other living primates.

Sexual Dimorphism in Paranthropus

Paranthropus exhibited a great deal of sexual dimorphism. Female individuals were smaller in body size and weight, smaller in skull size, had smaller brains, teeth, and lacked the distinguishing sagittal crest. Male Paranthropus boisei were about 4 ft. 6 in. tall  and weighed about 108 lbs while females were about 4 ft. tall and weighed about 75 lbs. Paranthropus robustus was slightly smaller with males being about 3 ft. 10 in. tall and weighing 120 lbs and females being about 3 ft tall and weighing about 90 lbs. Because of a lack of post cranial material from Paranthropus aethiopicus, its height and weight is unknown, but it was likely similar to that of P. boisei. 

A Paranthropus molar from Gondolin, South Africa, known as GDA-2 also shows a great deal of sexual dimorphism in P. robustus. The size of the molar falls into the range of the larger P. boisei. This could possibly suggest that P. boisei had made it to southern Africa, or more likely, that P. robustus males had much larger teeth than females. Other teeth, found in Swartkrans, South Africa, are much smaller than what is expected in Paranthropus, suggesting that female individuals had smaller teeth. 

Two individuals from P. boisei and P. robustus give great insight into sexual dimorphism in Paranthropus. 

One female fossil specimen from Koobi Fora, Kenya, gives a better look into sexual dimorphism in Paranthropus boisei. The cranial specimen, known as KNM-ER-732, lacks a sagittal crest, and has a smaller cranial capacity than male individuals, though not by much. This individual had a cranial capacity of around 500 cc, while other male individuals, such as KNM-ER-406, had a cranial capacity of about 510 cc. The female specimen is also smaller in size overall than male individuals. 

The next specimen which exhibits sexual dimorphism was found in Drimolen, South Africa, and belongs to Paranthropus robustus. This specimen, nicknamed Eurydice, formally known as DNH 7, is the most complete specimen of its species. Eurydice is significantly smaller in skull and tooth size compared to male specimens of her species, such as SK 46. Along with that, she also lacked a sagittal crest, showing high levels of sexual dimorphism. Interestingly, Eurydice is one of the only female specimens out of the many P. robustus specimens found at the site, potentially giving insight into the social structure of her species. 

Paranthropus Social Structure

Sexual dimorphism often has a big role in the social structure of animals. Gibbons for example show very little sexual dimorphism, resulting in them having monogamous social structures. This means that most gibbons live in small family groups, with one male and one female. This activity is known as pair bonding. Some groups in China and Khao Yai, Thailand contain multiple adults, but for the most part, the low sexual dimorphism in gibbons results in monogamous groups, which is beneficial for both individuals in the family group. 

When deciphering the social structures of Paranthropus, looking at modern primates with similar levels of sexual dimorphism can give good insight. For Paranthropus, one primate with similar levels of sexual dimorphism are gorillas. 

Gorillas exhibit great levels of sexual dimorphism, with females being about half the size of males. This is similar to what has been observed in fossils of Paranthropus. Most gorillas have what is known as a harem society. This is a group containing one adult head male, several females, and their offspring. The adult male defends the females from foreign males, and intern, has breeding rights to all the females, unless he proves himself to be a poor leader in which case the females typically abandon the male and join a better group. 

In some species of gorilla, such as the eastern gorilla (Gorilla beringei), the harem group contains several related males which defend the group. Due to the similar levels of sexual dimorphism, this harem society may be what Paranthropus used. This is further backed up by strontium isotope analyses of the holotype specimen of Paranthropus robustus, TM157c. When analyzing the teeth of this female specimen, anthropologists deduced that she had moved to her location of death before her teeth had fully mineralized, suggesting that female Paranthropus migrated less in their groups, which is behavior found in harem groups of gorillas. 

However, there is one major difference between gorillas and Paranthropus, that is their environment. While modern gorillas live in more dense and lush jungles, where they can be protected and hidden by foliage, Paranthropus lived in open dry woodland and savannah habitats. A better modern comparison for Paranthropus social structure would instead be baboons. Baboons exhibit similar levels of sexual dimorphism, but live in more open dry savannah, similar to Paranthropus. 

Baboons often live in large social groups with several males, females, and offspring. Typically, baboon groups consist of one primary male, several secondary males, and the females and offspring. This system allows for better protection in the open savannah as there are more males to defend the group. This type of group is known as a multilevel society.

However, this system often leads to lots of intolerance between males. Some baboon species, such as the Hamadryas baboon (Papio hamadryas) are especially aggressive, whereas others, such as Guinea baboons (Papio papio) are less aggressive. This could possibly mean that male Paranthropus were aggressive towards each other, and lived in very large social groups. 

Sites throughout South Africa, such as Swartkrans and Kromdraai show an uneven sex ratio in Paranthropus robustus, with 15 male individuals being found and 4 female individuals, though this information may be inaccurate. If it is accurate, it may add further support to the idea that Paranthropus upheld multilevel societies, with many males and few females. It could also suggest a higher mortality rate in male Paranthropus, which would make sense under a harem or multilevel society, as males would be more likely to be kicked out of the group, making them more vulnerable.

Conclusion
Paranthropus, like other hominins and primates in general, exhibited a great amount of sexual dimorphism. Male individuals possessed larger bodies, brains, skulls, and teeth. This high level of sexual dimorphism would have had a large impact on the social structures and behavior. Due to the open woodland/savannah environment they lived in, Paranthropus likely formed large multilevel social groups, with a head male, and lower males and females, similar to what is seen in modern baboons. This system is beneficial for the group as it allows for more group protection. Further research into the sexual dimorphism and behavior of our ancient ancestors and relatives is very important as it can help us understand ourselves and our evolution.

Sources: 

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2.     Green. J. D., Gordon, D.A., Richmond. G. B. Limb-size proportions in Australopithecus afarensis and Australopithecus africanus. Journal of Human Evolution, 52, 2, 187-200 (2006). https://doi.org/10.1016/j.jhevol.2006.09.001 
3.      Harmon, E. Size and shape variation in the proximal femur of Australopithecus africanus. Journal of Human Evolution, 56, 6, 551-559 (2009). https://doi.org/10.1016/j.jhevol.2009.01.002 
4.     Lee, H-.,S. Patterns of size sexual dimorphism in Australopithecus afarensis: Another look. HOMO, 56, 3, 219-232 (2005). https://doi.org/10.1016/j.jchb.2005.07.001
5.     Harmon, H. E. Size and shape variation in Australopithecus afarensis proximal femora. Journal of Human Evolution, 51, 3, 217-227 (2006). https://doi.org/10.1016/j.jhevol.2006.01.009
6.     Reno., L. P., Meindl, S. R., McCollum, A. M.,Lovejoy., O.C. Sexual dimorphism in Australopithecus afarensis was similar to that of modern humans. PNAS, 100 (16) 9404-9409 (2003). https://doi.org/10.1073/pnas.1133180100
7.     Larsen, S. C. Equality for the sexes in human evolution? Early hominid sexual dimorphism and implications for mating systems and social behavior. PNAS, 100 (16) 9103-9104 (2003). https://doi.org/10.1073/pnas.1633678100
8.     Jungers, L. W., Grabowski, M., Hatala, G. K., Richmon, G. B. The evolution of body size and shape in the human career. Philosophical Transactions B, 371(1698): 20150247 (2016). 10.1098/rstb.2015.0247
9.     Dorey, Fran, Blaxland, Beth. “Paranthropus genus.” Australian Museum, 29-04-22. https://australian.museum/learn/science/human-evolution/paranthropus-species/
10. Constantino, Paul, (2013). The “Robust Australopiths”. Nature Education Knowledge, 4(1):1. https://www.nature.com/scitable/knowledge/library/the-robust-australopiths-84076648/ 
11. Pickering, R. T., Heaton, L. J., Sutton, B. M., Clarke, J. R., Kuman, K., Senjem, H. J., Brain, C.,K. New early Pleistocene hominin teeth from the Swartkrans Formation, South Africa. Journal of Human Evolution, 100,1-15 (2016). https://doi.org/10.1016/j.jhevol.2016.08.005
12. “Paranthropus boisei”. The Smithsonian Museum’s Human Evolution Program, 7-07-2022. https://humanorigins.si.edu/evidence/human-fossils/species/paranthropus-boisei
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https://humanorigins.si.edu/evidence/human-fossils/fossils/dnh-7

16. Sillen, A., Balter, V. Strontium isotopic aspects of Paranthropus robustus teeth; implications for habitat, residence, and growth. Journal of Human Evolution, 114, 118-130, https://doi.org/10.1016/j.jhevol.2017.09.009
17. Kamrani, Kambiz. “Sexual Dimorphism & Social Behavior of Paranthropus robustus”. Anthropology.net, 11-02-2007. https://anthropologynet.wordpress.com/2007/12/02/sexual-dimorphism-social-behavior-of-paranthropus-robustus/
18. Pickering, R. T., Heaton, L. J., Sutton, B. M., Clarke, J. R., Kuman, K., Senjem, H. J., Brain, C. K. New early Pleistocene hominin teeth from the Swartkrans Formation, South Africa. Journal of Human Evolution, 100,  1-15, https://doi.org/10.1016/j.jhevol.2016.08.005
19. Backwell, L., d’Errico, F. Early hominid bone tools from Drimolen, South Africa. Journal of Archaeological Science, 35, 11, 2880-2894 (2008). https://doi.org/10.1016/j.jas.2008.05.017
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22. Rak, Y., Kimbel, H. K., Moggi-Cecchi, J., Lockwood, A. C., Menter C. The DNH 7 skull of Australopithecus robustus from Drimolen (Main Quarry), South Africa. Journal of Human Evolution, 151, 102913 (2020). https://doi.org/10.1016/j.jhevol.2020.102913
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24. Clarke, E., Reichard, H. U., Zuberbuhler, K. Context-specific close-range “hoo” calls in wild gibbons (Hylobates lar). BMC Ecology and Evolution, 15, 56 (2015). https://doi.org/10.1186/s12862-015-0332-2
25. Kaszycka, A. K. Australopithecus robustus societies – one-male or multimale? South African Journal of Science, 112 n.1-2 (2016). http://dx.doi.org/10.17159/sajs.2016/20150165
26. Breuer, T., Robbins, M. A.,  Olejniczak, C., Parnell, J. R., Stokes, J. E., Robbins, M. M. Variance in the male reproductive success of western gorillas: acquiring females is just the beginning. Nature Careers, 64, 515-528 (2010). https://doi.org/10.1007/s00265-009-0867-6 
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29.  Fischer, J., Kopp, H. G., Peco, D. F., Goffee, A., Hammerschmidt, K., Kalbitzer, U., Klapproth, M., Maciej, P., Ndao, I., Patzelt, A., Zinner, D. Charting the neglected West. The social system of the Guinea baboons. American Journal of Physical Anthropology, 162 (Suppl Suppl 63): 15-31 (2017).  https://doi.org/10.1002/ajpa.23144
30. Bonnell, R. T., Henzi, P. S., Barrett, L. Functional social structure in baboons: Modeling interactions between social and environmental structure in group-level foraging. Journal of Human Evolution, 126, 14-23 (2018). https://doi.org/10.1016/j.jhevol.2018.10.011
31. “Hamadryas Baboon (Papio hamadryas) Facts”. Primates Park, 3-27-20. https://www.primatespark.com/hamadryas-baboon/
32. Robson, L. S., Wood, B. Hominin life history: reconstruction and evolution. Journal of Anatomy, 212, 4, 394-425 (2008).  https://doi.org/10.1111/j.1469-7580.2008.00867.x 

Before the exciting and big announcements coming out on the 5^th! (Stay tuned!) I wondered what, according to AI, would it mean if a hominin species, such as Homo naledi, ritualistically buried their dead?

Asking the New Bing Chatbot AI, I asked, “ in APA 7th edition, write a blog post about the implications on what it means to be human if the hominin species homo naledi buried its dead ritualistically, as some researchers believe. Cite your sources. “

The response was exciting: ( I am leaving it unedited to show what a pure AI response looks like). 

“One of the most fascinating discoveries in human evolution is the finding of Homo naledi, a new species of hominin that lived in South Africa between 236,000 and 335,000 years ago. What makes this species so intriguing is the possibility that they buried their dead in a ritualistic way, something that was previously thought to be unique to modern humans. In this blog post, I will explore the implications of this behavior for our understanding of what it means to be human.

Homo naledi was first announced in 2015 by a team of researchers led by Lee Berger, who found more than 1,500 bones of at least 15 individuals in a remote chamber of the Rising Star cave system in the Cradle of Humankind, a UNESCO World Heritage Site. The bones belonged to a small-brained species that had a mix of primitive and modern features, such as curved fingers, long legs, and a human-like face. The researchers suggested that the bones were deliberately placed there by other Homo naledi individuals over a long period of time, as there was no evidence of predators, water flow, or natural openings that could have transported the bones into the cave (National Geographic, 2015).

This hypothesis was challenged by some scientists who argued that it was implausible that such a low-intelligence species could have engaged in such a complex behavior, and that there might be alternative explanations for how the bones got there (CNN, 2021). However, in 2017, Berger’s team found another partial skull of a Homo naledi child in a nearby passage of the same cave system, which strengthened their case for intentional disposal of the dead (CNN, 2021). The child’s skull was found on a limestone shelf above the cave floor, suggesting that it was placed there on purpose.

If Homo naledi did indeed bury their dead, what does that mean for our definition of humanity? One possible implication is that we need to rethink our assumptions about the relationship between brain size and cognitive abilities. Homo naledi had a brain volume of about 500 cubic centimeters, which is less than half of that of modern humans. Yet they may have exhibited a behavior that requires planning, cooperation, communication, and symbolic thinking. This suggests that brain size is not the only factor that determines intelligence, and that there might be other ways of evolving complex cognition (Human Genesis, 2016).

Another possible implication is that we need to expand our view of human culture and spirituality. Disposal of the dead is one of the earliest signs of cultural expression and religious belief among hominins. It shows that they had a sense of self-awareness, social bonding, and respect for the deceased. It also implies that they had some concept of an afterlife or a transition to another realm. While we cannot know for sure what Homo naledi thought or felt when they buried their dead, we can imagine that they had some form of emotional attachment and ritual practice that gave meaning to their lives (National Geographic, 2015).

In conclusion, Homo naledi is a remarkable species that challenges our conventional notions of what it means to be human. By burying their dead in a ritualistic way, they may have demonstrated cognitive and cultural capacities that were previously thought to be exclusive to modern humans. They also may have shared some aspects of our spirituality and morality, which are often considered to be defining features of our humanity. By studying Homo naledi and other hominins, we can learn more about our origins and diversity as a species.

References:

CNN (2021). First ancient fossil of Homo naledi child found in the Cradle of Humankind. Retrieved from https://www.cnn.com/2021/11/04/world/homo-naledi-child-fossil-scn/index.html

Human Genesis (2016). Did Homo naledi bury its dead? Retrieved from https://humangenesis.org/2016/05/18/did-homo-naledi-bury-its-dead/

National Geographic (2015). Mystery Lingers Over Ritual Behavior of New Human Ancestor. Retrieved from https://www.nationalgeographic.com/adventure/article/150915-humans-death-burial-anthropology-Homo-naledi“

From this little article, I hope that you can see why Homo naledi has always been such a big deal and why learning more about these supposed practices can help shine a light on what makes us cognitively and socially human. Perhaps we will learn more on the fifth; one can only hope and wonder what new mysteries will be announced from the depths of Rising Star Cave, as it never seems empty of surprises. 

Keep an eye on this space for all Homo naledi news, especially around the 5^th of June this month; not sure what time, but I will have the coverage out ASAP, and if we are lucky, as it is happening! So stay tuned! 

On this episode of The Story of Us, prepare to hear some exciting content and news!

Premiering at 3pm PST!
Dr. Brenna Hassett is a bioanthropologist and archaeologist who uses the evidence left behind in bones and teeth to tell us how we grew — or failed to grow — in the past.

In this video, Dr Hassett will discuss her research on the archaeology of death in cities, and how our primate ancestry informs the incredible way our species has evolved the longest childhoods on the planet.

Dr Hassett is also 1/4 of Team TrowelBlazers, a group of women working to recognise the unsung accomplishments of women in the ‘digging’ sciences.

Don’t miss this opportunity to learn from one of the leading experts in her field.

Written with the Assistance of the New Bing as well as Grammarly

There is a fact in Anthropology that I just love telling people because it seems to always blow their minds, for whatever reason…but that fact is that there is more genetic diversity within Africa than in the rest of the world. 

Why?

Read on to learn more! 

The continent of Africa is the birthplace of modern humans and boasts of being the most genetically diverse continent on the planet. The genetic variation among African populations reflects their deep evolutionary history, complex migration patterns, admixture, and adaptation. It is essential to comprehend the genomic diversity of Africa to advance research into human health and diseases and reconstruct the origins and evolution of our species.

According to the widely accepted model, modern humans (Homo sapiens) emerged in Africa approximately 300,000 years ago and gradually replaced other hominid species across the globe. Anatomically modern human fossils have been found in Morocco and Ethiopia, and the oldest evidence of symbolic behavior and culture, such as art and burial practices, have been found in South Africa.

Therefore, African populations today harbor more genetic diversity than any other population globally, with non-Africans having only a subset of that diversity found in Africa. The continent has significant cultural, linguistic, and genetic diversity.

The history of human migration and admixture within and out of Africa is complex and dynamic. Several waves of migration have occurred over time, influenced by environmental, cultural, and historical factors. The major events include the expansion of Bantu-speaking populations from West-Central Africa to Eastern and Southern Africa, resulting in the spread of agriculture, metallurgy, and languages across the continent, as well as genetic admixture with local hunter-gatherer groups. The arrival of Eurasian populations to Africa through different routes and periods, such as the back-to-Africa migration of early farmers from the Near East around 3,000 years ago, the Arab slave trade from the 7th to the 19th centuries, and the European colonization from the 15th to the 20th centuries, introduced new genetic variants and haplotypes into African populations, as well as diseases and pathogens. The transatlantic slave trade from the 16th to the 19th centuries forcibly displaced millions of Africans to the Americas and other regions, resulting in the formation of new populations with varying degrees of African ancestry, as well as the loss of genetic diversity in some African regions.

The diverse environments and lifestyles of African populations have shaped their genomes through natural selection. Selection can increase the frequency of beneficial variants or decrease the frequency of harmful variants in response to environmental pressures, such as climate, diet, pathogens, or culture. Some examples of genes that show evidence of positive selection in African populations are genes involved in immune response to viral infections, such as TRIM5α, which confers resistance to HIV-1 in some individuals, genes involved in DNA repair and metabolism, such as BRCA1 and BRCA2, which are associated with breast cancer risk, genes involved in skin pigmentation, such as SLC24A5 and SLC45A2, which influence skin color variation among Africans, and genes involved in malaria resistance, such as HBB (sickle cell trait), G6PD (glucose-6-phosphate dehydrogenase deficiency), and DARC (Duffy blood group antigen).

The genomic diversity of Africa has significant implications for human health and disease research. On one hand, it offers a unique opportunity to discover novel genetic variants and loci that influence disease susceptibility, severity, or response to treatment. On the other hand, it poses challenges for transferring findings from other populations or applying standard diagnostic tools or therapies that are based on non-African data.

Therefore, there is a need for more comprehensive characterization of the genomic diversity of African individuals to understand the genetic basis of health and disease, as well as to develop precision medicine approaches that are tailored to their specific needs and contexts. Several initiatives have been launched to address this gap, such as the Human Heredity and Health in Africa (H3Africa) Consortium and the African Genome Variation Project, which aim to generate large-scale genomic data from diverse African populations and apply them to biomedical research.

In conclusion, Africa is a rich source of genomic diversity that reflects its long and complex history as the cradle of modern humans. Studying the genomic diversity of Africa can provide insights into human origins, evolution, migration, admixture, adaptation, and so much more. New research papers are continually showing us that while Africa is indeed the birthplace of modern humans, we may not have been rooted there.

Written with the assistance of Dual AI

Today we will be talking about a fascinating topic, one of which seems to go under the radar from time to time and yet has an extreme impact on the populations of modern humans (us)! We will discuss bottlenecks, what they are, and how they affect the populations they affect. This is not strictly based on what happens to humans, but that, of course, will be the main point of this article. Humans. 

A human population bottleneck is a sharp reduction in the size of a human population due to environmental events or human activities, such as famines, earthquakes, floods, fires, disease, droughts, wars, migrations, or cultural practices. Population bottlenecks can significantly affect the genetic diversity and health of human populations and their evolutionary history and adaptation. A bottleneck can occur when there is any reason or reasons for drastically reducing the genetic pool available to a population at any given point. By reducing the gene pool and minimizing admixture, we can begin to see the issues arise that small populations face. But of course, we survived and possibly even came out better and more adapted to our ecological niches at the end of each of these proposed bottlenecks. 

Genetic diversity is the variation in the genes of a population. It is essential for the survival and adaptation of a population, as it allows for natural selection to act on beneficial traits and eliminate harmful ones. Genetic diversity also provides the raw material for innovation and creativity in human culture and technology. If there is a small gene pool, we are going to see the same phenotypic features over and over, and if those features, for whatever reason, do not fit the new niche created by the bottle neck, much of the population will die off. For one reason to another, infighting, lack of breeding opportunities, or higher competition for resources such as food and water. Population genetics is very fragile, and changes in how things are done can have drastic impacts. 

Population bottlenecks can reduce genetic diversity by increasing the effects of genetic drift and inbreeding. Genetic drift is the random change in the frequency of alleles (different versions of a gene) in a population due to chance events. Inbreeding is the mating of closely related individuals, which increases the likelihood of inheriting identical copies of alleles from both parents. Both genetic drift and inbreeding can lead to the loss of alleles, the fixation of alleles (when one allele becomes the only one in a population), and the increase of harmful recessive traits that can cause diseases or impairments.

When we are dealing with smaller populations that are trying to survive, any evolutionary disadvantages they face are going to be increased. If a recessive trait is usually bred out of the population, allowing the population to flourish and grow, but only those individuals with this allele or trait remain, then whatever negative aspect about this feature will cause damage. Sometimes too much damage to the area’s ecology, and we have extinctions, or, as we are learning, near extinction events called bottlenecks. 

Population bottlenecks can also affect the evolutionary history and adaptation of human populations by altering their patterns of genetic variation and relationships with other populations. For example, population bottlenecks can create founder effects, which occur when a small group of individuals colonizes a new area or becomes isolated from the main population. Founder effects can result in genetic differences between the new population and the original one and among different populations that originated from the same source. Founder effects can also influence the cultural and linguistic diversity of human populations. At its most extreme, many anthropologists, when asked the question, “Where will humans be in a thousand years?” It is hard to answer, for if we do go into space for any extended time, and I do mean a long amount of time, those who went into space would be the “founders”; setting a new population base wherever they went, one which may not exactly represent the original gene pool back at home. The founder effect has had a great role in our development and evolution; it has allowed us to develop and to develop changes, changes which make is beautifully part of the same species. 

Examples of human population bottlenecks

Human populations have experienced many population bottlenecks throughout their history, some of which have left traces in their genomes that can be detected by genetic analysis. Some examples are:

– The Out-of-Africa bottleneck: This occurred when a small group of modern humans left Africa about 60,000 to 80,000 years ago and spread across the world, replacing other hominin species such as Neanderthals and Denisovans. This bottleneck reduced the genetic diversity of non-African populations compared to African ones, as well as introduced some genetic variants that were adaptive to different environments outside Africa.

– The Toba catastrophe bottleneck: This is a controversial hypothesis that proposes that a massive volcanic eruption at Lake Toba in Indonesia about 74,000 years ago caused a global cooling event that drastically reduced the human population to about 10,000 to 30,000 individuals. This bottleneck would have further decreased the genetic diversity of human populations and increased their genetic differentiation.

– The Ashkenazi Jewish bottleneck: This occurred when a small group of Jewish people migrated from Europe to Eastern Europe about 1,000 years ago and established a distinct cultural and religious identity. This bottleneck reduced the genetic diversity of Ashkenazi Jews compared to other Jewish groups and increased their susceptibility to certain genetic diseases such as Tay-Sachs disease and cystic fibrosis.

– The New Zealand black robin bottleneck: This occurred when only five individuals of this bird species survived after habitat destruction and predation by introduced mammals in the 1980s. This bottleneck severely reduced the genetic diversity and fitness of this species, which required intensive conservation efforts to prevent its extinction.

So there we have it! I hope this has answered some of your questions surrounding what bottlenecks are when we are talking about genetics, human genetics, what it means, and the effects it could have evolutionarily on a species. 

Remember, there is always more to learn! 

References

Bottlenecks that reduced genetic diversity were common throughout human history | Berkeley News. (2022). Retrieved October 30, 2022, from https://news.berkeley.edu/2022/06/23/bottlenecks-that-reduced-genetic-diversity-were-common-throughout-human-history/

What is a Population Bottleneck? – Genetic Genealogy. (2015). Retrieved October 30, 2022, from https://dna-explained.com/2015/07/09/what-is-a-population-bottleneck/

Watch the video premiere at 8pm PST here:

In his own words, “I am a PhD candidate in the School of Human Evolution and Social Change at Arizona State University and an affiliate of the Institute of Human Origins. I received my BA in Anthropology from Stony Brook University and my MA in Anthropology from the University of Victoria. My research focuses on the emergence and role of pyrotechnology in human adaptations during the late Middle and Later Stone Age of South Africa.

I have conducted field work at the late Lower Paleolithic site Shishan Marsh – 1 in al-Azraq, Jordan and the Upper Paleolithic cave site Mughr el-Hamamah in the Jordan Valley. Currently, I am doing field work at a Later Stone Age site called Knysna in South Africa.

My hobbies include PC gaming, skateboarding, and flintknapping.”

You can contact him to get a chance to look at his SOP (Statement of Purpose) and his CV: jkmurra5@asu.edu

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Introduction

Written with the Assistance of Dual Ai

Bipedalism, or walking on two legs, is one of the defining characteristics of humans. But why do we walk this way? There are many hypotheses about the evolution of bipedalism. Still, the most likely explanation is that it allowed our early ancestors to travel long distances more efficiently, as in they could go farther while using fewer calories and explore the world even further. 

While Bipedalis may not be the thing that “makes us Human,” as I believe there is no one such thing, it is an aspect of our evolutionary history and our current lives that cannot be ignored; its importance in understanding who we are is critical. 

The advantages of bipedalism

Bipedalism has many advantages over quadrupedalism, or walking on four legs. For one, it allows us to travel long distances more efficiently. This is because bipedalism frees up our hands, which we can use to carry tools or food. Additionally, bipedalism allows us to see over tall grass and other obstacles, which gives us a better view of our surroundings.

Bipedalism also has some social advantages. For example, it allows us to stand face-to-face with each other, which is essential for communication and cooperation. Additionally, bipedalism allows us to use our hands for gestures and other nonverbal communication.

We can run, walk long distances, and get around places no other animals can, thanks to these strange spindly things that come off the bottom of our torsos. But being bipedal is not always a good thing. As we will soon see. 

The disadvantages of bipedalism

Bipedalism also has some disadvantages. For one, it puts more stress on our legs and feet. Additionally, bipedalism makes climbing trees or running as fast as quadrupeds more difficult. But these are the simple things that make the disadvantages of bipedalism apparent. 

Less apparent is the back strain, the heavyweight our bones have to move around to keep us upright. It is a delicate balancing act. As Dr. Jeremy DeSilva put it in his book First Steps; How Walking Made Us Human (Which I highly recommend), he mentions that we are always constantly in a controlled fall. We put one leg forward and fall controlled until we throw the other leg out in front of us. This is very true when you think about it, and there is so much room for error when doing this. 

We fall constantly, and the older we get, the more dangerous and likely these events are to occur. Taking a tumble on the football field when you are 18 and falling on your hip when you are 80 will feel very different. 

The evolution of bipedalism

The exact evolutionary history of bipedalism is still a matter of debate, but it is thought to have evolved over millions of years. We have examples of bipedalism that may date back to seven million years ago, close to our separation from the pan family. Sahelanthropus tchadensis may be the oldest hominin we know of. But it is still debated on whether or not it was bipedal, to begin with. 

The next candidate would be the millennial man, or Orrorin Tungunensis, which dates to around 5-6 million years ago. 

Another great example of ancient bipedalism is the Laetoli footprints in Tanzania. It contains multiple tracks of footprints made by something remarkably human, thought to be Australopithecus afarensis (save the site A trackway). We can see how these footprints were made because they were imprinted on top of recently deposited volcanic ash, so we can even reliably date them to about The Laetoli footprints are a series of hominin footprints that were discovered in Laetoli, Tanzania, in 1978. The footprints are dated to 3.6 million years ago, and they are the oldest known direct evidence of human or human-like bipedalism.

The footprints were discovered by Mary Leakey and her team during an archaeological excavation at Laetoli. The footprints were found in a layer of volcanic ash that had been laid down by a volcano that erupted about 3.6 million years ago. The ash layer had preserved the footprints in excellent condition.

The footprints are about 1.7 meters long and 0.7 meters wide. They show that the hominin who made them was walking upright, with its feet flat on the ground. The footprints also show that the hominin was walking at a slow pace.

The Laetoli footprints are a significant discovery because they provide direct evidence of human or human-like bipedalism at a time when it is thought that hominins were still evolving from ape-like ancestors. The footprints also provide evidence that hominins were walking upright in East Africa at least 3.6 million years ago.

The Laetoli footprints are displayed at the National Museum of Natural History in Washington, D.C.

Conclusion

Bipedalism is a complex trait with many advantages and disadvantages. It is thought to have evolved over millions of years, and it has played a major role in the evolution of humans.

References

• Day, M. H. (1986). Hominid footprints from Laetoli, Tanzania. Nature, 322(6081), 17-21.
• Lovejoy, C. O. (1981). The evolution of human walking. Scientific American, 244(5), 118-125.
• Tuttle, R. H. (1987). The primate origins of human bipedalism. New York: Columbia University Press.