NZASE article

Recent evidence in evolution

Nik vuk, By Mary Morgan-Richards, Steve Common ancestor CC BY-SA, Trewick and Murray Cox, Massey Wiki- Fossil and genetic evidence both suggest that media University, Palmerston North. Commons modern populations of sapiens share a Our understanding of the evolution and range common ancestor about 300,000 to 200,000 expansion of Homo sapiens is improving rapidly, years ago. This ancestral population must but information as yet undiscovered will alter our have lived somewhere in Africa. Re-dating of a current model and improve the story. Moroccan fossil in 2017* places our ancestors in north Africa about 300,000 years ago, and Evidence for our origins comes from studying in east Africa more recently, about 200,000 to old bones and the DNA of living people. 150,000 years ago. The east African fossils have The bones of those who died thousands of most of the key features associated with Homo years ago provide information about their sapiens that we use to classify different species. anatomy and DNA. Some hominin lineages Modern populations of Homo sapiens vary we know only from their bones, such as Homo widely in skin colour and body size, but all floresiensis in Indonesia and Homo luzonensis share four important traits: A large globular in the , and some we know best braincase; small teeth with reduced jaw from DNA, such as . architecture (the shape and structure of the Bone discoveries enable theories from bones and muscles of the mouth, which is and population genetics to be closely associated with what food is eaten, tested against each other. However, biologists and eating behaviour); a narrow pelvis; and in different fields can have different criteria for distinct anatomy of the middle and inner ears. how they recognise a group as distinct enough The east African fossils have most of the to be named as a separate species. This is features that we associate with Homo sapiens. important when assigning fossils into species, Interestingly, the older fossils from Morocco and interpreting interbreeding between have some traits of modern , such as distinct populations. reduced jaw architecture, but not others such as the typical braincase shape. Deciding which sections of a lineage that has evolved through

Figure 1. Successive dispersals from Africa; (yellow), Homo neanderthalensis (ochre) and Homo sapiens (red). Wikipedia Commons.

* Hublin, J-J., Ben-Ncer, A., Bailey, S. E., Freidline, S. E., Neubauer, S., & Skinner, M. M. (2017). New fossils from , Morocco and the pan-African origin of Homo sapiens. Nature, 546 (7657). DOI: 10.1038/nature22336

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Figure 2. Hypothesis of range expansion and interbreeding in hominin evolution. Vertical lines represent interbreeding between different hominin lineages, which enabled the transfer of distinct alleles and parasites. time are separate species is very difficult. children with a mix of traits from both parents. Analyses of fossil anatomy and DNA In Africa there is genetic evidence of older sequences from archaic hominins suggest Homo lineages interbreeding with our own. multiple waves of dispersal from Africa (Figure When Homo sapiens expanded their range 1). Two groups arrived in Eurasia about into Eurasia, they interbred with 700,000 to 400,000 years ago and led to the (usually classified as Homo neanderthalensis) establishment of the Neanderthals and the (Figure 2). A third lineage in Asia, Denisovans, Denisovans, while another group of humans also interbred with both humans and expanded their range from Africa into Eurasia Neanderthals. at least 50,000 years ago (Figure 2). These periods of interbreeding resulted in our DNA being a mix of different lineages Interbreeding (Figure 3). For example, modern Pacific populations have more archaic hominin Our previous theories of hominin speciation ancestry than anyone else in the world. have been upset by new evidence that It is not uncommon for archaic alleles, about members of Homo sapiens successfully half and half , to make interbred, at various times and places, with up five to eight percent of some modern human a number of related lineages that are usually genomes - several hundred genes scattered considered separate species. (Remember, across the chromosomes (Figure 3). usually separate species do not successfully Many of these genes resulted in differences interbreed, but the boundaries of species are in structure, function or behaviour, such often not clear.) This interbreeding produced as alleles associated with colour or

Representing the needs of science teachers NZASENew Zealand Association of Science Educators Figure 2. Genetic lineages in modern human chromosomes. Human chromosomes in this image show the location of genes that commonly have alleles of Denisovan origin (orange) and those without (blue). Megabases (Mb) indicates DNA length

susceptibility to depression. For example, you might be able to fight off a virus because of the Evidence from parasites Neanderthal versions of immune genes that Modern human head lice, Pediculus humanus, you carry. right, are composed of at least six lineages. There are two alternative theories Our best estimates are that this diversity explaining why our genome contains only a is about one million years small proportion of widely scattered, archaic old, suggesting that human alleles. The first theory is that interbreeding populations may have acquired resulted in offspring with low fertility, so that lice populations that evolved few alleles were passed on. The second theory in association with archaic suggests that the populations of Neanderthals hominin hosts. For example, were small compared with humans, explaining interbreeding between humans why the proportion of archaic alleles is small. and Neanderthals might have This theory argues that the offspring of the resulted in an exchange of parasites. interbreeding were healthy and fertile, and One of our six lice lineages is common, and that the different populations merged. contains genetic diversity that formed while Geneticists are investigating the humans were leaving Africa (100,000 to 50,000 exact scenario of interbreeding between years ago), showing that the population of populations of Homo lineages in Europe and head lice grew at the same time. This suggests Asia, using larger and larger DNA sequence that lice travelled with humans out of Africa, datasets from living populations and more and that interbreeding between archaic sophisticated mathematical and population hominins resulted in the addition of new head models. Population interactions were also lice lineages to our existing parasites. likely to have also involved the spread of new A range of commensals (unrelated species parasites and diseases. living together without harming or benefiting each other) and parasites that travelled and evolved with humans shows that their

Representing the needs of science teachers NZASENew Zealand Association of Science Educators population history (inferred from genetic diversity) often matches their host (human) population history. Examples include the stomach microbe Helicobacter pylori and malaria Plasmodium falciparum. Interestingly, a new type of louse has also evolved since humans began wearing clothes – the human body-louse is adapted to living in clothes and almost never reproduces with head-lice, even on the same human host.

Adaptation in Eurasia Interbreeding among archaic hominins might have benefited populations moving from Africa into new environments in Eurasia. Expanding populations usually have low genetic diversity, which would leave the population less able to adapt to challenging new environments. It is possible that mating with locals added to the gene pool alleles for a warmer covering of hair, or protection from Neanderthal child by Alberto Álvarez Marsal, CC diseases with improved immune responses. BY-SA, Wikimedia Commons. A few alleles, known to have been in the genomes of Denisovans or Neanderthals, originated with a Denisovan population and have been found to be common in particular been introduced into human populations via human populations, suggesting they interbreeding. provide a selective advantage in particular environments. For example, an allele of the EPAS1 gene that confers resistance to Open access links hypoxia at high elevation is very common in the modern Tibetan population. The allele • Blaxland, B. (2018). Hominid and provides a selective advantage to people hominin – what’s the difference?https:// living at high elevation where air pressure australianmuseum.net.au/learn/science/ reduces the available oxygen. This particular human-evolution/hominid-and-hominin- allele of the EPAS1 gene seems to have whats-the-difference/ • Danneman M., Kelso, J. (2017). The contribution of Neanderthals to phenotype From variation in modern humans. The American Ngā Kupu Journal of Human Genetics 101: 578–589. Paekupu Hanumi – Interbreeding https://doi.org/10.1016/j.ajhg.2017.09.010 Huakita taupiri – Commensal bacteria • Wei-Haas, M. (2019). Multiple lines of

Huinga ira – Genome and mysterious ancient humans interbred with Kukuwhatanga – Evolution

Te Aka Dictionary us. https://www.nationalgeographic.com/ Pirinoa – Parasite science/2019/04/enigmatic-human-relative- Pītau ira – DNA outlived-neanderthals/ Pūira – Chromosome Urutaunga whaiaroaro – Functional or physiological adaptation Whakapapa– Lineage

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