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LENScience Senior Biology Seminar Series Walking Upright: The cost of human evolution Questions and Discussion Pre‐seminar School Discussion During the past two years you have looked in detail at the process and patterns of evolution. Human evolution is based on these same underpinning processes and patterns. Evidence for and understanding of human evolution has itself evolved during recent history, with the advent of molecular technologies contributing to this field. The development of large brains and relatively long life spans distinguish Hominins from all other Hominoids. The reasons for this development are complex. Multiple inter‐
related factors have led to the development of intelligence in humans and the success that has accompanied this for the species. Key to understanding evolution is the concept that collectively adaptive advantage must outweigh adaptive cost for the evolutionary success of a species. This seminar explores factors that have led to the evolutionary success of the human species. Pre‐seminar review questions: 1. Humans are members of the Hominin group which is a subset of the Hominoid group. What are the key factors that define Hominins within the Hominoids and what is the relationship between these groups and the primates. 2. Natural Selection is a term that is used extensively in discussion of evolution. Define what this term means and discuss factors that contribute to selection. 3. What is meant by FITNESS in evolutionary terms. Explain the relationship between evolutionary fitness, adaptation and selection. 4. Adaptive Radiation can be observed in multiple groups of living organisms. The mammals and primates are one such group. Define what is meant by ADAPTIVE RADIATION and using examples, discuss factors that lead to adaptive radiation. 5. Sickle cell anaemia anis found extensively in African populations despite the devastating impact of this condition in the homozygous individual. Define the terms heterozygous advantage and explain why the HbS allele is common in African populations yet rare in most other populations around the world. 1 Post‐Seminar Challenge Questions 1. The Genetics of Drinking Milk Adapted from Principles of Evolutionary Medicine. Gluckman, Beedle and Hanson, 2009, Page 6‐7 For most adults of northern European origin, drinking milk is a normal part of the diet. But for the majority of the world’s population, to do so would be the precursor to some unpleasant gastrointestinal symptoms. The reason is that most human adults cannot digest the disaccharide lactose, which is a major constituent of milk. The World Health Organization classifies such ‘lactose intolerance’ as a metabolic disorder, although in fact this trait represents the normal and ancestral human condition. All young mammals rely on their mother’s milk, which is high in the disaccharide lactose, for early nutrition. They can tolerate the lactose because their small intestine contains the enzyme lactase, which breaks down lactose into the two easily absorbed sugars glucose and galactose. But after weaning, production of the enzyme is largely switched off – most animals will never encounter large amounts of lactose again, so why waste resources synthesizing the enzyme? In most human populations, lactase is lost between 2 and 5 years of age. Without lactase in the intestine, lactose in the diet cannot be absorbed and causes gastrointestinal upset, both because of its osmotic activity, causing water to be drawn into the gut, and because intestinal bacteria ferment the sugar, leading to gas production, bloating and cramps. Yet a minority of the world’s population continues to express lactase and is able to drink fresh milk in adulthood – they show ‘lactase persistence’ (Fig 1). This ability is genetically transmitted as a dominant trait. Fig 1 Worldwide distribution of lactase persistence The genetic basis for lactase persistence in populations of northern European origin has been traced to a single nucleotide polymorphism (C‐13910T) in a regulatory element upstream of the lactase gene, with the T allele completely associating with lactase persistence. Estimates from modern populations for the age of this allele centre on about 10500 years BP, roughly in line with estimates of the introduction of domestic cattle to Europe some 8000 to 9000 years BP. Furthermore, there is evidence from Neolithic and Mesolithic remains that the allele was not widespread in Europe before that time. There are also pastoralist populations in East Africa who also show lactase persistence. Remarkably, those populations do not carry the C‐13910T allele but instead carry several other genetic changes in the same regulatory region upstream of the lactase gene, of which G‐14010C is the most common and the most tightly linked to lactase persistence. That allele appears to have spread to its present high frequency in Kenyan and Tanzanian populations within the past 3000 to 7000 years, one of the strongest examples of recent positive selection in the human genome. Yet another lactase persistence allele appears to have arisen in Arab populations, possibly associated with the consumption of camel’s milk. (a) Discuss the potential adaptive advantage of selection for the lactase persistence allele in these populations and the link between cultural development, technological innovation and the emergence of this selection pattern in these populations at this time. (b) Lactase persistence has been shown to have independently arisen in three geographic locations (Europe, Eastern Africa, and the Middle East). Name the pattern of evolution displayed by the independent emergence of these mutations and discuss evidence for your decision. 2 2. Humans have evolved to have a very large brain in relation to body mass. This brings with it a high meta‐
bolic cost with humans expending about 20% of their metabolic intake on the brain in comparison to 10% in most other primates. Discuss the relationship between the adaptive cost (metabolic and reproductive) of brain expansion and adaptive advantage of the large brain. 3. Evidence suggests that bipedalism arose during a period of hominin history in which there was significant environmental change in eastern Africa. Discuss the potential adaptive advantage of bipedalism during the late Miocene period (approx 5‐4 MYA) in eastern Africa, that may have contributed to the development of bipedalism. 4. In the past 60,000 years, development of technologies such as tools, fire and agriculture has been an emerg‐
ing force which has influenced human evolution. Discuss the impact of key technologies on human evolution during this period and consider the potential influence of modern technologies on evolutionary fitness of the human population in the future. A reminder of the 2006 Scholarship Human Evolution Question: QUESTION THREE HOMININ PHYLOGENY Although there are differences in interpretation of the evidence, it is generally accepted that human biological evolution has not been a linear progression from one species to the next. In fact, there are now thought to have been between 5 and 7 hominin genera, and at several points there have been 2 or more species andԜ /Ԝ or genera in existence at the same time. Significant factors involved in the biological evolution of humans include: • genetic drift • natural selection • cultural evolution. Using selected named hominins, discuss how each of these three factors has contributed to the biological evolution of humans. (A diagram similar to the one below accompanied this question in the examination paper) Key terms Adaptation Adaptive Advantage Adaptive Cost Adaptive Radiation Australopithecus afarensis Biological Evolution Bipedalism Cultural Evolution Evolutionary Fitness Hominin Hominoid Homo erectus 3 Homo habilis Homo neanderthalensis Homo sapiens Life History Primate Selection Level 3 Achievement Standards linking to this seminar: AS 90717 Biology 3.5 Describe processes and patterns of evolution AS 90719 Biology 3.7 Describe trends in human evolution Key Concepts from Level 3 Biology that link to this seminar: Below are selected objectives from the Y13 biology programme that link to this seminar. THESE ARE NOT A FULL LIST OF THE CONCEPTS IN YOUR COURSE. You should review these concepts before the seminar. Processes and Patterns of Evolution Remember these are only the objectives linking to this seminar—refer to your unit hand out at school for a full list. A number of the objectives listed here come from the Y12 Biology programme. Understanding of relevant core concepts from the Y12 programme underpin the development of concepts in the Y13 programme.  Define the term species and ways in which speciation occurs  Define gene and allele frequency, speciation, gene flow, genetic equilibrium.  Identify sources of genetic variation and agents of change that lead to change in a gene pool.  Define the terms genetic drift, founder effect and bottleneck effect.  Explain the role of natural selection in speciation  Describe patterns of evolution: convergent, divergent (incl. adaptive radiation), co‐evolution, and the speed of evolutionary change i.e. punctuated equilibrium, gradualism. Trends in Human Evolution Please remember these are only the objectives linking to this seminar—refer to your unit hand out at school for a full list.  Define the hominin lineage and describe the characteristics of major species in that lineage  Describe trends in biological evolution of the hominins with respect to: -
skeletal changes linked to bipedalism -
changes in skull and endocranial features -
changes in manipulative ability of the hand  Describe trends in cultural evolution of the hominins with respect to use of tools, fire, shelter, clothing, abstract thought (communication, language, art), food‐gathering, and domestication of plants and animals.  Describe patterns of dispersal of hominins (multiregional and replacement hypotheses) and the evidence supporting these hypotheses.  Describe recent developments in interpretations on the origins and trends of human evolution based on current scientific evidence which is widely accepted and presented in peer‐reviewed scientific journals. Copyright © Liggins Institute 2009 LENScience 4