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B io Factsheet www.curriculum-press.co.uk Number 201 Humans: evolution or creation ? In some parts of the US, the teaching of evolution, particularly human evolution, is considered blasphemous. Many people cannot accept that humans have evolved from other species. This Factsheet reviews the controversy as well as recent exam questions on human evolution. The evidence for evolution includes: Common biochemistry Humans and other primates such as chimpanzees, gorillas and orangutans also have many distinctive physical and social similarities. • • Paleontology all life has DNA or RNA as its genetic material all life has the same 20 amino acids Acanthostega lived 365 million years ago. Fig 1 shows an Acanthostega fossil. Like other invertebrates it has a backbone and limbs. But it has 8 fingers and 7 toes, unlike anything existing now. Haemoglobin in mammals is made up of four polypeptide chains, two identical alpha chains and two identical beta chains. The sequence of amino acids in these chains has been determined for a number of different mammals. Fig 2. Acanthostega fossil Table I below shows a sequence of fifteen amino acids in an alpha chain from four different primates: a chimpanzee, a human, a gorilla and an orang-utan. Table 1 eight fingers Primate Amino acid sequence in alpha chain Human KAAWGKVGAHAGEYG Gorilla KAAWGKVGAHAGDYG Chimpanzee KAAWGKVGAHAGEYG Orang-utan KTAWGKVGAHAGDYG A= alanine G = glycine T = threonine Y = tyrosine D = asparragine H = histidine V = valine seven toes E = glutamic acid K = lysine W = tryptophan This translates into similar proteins in these species, and indicates that humans and chimpanzees may have had a common ancestor. Since humans and chimpanzees have exactly same sequence, they must be placed together. The gorilla differs by one amino acid, whilst the orangu-tan by two, so it follows that the gorilla is more closely related to humans. This suggests vertebrates change over time. Like most amphibians, reptiles and mammals, it has 4 legs but its fish-like tail and gills suggest it lived in water. It is considered one of the no-longer missing links – it shows us how land vertebrates could have evolved from fish. However, in order to find out what an ancestor looked like or how it lived, the fossil record must be studied. Such comparisons of amino acid sequences have been used to determine evolutionary relationships in the primates (Fig 1). Fossils can be accurately dated, so we know when the organism lived and died. They allow a sequence of changes can be seen e.g. the fossil record clearly shows: Fig 1. Evolutionary relationships in primates Oran-utan Common ancestor Chimpanzee Human Gorilla 1 • the trend from quadripedal to bipedal locomotion • the changes in hands which increased dexterity • changes in jaws/teeth reflecting changes in diet • changes in skull size and shape which indicates the evolution of the brain Bio Factsheet 201. Humans: evolution or creation ? www.curriculum-press.co.uk Typical Exam Question Homologous structures The diagrams show reconstructed skulls of individuals of the genus Homo There are incredible similarities between very different groups of organisms. The pentadactyl limb – or adaptations of it – are found in very different organisms (Fig 3). This suggests that they developed from a common ancestor. Fig 3. The pentadactyl limb mole A B C porpoise (a) Which is the most modern skull? (1) (b) What are the disadvantages of using the fossil record as evidence for human evolution? (3) horse human Markscheme (a) Skull A. Humans have less prominent brow ridges and a more domed cranium than our ancestors. The face is flatter the jaw shallower and the teeth are smaller. bat (b) bodies/(soft) body parts are often not preserved; require special conditions for preservation; very few fossils are found / gaps in fossil record; difficult to get a full picture from few parts/organisms; Humans and chimpanzees are both primates. Many other primate species are now extinct. Fig 4 shows one suggested relationship between modern humans, some of the now extinct human-like species and chimpanzees. The number by each species indicates the average brain size in cm3. The fossil record often consists of a few fragments of bones and teeth and is certainly not complete. The huge gaps in the fossil record are seized upon by creationists who argue that scientists have insufficient evidence for human evolution. However, even though scientists don’t completely agree about some of the evolutionary relationships between one species and another, they don’t accept that the missing fossil evidence weakens the theory. They point out that: • 0 1 The fossil record is consistent with evolution There is huge amounts of supporting evidence e.g. DNA, carbon dating, and behaviour There is no contradictory evidence Millions of years ago • • Fig 4 Suggested relationship between modern humans and extinct human-like species Geographical distribution of living organisms Organisms with common ancestry found in areas geographically separated have different adaptations i.e. they show divergent evolution; e.g. Darwin’s finches in the Galapagos Islands / New World monkeys in America and Old World monkeys in Africa / marsupials in Australia; 2 Homo sapiens 1400 cm3 Homo neanderthalensis 1500 cm3 chimpamzee 400 cm3 Homo erectus 900 cm3 Homo habilis 550 cm3 Australopithecus 450 cm3 3 4 5 6 7 the number (cm3) indicates average brain siize 8 Typical Exam Question (a) Name one homo species that became extinct less than 1 million years ago. (b) How can some of the information in Fig 4 be explained by Darwin’s theory of natural selection? (a) Neandertha/ erectus (b) development of new species over time; extinction of smaller brain size/less adapted species more recent species show increasing brain size; better adapted/ more intelligent more likely to survive; able to pass on advantageous characteristics; advantages may be language/tool making; example of exception (Neanderthal or chimpanzee; species over reproduce; Organisms that live in similar habitats have similar adaptations i.e. show convergent evolution e.g. streamlined shape of dolphins and fish. Answers 2 Bio Factsheet 201. Humans: evolution or creation ? www.curriculum-press.co.uk Brain size Fig 5a and b show the estimated brain volume and body mass of some early hominids as deduced from their fossil remains. Fig 5a estimated brain volume Fig 5b estimated body mass estimated body mass /kg2 estimated brain volume /cm3 Homo sapiens 1500 Homo erectus 1000 Homo habilis Australopithecus 500 3.0 2.0 1.0 millions of years ago 0 Age/million years ago Homo sapiens Homo rhodesiensis 0.6 0.8 1.0 Asia Answers 1. (a) H. sapiens; (b) H. sapiens dates back 200 000 years in Africa; the oldest ancestor, H. ergaster, originated in Africa; H. sapiens evolved from H. rhodesiensis, H. antecessor mauritanicus and H. ergaster, all in Africa; (c) H. erectus because it lived longer (1.5 million years compared to 700 000 years for H. antecessor/mauritanicus); H. erectus because it lived more recently; uncertain since climate during period of either species unknown; uncertain since population size of either species unknown; H. erectus (existed for a longer period) so may have had a greater absolute number of individuals therefore chance of fossilization is also greater; 0.4 Homo erectus Homo antecessor/ manritanicus 1.2 1.4 1.6 0 2. (a)?we are able to treat most diseases most people live and reproduce all genes passed on humans are able to control their environment plenty of food/ temperature control (b) many people of child bearing age die of AIDS those who are more resistant to HIV survive resistant people bring up more children resistant characteristic spreads throughout population 1. Newly-discovered fossilized skulls from Ethiopia have led to different theories about the origins of H. sapiens. The diagram below shows one of these theories. Homo neanderthalenis Australopithecus However, most scientists still believe that we are subject to the powerful evolutionary forces that have created and destroyed many species over the past three billion years. (a) Identify three aspects of Western lifestyle that could be used to argue that we have overcome all the forces of natural selection. (3). (b) In 2007 in Africa 1.6 million people died of AIDS. Another 1.7 million became infected. Outline how AIDS may act as an evolutionary force influencing human evolution in Africa.(3) Practice Questions 0.2 Homo habilis 2. Some biologists believe a Western lifestyle now protects humanity from the forces of natural selection. They suggest we are no longer evolving. Despite this and much other evidence, some people find it hard to accept that humans have evolved from other species. Reasons include: • we seem to be different from animals ( they implicitly state that humans are different from, rather than an example of an animal). • only humans have language, self awareness, morality, highlydeveloped intelligence and technology, so it is highly unlikely that we have a common ancestor with chimpanzees • religious books such as the Bible describe creation • the theory of evolution breaks a special relationship with God • some people consider humans superior • it is difficult to imagine the incredibly long timescale Africa 20 (a) Which species that shows the greatest geographic distribution?(1) (b) What evidence is there in the figure that human evolution originated in Africa?(2) (c) Would H. antecessor/mauritanicus or H. erectus be most likely to provide the best fossil evidence?(2) Note that the increase in brain size is much greater than the increase in mean body mass. In other words, the brain volume to body mass ratio has significantly increased over the last 3 million years. This translates into a greater capacity for learning and greater intelligence. Europe Homo sapiens Homo erectus 40 3.0 2.0 1.0 millions of years ago The volume of the cranial capacity was measured using sand or water in models of the brains. Body mass was estimated by measuring the length of limb bones and extrapolating with the bones of modem humans. 0 60 Homo ergaster 1.8 Acknowledgements: This Factsheet was researched and written by Kevin Byrne. Curriculum Press, Bank House, 105 King Street, Wellington, Shropshire, TF1 1NU. Bio Factsheets may be copied free of charge by teaching staff or students, provided that their school is a registered subscriber. No part of these Factsheets may be reproduced, stored in a retrieval system, or transmitted, in any other form or by any other means, without the prior permission of the publisher. ISSN 1351-5136 2.0 3