Human Origins and Evolution Bio HL Human Origins and Evolution

Full Classification of Humans Kingdom - Animalia Phylum - Chordata Class - Mammalia Order - Primata Family - Hominidae Genus - Homo Species - Homo sapiens subspecies - H. s. sapiens

Humans are primates?? Primates are an order of mammals including monkeys, tarsiers and lemurs We share this classification because we have similar anatomical features that are characteristic of that order Grasping limbs with long fingers with a separated opposable thumbs Sensitive fingers with nails Mobile arms with shoulder joints that allow movement in three planes Our arms have a shoulder girdle that allow weight to be transferred via the arms Stereoscopic vision with forward facing eyes on a flattened face giving overlapping fields of view Excellent hand-eye coordination Skull modified for upright posture

Anatomical and Biochemical Evidences 98% of Human and Chimpanzee DNA is the same Fossils of human intermediate species have been found Similarities with how we raise our youth for a relatively long time before being considered an adult

Hominid Fossil Trends Hominids are members of the family Hominidae Includes humans Primary feature – bipedalism Humans are currently the only species in this family but others have existed in the past Fossils show two major trends: Increased adaptation to bipedalism Increased brain size to body size ratio

Other Fossil Changes and Trends Enlargement of brain and taller and more erect structure. The spike connection to the skull becomes more central to balance centre of gravity. Pelvis changes to support organs in walking. Pelvis shorter and broader to attach walking muscles. Legs become stronger and longer while arms become shorter and weaker. Knee can now be fully straightened. Foot forms more of a platform and rigid shape without opposable toe.

Hominids Australopithicus afarensis: 3 - 3.9 million years – ape-like face A. africanus: 2.3 - 3 million years – flatter face, larger molars for plant based diet A. robustus: 1.4 - 2.2 million years – very large molars, bones and skull Homo habilis: 1.6 - 2.4 million years – smaller teeth and jaw for meatier diet, first with tools, size like humans H. erectus: .4 - 1.8 million years – more complex tools so meat significant part of diet and changed teeth. H. neanderthensis .5 million years – larger brains and bones, larger teeth and jaw, shorter limbs for the cold H. sapiens

Dating Fossils Radioisotopes – radioactive isotopes (have different numbers of neutrons) of a chemical element As an atom of a radioactive isotope decays, it changes into another isotope and gives off radiation Most common radioisotope used are 14C and 40K The rate of decay varies between different isotopes Half-life = the time taken for the radioactivity to fall to half of its original level

Decay Curves Radiocarbon dating – the percentage of surviving 14C atoms in the sample is measured In potassium-argon dating, the proportions of parent 40K atoms and daughter 40Ar atoms are measured. The age in half-lives can be deduced from the decay-curve Half-life of 14C is 5730 years (useful for 1,ooo to 100,000 years old) Half-life of 40K is 1250 million years old (useful for samples older than 100,000)

Decay Curve Examples

Fossil Record – as a whole Missing major portions of all species that have ever existed – very incomplete Only a tiny portion of animals became fossils REGARDLESS – shows how intermediate species have developed Humans => Hominid trends Horses => transition from 4 toes to only one

Horse Toes!!

Hominid Fossil Record Consists of only bones and teeth Hominid fossil record is FAR from complete – “missing links” are still missing Small findings can lead to major changes in theory because we don’t completely understand how we transitioned from species to species Australopithecus species shares similar characteristics to Ardipithecus ramidus and Australopithicus afarensis Dating of fossils of the three species suggest that they did not co-exist but form an evolutionary lineage

What spurred the evolution of man? Climate changes in Africa – transition from a woodland to a drier, more sparse environment Switch from tree-dwellers to land-dwellers came with the depletion of the forests Later, Africa became cooler – advantage to groups of hominids working together to hunt, use of tools, etc

Hominid Diet Earliest hominids (Australopithecus) were only slightly larger in body/brain size than apes. They had powerful teeth and jaws indicating a primarily vegetarian diet. Later hominids (once Africa cooled) Homo hominids began developing tools. With this came the ability to eat meats. Transition from vegetarian to omnivorous diet.

Advantages of Eating Meat More meat = more protein = more energy Meat = more fat = more energy More meat + more fat = larger brain capability and size Natural selection will begin to work and favor individuals with the biggest brains and intelligence Will also favor individuals who are able to work together

Advantages of Culture Learn to hunt and work together Language Learn to make better tools – better survival Learn to limit environment’s influence : make clothing, build shelters Cost = mature individuals take longer time to develop, bigger investment

Genetic and Cultural Evolution Cultural evolution – able to slow and even hamper the effects of genetic evolution Language Tool making and other skills Religion and art Medicine Genetic evolution Involves inherited differences and allele frequencies

The Hardy-Weinberg Principle and NeoDarwinism

Neo-Darwinism Synthesis of our understanding of Natural Selection blended with our understanding with genetics Idea that mutations occur all the time Changes to our genes “mutations” occur Can lead to new potential alleles and phenotypes IF they are inheritable changes

Gene Mutations vs Chromosomal Mutations Gene mutations – a change that occurs in a particular point in the DNA Affects a single gene – a single protein malfunctions Examples: PKU or phenylketonuria cystic fibrosis Chromosomal Mutations – a change that affects part or all of a chromosome Klinefelter’s syndrome (caused by non-disjunction of the X chromosome, leads to XXY)

Hardy-Weinberg Principle Evolution involves changes in allele frequencies Hardy-Weinberg equation is used to calculated the changes in allele frequencies The total frequency of the alleles in the population is 1, so… p + q = 1 Where the two allele possibilities in a population are represented by p and q

Hardy-Weinberg Continued If random mating occurs the chances for inheriting two copies of the p allele is = p x p or p2 The same is true for q = q2 The same can be said for the heterozygote = pq In all it’s glory, the Hardy Weinberg Equation p2 + 2pq + q2 = 1

Seriously… What did I just read??? Hardy-Weinberg Assumptions Random mating must occur Natural selection will not cause a higher mortality rate for one allele over the other There is no mutation occurring The population isn’t small There is no immigration or emmigration

Example 1 Genotypes of pure breeding varieties are TT and tt An experimental pea plant is established by sowing seeds of pure breeding tall and dwarf varieties in a ratio of three tall to one dwarf. The plants are allowed to disperse seeds naturally. What proportion of tall and dwarf pea plants are expected after several generations? Genotypes of pure breeding varieties are TT and tt Frequency of T (p) is 0.75 Frequency of t (q) is 0.25 Frequency of dwarf plants (tt) = 0.252 = 0.0625 Frequency of tall plants (TT or Tt) = 1 – 0.0625 = 0.9375

Example 2: 461/1600 = (tt) = 0.288 SO 0.288 = p2 p = 0.537 The gene that controls the ability to taste (PTC) has two alleles: ability to taste (T) and non-tasters (t). 1600 people where tested in a survey. 461 were non tasters (tt). What are the frequencies of the p and q alleles? 461/1600 = (tt) = 0.288 SO 0.288 = p2 p = 0.537 If q = frequency of the T allele, q = (1 – p) = 0.463

Classification and Phylogenetics

Biochemistry and Common Ancestry All living organisms use DNA or RNA as their genetic material All use the same basic universal code All use the same 20 amino acids in their proteins All use left, and not right-handed, amino acids

Phylogeny Tracing evolutionary history, links and origins is known as phylogeny Studied by comparing the protein structure or other biochemical that they contain Typically, results match the existing classification of the group

Evolutionary Clock Differences in base sequences of DNA (and therefore the amino acids sequence of a protein) accumulate gradually over time. Accumulation occurs at a roughly constant rate – allows us to “time” how long ago mutations occur and how long ago a species split from a common ancestor

Clades, Cladograms and Cladistics Node – show groups of organisms which are related Share common ancestry Also known as a clade A clade is a group of organisms that evolved from a common ancestor Can be large or small groups Can have far distant relatives (large groups) Can have close relatives (small groups) Tree diagrams showing clades are called cladograms Study of classification is known as cladistics