Chapter 20: Evolutionary Biology

What is included in the order of primates?

Lemurs, monkeys, apes

What is included in the suborder Catarrhini?

Old world monkeys and apes

What is included in the family Homnidae?

Great apes and humans

What is included in Hominins?

Anything more closely related to Homo sapiens the anatomically modern human, than to other apes

What are the closest relatives to humans?

Pongo pygmaeus, Gorilla gorilla, Pan troglodytes, and Pan paniscus (orangutan, gorilla, standard chimpanzee, bonobo

What clade to humans belong in?

The same clade as African great apes, we have synapomorphies such as elongated skulls, enlarged brow ridges, shortened canines, wrist bone function, reduced hair, etc

What is the relationship between humans and african apes?

,humans and both chimpanzee species share features of skull, teeth, limbs, and delayed sexual maturity, some molecular analyses place humans and gorillas as sister taxa

What is a difference between apes and humans?

Gorillas and chimpanzees share knuckle walking which humans lack

What is the Dryopithecus?

An extinct European ape 10 million years old, shares many traits with gorillas that humans and chimps lack, if these characters are ancestral and humans and chimps don't have them it is most parsimonious for humans and chimps to be sister species

How can we attempt to answer the chimp/gorilla question? (Which are humans closer related to?)

Can use mtDNA phylogenetic trees or Y chromosomes or nuclear DNA

Why is there criticism of phylogenetic trees for the chimp/human relationship?

Because they are gene trees and not species trees, if an ancestor was genetically variable for a particular locus the gene tree may not accurately represent the species tree, ancestor may pass on a subset of its alleles for a gene to each descendent species, that gene will not give an accurate estimate of species phylogeny

What are ancestral polymorphisms?

Genetic variants that arose prior to the speciation event that generated the species in which they are currently found

What is the difference between a gene tree and a species tree?

A species tree depicts the evolutionary history of species, while a gene tree depicts the evolutionary history of a specific gene

What is Introgression?

The stable integration of genetic material from one species into another through repeated back crossing

What is back crossing?

crossing two pedigrees and getting an F1 generation but going back and crossing the F1 generation with a pedigree again.

How can you test the issue of gene versus species trees?

Use as many genes as possible and see which are congruent, for example in 14 independent genes, 11 showed humans and chimps together, 1 showed humans and gorillas so human/chimp relationship is more likely

How can we tell what intermediate ancestors lived between chimp/human ancestors?

Fossils provide some ancestors but the fossil record is incomplete, scientists disagree on placement of fossils on hominid tree

What is humans and chimps most recent common ancestor?

We last shared an ancestor with chimps about 5-7 Mya, most recent was a knuckle walker that ate mostly fruit, lived in many habitats, had complex social groups, and made tools

What is Sahelanthropus tchadensis?

Earliest known hominid 6-7 million years old, skull has a combination of primitive and advanced features, perhaps the missing link between hominins and other apes

Why is Sahelanthropus so interesting?

At 6-7 million years old this is the earliest known record of the human family and predates what molecular evidence tells us, skull discovered in Chad Africa and is nicknamed Toumai comes from a crucial and little known interval when human lineage was becoming distinct from chimps

What are Australopithecines?

Among the earliest humans, had two main body forms (robust and gracile), bipedal like modern humans ( known from limb structure and foot prints), they were short with small brain cases, modern human structure is similar to gracile australopithecines

What were the robust australopithecines?

They had enormous teeth and very strong jaw muscles for biting tree branches like gorillas do today (Paranthropus)

What was the first Homosapien?

H. habilis, Homo had larger brain cases and smaller teeth than Australopithecus, Homo was taller with less sexual dimorphism in size, Homo rudolfensis may be the same species as H. habilis but have some skeletal differences

What are some other recent human ancestors?

- H. Ergaster is more recent ancestor from africa

- H. erectus was the first human to leave africa

- H. heidelbergensis is its descendent

- H. neanderthalensis may be our ancestor or a sister species that died out

When did anatomically modern Homo sapiens appear?

Approximately 100k years ago, prior to homosapiens as many as 5 human species existed at the time some in the same regions

What did Strait construct that was technically incorrect?

reconstructed a cladogram using fossils, incorrect because ancestor descendent relationships are not adequately depicted and all species appear as terminal taxa

What hypothesis did Strait also construct?

A hypothesis of descendent relationships where a time scale allows testing by the fossil record, and new fossils should be found from ages depicted in correct hypothesis

What is Homo naledi?

Small ape-like brain, dated 300k years ago found in 2013

What are modern humans today?

We are the sole surviving species of a much larger human radiation, in the past as many as 5 species existed, new data and new technology will clearly introduce a new theory on the evolution of human ancestors

Why do do paleontologists disagree about taxonomic status of H. ergaster?

They are unsure if it is the same species as H. erectus or different, new H. erectus fossil recently found in Georgia from 1.75 mya

Why do paleontologists disagree about the status of H. neanderthalensis?

Species or subspecies of H. sapiens, H. antecessor may be ancestor of H. sapiens and H. neanderthalensis

What are the hypotheses about the transition from H. erectus/ergaster to H. sapiens

- African replacement, H. sapiens evolved in Africa, migrated to Europe and Asia, and replaced H, erectus and H. neanderthalensis without interbreeding

-Multiregional evolution, H. sapiens evolved concurrently in Europe, Africa, and Asia with sufficient gene flow to maintain their continuity as a single species, current gene pools are a mixture of all of these regional variants

What model is between the two extreme hypotheses about transition to H. sapiens?

Hybridization and Assimilation, H. sapiens evolve in Africa and migrated to Europe and Asia with some amount of hybridization, some European and Asian genes were assimilated and persist into modern humans

What did Frayer argue about the African replacement hypothesis?

Frayer argued that it could only be correct in African H. sapiens had superior tools to allow him to defeat H. erectus, no such tools have been found, Australian aborigines have similar features to Homo erectus

What did Lieberman and Waddle do?

Predicted cladograms based on African replacement and multiregional evolution models, predicts the relationships of modern humans and can be tested with molecular evidence

What is the problem with using cladograms to predict old human relatedness?

the problem is the prediction is the same for African replacement and multiregional evolution the only difference is the time scale, the out of africa model says differentiation of races began 200k years ago and multiregional says it becan 1.8 million years ago (Quantitative reather than qualitatie differences)

What did Hedges test with mtDNA?

Tested the models with mtDNA, found 189 people produced phylogeny which lead back to a single mitochondrial haplotype, all non-african haplotypes were nested within African haplotypes

What hypothesis did edges mtDNA analysis support?

The African replacement model

What was the issue with Hedges analysis supporting the African replacment model?

Because mtDNA is effectively all a single gene ( mother inherited) we need independent estimates of the age of the split, mtDna may be estimating the split to be too young, populations connected by gene flow may diverge before their alleles do

What did Bowcock examine?

30 nuclear loci from 14 human populations, the deepest split is African and non African populations the split occurred 75k-287k years ago this supports the African replacement model

What did Tishkoff examine?

Nuclear allelic variation on chromosome 12, African populations had highest allelic diversity, data the split to be 102l to 450k years old, consistent with African replacement model

What did Paabo recover?

Genome sequences of three H. neanderthalensis bones and a Denisovan specimen ( undescribed human species from siberia) samples were from 30k to 40k years old he also sequences 663 modern humans, 7 chimpos and 2 bonobos

What did Paabo find from his discoveries?

Found that modern humans from Europe, Asia, America, Australia, and Oceania are more closely related to each other than any is to H. neanderthalensis or the Denisovan fossil, he estimated divergence of Neanderthal to modern humans to be 317k to 741k years old this also supports the African replacement model

What did Green study?

He did a SNP study with the same data neanderthals and Denisovans, supports hybridization and assimilation model, leaky replacement

How similar are modern humans to Neanderthals and Denisovans?

Gene flow occurs between Neanderthals and humans in secondary contact after speciation, your genome is 1.5 to 2.1% neanderthal and 3-6% Denisovan

What are some unique human traits?

Walking bipedally, large brains, use of complex tools, and use of language

Can apes and other animals make tools?

Yes, but only humans make and use complex tools, other species tools are more simple

How old are the oldest known tools?

2.5 to 2.6 million years old from Gona Ethiopia, likely made by a robust australopithecine since they had three hand muscles that chimps lack they were similar to modern humans and could grasp things

How old is the oldest homo fossil?

2.3 million years old, Homo habilis

Evolution of language in humans

Language is a complex adaptation involving neural circuitry in the brain, appears to be an innate trait in humans and involved throat adaptation

How has the throat adapted between humans and apes?

In apes and human babies, larynx is high in the throat and seals with nasal cavity to prevent choking, in mature humans, larynx is lower to allow greater diversity of sounds but increases choking risk

What do some archeologists argue about language?

Language cannot be proven without arbitrary symbols, cave paintings in europe are over 23k years old but humans built boats and traveled to Australia by 40k years and must have had language to accomplish this

How did hominids first use language?

A 60k year old neanderthal skeleton from Israel had an intact hyoid bone, which anchors throat muscles to larynx, found hyoid bone to be nearly identical to modern humans and completely different from chimpanzees

Which hominid first used language?

Since brain size increased steadily in homosapiens it enabled early man to speak, this was costly because large brains require much energy to maintain, Endocasts reveal similar brain structure in extinct homo compared to modern homo with speech centers, language may be 2 million years old

What is a hominid?

An early ancestor of humans

What new findings were found in the 2004 cave excavation in southeast Asia?

We are the only currently living species of the genus homo but the cave excavation showed we coexisted with another species until much more recently than previously thought (Homo florensiensis)

What do skeletal remains tell us about Homo floresiensis?

They were only 1 meter tall, had a brain one third of the size of modern humans, lived on an isolated island long after homo sapiens had migration through the south pacific region

What happened to Flores (the home of Homo Floresiensis)?

Volcanic eruption 12k years ago killed of many species including Komodo dragons, large lizards and tortoises, enormous rates, tiny primitive elephants, and as we now know tiny primative people

What did Homo floresiensis likely descend from?

Full sized Homo erectus that made landfall on Flores as much as 900K years ago, the islanders doded the dragons and hunted the elephants, individuals of this population got smaller with each generation from endemic dwarfing in small inbred islands until they became a new species (Homo erectus became Homo floresiensis on this island)

What does Homo floresiensis represent?

Evolutionary reversal in hominin brain and body size in an insular environment, even more pronounced dwarfism in newly discovered 700k year old Flores fossils

What does the small stature of Homo floresiensis mean for humans now?

Humans are subject to the same evolutionary forces that made other mammals shrink when in genetic isolation under ecological pressure such as on an island with limited resources, Homo erectus was found to have lived on a nearby island 1.6 mya and Flores hominids were likely descendents

What did Flores tiny humans do while humans were colonizing the area?

Made tools and hunted tiny elephants