The Units of Life

The Units of Life

• Cells are the basic units of life, capable of self-reproduction.
• Prokaryotes are single-celled organisms
• Eukaryotes are complex, multicellular organisms.
• Eukaryotic cells contain a nucleus housing DNA; prokaryotic cells do not.
• Somatic cells form the body's structural components.
• Sex cells (gametes) are involved in reproduction
• The sex cells unite to form a zygote.
• Animal sex cells include ova (eggs) and sperm.
• Mitosis is the cell division of somatic cells, producing two genetically identical daughter cells.
• Meiosis is the cell division of sex cells, involving two divisions and resulting in four daughter cells with half the original genetic material (23 chromosomes each)
• Genes are the fundamental units of heredity, composed of DNA sequences.
• A genotype is an organism's genetic material.
• A phenotype is the observable trait produced by gene expression.
• Alleles are variations of a gene that can lead to the expression of specific traits.

Gregor Mendel and the Laws of Heredity

• Gregor Mendel's 19th-century work on inheritance was rediscovered in the 20th century.
• Cell theory influenced Mendel's experiments with pea plants to understand trait inheritance.
• Plants that breed true produce only one kind of offspring when self-crossed.
• Mendel selectively bred purebred pea plants (P1 generation).
• Mendel studied seven traits with two distinct phenotypes each in over 28,000 plants.
• A monohybrid cross is a mating between two purebred individuals differing in a single characteristic.
• Mendel found that hybrid offspring from purebred parents expressed only one trait (dominant), while the other (recessive) disappeared, reappearing in a 3:1 ratio in the next generation.
• Mendel's law of segregation states that allele pairs separate during gamete formation and combine randomly during reproduction; this aligns with the process of meiosis.
• A dihybrid cross involves individuals differing in two gene pairs
• Mendel's law of independent assortment states that alleles for different traits sort independently during meiosis
• The expression of one trait does not influence the expression of another.

Mendelian Inheritance in Humans

• Mendel's laws apply to humans, including traits like blood type which has three phenotypes (A, B, and O) based on three alleles.
• If only the A allele or both the A and O alleles are present, the phenotype is A
• If only the B allele or both the B and O alleles are present, the phenotype is B
• If both A and B are present, the phenotype is AB.
• If neither A nor B is present, the phenotype is O.
• O is recessive to A and B, while A and B are codominant.
• Codominance means that both alleles are expressed.
• Mendelian traits controlled by a single gene include Huntington’s disease, widow’s peak, cystic fibrosis, sickle cell anemia, Tay-Sachs disease, hemophilia, and red-green color blindness.
• Most human traits are polygenic, involving multiple genes, and can be influenced by environmental factors.
• Genetic diversity and variation are essential for species survival.

What Is a Primate?

• Primates, including humans, possess distinct physical features.
• Opposable thumbs and (in nonhuman primates) opposable big toes.
• Five digits on appendages.
• Flat nails instead of curved claws.
• Pads at the tips of fingers.
• Reduced reliance on smell and a smaller snout.
• Depth perception and binocular vision.
• Relatively slow reproductive rate and large brain size.
• Postorbital bars (bony rings around the eyes).
• Primates emphasize vision over smell compared to other mammals.

Primate Behavioral Variation

• Comparing human and nonhuman primate behavior helps define culture.
• Studying primates in their environment reveals behavioral variations.
• Chimpanzees in different environments exhibit different hunting techniques and gender roles.
• Tool use by nonhuman primates is crucial for understanding human ancestors.
• Culture in nonhuman primates is seen in the exchange of ideas, teaching, and knowledge transfer, such as chimpanzees teaching termite-fishing.

Explaining Primate Success

• The arboreal theory suggests primate traits evolved as adaptations to life in trees.
• The visual predation hypothesis suggests primate features are adaptations for hunting insects and small prey in forests.
• The angiosperm theory proposes primate traits developed with the rise of flowering plants for feeding on fruits, berries, and seeds

Primate Classification and Taxonomy

• Primates are classified into two suborders: Strepsirrhini (prosimians) and Haplorrhini (tarsiers and anthropoids).

The Strepsirrhini or Prosimians

• Strepsirrhini are primitive primates that evolved earlier which includes lemurs and lorises.
• They possess a grooming claw on the second toe and a toothcomb formed by tightly packed lower incisors.
• All seven families of living strepsirrhines are found in the Old World (Africa, Asia, and Europe).

The Haplorrhini or Anthropoids

• Haplorrhini is divided into Simiiformes and Tarsiiformes.
• Simiiformes is divided into Platyrrhini and Catarrhini.
• Platyrrhini (New World monkeys) are found exclusively in Central and South America.
• New World monkeys have rounded nostrils that open to the sides and prehensile tails.
• Catarrhini are found throughout Africa and Asia and possess narrow, downward-facing nostrils.
• Catarrhini contains two superfamilies, Cercopithecoidea and Hominoidea, and are exclusively Old World.
• Cercopithecoidea includes cheek pouch monkeys and leaf-eating monkeys with molars exhibiting two parallel ridges.
• Hominoidea do not have tails and are largely terrestrial, including gibbons, chimpanzees, gorillas, orangutans, and humans.

The Tarsier Puzzle

• Tarsiers have both prosimian and anthropoid characteristics, making classification difficult but are currently classified under their own classification under the haplorrhines.
• Tarsiers cannot manufacture their own Vitamin C.
• They are the smallest known primate, nocturnal, and have extremely large eyes that take up much of the space in their skull.
• Tarsiers cannot rotate their eyes, rotating their heads 360 degrees instead.
• Tarsiers are the only primate carnivores.
• Tarsiers are sensitive to noise and stress and can die by suicide.

Understanding Concepts of Time

• Geological eras are based on fossil life forms.
• The Cenozoic era (65 MYA to present) is where most primate evolution fossil evidence comes from.
• The Cenozoic era is divided into epochs, each associated with specific primate forms

Fossils and Dating Methods

• Fossils are preserved remains of plants or animals.
• Fossil formation is favored by volcanic ash, limestone, and mineralized groundwater.
• The fossil record is incomplete; only an estimated 3% of primate species have been found.

Making Sense of Fossils

• Determining the age of fossils is important for reconstructing primate evolutionary history.
• Relative dating calculates age compared to other specimens.
• Absolute dating calculates biological age in years.

Relative Dating Techniques

• Stratigraphy dates fossils based on their layer in the soil, with older layers being deeper.
• Indicator artifacts help indicate the relative age of fossils.

Absolute Dating Techniques

• Many absolute dating methods are based on the rate of decay of radioactive isotopes.
• They emit radiation at known and stable rates.

C-14

• Carbon-14 dating is used to determine how long ago a plant or animal died.
• It is based on the amount of 14C remaining in their cells.
• Carbon-14 has a half-life of 5,730 years.

Thermoluminescence

• Thermoluminescence dating requires exposure to a high-temperature event.
• It calculates age based on accumulated radioactive elements since the event.

Primates of the Paleocene Epoch

• The Paleocene epoch (65–54 MYA) is the most poorly understood epoch of the Cenozoic era.
• Purgatorius, the most primitive primate identified, was found in Montana.
• It has an elongated last lower molar and an enlarged upper central incisor.

Primates of the Eocene Epoch

• The Eocene epoch (54–34 MYA) is marked by the disappearance of Purgatorius.
• There are first appearances of primates that closely resemble modern-day primates
• The primates in the Eocene possess postorbital bars composed entirely of bone as well as tooth combs and grooming claws.
• Fossil primates in Eocene deposits are common in North America and Europe.

Primates of the Oligocene Epoch

• The Oligocene epoch (34–22 MYA) marks the appearance of the first fossil monkeys.
• The earliest unambiguous haplorrhine fossils were found at the Fayum in Egypt
• Fayum primates are divided into Parapithecoidea and Propliopithecoidea.
• Propliopithecus represents the earliest New World monkeys and Propliopithecoidea represent the earliest catarrhine primate.

Miocene Apes

• The Miocene epoch contains fossil evidence of some of the earliest apes.
• Proconsul lacked long, curved digits and a tail and their teeth show a pattern of 2.1.2.3.
• Sivapithecus skulls show a resemblance to orangutans and is a common fossil throughout Asia.
• Samburupithecus is a large late Miocene ape found in northern Kenya that resembles modern African apes.
• Ouranopithecus, found in Greece links to both African apes and humans.

Walking on Two Feet

• Hominin refers to all species in direct lineage to humans.
• Hominids refers to all modern and extinct great apes.
• All hominins share bipedal locomotion.
• Angling of the femur inward positions knees and feet under the pelvis and bipedal hominins have spinal curves.
• The evolution of the arch in the foot and realignment of the big toe transmit weight.
• The Laetoli footprints discovered by Mary Leakey indicate a modern hominin could stride.

Miocene Hominids

• The first hominid fossils appear in the late Miocene, 10 to 5 MYA.
• Sahelanthropus tchadensis is a fossil ape that lived approximately 7 MYA
• Some researchers claim it is the last common ancestor of humans and chimpanzees with a mere cranial capacity of 350 cubic centimeters (cc).
• Orrorin tugenensis was dated to approximately 6 MYA and it was proposed to be a hominin due to anatomical traits that suggest bipedalism.

Pliocene Hominins

• The Pliocene epoch extended from 5 MYA to 1.8 MYA.
• Ardipithecus ramidus was found in Ethiopia in 1992 by American paleoanthropologist Tim White and was dated to about 4.4 MYA
• It is the first discovered hominin species to be dated to the Pliocene era
• It can be concluded that Ardipithecus was bipedal and its upper arm bones are very small.

The Robust and Gracile Australopithecines

• Australopithecine species are classified into gracile and robust forms.
• Gracile species had more pronounced projections of the jaw (prognathism), less flared cheeks with no sagittal crest, and smaller teeth/jaws.
• Robust species had sagittal crests to accommodate large temporalis jaw muscles.
• Gracile species emerged around 4 MYA and disappeared 2 MYA.
• Robust species continued to exist for another million years.

Australopithecus africanus

• Australopithecus africanus was the first australopithecine discovered in 1924 by Raymond Dart
• The most notable specimen was a skull from a child as the Taung child represents “an extinct race of apes intermediate between living anthropoids and man”.
• The forward position of the foramen magnum indicated that the skull was poised on top of the vertebral column, suggesting bipedalism and an upright posture.

Australopithecus afarensis

• In 1973, Donald Johanson found a good portion of a skeleton (about 40 percent) and he called her Lucy.
• It was dated to around 3.75–2.8 MYA and was determined to be a member of the species Australopithecus afarensis.
• KNM-AL-288 stands for the Kenya National Museum and the Afar locality where the fossil was found.
• There are two morphological features that provide evidence that the species moved more like a great ape than a human.
• First, it had arms that were substantially longer than modern humans’. Also, A. afarensis possesses finger and toe bones that are long and curved.

Australopithecus garhi

• Also found in Ethiopia, Australopithecus garhi is dated to approximately 2.5 MYA
• It has incisors that are larger than those of any of the known australopithecines or Homo
• A. garhi provides evidence of the earliest use of stone tools by a hominin as A. garhi fossils were found with fossil bones that displayed numerous cut marks.

Australopithecus sediba

• In 2008, the clavicle bone of Australopithecus sediba was discovered by Matthew Berger which uncovered two partial skeletons, one of an adult female and the other a younger juvenile.
• A. sediba is considered an important species because it appears in the fossil record around the time of the first emergence of the genus Homoaround 2 mya.
• Anthropologists classified A. sediba as a species of Australopithecus as its combination of traits suggests both tree climbing and bipedal adaptations.

Paranthropus robustus

• Robert Broom discovered Paranthropus robustus at a site called Kromdraai in South Africa.
• Its features include a sagittal crest and a flared zygomatic arch for the attachment of a large temporalis muscle.
• It is used for chewing a diet reliant on hard nuts and seeds.

Paranthropus boisei

• Louis and Mary Leakey found the first hominin fossil, Paranthropus boisei (OH-5)—originally classified as Zinjanthropus boisei—in 1959.
• It is often referred to as the hyper-robust hominin because of its mohawk of bone on the top of the skull.
• Other features include a low or absent forehead, a flat face, large jaws, and large attachment sites over the entire skull for chewing muscles.

Paranthropus aethiopicus

• There is little knowledge about Paranthropus aethiopicus which has been dated to about 2.5 MYA and is referred to as the “black skull.”
• It is believed that this species falls somewhere between the robust and gracile australopithecines, having characteristics of both.

Landmarks and Questions

• Fossils discovered raise questions related to phylogenetic relationships and points of divergence.
• The discoveries that have been made represent important landmarks which provides clues that will lead to the next steps in the human journey.

Mitochondrial Eve

• The Human Genome Project sequenced about 99 percent of the human genome in 2003.
• Genetics has confirmed the Out of Africa theory.
• Early humans left Africa around 100,000 years ago.
• Some interbred with species like the Neanderthal.
• Molecular anthropologists determine when human populations began diverging.
• Genetic studies are based on mitochondrial DNA (mtDNA), which is passed on maternally.
• The mitochondria of every living person is a copy from a population referred to as Mitochondrial Eve, believed to have lived in southern Africa 100,000–200,000 years ago.
• Genetic variation is greatest in Africa.

How the Genome of Lice Can Fill in the Gaps

• Two questions that this louse research has already begun to ask are when did humans become less hairy and when did humans start wearing clothes.
• Human head and body lice share a common ancestor with chimpanzee lice and tracking the coevolution of lice helps estimate when humans lost extra hair and when humans started to wear clothes.
• Research on lice provides further support for the Out of Africa model of human migration.
• Humans lost body hair about a million years ago and didn’t start wearing clothes until around 170,000 to 190,000 years ago.

Natural Selection and Human Variation: Are Humans Still Evolving?

• Human variability is due to environmental and genetic factors, like social status, ethnicity, age, nutrition, and quality of life.
• The evolutionary mismatch hypothesis proposes that bodies are best suited to past environments.
• Human bodies are still adapting to the grain-based diet brought about by agriculture.
• Currently 65 percent of humans are unable to digest cow’s milk due to lactose intolerance.
• Dental caries are another problem linked to the agricultural diet as there is adaptation to variation in skin pigmentation related to ultraviolet radiation.
• Each of these three groups faces the same environmental challenge and each has responded with unique adaptations as Tibetans compensate for low oxygen levels by taking more breaths.
• Those in the Andes living at high altitudes have been found to have higher concentrations of hemoglobin.
• This chapter has explored some of the immense biological and cultural diversity of the genus Homo.
• Variation is the key to survival.