Lecture 4: Major Anatomical Adaptations of the Human Lineage PDF

🐣 Lecture 4: Major anatomical adaptations of the human lineage LO: Summarise the shared anatomical features of humans in reference to other primates What is a human? Kingdom: Animali...

🐣 Lecture 4: Major anatomical adaptations of the human lineage LO: Summarise the shared anatomical features of humans in reference to other primates What is a human? Kingdom: Animalia Phylum: Chordata Class: Mammalia Order: Primates Family: Hominidae Genus: Homo Species: sapiens Lecture 4: Major anatomical adaptations of the human lineage 1  What is a primate? A biological order comprising of prosimans, monkeys, apes, and humans Evolutionary trends in modern primates Limbs and locomotions Generalised skeleton Tendency toward upright posture Flexible, generalised limbs Arboreal - living in trees “Generalised” referring to features adaptable for multiple types of movement and activities Hands and feet Adapted for grasping Opposable thumb and big toe Five highly sensitive digits Nails instead of claws Senses and brain More reliant on vision than olfaction (short, reduced face) Orbital convergence (stereoscopic vision) Lecture 4: Major anatomical adaptations of the human lineage 2  Post-orbital bar/wall - tend to be more closed or complete in modern primates Expansion & increased complexity of brain Reproductive traits and features One pair of nipples Pendulous penis Long gestation period Behaviour trends Strong mother-offspring bonds Gregarious and social animals LO: Outline the anatomical underpinnings of some of the unique trends of humans that we can find in the fossil record Things to remember when studying our evolution We (largely) lack genetic data on extinct humans Limited behavioural info (primarily archaeological) “Species” distinctions are morphological Chimpanzees have also evolved from the last common ancestor (LCA), and may not a good proxy Lecture 4: Major anatomical adaptations of the human lineage 3  Context of our evolution Evidence of the earliest hominins were found largely in South Africa and Eastern Africa (Ethiopia, Kenya, Tanzania, etc.) Some appeared in Chad Humans split from chimpanzee ~5-7 mya lineage-wise, leaving Africa ~1.7 mya Homo sapiens didn’t appear until around 200,000 years ago There are multiple major anatomical adaptations unique to humans- but there are 3 with more extensive fossil evidence: Large brain (encephalisation) Habitual bipedality (Powerful) opposable thumb LARGE BRAINS Things to consider: Relative vs absolute brain size, and size vs complexity → eg. elephant’s brain are larger than us but our brain are more complex and we are smarter No soft tissue (when studying the brain in fossil records) = brain proxies must be used (indirect evidence) Cranial capacity Endocasts (in-filling of the brain) Encephelation was a gradual process → humans have increasingly larger brains through time, resulting in brains almost 3 times the size of our other ape relatives We have hominins using tools, acquiring meat, etc later in the fossil record, but they have brains similar in size to chimpanzees BIPEDALISM Foramen magnum Lecture 4: Major anatomical adaptations of the human lineage 4  Foramen magnum has to rotate underneath the skull Chimpanzees: more posterior than humans Humans: centre of cranial base Short, broad vertebrae Quadrupeds: all vertebrae are about the same size Bipeds: much larger vertebrae at the base of the spine (weight bearing) Vertebrae become progressively larger as you move down the spine because they need to support increasing amounts of weight from the head, thorax, and upper limbs → this design ensures that the spine can efficiently distribute and manage the body's weight, thereby supporting the upright posture and movement typical of bipedalism. S-shaped spine (vs. C-shaped spine) Human spine has two main curvatures: the cervical (neck) curve that bends forward (lordosis) and the lumbar (lower back) curve that also bends forward, and a thoracic (mid-back) curve that bends backward (kyphosis) S-shaped alignment helps balance body’s weight over the pelvis & lower limbs Lecture 4: Major anatomical adaptations of the human lineage 5  Humans are born with a C-shaped spine, similar to that of quadrupedal animals, which is suited to the fetal position and early infancy. As the child grows and begins to lift their head, sit up, and eventually walk, the spine develops its characteristic S-shape Consequences to reorientating the spine (we are not perfectly adapted) Eg) herniated disk - shift to bipedalism placed additional stress on vertebral column → human more prone to issue like herniated disk (occurs when the soft inner gel of an intervertebral disk pushes through a tear in the tougher outer layer) → press on nearby nerves, leading to pain, numbness, or weakness. Lecture 4: Major anatomical adaptations of the human lineage 6  Short, broad, bowl-shaped pelvis Orientation and size of pelvis reflects gluteal muscle function: Chimpanzee: long, tall iliac blades in the coronal plane Human: short, broad iliac blades oriented toward the sagittal plane Change in the iliac blade with the gluteal muscle attach to it: In chimpanzees, the gluteal muscles are primarily extensors, aiding in propulsion in a quadrupedal stance. In humans, the gluteal muscles, particularly the gluteus medius and minimus, have adapted to function more as abductors and stabilizers. Lecture 4: Major anatomical adaptations of the human lineage 7  OPPOSABLE THUMBS Power and precision Opposable pollex (thumbs) and hallux (big toes) are typical primate traits "Opposable" means that the thumb or big toe can be moved to touch the other fingers or toes, allowing for a better grip and manipulation of objects. Humans have increased length and robuscitity of pollex Larger muscle attachement sites Increasing sophistication of tools Consequences: Adaptation also made the wrist and hand more susceptible to conditions like carpal tunnel syndrome The carpal tunnel is a narrow passage in the wrist through which the median nerve and finger-controlling tendons pass. Repetitive hand and thumb movements can cause tendon inflammation, leading to compression of the median nerve and resulting in carpal tunnel syndrome symptoms like pain, numbness, and tingling. LO: Briefly outline other features of the human lineage with limited fossil evidence Lecture 4: Major anatomical adaptations of the human lineage 8  LANGUAGE (VOCAL TRACT CHANGES) - ie. the development of symbolism and language Vocalisation is not a language - language is not just anatomical, and must require all these features: Spoken: humans have anatomical specilisations for speech Semantic: words have meaning Phonemic: words are from sound elements called phonemes, which can be combined in an near-infinite number of ways to produce different words Grammatical: an implicit set of rules that governs how categories of words are used Symbolic: there is not intrinsic association between a word and the concept it represents Vocal tract modification Anatomical structures for speech: Lower larynx (voice box) Expanded pharynx Shortened tongue Basicranial flexion Lecture 4: Major anatomical adaptations of the human lineage 9  Brain asymmetry (endocasts) Potential genetic influence FOXP2 - a gene involved in speech and language Derived FOXP2 variant of Modern Humans was shared with Neanderthals SKIN COLOUR VARIATION Human skin functions: Protection, prevention of water loss, temp. regulation, metabolic regulation, immune defence, sensory reception, excretion by means of secretion Human skin structure: Epidermis: Melanocytes - produce melanin Dermis: Hair follicles Sweat glands Lecture 4: Major anatomical adaptations of the human lineage 10  Blood vessels Nerves Hypodermis Fat Pigmentation: Skin colour derived from three pigments: Carotene Least common; orange-yellow pigment from diet Haemoglobin Pigment of blood; varies with oxygen content,Colour tinges epidermis from dermis Melanin (Eumelanin [brown]/pheomelanin [red]) Most common pigment; produced by melanocytes in stratum basale Primary determinant of variability in skin colour (density, amount, distribution) Problems with too much sun Sunburn - can permanent damage skin, interfere with body’s ability to cool itself, wounds vulnerable to infections Skin cancer - very light skin is significantly more susceptible to skin cancer Folate degradation Vitamin B9 is essential for DNA synthesis and cell reproduction UV radiation exposure causes a breakdown of folate in the blood stream Deficiencies during pregnancy (specifically the first month) cause neural tube defects Problems with too little sun Lecture 4: Major anatomical adaptations of the human lineage 11  Vitamin D deficiency Vitamin D aids in calcium metabolism and is necessary for normal bone development Rickets: weak bones (affects movement and childbearing) Skin colour as an adaptation Human skin colour shows a strong correlation with latitude and altitude Darkest skin near equator and lighter skin with increasing distance from equator Darker skin at higher altitudes (at same latitude) Increased skin pigmentation is an adaptation for protection against UV radiation that causes sunburn, skin cancer, and folate degradation Decreased skin pigmentation is an adaptation to allow sufficient UV radiation required to synthesize vitamin D Delicate balancing act over thousands of years TAKE HOME MESSAGES Lecture 4: Major anatomical adaptations of the human lineage 12