Human Bio Chapters 23-25

Stages of Chemical and Biological Evolution

The universe is theorized to have started as lots of hot gases, including water vapor. As the atmosphere began to cool, the water went from gas to liquid and rain began to fall. Oceans began filling at that point, and a lot of energy was present. This caused the gases to react and create small organic compounds: the first stage of evolution. Stage 2 is the macromolecules, made of the compounds joining together. The RNA first hypothesis states that RNA came before proteins, but there is also the protein first hypothesis. Stage 3 is Protocells, where lipids in the atmosphere began to associate and form lipid protein membranes. Phospholipids with hydrophobic and hydrophilic parts, will naturally combine to form a membrane in a solution. These are metabolic but cannot divide, are heterotrophic which means that they use other small molecules as their food source. Stage 4 was where living cells are created, so they are able to divide. RNA first hypothesis says that RNA was used to create proteins and enzymes, which are then used to create DNA. Reverse transcriptase does the same thing. Protein first says that enzymes synthesize DNA from the nucleotides in the ocean.

Biological Evolution

Two aspects to this: There is a common ancestor which gave rise to all living things (not discovered) and adaptation to the environment by these living things. It makes them better able to survive and reproduce in their particular environment. The mechanism for this process is natural selection, also called descent with modification. Through this, favorable traits are selected over unfavorable traits, to be passed on to the offspring and perpetuate throughout the species. This allows for the development of new species.

Lamarck versus Darwin

Lamarck hypothesized that characteristics are acquired over time, but these acquired characteristics cannot be passed on. His theory has been disproven. Darwin stated that desired characteristics are selected. If a certain characteristic of the animal was unfeasible and did not allow them to survive, they would die off and only the desired traits would remain in the surviving animals. The environment basically selects the favorable traits of the animal by killing off the weaker animals. That allows for the organism to survive and pass their genes to their offspring.

Critical Elements of Natural Selection

Variation in physical characteristics are important, and are passed down to offspring. The second factor is competition for limited resources, which helps to limit population size because of unequal reproductive rates. With limited food, you will only be able to support a certain amount of organisms. Adaptation is where advantageous traits which capture more resources are passed down. This causes the frequency of certain genes to change, and that is the mark of evolution.

Evidence of Evolution: Fossils

Hard tissues mineralized into sediment, and sedimentation created layers/strata, which helps with dating. Organisms found in the sediment of the deep layers of the sediment would be older than organisms closer to the surface. The fossil record is the most direct evidence of evolution because deep in the layers, there are organisms that no longer exist. They died off, but species still changed over time. An example is the evolution of whales. The prehistoric organism had four limbs and was able to walk and swim because of webbed feet. Another organism had reduced hind limbs and a nasal opening closer to the top of the head. A whale has very reduced limbs and a blowhole on top. There is a progression of changes over time with mammals adapting to live in water.

Evidence of Evolution: Biogeographical

Distribution of plants and animals throughout the world. This means that organisms evolved and developed before migrating. Marsupials in Australia and South America are very diverse between the two regions. Australia has very few placental mammals and are diversified, but in South America, marsupials have a lot of placental mammals and have less diversity.

Evidence of Evolution: Anatomical

Common descent explains anatomical similarities. Homologous structures show that some organisms are related. For example, vertebrate forelimbs bones are the same, like the radius and ulna in the forearm, the metatarsals and phalanges. Analagous structures are structures with the same function but different structure. This does not provide evidence of relationship. Vestigial structures are fully developed structures in some organisms and partially developed in others. Snakes and whales have remnants of pelvic girdle and legs although they do not walk. Ostriches have wings but can’t fly, and humans have tailbones but don’t have tails.

Evidence of Evolution: Embryology

Closely related organisms have similar embryos. Early on in development, vertebrate embryos are very similar. For isntance, a pig and a chick embryo are very similar, with pharyngeal pouches and a post anal tail. Pigs retain the tail for balance, and chicks completely lose their tail.

Evidence of Evolution: Biochemical

There is universality of all organisms starting from genetic code. The table of 64 different codons is the same for all organisms. There is universality in the structure of DNA, ATP, and enzymes. There are differences in enzymes, and the ones involved in basic functions are the same between species. Cytochrome c is a molecule involved in cellular respiration, and it usually differs by a few amino acids compared to another organism’s cytochrome. We are very closely related on a biochemical level to all living creatures based on these facts. rRNA analysis determined three domains: prokarya (single-celled bacteria), archaea (single celled prokaryotic), and eukarya (multicellular organisms).

Classification of Humans

Humans are primates, including prosimians (lemurs, tarsiers, lorises) and anthropoids (monkeys, asian apes like gibbons and orangutans, and african apes). Characteristics of primates are adapted to living in trees, have mobile forelimbs and hind limbs, grasping hands for climbing, flattened face, binocular vision with eyes pointing forward for depth perception. Color and sharp vision is included. The important feature is our large and complex brain. We have a reduced reproductive rate which allows us to focus on the slow development of our offspring. We are distantly related to lemurs, but closely related to chimpanzees and gorillas.

Comparison of Humans and Chimpanzees

The human spine exits from the underside of the skull, but in chimpanzees it exits from the rear of the skull. This has to do with the fact that humans are upright, but chimpanzees are more effective using all four limbs. The human spine is S shaped, and the chimpanzee’s is C shaped. The curvature of the human spine also shows that we are upright bipedal organisms. The human pelvis is bowl shaped, wide enough to accommodate the organs in it. The chimp pelvis is longer, because they walk on all fours so the pelvis does not bear the weight of the internal organs. Human femur angles inward, while the chimpanzee’s bows outward. They are bow legged because they walk on all fours. The human needs to displace the center of gravity on the knee, so the femur bows inward where the knee is. The human knee can support more weight than the chimpanzee knee. While the chimpanzee can walk on its hind legs for some time, it is not efficient. Finally, the human foot has an arch, while the chimpanzee’s does not. This has to do with us being bipedal. That arch gives the feet much more flexibility to allows us to lift them upward during walking. Because chimpanzees do not solely rely on hind limbs for moving, they do not require that flexibility.

Evolution of Hominins

Some hominids are extant apes (gorilla, orangutan, chimpanzee, humans) which are still living, and some are extinct relatives. Hominines include gorillas, chimpanzees and humans. Hominins include members of the Homo genus, like humans and closely related descendants. Early hominins of the human line are determined by fossils. When a paleontologist finds a fossil, they look at its characteristics to see if it belongs within the hominin line. Key ones are bipedalism (looking at the skeleton/spine/pelvis/feet), the shape of the face (flatter, pronounced chin, shorter jaw, teeth patterns like smaller canines), brain size (humans is 1360 ccs and chimp brain is 400 ccs). Most paleobiologists focus on bipedalism for evidence

Evolution of Hominins: Examples

Very early hominids are the sahelanthropus, which are quite similar to humans, with small canines and thick tooth enamel. It is not clear if they were bipedal because the skeletons discovered were incomplete and the brain size is smaller, closer to an ape’s. It is a distant relative. The orrorin have limbs which suggest bipedalism. They have large pointed canines, and their arms are more adapted for tree climbing. The ardipithecines have two different species which have been discovered: A. kadabba, and A. ramidus (Ardi). They have small canines, but have a very small head. They have a muzzle that is more ape-like and have heavy eyebrow ridges. There is evidence of bipedalism, but a retained opposable big toe, a common trait in apes but not in humans. While the pelvis and leg structures suggest bipedalism, the toes suggest that they are still adapted to living in trees. All of these hominids have been discovered in Africa.

Evolution of Hominins: Timescale

The sahelanthropus is very far back in time, about 6 million years ago. Early hominids were australopithecines, which are from Africa. They are the species that gives rise to the homo genus. Types of autralopithecines are A. afarensis, “Lucy,” a relatively complete fossil discovered in Africa. Footprints show evidence of bipedalism. It is thought that this was a completely upright ape. A. africanus was discovered first in Africa, and carbon dating suggests that afarensis lived earlier than africanus. Both species are found in Africa, suggesting that humans came from Africa originally. On the evolutionary scale, australopithecines are much closer evolutionarily in time to humans. They lived about 1.5-4 million years ago. Members of the homo genus are determined by the brain size being bigger than 600 cc. It is also if they have jaw and teeth like humans, such as smaller canines, thicker enamel teeth that are smaller and flatter. Finally, evidence of tool use shows a closer relation to humans.

Evolution of Humans: Early Homo species

Early Homo species (hominins) include homo habilis have small teeth, omnivore diet, and use tools. There was scarring on animal bones which implied that this species hunted them down then scraped the meat off the bones. Brain areas related to language are enlarged, meaning that they might have had a primitive form of language. Language leads to cooperative, hunting, society, and culture. That is a profoundly human characteristic. Another species is homo ergaster, which has a skeleton indicating bipedalism. They had a larger brain, flatter face, evidence of using fire and tools, it was also found in Africa and is similar to homo erectus. Homo erectus was found in Asia and Europe, hypothesized to have migrated to there from Africa. On the timescale, homo habilis is 1.5 million years ago, and homo erectus was less than 500,000 years ago.

Evolution of Humans: Later Homo species

H. neandertalensis/Neanderthals, which originated in Europe. They had large brow ridges, a protruding jaw, protruding teeth, protruding nose, a very long pubic bone in the pelvis, a larger brain, larger muscles, and used fire and tools. It is thought that Neanderthals had bigger brains because they were larger animals in general. It also seems like they buried their dead relatives. Homosapiens, somehow, survived and Neanderthals did not. Perhaps neanderthals were not well equipped to survive in their developing environment, so they died off. Interestingly, many people discover they carry Neanderthal DNA. Other homo species included earliest modern homo sapiens like Cro-Magnon. They have the modern appearance of homo sapiens, with more advanced tools, evidence of culture, language, and art. These are what we think of as cave men. On the timescale, homo sapiens showed up 0-2.5 million years ago. One theory states that humans evolved in Africa then migrated to Eurasia, replacing extinct homo species.

Human Variation in Ethnicities

Although humans are the same species, we have different varieties because of our adaptations to the local environment. For example, darker skin color is usually a result of being in an environment with high UV rays, so our bodies concentrate lots of melanin to protect the underlying skin layers from those UV rays. Light skinned individuals come from places of low UV light. When there’s low levels of UV, it’s harder to make vitamin D, so in those regions it is better to lighten the skin so the UV light can be absorbed better and produce vitamin D. Our body adapts to where we are. For body size, in colder regions people have larger bodies, decreasing the surface area to volume ratio and retaining heat better. Warmer regions promote smaller bodies to increase surface area to volume and promote the release of heat. People in cold regions are short and stocky with big bones, but people who live in East Africa are more tall and thin. Some variations have nothing to do with the local environment. These are things like hair texture, upper eyelid folds, and lip shape. There is more variation within ethnicities than between. There are slight differences between phenotypes, but people within ethnicities are generally pretty similar.

Ecosystems

Defined as organisms and the physical and chemical environment in which they live. There are two types of biomes: aquatic and terrestrial. Terrestrial includes tundra, deserts, forests, etc. It is challenging to classify each region, but there is a lot of diversity in biomes. Components of these systems include abiotic factors: soil, water, and weather. Biotic factors are all living organisms in it.

Trophic Levels

Different energy levels based on the form of consumption of energy. Autotrophs use inorganic molecules and solar energy to derive organic molecules. They are producers like plants, which use solar energy and carbon dioxide to create organic molecules like glucose. Heterotrophs cannot create their own organic materials, so they need to obtain organic nutrients from other sources. This includes consumers like herbivores (plant eaters), carnivores (meat eaters), and omnivores (eat both plant and meat). Detritivores are heterotrophs which derive organic material from feeding off of decomposing organic matter. These are considered decomposers, examples being bacteria and mushrooms.

Energy Flow in an Ecosystem

Solar energy is used by producers to create organic matter, and the consumers consume the producers. The decomposers consume organic material from the producers and consumers after they have died and started decomposing. Throughout this process, heat is lost to the environment. All living organisms require a constant supply of solar energy for the energy flow in the system to continue.

Nutrient Flow in an Ecosystem

Producers are used by consumers as their food source. Decomposing producers and consumers are a food source for decomposers. Decomposers break down the organic material into inorganic material, which forms an inorganic nutrient pool. The producers pull from that inorganic nutrient pool to create their organic matter. This creates a constant flow of nutrients.

Food Webs

This is two categories of activities: raising patterns and detrital patterns. Organisms within an ecosystem behave in a very complex manner where some organisms feed off of others in their living form, while others feed off of decomposing organic material. This complex relationship between organisms is necessary to maintain that flow of energy and nutrients.

Energy Flow in an Herbivore

An herbivore will take in energy derived from producers (plants). They use some of that energy for cellular respiration (energy), and the organic material is used for that purpose. A significant proportion of that energy is lost in the form of heat. Energy through death, excretion, and defecation is passed on to detritus or detritus feeders, which is where they derive their energy. Energy is used for growth and reproduction of the herbivore, which is passed on to carnivores. Only 10% of the energy taken in by herbivores is passed on to the carnivore. This is a very inefficient flow of energy through the different trophic levels of the food web. The highest organisms on that food pyramid only drive a small proportion of energy that was created in the producer.

Ecological Pyramids and Biomass

Biomass is the mass of living organisms in an ecosystem, measured as grams per square meters. An example is 809 g of producers per square meter, 37 g herbivores per square meter, 11 g carnivores per square meter, and 1.5 g top carnivores/square meter. There is a sharp drop in biomass from producers to top carnivores because of the inefficient flow of energy between trophic levels. There is a lot of energy required for the lowest level of the ecological pyramid, in order to support the higher levels. And these lower levels are deriving that energy entirely from solar energy.

Water Cycle

The sun’s rays cause water to evaporate from the ocean. There’s also evaporation from freshwater sources and the moisture in soil. Water is derived from plants through transpiration. There is net transport of water vapor by wind, spreading throughout the planet. Precipitation over the land (rain) refills oceans, lakes and streams. If the precipitation doesn’t enter the ground, it instead flows directly into water sources. This is called runoff, and the freshwater runoff will feed into the oceans. Some of the runoff does not enter the ocean or get saturated by the soil, so it becomes part of aquifers which store groundwater.

Human Interference - Water Cycle

Humans interfere by withdrawing water from aquifers. This is our water source. We clear vegetation from land, preventing percolation and increasing runoff into oceans and streams. We interfere with natural water purification by adding chemicals and pollutants, making it unsafe to consume. It makes water unsafe for other organisms as well.

The Carbon Cycle

Carbon dioxide from the environment is used by photosynthetic organisms (plants and trees) to generate organic molecules. Consumers like herbivores will consume the organic material created by the producers, and they themselves will be consumed by carnivores. The decomposers will consume the decomposing flesh and organic materials from dead producers and consumers. All these organisms will return carbon dioxide back to the atmosphere. Producers and consumers do so through cellular respiration, and decomposers do that through decay. Carbon dioxide completes that cycle. Fossil fuels arise when organisms die and do not fully decompose. We have deposition of this organic material beneath the Earth’s surface. Carbon dioxide enters down into the aquatic life and is converted into bicarbonate. Once it reacts with water, bicarbonate is then the source of carbon for aquatic producers. Aquatic producers then create organic materials from this bicarbonate. When aquatic organisms undergo cellular respiration, they create carbon dioxide, which is released and converted into bicarbonate. Carbon dioxide is converted and goes back into the atmosphere through diffusion.

Human Interference on the Carbon Cycle

The amount of carbon stored through photosynthesis should be equal to the amount of carbon released through cellular respiration and decomposition. Because of human interaction, there is more carbon being released than being stored.