Chapter 3

Early Evolutionary Theories

Remember, a theory isn't just a hunch or a guess. A theory is an explanation for an observable phenomenon that is well-supported by the evidence. The theory of evolution is an explanation for the process of change and adaptation over time. In fact, there are multiple theories of evolution. The theory itself evolved. Here are some early evolutionary thinkers:

• Nasir al-Din al-Tusi (1201-1274) was a Persian intellectual who wrote about math, philosophy, science, religion, and more.  In his most significant work Akhlaq-i Nasiri (The Nasirean Ethics), he proposed the idea of species transformation and the potential for the emergence of new species over a long period of time.

• Georges­ Louis Leclerc, Comte de Buffon (1707-1788) was a French naturalist and another early evolutionary thinker. In 1749, he began publishing an encyclopedia, which was the first modern attempt to systematically present all existing knowledge in the fields of natural history, geology, and anthropology.  He believed species change over time in response to their environment. He also proposed that all living organisms share a common ancestry and acknowledged the role of environmental factors in shaping biological variation.

• James Burnett, Lord Monboddo (1714-1799) was a Scottish judge, linguist, and philosopher. His 1773 book Of the Origin and Progress of Language, he claimed that humans were descended from apes and shared a common ancestor. During this time, writers didn't use the word "evolution". Instead, they discussed the "transmutation of species."

• Jean-Baptiste Lamarck (1744-1829) was a French biologist and another early proponent of evolutionary theory. In his major work Philosophie Zoologique (Zoological Philosophy), first published in 1809, he proposed that species change over time through the inheritance of acquired characteristics. He also proposed that organisms can develop new traits during their lifetime in response to their environment, and these acquired traits can then be passed onto future generations.

Check out The History of Evolutionary Thought. Biological anthropologists often pay particular attention to the contributions of Thomas Malthus, Gregor Mendel, and Thomas Hunt Morgan.

Natural Selection

In 1859, Charles Darwin published a book that would change history. It was called On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. At its most basic level, Darwin's theory posits that traits that enhance the chances for survival and reproduction in a given environment become more common in a population over time. Varying environmental factors result in populations with different traits.

Key Concepts

There are some key concepts pertaining to natural selection.

Variation

Variation refers to the diversity of traits within a population. Individuals within a species can exhibit differences in physical characteristics, behaviors, genetic makeup, and so on.

Inheritance

These varying traits are inherited. They are passed from one generation to another. Today we know this inheritance happens through DNA. There are DNA copy errors that result in random mutations. Some mutations are better suited for survival (depending on the environment) compared to other random mutations.

Differential Reproductive Success

Individuals with advantageous traits are more likely to survive and reproduce, passing those traits to their offspring, while less advantageous traits may diminish over time.

Adaptation

Organisms change over time in response to their environment, leading to traits that enhance survival and reproduction.

Human Adaptations

We will study modern human biology more closely in a later chapter, but for now we can explore two examples of modern human adaptation to the environment.

Skin Tone

The earliest humans, from whom we are all descended, were dark skinned and came from Eastern Africa.  Dark skin tones have higher melanin levels, offering improved protection against excessive ultraviolet (UV) radiation in equatorial regions. When some earlier modern humans migrated beyond Africa (about 60-80 thousand years ago), they moved to areas with limited sunlight... making it harder to get Vitamin D. They began producing lower levels of melanin as an adaptive trade-off between UV protection and vitamin D synthesis. This was a change that occurred over hundreds of generations. Refer to Chaplin (2004).

Sickle cell trait

Sickle cells are red blood cells that have a unique crescent shape due to a genetic mutation in hemoglobin. The cells can get sticky and cause blockages, causing tremendous pain, strokes, infections, and other terrible outcomes. Contrary to a common belief associating it solely with Black populations, the sickle cell trait is also prevalent in regions like the Mediterranean, Arabia, and parts of South Asia and Africa. In some Greek areas, up to 30% may carry this trait. This prevalence is linked to its protective effect against malaria, reducing people's chances of getting malaria or having a severe case if they do get it (Herbes-Sommers, 2003).

Ok, back to anthropology class.

Evolutionary Mechanisms

There are several mechanisms that are at play when studying evolution by natural selection.

Character Displacement

Character displacement occurs when closely related species sharing the same environment and ecological roles evolve differences in order to reduce competition for resources. There are multiple species of Galapagos finches. Each of these finch species varies in beak size and depth, which enables their coexistence by consuming specific seeds that match their beak characteristics. Finches with larger, stronger beaks consume tougher, larger seeds, while those with smaller beaks feed on softer, smaller seeds. Here's where it gets interesting, in areas where species have less overlap and competition for resources, the features that differentiate them are less exaggerated.

Gene Flow

Gene flow occurs with the transfer of genetic material between populations, enhancing genetic diversity and countering the effects of genetic isolation. Gene flows occur during migrations and when different groups of the same species come into contact with one another.

Genetic Drift and in Small Populations

Genetic drift in small populations occurs when chance events lead to changes in allele frequencies, which potentially results in the loss of genetic diversity over generations. Chance events can be related to the bottleneck effect and the founder effect. The bottleneck effect occurs when a sudden reduction in population size due to a catastrophic event, disease outbreak, or natural disaster leads to a random loss of diversity. According to Gibbons (1993), the eruption of Mt. Toba about 75,000 years ago killed off most people leaving only a few thousand. Since all humans today are descended from these same few thousand individuals, we don't have much genetic diversity compared to other animals.

The founder effect occurs when a small group of individuals establishes a new population. The genetic makeup of the founders becomes the basis for the new population's genetic diversity.

Sexual Selection

Traits that enhance an individual's mating success often lead to the development of striking and diverse characteristics. Examples include peacocks' vibrant tail feathers, elk's impressive antlers, and lions' manes.

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Genetics

Genetics is the study of heredity, where biological parents pass genetic traits to their offspring. While children often resemble their parents, traits can vary in appearance or function. For instance, two parents with normal color vision can have a son with red-green colorblindness. Patterns of genetic inheritance will be discussed later. Molecular geneticists examine the biological processes that generate differences among individuals, focusing on aspects such as DNA mutations, cell division, and the regulation of genetic activity.

Molecular anthropologists use genetic data to explore anthropological questions, often utilizing ancient DNA (aDNA) extracted from remains of once-living organisms. Although aDNA can degrade over time, specialized techniques can amplify short segments for analysis. A recent example of aDNA research involves Native American immunity to European diseases.

Molecules of Life

All organisms are made up of four essential molecules: proteins, lipids, carbohydrates, and nucleic acids. Proteins shape cells and perform most cellular tasks, from receiving signals to initiating responses. Lipids, including fats, oils, and hormones, form the cell membrane’s phospholipid bilayer. Carbohydrates, such as glucose, provide energy for cells. Nucleic acids, like DNA, carry an organism's genetic information.

• Proteins

  • Composed of long chains of amino acids and often folded into complex 3D shapes related to their functions.

  • Interact with other proteins and molecules.

  • Categories include:

    • Structural proteins (e.g., collagen, keratin, lactase, hemoglobin, cell membrane proteins)

    • Defense proteins (e.g., antibodies)

    • Enzymes (e.g., lactase)

    • Hormones (e.g., insulin)

    • Motor proteins (e.g., actin)

• Lipids

  • Insoluble in water, with a hydrophilic head and a hydrophobic tail.

  • Includes fats, like triglycerides, which store energy.

  • Steroid hormones (e.g., estrogen, testosterone) act as chemical messengers, aiding in cellular communication and pathways.

• Carbohydrates

  • Large group of organic molecules made of carbon and hydrogen.

  • Starches and sugars (e.g., blood glucose) provide energy to cells.

• Nucleic Acids

  • Carry the genetic information of an organism.

  • Examples include deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).

Cells

In 1665, Robert Hooke observed plant cork under a microscope, noting structures resembling “cella,” or “small rooms” in Latin. Nearly 200 years later, biologists recognized the cell as the basic unit of life, with all organisms composed of either prokaryotic cells, which lack a nucleus, or eukaryotic cells, which contain a nucleus.

Prokaryotes, such as bacteria and archaea, are single-celled and lack membrane-bound DNA or organelles—specialized cell structures that perform distinct functions. While some bacteria, like E. coli and Salmonella, can cause illness, others in the human microbiome aid in digestion, immunity, and vitamin production.

Eukaryotes, in contrast, have membrane-bound DNA and organelles and can be single- or multi-celled. Examples include single-celled phytoplankton, which produces oxygen, and multicellular organisms like plants and animals. Plant and animal cells share similarities but differ in some structures, like the cellulose-based cell wall in plants, which helps prevent water loss, while animals have diverse tissues like skin, cartilage, and brain tissue.

Animal Cell Organelles

An animal cell is enclosed by a phospholipid bilayer—a double membrane made of lipids and proteins that regulates molecule and ion passage. Inside, the jelly-like cytoplasm houses organelles, specialized structures like the nucleus, which contains DNA, and mitochondria, which generate energy (ATP) for the cell. Multicellular eukaryotes can have numerous mitochondria per cell, each with its own DNA (mtDNA), as mitochondria evolved from symbiotic bacteria. Proper organelle function is essential for cell health, and dysfunction can lead to disease.

• Centrioles

  • Assist with organizing mitotic spindles, which extend and contract to facilitate cellular movement during mitosis and meiosis.

• Cytoplasm

  • Gelatinous fluid inside the cell membrane that contains organelles.

• Endoplasmic Reticulum (ER)

  • Continuous with the nucleus, this membrane network helps transport, synthesize, modify, and fold proteins.

  • Rough ER has embedded ribosomes, while Smooth ER lacks ribosomes.

• Golgi Body

  • Layers of flattened sacs that receive messages from the ER to process, secrete, and transport proteins within the cell.

• Lysosome

  • Located in the cytoplasm; contains enzymes to break down cellular components.

• Microtubule

  • Involved in cellular movement, including intracellular transport and cell division.

• Mitochondrion

  • Responsible for cellular respiration, producing energy by converting nutrients into ATP.

• Nucleolus

  • Located inside the nucleus, it is the site of ribosomal RNA (rRNA) transcription, processing, and assembly.

• Nucleopore

  • Selectively permeable pores in the nuclear envelope.

• Nucleus

  • Contains the cell's DNA and is surrounded by the nuclear envelope, a double membrane with pores that regulate molecule exchange with the cytoplasm.

• Ribosome

  • Located in the cytoplasm and on the rough ER, where messenger RNA (mRNA) binds to synthesize proteins.

DNA Structure

The 1953 discovery of the molecular structure of deoxyribonucleic acid (DNA) is considered one of the greatest scientific achievements. Rosalind Franklin used X-ray crystallography to produce an image that revealed DNA's double helix shape. Despite her significant contribution, Franklin received less recognition than her colleagues, James Watson, Francis Crick, and Maurice Wilkins, who were awarded the Nobel Prize in 1962 for their biochemical model of DNA. Franklin passed away in 1958, but her contributions are now widely acknowledged.

DNA can be described as a twisted ladder, consisting of two antiparallel strands made of nucleotides with a sugar-phosphate backbone. There are four types of DNA nucleotides: adenine (A), thymine (T), cytosine (C), and guanine (G). The strands are held together by base pairs, following complementary pairing rules: A bonds with T, and C bonds with G. These bonds are formed by weak hydrogen interactions, allowing the strands to separate easily. A DNA sequence refers to the order of nucleotide bases along one strand. For example, if one strand has the sequence CATGCT, the complementary strand will be GTACGA. In total, human cells contain approximately three billion DNA base pairs.

Primates

Primatological observation involves studying non-human primates in their natural habitats to gain insights into primate behavior, social structure, and evolutionary relationships. Jane Goodall's (1971) long-term field study of chimpanzees at Gombe Stream National Park in Tanzania is a landmark example of Primatological observation. Goodall's meticulous observations provided groundbreaking insights into chimpanzee social dynamics, tool use, and communication, reshaping our understanding of primate behavior.

Classification

Taxonomy

Remember Carolus Linnæus (1753) who gave us the foundation for modern taxonomy? We have kingdom, phylum, class, order, family, genus, and species which are all organized by shared characteristics. Today, biological anthropologists use many more categories than the ones conceived by Linnæus. Refer to the chart to make sense of how life is organized.

Primate Characteristics

Members of the Primate Order generally have the following characteristics:

• Forward-Facing Eyes

• Grasping Hands and Feet

• Nails Instead of Claws

• Large Brain-to-Body Ratio (compared to other animals)

• Complex Social Structures

• Dietary Flexibility

• Parental Care and Learning

Clades

One problem with using taxonomy is that it relies on shared characteristics, not shared ancestry. Sometimes, two life forms may have similar physical characteristics, but not a recent common ancestor. This can happen through convergent evolution, which is a biological phenomenon in which unrelated or distantly related organisms independently evolve similar traits or characteristics in response to similar environmental or ecological challenges. For instance, both dolphins (mammals) and sharks (fish) have streamlined bodies adapted for efficient swimming, but they do not share a recent common ancestor. Their similar body shapes evolved independently in response to similar ecological pressures for aquatic locomotion.

When studying evolution, inheritance, and genetics, ancestry is pretty important, so that's why we use clades. A clade is a group of organisms that share a common ancestor. Clades are organized by groups like family trees. Here are some of the clades that contain human ancestry.

• Bilateria

• Nephrozoa

• Amniota

• Sarcopterygii (Lobe-finned fish)

• Synapsida

• Mammaliaformes

• Eutheria

• Olfactores

• ParaHoxozoa

Living Primates

In this section, we will explore all of the living primates, except humans. Yes, humans are primates. We are also considered apes... great apes specifically.

First, let's explore the wet-nosed primates. It may be helpful to follow along with the Primate Taxonomy Chart.

Next, let’s explore the dry-nosed, non-Ape Simiiformes. We'll study apes below.

Now, we can study the non-Hominina Great Apes.

The only remaining great apes and primates we have to study are the subtribe Hominina, which includes modern humans and other other extinct species. We'll explore them in Chapter 4.

Conservation Biology

Some biological anthropologists work in conservation biology, which is an interdisciplinary field focusing on the following issues:

• Habitat Loss and Fragmentation: Addressing the loss, degradation, and fragmentation of primate habitats due to human activities, agriculture, logging, urbanization, and infrastructure development.

• Illegal Wildlife Trade: Combating the illegal trade of primates for pets, traditional medicine, bushmeat, and other commercial purposes.

• Climate Change: Understanding and addressing the impacts of climate change on primate habitats, food resources, and survival.

• Human-Wildlife Conflicts: Managing conflicts between humans and primates, implementing strategies for coexistence, and reducing negative interactions.

• Endangered Species Protection: Identifying endangered and critically endangered primate species, implementing conservation strategies, captive breeding programs, and reintroduction efforts.

• Biodiversity Conservation: Promoting biodiversity conservation by protecting primate habitats, ecosystems, and the interconnected web of life.

• Community-Based Conservation: Engaging local communities in conservation efforts, promoting sustainable livelihoods, and empowering communities to protect primates and their habitats.

• Research and Monitoring: Conducting scientific research, monitoring primate populations, behavior, health, genetics, and implementing evidence-based conservation strategies.

• Policy and Legislation: Advocating for policies, legislation, international agreements, and enforcement mechanisms to protect primates, their habitats, and combat illegal activities.

• Education and Outreach: Raising awareness, educating the public, stakeholders, and policymakers about primate conservation issues, threats, and the importance of biodiversity conservation.