3.2

Learning Outcomes

  • Describe a physical difference that has been identified in the Bajau people compared to other human populations.

    • The Bajau people possess larger spleens than average, which may provide advantages in their aquatic lifestyle.
    • This anatomical adaptation allows for better oxygenation of the blood during prolonged diving, enhancing their diving efficiency.

  • Describe the differences in abilities among the Bajau compared to neighboring communities.

    • The Bajau are skilled divers, spending up to 5-8 hours underwater searching for food without breathing equipment, showcasing a unique adaptation to their marine environment.

  • Explain how scientists determined what led to differences between the Bajau, Saluan, and Han and what those differences are.

    • Genetic studies revealed that the Bajau have mutations in the PDE10A gene, affecting thyroid hormone levels and spleen size.
    • The BDKRB2 gene is also associated with enhanced diving reflex, distinguishing the Bajau from the Saluan and Han communities.

  • Explain what “conserved” means in evolutionary terms.

    • In evolutionary biology, “conserved” refers to traits or genes that have remained unchanged throughout evolution due to their critical role in biological functions. For instance, Wnt signaling proteins are conserved across diverse species.

  • Describe the relationship between teeth and elephant tusks.

    • Elephant tusks are modified incisor teeth that continue to grow throughout the elephant's life, similar to human incisor teeth. They serve multiple purposes including defense, foraging, and social interactions.

  • Explain how different tusk sizes might affect the ability of individuals within a population to survive and reproduce.

    • Individuals with larger tusks may excel in competition for mates or resources, thereby enhancing reproductive success.
    • Conversely, a smaller tusk size might indicate an adaptation to certain environments where less tusk use is needed, influencing survival rates based on environmental demands.

  • Predict how this could lead to changes in tusk size (or presence) over time within a population.

    • Over generations, natural selection could favor certain tusk sizes that provide advantages in specific environments, leading to a gradual shift in the population’s average tusk size.

Natural Selection and Evolution

  • Natural selection occurs, in part, because there is variability in a population.

    • Variability is created through genetic mutations and environmental influences, such as diet and habitat.

  • Selection occurs if some particular variation offers an advantage in a particular environment.

    • This selection could lead to survival and increased reproduction of individuals with beneficial traits.

  • In groups: What is responsible for this variation that can be passed on to offspring and lead to evolution?

    • Genetic mutations and sexual reproduction contribute to variation, and environmental stresses can select for advantageous traits.

Definitions and Concepts

  • Evolution = change in gene frequency in a population over time.
    • Descent with modification indicates that species evolve from common ancestors through gradual changes.

Tusk Size and Population Data

  • Percent of tuskless female elephants in Zambia’s South Luangwa National Park was:
    • 10.5% in 1969 and rose to 38.2% in 1989.
    • In Addo Elephant National Park, South Africa, 98% of elephants are tusk-free, indicating selective pressures against tusks.

Elephant Characteristics

  • Comparison between African and Asian elephants:
    • African: Two humps on forehead, ears don’t cover shoulders, five toes on each foot, larger body size.
    • Asian: Smoothly curved forehead, ears cover shoulders, fewer toes (four or five), smaller body size.
    • Tusks: African elephants typically have larger, more prominent tusks compared to Asian elephants, many of which are tuskless.

Elephant Anatomy and Environment

  • Tusks cannot be removed without killing the animal.
    • A tusk is described as a permanently growing incisor tooth of the upper jaw, intricately connected to the elephant's vascular system, with a third of its length embedded in the skull.

Legal Aspects and Conservation

  • Is it legal to bring elephant tusks into the US?
    • As of March 2018, trophy imports were permitted under the Trump Administration.
    • The US and UK are reported to have the highest number of trophy imports from elephants.
    • Proposed regulations by U.S. Fish and Wildlife will take into account the population stability of elephant populations.

Role of Mutations in Evolution

  • Mutations are random genetic changes that can introduce new variation into a population.

    • Beneficial mutations may become more common through natural selection, contributing to evolutionary changes.

  • Environmental factors determine the success of specific traits.

    • This could include how effectively an adaptation helps an organism survive within its habitat.

Advantages of Tusks

  • Advantages of having tusks include:
    • Offense: Used to fight off predators like hyenas.
    • Foraging: Helps in food acquisition for both elephants and other species.
    • Reproductive success: Used in sexual selection to compete for mates.
    • Tools for digging for salt and breaking through obstacles to reach food sources.

Unique Adaptations of Narwhals

  • Narwhals have prolonged tusks (modified teeth) up to 9 ft long, potentially aiding in foraging by stirring up prey on the ocean floor.

Genetic and Experimental Studies

  • Conservation of traits in genes: If a gene or trait is highly "conserved," it suggests strong evolutionary pressure to maintain that trait due to its importance in survival and reproduction.
  • Example: Wnt signaling proteins are conserved across many life forms, highlighting their fundamental role in development.

Experimental Animal Studies

  • Research on genetic deletions (e.g., Wnt10a-null mice) has shown significant impacts on tooth development, which can inform our understanding of human dental anomalies.

Human Evolution and Genetic Changes

  • Do human populations evolve?
    • Yes, genetic mutations can arise, and advantageous mutations are passed on through reproduction.
    • Common examples of human adaptations include:
    • Lactose tolerance (lactase persistence) through specific point mutations.
    • Adaptations in the Bajau people related to their marine environment.
    • Genetic changes that allow for survival at high altitudes among Tibetan populations.

Geographic and Cultural Aspects of Bajau Lifestyle

  • The Bajau people have a long history of living at sea, displaying unique cultural adaptations to their environment, including stilt houses and nomadic fishing practices.

Biological and Health Implications of Adaptations

  • The spleen plays a crucial role in the immune system by filtering blood and can serve as a reservoir of red blood cells, providing oxygen during diving.

Hypoxia and Medical Research

  • Research into hypoxia in Bajau populations contributes meaningful insights for medical science, particularly regarding acute hypoxia effects on organs.

Evolutionary Changes in Tibetan Populations

  • Tibetans have evolved to thrive in chronic hypoxia environments at heights above 14,000 ft without suffering the same negative effects that other populations experience.

Lethal Gene Frequency Changes and Adaptation

  • Changes in gene frequencies in different populations, such as lower hemoglobin levels in Tibetan populations, reflect adaptations to high altitudes where oxygen availability is lower.

Evolution by Natural Selection Mechanics

  • Natural selection fosters evolution through:
    • Heritable variation with genetic basis.
    • Enhanced survival and reproduction of advantageous traits.
    • Changes in allele frequencies within populations, potentially leading to speciation.

Evolutionary Mechanisms and Population Dynamics

  • Natural selection operates at the population level, with individuals exhibiting heritable traits contributing to the gene pool over generations.

Environmental Impacts on Evolutionary Trajectories

  • Adaptations are context-specific and only effective within certain environmental conditions, which could rapidly change and exert new selection pressures on populations, exemplified in multiple species adaptations to climate change-related phenomena affecting breeding and food sources.