Natural Selection and Adaptation in Snakes

• Natural Selection and Adaptation are core evolutionary processes

Snakes and their Unique Features

• Snakes possess movable skull bones allowing them to swallow prey much larger than their heads
• Snake lower jawbones are not fused, enabling them to drop away from the skull
• Snake upper jawbones can flex outward, and independently move to pull prey into the throat

Adaptation and Natural Selection

• Adaptation is any characteristic that enhances an organism's survival or reproduction relative to other character states
• Natural selection is the mechanism by which adaptations evolve
• Natural selection explains the design of life without involving a supernatural designer
• Natural selection has been described as "Darwin's dangerous idea" due to its revolutionary scientific and philosophical impact

Historical Context

• Adaptive design had been attributed to an intelligent designer for centuries
• William Paley compared living organisms to a watch, implying a purposeful creator in his "argument from design"
• Darwin's theory of natural selection provided a materialistic explanation for adaptation

Teleology in Biology

• Adaptive processes can appear goal-directed, but these processes are governed by genetic programs shaped by natural selection, rather than conscious goals
• Modern biology views development, physiology, and behavior as mechanical processes driven by interactions between DNA and the environment

Observed Evolutionary Changes

• Hundreds of examples of rapid adaptive evolution exist today, despite Darwin's belief that evolution was too slow to observe
• Rapid evolution often happens in species adjusting to new settings or affected by human activities

Rapid Adaptation

• Soapberry bug populations have adapted to new food plants
• Texas soapberry bugs have evolved longer beaks to feed on larger seedpods
• Florida soapberry bugs have evolved shorter beaks for smaller pods
• Bacteria rapidly evolve resistance to antibiotics
• Hundreds of insect species have evolved resistance to chemical pesticides
• Many weed species evolved herbicide resistance within 10–20 years of exposure
• Plants in contaminated soils evolved tolerance to toxic metals, although at a cost in non-contaminated soils Atlantic cod (Gadus morhua) mature at an earlier age and at smaller sizes due to commercial fishing
• Bighorn sheep (Ovis canadensis) evolved smaller horns due to selective hunting of large-horned individuals
• Northern populations of pitcher-plant mosquito (Wyeomyia smithii) now enter diapause later in the fall because of warmer temperatures

Natural Selection

• Natural selection is any consistent difference in fitness among distinct groups of biological entities
• Fitness is the the number of offspring an individual leaves in the next generation, combining survival and reproduction, and is also called reproductive success
• For a plant species, if 1 of every 1000 seeds survives and produces 3000 seeds, its average fitness is 3

Conditions for Evolution by Natural Selection

• Evolution by natural selection occurs given the following conditions:
  • There is a correlation between an individual's phenotype and its fitness
  • Variation in the phenotype is correlated between parents and offspring
• In asexually reproducing plants with genotypes A and B, if A has a fitness of 3 and B has a fitness of 4, B will dominate over generations
• The frequency (proportion) of genotype B has increased

Natural Selection Details

• Fitness includes mating success (sexual selection) in sexually reproducing animals
• Though evolution is often explained in terms of individual selection, it can be more useful to focus on genes selected across generations
• While natural selection typically assumes genetic inheritance, it can also apply to epigenetic or cultural transmission

Natural Selection and Chance

• Natural selection and evolution are not synonymous
• Natural selection can occur without evolutionary change by maintaining the status quo
• Other factors can cause evoltion
• Genetic drift is the random fluctuation in gene frequencies within a population
• Neutral alleles do not affect fitness, yet their frequencies change due to genetic drift

Genetic Drift

• Genetic drift causes allele frequency changes unrelated to natural selection because there is no differing fitness
• Unlike genetic drift, natural selection involves consistent differences in reproductive success
• Genetic changes are attributed to natural selection only by assessing reproductive success among respective individuals

Environment and Natural Selection

• Environmental factors influence natural selection through species' characteristics and evolutionary history
• Organisms construct their ecological niches, either literally or metaphorically
• Organisms can screen off parts of their environment to reduce the pressure of natural selection
• Species reliant on chemical signals might lose the need for sight as visual natural selection decreases or becomes negative
• Humans have lost olfactory receptor genes as they relies more on vision rather than smell

Levels of Selection

• Natural selection is based on fitness differences among individuals, but it occurs at different levels: genes, cells, individuals, populations, or species
• Genic selection occurs when transposable elements copy themselves in the genome

Selfish Genetic Elements

• Selfish genetic elements are harmful or neutral to the organism, but spread faster than other genes
• Some alleles show segregation distortion, meaning they are passed to gametes more than 50% of the time

Segregation Distortion Example

• T allele sperm is killed by t allele sperm in male mice with Tt genotype
• 90% of sperm have t alleles
• However, tt homozygotes die or are sterile

Selfish Gene and Unselfish Behaviors

• Natural selection enhances the frequency of an allele if it results in more copies in future generations
• J. B. S. Haldane argued that self-sacrificial behavior spreads if it aids relatives (e.g., worker bees helping queens) to survive
• Selection can act on genes based on their effects whether on, pollen production, behaviors, or other traits

Selfish Gene

• A gene that increases in frequency has been named the "Selfish Gene"
• Traits can evolve due to kin selection where the selection and support of relatives increases gene frequency
• Kin selection defines altruistic traits where an altruist helps relations increasing survival of shared copies of particular genes with some cost to themself
• Alleles that promote caregiving can have a net-benefit to the population due to the frequency of caregiving alleles in offspring

Individual Selection

• Traits do not evolve ensuring the survival of a species
• Natural selection lacks forethought or focus on the future
• Traits evolve by individual selection; the reproductive success of individuals and not the species is the main focus

Group Selection

• Altruistic behavior doesn't evolve if it decreases reproductive success even if it benefits a wider population
• Genetic compositions between groups might evolve depending on survival rate, allowing specific traits to evolve

Individual vs Group Selection

• George Williams advocated that individual selection usually triumphs because the rate of reproduction is faster than in populations
• Most evolutionary biologists believe most traits evolve by way of individual or kin selection, instead of ensuring benefit to a wider species

Species Selection

• Species selection is based on species characteristics, and will affect rates of extinction or speciation
• Species selection influences the variation among biological characteristics, not on adaptations

Changes from Species Selection

• Species selection creates changes in the proportion of species with given traits over time
• Asexual lineages are usually shorter and closely resemble sexual lineages to a degree suggesting asexual lineages don't survive for as long

Adaptation

• Adaptation is an evolutionary process and a characteristic that increases survival or reproduction
• A characteristic must improve fitness with respect to its ancestry to be an adaptation

Adaptation Examples

• Preadaptation is a feature that can accidentally serve new functions
• An exaptation is a feature that is adapted for a new function
• Over time, exaptations will be refined through natural selection

Selection of vs. Selection for

• Specific traits are selected in order to enhance fitness, but may cause incidental side effects or incidental traits
• Discussing form and function implies natural selection

Recognizing Adaptations

• Not every characteristic should be considered an adaptation
• Traits can be the products of chemical or physical law
• Traits may also result from genetic drift, therefore, not from natural selection
• An adaptation might be the direct result of a phylogenetic history

Complexity

• It is often assumed that a complex biological feature is a direct adaptation for an environmental selection pressure

Design

• In order to accomplish a task, it is inferred that the function of a feature corresponds with the design an engineer might use, or with model predictions

Experiments

• Experiments can show if a biological feature increases performance, reproduction, or an organisms survival

Comparative Method

• By comparing species, the comparative method assists inferring adaptive significance of particular feature
• Convergence is observed in order to establish a better understanding how similar features can evolve on many separate occasions across separate evolutionary pathways

Imperfections and Constraints

• Selection fixes genetic variants with higher fitness relative to other variants, but it may not be the best fitness possible
• Natural selection can only select from existing traits
• Evolutionary perfection is limited by constraints such as trade-offs
• Lack of fitting mutations or lacking genetic variation keeps adaptations from evolving

Phylogenetic Constraints

• Phylogenetic constraints cause species to retain nonadaptive traits, or prevent adaptation

Evolution of Diversity

• Organisms have suited characteristics to deal with tasks that depend on different contexts
• Selection pressures base themselves on the physical environment, prey, predators, and competitors to drive selection

Competition and Divergence

• Competition for resources causes species to diverge
• Character displacement occurs when species that interact and diverge reduce competition
• Adaptive radiations are when different species diversify in order to exploit resources in a wider area

What NOT to Expect from Natural Selection

• Natural selection favors genes with the highest reproductive success and selfishness
• Selfish behaviors, such as territory defense and parasitism, occur naturally
• Explanations like kin section are found in situations where there is cooperation

Morality and Natural Selection

• Natural selection does not have morality, it just describes differences in reproductive success
• Behaviors that benefit a species cannot be produced by natural selection for ones own good

The Nature of Behaviors & Natural Selection

• Behaviors that help other species occur due to deception or benefiting the individual that performs the act
• Harmony is not needed for Ecological balance, species will simply adapt to the environment

How adaptation works in ecosystems

• The drive for ecosystems to to work effectively arises from competition, not from an ecosystem making a point to work better

Explore natural selection and adaptation, focusing on snakes' unique features like flexible skulls and jaws for swallowing large prey. Learn how these adaptations, driven by natural selection, enhance survival and reproduction, challenging traditional views of design in nature.