The Elements of Evolution – Behavior


The assertion that “culture” explains human variation will be taken seriously when there are reports of women war parties raiding villages to capture men as husbands, or of parents cloistering their sons but not their daughters to protect their sons’ virtue, or when cultural distributions for preferences concerning physical attractiveness, earning power, relative age, and so on show as many cultures with bias in one direction as in the other. ~ American anthropologist John Tooby

Behaviors have a biological basis. Mentotype is an entangled partner with phenotype and envirotype (environmental influences).

Female frogs prefer males that produce loud, fast, continuous calls, as these indicate a healthy mate. Such flamboyance also risks attracting predators. Boisterous frogs that don’t croak from such croaking must have something on the ball.

The poison frogs of Central and South America evolved conspicuous colors and patterns to advertise their unpalatability. The more toxic a frog, the more graphically noticeable it is, and the louder and prouder it sings.

Personality is a product of mentotype. Variations in individual behavior patterns offer an evolutionary edge. The herd instinct may generally serve a population, but when times are tough, it is often individuality that engenders survival.

 Attitude Counts

The bottom line is that he was much smaller, and eagles always prey on things that are weaker than them. ~ Canadian ornithologist David Bird

In the spring of 2017, a bald eagle on Vancouver Island in Canada brought home to its chicks something tasty for dinner: a red-tailed hawk chick. Dumped into the nest, the little red-tailed hawk found itself among 3 bald eaglets 4 times its size.

Unintimidated, the tiny hawk felt like having a meal rather than being one. Showing spunk instead of fear, the hawk chick insistently begged to be fed. The eagle parents obliged.

My guess is that this little guy begged loud and hard for food; not even thinking about the danger. Food overrides everything in these birds. He begged away and mom and dad said, “OK, here’s an open, gaping beak. Let’s put food in it.”

If the eaglets happened to get hungry it would have been curtains, but there was always lots of food in the nest. That and the hawk’s attitude, being aggressive. He was running through the legs of the 3 eaglets and taking food from their beaks. ~ David Bird

It’s quite something to see the way the hawk is treated. The parents are quite attentive. The eagle nestlings are keeping their distance – they know it is something different. ~ Canadian ornithologist Kerry Finley

Within a few weeks, the eaglets had grown used to their scrappy little nestmate.

The eaglets that he was raised with seem to have accepted him as another sibling, and the parents seem to have adopted him as their young. ~ David Bird


Ethology is the study of animal behavior, particularly patterns that occur in natural habitats. From an evolutionary perspective, ethology covers individuals (evolutionary psychology) and groups (sociobiology).

How individuals relate to one another affects both personal and social dynamics. Consistent patterns in these behaviors characterize species sociality.

Human Mating Strategies

In all comparative analyses, humans always fall on the borderline between obligate monogamy and polygamy. While males are more promiscuous than females overall, within-sex variation of these variables is best described by 2 underlying mixture models that slightly favours monogamy in females and promiscuity in males. The presence of 2 phenotypes implies that mating strategy might be under complex frequency-dependent selection. ~ English psychologists Rafael Wlodarski & John Manning, & English anthropologist Robin Dunbar

Men are generally more promiscuous than women. This owes to males having greater reproductive success by their sowing seeds in multiple fields. Meanwhile, women do better reproductively in taking care of their progeny. That withstanding, human mating strategies are more complicated than that. Fidelity is not solely a womanly virtue. Many men are reliable dads and many women sexually stray.

More generally, both sexes adopt distinct mating tactics. From a population perspective, the ideal mating strategy for either sex favors some diversity.

The extreme altricial nature of human offspring means that the optimal population prospect would be for most men to be good fathers. Women may not have more offspring through extra pair-bonding, but the extracurricular activity does produce greater genetic diversity.

One advantage to this comes in disease susceptibility. All the eggs in one genetic basket means a greater chance of one’s progeny being wiped out by an infectious disease outbreak. Better to hedge the bets.

Male cads outnumber dads by a ratio of 57:43. Females with fidelity outnumber loose women by only 53:47. These equilibria correspond with optimal results that might be obtained via game theory, which is the mathematical study of strategic decision-making. At the population level, human mating behaviors follow a coherent mathematical rule set. This statistical coincidence of optimality is mysterious.

Parasitic Ants

Parasitism is the most common lifestyle on Earth. Parasites target hosts across the spectrum of life, from single cells to individuals to societies. Hosts fend off assaults via constitutional defenses, physiological responses (immune systems), and behaviors.

Colonies are especially attractive, as they contain rich resources by their high densities of hosts. Some social insects evolved to parasitize other social insects.

Social parasites are especially common among ants, where they appear in 3 categories: slavers, resident inquilines, and provisional inquilines. Permanent inquilines coexist with their host colony. Slave-making ants raid other colonies to capture and enslave their brood.

Temporary inquiline queens invade a host colony, kill its queen, initiate egg-laying, and rely upon the brood care behaviors of host workers to succeed. Parasitic success spells the loss of the host colony’s reproductive output. Social parasite queens exhaust a colony after a generation – enough time to produce parasitic prodigy which proliferate to other nests.

A provisional parasite queen needs to be able to enter the host colony, be accepted by host workers, and ensure that the host workers rear her offspring. The first line of defense is detection of an intruding queen, either by looks, behaviors, or chemical cues. Evolved camouflage and mimicry can defeat the initial opportunity by hosts to avert a dire fate.

Once a parasite queen is established, targeting the alien offspring is the only way a host colony may recover. The onus falls upon host larvae, who can save the colony by eating the eggs of the parasite queen.

Larvae participate in post-infection defence by selectively removing parasite eggs, thus acting as a 2nd line of defence. ~ Finnish evolutionary zoologist Liselotte Sundström et al

Adult ants smell with their antennae, which larvae lack. How larvae discriminate between the eggs of sisters and those that pose to a threat to colony survival is not known, but a critical element is precocious knowledge: innately understanding the situation and knowing what to do.

Parasitic Manipulation

From viruses on up, many parasites manipulate host behaviors to their whims. How these parasites adaptively learned their Machiavellian tricks is empirically inexplicable.

Endoparasitic flukes induce ants to move up onto blades of grass during the night and early morning. There the ants rigidly attach themselves with their mandibles and are consumed during the day by grazing sheep, the fluke’s final host.

Terrestrial insects parasitized by hairworms commit suicide by jumping into water, where the adult worms reproduce.

 Caterpillar Bodyguards

Braconid wasps lay their eggs in caterpillars. The eggs hatch and the parasitoid larvae feed on the body fluids of their caterpillar host. (The specific characters in this story are the braconid parasitoid wasp Glyptapanteles sp. and Thyrinteina leucocerae caterpillars, which are in the geometer moth family (Geometridae).)

The caterpillar continues feeding, moving, and growing, seemingly unfazed. Full grown parasitoid larvae emerge together through the host’s skin and start pupating nearby.

The caterpillar is still alive but brainwashed. It stops feeding and becomes a bodyguard: protecting the wasp pupae against predators with violent head swings. Protect-and-serve caterpillars expire soon after the parasitoids emerge from their pupae as adults: fortuitous timing for the wasps.

Baldwin Effect

In 1896, American psychologist James Baldwin suggested that learned behavior can affect evolution: a Lamarckian-like effect that was long ignored. Only the discovery of epigenetics in the late 20th century opened the door for the Baldwin effect to be taken seriously by most evolutionary biologists.

The development of lactose intolerance in human populations with a tradition of dairy farming is a commonly cited example of the Baldwin effect.

Parenting exemplifies the Baldwin effect, which house finches illustrate.

 House Finches

The house finch is a small songbird, once endemic to western North America, ranging latitudinally from southern Oregon to Oaxaca, Mexico, and as far east as southwest Wyoming. Then humans inadvertently decided the little birds deserved a broader range.

In the 1850s, a small number of house finches from coastal California were introduced to Oahu. By the turn of the 20th century, house finches were abundant throughout the Hawaiian Islands.

In the 1930s, to avoid prosecution for illegally selling birds, pet store owners released ~100 house finches in New York City. By 1995, they had spread across the eastern US and southeastern Canada.

Meanwhile, during the 1940s–1950s, western house finches expanded their range. In 2002, western and eastern house finches met in Montana for the first time.

This geographical expansion was accompanied by rapid divergence. In some instances, new populations differed in various traits, such as sexual dimorphism, by up to 2 standard deviations from the mean in less than 10 generations.

This wide radiation can only be accounted for by female mating selection and breeding success which reflects maternal care quality. Female mating preferences and mothering behaviors brought forth the great diversity of house finches during the 70 years that were the fastest dispersal of birds in modern times.