An Evolutionary View of Humans 5: The Opposite Sex

Efe people
Ituri Forest
Anthrophoto is an
excellent source for
anthropology stock

There have been many studies of what impresses us about members of the opposite sex, but to my knowledge these studies are largely centered on Western societies, and never of foragers. There has been consideration of this issue, but no large scale surveys. One of the reasons for this is that you can’t do large scale surveys in so-called “small scale” societies, because there are just not enough people.

But I can provide a few insights on what might be impressive to the ladies (things about men) in forager societies. Keep in mind, however, that this is strictly speculation, though informed speculation.

I had previously talked about sharing, and here I’d like to expand on one aspect of sharing … the so called “distribution and redistribution system,” and it’s meaning in relation to courting.

There is a pattern that has been observed in virtually all forager groups, whereby men divide up the spoils of the hunt in a certain, largely ritualized way, then pass these packages of meat over to the women, who then redistribute the meat in a manner commensurate with the needs of members of the group. I’d like to describe how this works specifically with the Efe Pygmies as an exemplar for foragers in general. Many aspects of what I’m describing here are nearly universal among foragers. Moreover, I’m going to specifically talk about “group hunting” when several men are involved in one cooperative hunting episode. However, the principles involved here actually apply to other forms of hunting as well, to varying degrees.

The most common Efe group hunt is called “mota.” In this method of hunting, a number of men spread out in the forest to surround an area, with one man (the “beater”) going to the center of this area with one or more dogs. The dogs are released by the beater, sent out into this area and called back again and again. Game that is roused by the dogs are then subject to being shot at with arrows by the archers who had previously spread out. If an animal is hit, help from other hunters or from the dogs may be solicited, and the animal run to ground and dispatched.

The animals are usually carried back to Continue reading

An Evolutionary View of Humans 4: Sharing

Efe people
Ituri Forest
Anthrophoto is an
excellent source for
anthropology stock

One of the biggest differences between our nearest living relatives (The common chimpanzee, Pan troglodytes) and humans is our unique sense of the importance of a social contract. We have a concept of ownership, possession, exclusivity of access, etc. when it comes to material goods such as tools or resources, and of course, sexual relationships. It has been argued that this is a feature that can be found in primates. In a classic series of experiments done by Kummer with baboons, he showed that one male baboon perceived an ongoing sexual liaison between another male and a particular female. As long as the paired male was in sight, the focal baboon would not make sexual advances towards the paired female even though she was in a state of sexual receptivity. This was the case even when the focal male and the paired female were enclosed in a cage together, with the paired female enclosed in a different cage a safe distance away. Similar observations have been made in other primates including chimpanzees in captivity and in the wild.

However the presence of a vague ability to perceive danger … that you will likely be severely attacked by a large male under certain circumstances is expected in social primates. What Kummer’s experiment may really demonstrate is Continue reading

An Evolutionary View of Humans 3: Remembering Names

Efe people
Ituri Forest
Anthrophoto is an
excellent source for
anthropology stock

How good are you at remembering names? If you are really good … if you can hear someone’s name once and always remember it … you have a calling as a politician. If you would otherwise suck as a politician, but are good at explaining things, maybe a job as a teacher (but that requires other skills as well). In any event, you are a rare bird.

Humans have typically lived in small groups. This is especially true of foragers. Not only are these groups fairly small, but they are also fairly stable. The movement that does occur between groups is typically restricted to a larger “meta-group” consisting of a few different small groups. In other words, if you are a forager sitting around with the people you live with … the people in your “residence group” as we call it … the person sitting across from you is most likely someone whom you’ve known all your life (or visa versa, depending on your relative age).

Just as importantly, the total number of people you will know during your entire life well may stay in the hundreds. That’s total. Compare that to your own “Western” experience. Count the people in each neighborhood you’ve ever lived in (whom you knew), the people in all the different grades of school you’ve been in, and the people at all the different workplaces you’ve worked in. That is probably a large number. If it is a small number, then you don’t’ get out enough. You should get out more. At least go see a movie or something…

The point of this is Continue reading

An Evolutionary View of Humans 2: Sleep

Efe people
Ituri Forest
Anthrophoto is an
excellent source for
anthropology stock

There has been much recent discussion on sleep in the blogosphere, and everyone, especially those who sometimes have trouble sleeping, is interested in so called “sleep disorders.”

My understanding of modern sleep disorder theory is the following (very oversimplified): Each person has a “normal” amount of sleep that they seem to need each night. “Better” sleep is uninterrupted. You will feel lousy if you don’t get your sleep. However, if you miss the “normal” amount of sleep several nights in a row, you only need one “good night’s sleep” to totally readjust and get back to feeling normal again. (You don’t have to make up all the hours you missed … heavens, there IS a free lunch!)

Even the critical medical anthropologists are getting into this. I need to be careful here, because Continue reading

An Evolutionary View of Humans 1: Introduction

Efe people
Ituri Forest
Anthrophoto is an
excellent source for
anthropology stock

Humans have been indistinguishable as far as the fossil record shows from today’s Homo sapiens for a minimum of about 120,000 years. Bones of Homo sapiens from back this far fit into the range of modern humans. But the archaeological record suggests that our species – just as it is today – goes back farther. The kind of material culture that the 120,000 year old humans (in Africa) had goes back to 250,000 years. But some of the key aspects of that material culture … mainly in the way stone tools are made … go back even farther, perhaps between 350,000 and 500,000 years, in southern Africa.

(Interesting aside: People often wonder if Neanderthals evolved into modern humans. That questions seems a little dumb when we consider that the earliest modern humans predate the earliest Neanderthals.)

Humans invented agriculture (domestic plants and animals) only about 10,000 years ago or so, and at that time some groups started to live in permanent settlements. But even so, many humans continued to practice hunting and gathering as their only, or at least primary, means of subsistence. A mere 4 or 5 thousand years ago, half of the human species probably lived this way.

In other words, humans evolved as hunter-gatherers and have mostly been hunter-gatherers for for more than Continue reading

The Evolution of Modern Human Mating Systems and Sexuality

Professor Desmond Clark, the consummate British gentleman and Africanist archaeologist, was fond of telling his intro class “if we were chimpanzees instead of humans this class would be severely interrupted owing to the presence of at least one or two ovulating females in the room at this moment.” I never took a class from Desmond (different school) but this quip was passed on to me by Glynn Isaac, and Glynn has passed it on to all of his students, we to ours, and so on. So this little off-the-cuff joke is surely repeated sixty or seventy times per semester, worldwide.

But the point of this is not ribald humor. Among the great apes, we are odd ducks. Actually, we would not be so odd as ducks as we are as apes, because ducks are birds and our system of mating is far more bird-like than ape-like. Desmond was a contemporary and colleague of Louis Leakey, and part of the small group of well connected Africanists studying human evolution active in the mid 20th century. These scientists appreciated back in the 1950s and early 1960s that an understanding of ape behavior and ecology would be essential to understanding human evolution. This was an explicit effort to advance Darwin’s comparative methods. Louis Leakey was instrumental in setting up Birute Galdikas, Dianne Fossey and Jane Goodall for fieldwork in Southeast Asia and Central Africa. The fieldwork of these pioneers in ape studies has served, and continues to serve, this purpose: Placing human evolutionary biology in a firm comparative framework.

And it is from this place … the perspective of our nearest living relative, the chimpanzees … that humans are odd ducks in ways that demand an evolutionary explanation. Continue reading

The Evolution of Human Diet

Chimp, Australopith and
Human Teeth Compared.

The evolution of human diet followed a major zig (as in zig-zag) in a wholly unexpected direction, followed by the most significant biological innovation to ever occur among multi celled animals: The invention of cooking. I’m actually going to point you to two papers on this topic, and provide a brief summary of the ideas here.

Let’s start with the bold assumption that humans evolved from a chimpanzee-like animal. This is tantamount to saying that the last common ancestor of chimpanzees and humans was, essentially, pretty much like a chimpanzee. At another time, I’ll write a post on why this is a good assumption, but for now lets just go with it. Some large percentage of human evolution experts like this assumption, a bunch of others hate it (which is the usual pattern for most ideas in human evolution).

A mammal’s diet is reflected in physiological attributes that can be discerned from the fossil record. Body size, the nature of the teeth and associated muscles, possibly the shape of the mouth’s cavity, and even the overall size and shape of the gut may be closely connected with diet.

If we draw a direct line from a presumed chimpanzee-like ancestor to modern humans, Continue reading

How to think like an evolving organism.

In approaching evolutionary puzzles it is helpful to have certain thought-tools in mind. These are approaches to life, literally, including issues of survival, mating, and so on. My grad school advisor, Irv DeVore. used to tell his students to imagine what an animal would be thinking on first waking up in the morning (or evening if nocturnal) to get through the day: “How will I find food today? …. how will I avoid being someone else’s food? … Will I find a mate, or will one find me? …” (In writing that just now I can’t help but think DeVore may have been cribbing Jack London just a little.)

Anyway, here are some rules of thumb useful for thinking about both physical and behavioral systems.

Romer’s Rule. Romer’s rule is simply stated as “A frog is simply a fish trying desperately to remain a fish” Continue reading

The Modes of Natural Selection

There many ways of dividing up and categorizing Natural Selection. For example, there are the Natural Selection, Sexual Selection and Artificial Selection, and then there is the Modes of Selection (Stabilizing, Directional, and Disruptive) trichotomy.

We sense that these are good because they are “threes” and “three” is a magic number. Here, I’m focusing on the Mode Trichotomy, and asking that we consider that there are not three, but four modes of Natural Selection. This will cause tremors throughout the Evolutionary Theory community because Four is not a magic number, but so be it.

In Stabilizing Selection the extremes of a trait are selected against and the mean value of the trait remains the same. Mutations constantly introduced into the population tht produce traits out at the extremes are selected against. In Directional Selection the values of a trait at one end of the distribution are selected against and/or values at the other end are selected for, so that the distribution of values, and it’s mean, move in one direction. In Disruptive Selection the average values are selected against so that the distribution of the trait becomes bimodal.

That was pretty simple, but Continue reading

The Three Necessary and Sufficient Conditions of Natural Selection

Natural Selection is the key creative force in evolution. Natural selection, together with specific histories of populations (species) and adaptations, is responsible for the design of organisms. Most people have some idea of what Natural Selection is. However, it is easy to make conceptual errors when thinking about this important force of nature. One way to improve how we think about a concept like this is to carefully exam its formal definition.

In this post, we will do the following:

  • Discuss historical and contextual aspects of the term “Natural Selection” in order to make clear exactly what it might mean (and not mean).
  • Provide what I feel is the best exact set of terms to use for these “three conditions,” because the words one uses are very important (there are probably some wrong ways to do it one would like to avoid).
  • Discuss why the terms should be put in a certain order (for pedagogical reasons, mainly) and how they relate and don’t related to each other.

When you are done reading this post you should be able to:

  • Make erudite and opaque comments to creationists that will get you points with your web friends.
  • Write really tricky Multiple Choice Exam Questions if you are a teacher.
  • Evolve more efficiently towards your ultimate goal because you will be more in control of the Random Evolutionary Process (only kidding on this third one…)

Continue reading

Let The Eagle Soar

Golden Eagle

I hope I won’t disappoint you … this is not about John Ashcroft. It is about golden eagles (actually, maybe its about one golden eagle in particular).

The golden eagle (Aquila chrysaetos) has been in decline for a very long time, so you may not know it formerly bred in a much wider range of habitats, across the entire U.S. Today it is known as a mountain eagle because this is where it is generally found, at least in North America. Any experienced birder will tell you that in places like Minnesota nine out of ten, or maybe 99 out of 100 golden eagle sightings are immature bald eagles.

Last winter my wife, Amanda, and daughter, Julia and I attended a talk (on owls) at the Minnesota Raptor Center in Falcon Heights. While there we took a tour through the facility, where several captive birds are kept. Some of these birds are in rehab and will be released, others are permanent residents because of some major disability. As we were shown around, the gracious and knowledgeable volunteer told us “Golden Eagles are not native to Minnesota. You never see them here. We get a lot of people telling us they saw a golden eagle, but I guarantee you it is always an immature bald….” And at that moment we were directed around a corner to see, in all it’s glory, a majestic golden eagle in one of the enclosures. Now, this was just after the “all our birds are brought here by our people or game officers from locations all over Minnesota” speech, so I said … “Well, there’s one there … in that cage … a golden eagle. There must be some of them in Minnesota.” I was trying not to be snide, really. The volunteer made some sort of apologies for the eagle being there, admitted it was brought in from a site in Minnesota, but stuck Continue reading

Noah or NOAA?

Our faith based Federal Executive has been reluctant to admit to, let alone address, the fact that global warming resulting from release of fossil carbon into the atmosphere is a real phenomenon. It is a little surprising that today, NOAA came out with a press release that virtually admits that global warming is a real phenomenon (but stops short of discussing the cause).

The scientific community is generally united in recognizing the reality of this problem, but there are still holdouts. However, considering that so much of the funding related to this research still comes from industrial sources (as does much of the fossil carbon), that there are holdouts is not surprising.

This is a parable that may be insightful or even inspiring to some. First, a look at the “Yes, it’s real” position. One of the first mainstream institutions to embrace the idea was the Union of Concerned Scientists. This is an excerpt from their web site:

Earth’s surface has undergone unprecedented warming over the last century, particularly over the last two decades. Astonishingly, every single year since 1992 is in the current list of the 20 warmest years on record.[1,2] The natural patterns of climate have been altered. Like detectives, science sleuths seek the answer to “Whodunnit?” — are humans part of the cause? To answer this question, patterns observed by meteorologists and oceanographers are compared with patterns developed using sophisticated models of Earth’s atmosphere and ocean. By matching the observed and modeled patterns, scientists can now positively identify the “human fingerprints” associated with the changes. The fingerprints that humans have left on Earth’s climate are turning up in a diverse range of records and can be seen in the ocean, in the atmosphere, and at the surface

In 1999, James Hansen of NASA wrote an editorial for Goddard (GISS) that showed this graph:

Fig. 1: Climate model calculations reported in Hansen et al. (1988).

And provided this commentary: Continue reading

The Biology of Sex and Gender: What’s in a name?

This is the first of a series of posts on the biology of gender. This is a research interest of mine, and generally has a big part in my teaching as well.

Behavioral biology seeks to understand behavior in an evolutionary framework. The widely held central dogma of evolutionary biology is that selection works on allele frequencies. This leads to simple models of behavior that assume behavior is acted on by selection, and that underlying alleles are selected for or against over time. This sort of logic can be seen in biological racist doctrine, sexist racist doctrine, and more politically ambiguous research such as the famous twin studies, and about every other article in journals such as “Evolution and Human Behavior” (not that I have anything against that journal in particular … but … well, you’ll see…)

When thinking about the biology of behavior, a common guiding principle is that the stronger the effect, the “more biological” it is. There is a certain logic to this. If a certain aspect of, say, human behavior is observed over and over again, across cultures, and it is shown to persist even when social, economic, or cultural influences seem to work against it, then it makes sense that it is somehow predetermined. Continue reading

Of skinks and monkeys

I was recently looking at a practice AP biology test question on evolution, and sparing you the details, I found it interesting that two of the four parts dealt with genetic variation and speciation in such a way that it was difficult to tell them apart. As expected, students who answered these questions got confused as well, and tended to give perfectly good answers to Part B, but unfortunately, this was their answer to Part A. By the time they got to Part B they seemed a little confused, perhaps realizing that there was some overlap and conflation of concepts.

Inter and intra-specific variation is probably patterned such that the sum of variation among several species is greater than the partitioned variation within a given species. That’s pretty obvious.

(Just in case it is not: Imagine measuring the mass of several elephants. The variation can be represented by the standard deviation, range, or whatever you like, among your measurements. It is such and such. Now do the same thing with a bunch of mice. Again, you have some measure of variation. Now do it for the mice and elephants combined. Here, the variation will be larger than for either. This is not the same as if you want to compare variation or patterns of variation between mice and elephants. Do do that, you need to scale the variation, say by using the coefficient of variation. In this case, combining the coefficients of variation might show less variation when combined than for either group simply because of sample size effects. But what I’m talking about here is total variation. Mice are tiny, elephants are huge, so their total size variation runs Continue reading

Thinking of Global Warming

Amazingly enough, we (my family) are going to have to work very hard this year, as we did over the last two years, to get in even one or two good days of cross country skiing. And we live in the middle of Minnesota. This is partly because a good bit of the precip that falls on us these days is actually rain and not snow.

But this is of course a very selfish concern, to the extent that this change is related to human-induced global warming (which I’m betting on). And this reminds me of how often I get the question from students and others, “why worry about global warming … what’s wrong with a little warm weather anyway.”

For one thing I think it is safe to say that the “controversy” is over. No one is seriously questioning that there has been warming, that we are in a warming trend, and that this trend is caused primarily by human release of otherwise trapped (mainly fossil) carbon into the atmosphere. Nice to know that the Yahoos are pretty much silenced by the facts on that one…

Still, the question arises, “why is this important” … even in places where you might not expect it, like this discussion on the geology of the grand canyon: Another Timeline

There are a lot of resources available on this issue, but here is a short version of my two cents:
Continue reading

Jolly ol’ England

Old books can be wonderful sources of information, ideas, and even inspiration. I collect them and sometimes even read them. Reading a 100 year old book in your field of interest is a challenge and can be a rewarding experience.

It is a challenge because it is dangerous. I worry that I might accidentally learn something that is no longer true. What if I remember it at some later time, like at a cocktail party or while giving a lecture, but don’t remember the source: “… As is well known, flies spontaneously generate from certain forms of mud …” Continue reading