Yearly Archives: 2007

An Evolutionary View of Humans 1: Introduction

Evolutionary Biology, Palaeoanthropology, ,
Efe people
Ituri Forest
Anthrophoto is an
excellent source for
anthropology stock
photos

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 An Evolutionary View of Humans 1: Introduction →

The Evolution of Modern Human Mating Systems and Sexuality

Uncategorized,

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 Modern Human Mating Systems and Sexuality →

The Evolution of Human Diet

Uncategorized, , ,
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 The Evolution of Human Diet →

How to think like an evolving organism.

Evolutionary Biology

<img style=”margin: 10 5px 2px 0; float: right;”img src=”http://gregladen.com/wordpress/wp-content/graphics/OrganismThinking.jpg” width=”200″ ” alt=”” title=”” />
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 How to think like an evolving organism. →

The Modes of Natural Selection

Uncategorized,

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 Modes of Natural Selection →

The Three Necessary and Sufficient Conditions of Natural Selection

Uncategorized,

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 The Three Necessary and Sufficient Conditions of Natural Selection →

Let The Eagle Soar

Uncategorized
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 Let The Eagle Soar →

Noah or NOAA?

Uncategorized,

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 Noah or NOAA? →

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

Evolutionary Biology, Gender, Reproductive Biology, Sex

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

Of skinks and monkeys

Animals, Evolutionary Biology

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 Of skinks and monkeys →

Thinking of Global Warming

Climate Change, , ,

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 Thinking of Global Warming →

Jolly ol’ England

Falsehoods and Skepticism

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 Jolly ol’ England →