Category Archives: Evolutionary Biology

People have big heads, but children have giant heads.

A human is born with more neurons than they will have as adults. This is one of the main reasons that the size of the head of a child is not going to increase much as it grows. (Also, it is simply hard to make heads get bigger for various reasons, so it isn’t just humans that have large heads relative to body size when they are young.)

A person’s mass (weight) which roughly relates to volume goes up about 900% during growth. A person’s head circumference goes up about 35%. Big difference, even if you factor in the dimensional effect.

Try this: Find a small child. Preferably, your own, or if not, get permission. Show the child how you can touch your ear with the contralateral hand, by arching your arm over your head. Then, ask the child to try it. LOL.

This phenomenon, of head growth vs. body growth, comes up every time I teach about brain development, which I just did. And, it happens that right after doing that, I came across an interesting photograph. The photo is from a set of comparisons, putting an old family photo of one or more people when they were kids, to now, matching setting, clothing, props, body position, and facial expression.

When you do that, you see the head size thing really clearly in many photos. This one in particular shows it dramatically:

If you use the person’s right shoulder to help define her coronal plane, and visually project that onto the bricks, you can see that her head is close to three bricks tall in both photographs.

(I think the setting is not the same in both photos, by the way. Different bricks, different almost everything. But the person is the same, and that is what counts.)

Whitey Bulger Dead, and the Trivers Willard Hypothesis

The original version of this post was called “Whitey Bulger Caught, and the Trivers Willard Hypothesis.” A while after that, I wrote a post called “Whitey Bulger Convicted, and the Trivers Willard Hypothesis.” Today, it was announced that Whitey Bulger, Boston crime boss, is dead at 89. Thus, the new title.

Thumbnail image for 0470656662.jpgMost of you won’t know who Whitey Bulger is. He was for a while on the FBI’s ten most wanted list. He spent a lot of time overseas running from the Feds, but they eventually caught up with him, convicted him, and tossed him in jail.

Whitey was top dog in Boston’s Winter Hill gang. His brother was a Senator for the Commonwealth of Massachusetts, and served as Senate President for several years.

It is said that Whitey was an FBI informant, and that his handler, FBI Special Agent John Connolly, tipped Whitey off that he was about to be indicted on racketeering charges. No problem. Whitey had left stashes of cash in safe deposit boxes all around the world, in preparation for the day he had to go on the lam. So he took off in 1995. Special Agent Connolly spent several years on vacation in the stir.

I remember when Whitey disappeared, and ever since then, I’ve used him almost annually in lecture material describing the Trivers-Willard hypothesis. It goes like this:

Thumbnail image for 0470656662.jpgThe Trivers-Willard model (I prefer to call it a “model” rather than a “hypothesis” because it is not specific enough to really be a hypothesis … it’s a model that generates lots of hypotheses) states that selection should favor the ability to differentially bias investment in offspring by sex if the two sexes have differential variances in reproductive success, and if there is any way to predict offspring rank. That’s a bit thick, so it requires some examples and further explanation. Maybe a story about a mobster would help..

OK, so an example: Red deer (also known as Elk) give birth to one offspring (max) per year. Males compete for access to or to be chosen by females. So, only a small percentage of male red deer mate in a given year, a significant percentage may never mate at all, and a very small percentage sire many many little red deer. Male red deer have a high variance in reproductive success. If you tried to predict how many offspring a given randomly chosen male would have, knowing nothing at all, your best guess would be the average number of offspring red deer have in an average lifetime. But you would be wrong almost every time because the actual number is highly variable. Male red deer have high variance in RS.

Females, on the other hand, have a pretty standard number of offspring. There is not much competition among them, they can always find a male to mate with, etc. If you needed to guess how many offspring a particular randomly chosen female red deer would have in a life time, you could guess the average, and you would be right on or very close. Female red deer have low variance in RS.

So, male and female red deer have differential variance in RS. Males high, females low.

If a female red deer could somehow “predict” the likelihood of her offspring getting to mate, i.e., if she could tell if any offspring she had in the present year (male or female) would be average vs. high ranking, then selection should favor the evolution of a mechanism to actually give birth to the appropriate sex offspring (thus biasing investment in one sex or the other). It turns out that she can. A female red deer that is herself average or lower-quality (thin, ill, injured) is likely to give birth to an offspring that will be either low ranking or average. But if the mother-to-be red deer is high ranking, she is likely to give birth to an individual who will grow up to be high ranking.

Under these conditions, she should have a female offspring if she’s average or low ranking, but a male if she’s high ranking. And that, it turns out, is what red deer actually do.

That should be clear. But in case it isn’t, let’s take it down do real life, and bring in the gangsters.

You check the mail this afternoon, and there is a letter from a law firm you have never heard of. It says that your Great Aunt Tillie (whom you’ve also never heard of) just died, and left you with $1,000 in her will. The check is enclosed.

Thumbnail image for 0470656662.jpgThis may or may not be a recent photograph of a male red deer. Holy crap. Found money! What are you going to do with it? So you and your close advisors (your roommates, your cat, etc.) discuss it and you narrow it down to two choices. Choice A and Choice B.

Choice A is to go to your broker and buy $1000 worth of a nice, relatively safe mutual fund. The fund will buy and sell reliable blue chip stocks, thus spreading the risk over several companies, and over time you can expect to get a return of 50 bucks a years, easy.

Choice B is to buy 1000 one dollar lottery tickets. Your chances of winning are slim, but if you do, you will win 87 million dollars.

So, what do you do? The obvious sane choice is to buy the mutual fund.

But what if your cousin is Whitey Bulger? Whitey Bulger, as head of the Winter Hill Gang, is said to have owned the director of the Commonwealth Lottery agency.The connection between Whitey Bulger and the Lottery has never been proven. They don’t have a shred of evidence. He was, however, indicted for 21 counts of RICO-Murder. It is said that one of the things that tipped off authorities about this is that some of his relatives were winning the lottery a little more often than they should have. So, say your cousin is Whitey Bulger, and last time you saw him (at a family wedding) he told you … “hey, if you ever want to take a “chance” on the lottery, let me know … I can make that work for you…”

So now, you have two choices.

Choice A: Invest in a mutual fund and gain a return of 50 bucks a year (that’s dollars, not elk); and

Choice B: Buy 1000 PowerBall tickets and have a great deal of certainty of winning 87 million dollars.

What would you do?

In case it isn’t already clear. the baby male elk is a lottery ticket, the baby female elk is a mutual fund, but the female can guess pretty accurately if the lotter ticket (male offspring) will pay off. Because the elk’s cousin is Whitey Bulger. See?

How to choose the sex of your baby.

In order to make such a momentous decision, I insist that you learn the very interesting evolutionary biology behind it.

Start with this paragraph:

But for modern medical science, a baby’s sex would remain unknown until birth. But many mothers today know long beforehand whether a baby will be male or female. Routine ultrasound scans reveal fetal genitals a third of the way through pregnancy, and genetic tests identify sex even earlier. Yet basic questions remain. Is a baby’s sex like coin tossing, or can the male:female ratio be skewed? If sex bias occurs, does it happen through sperm sorting before fertilization or mortality differences in the womb after conception?

Then, CLICK HERE to read the rest of the story, by Robert Martin, expert on such things.

The Origin of Life and Life on Other Planets

The Origin of Life and Life on Other Planets

Several parallel discussions inspire me to write this post partly in the hope that you will chime in.

The chance of life elsewhere in the universe just went to near zero. Or did it?

Continue reading The Origin of Life and Life on Other Planets

NPR: For Every Woman Who Dies In Childbirth In The U.S., 70 More Come Close

This latest in a series of reports from NPR is out.

Over the past year, NPR and ProPublica have been investigating why American mothers die in childbirth at a far higher rate than in all other developed countries.

A mother giving birth in the U.S. is about three times as likely to die as a mother in Britain and Canada.

In the course of our reporting, another disturbing statistic emerged: For every American woman who dies from childbirth, 70 nearly die. That adds up to more than 50,000 women who suffer “severe maternal morbidity” from childbirth each year, according to the Centers for Disease Control and Prevention. A patient safety group, the Alliance for Innovation on Maternal Health, came up with an even higher figure. After conducting an in-depth study of devastating complications in hospitals in four states, it put the nationwide number at around 80,000.

I’m not going into great detail about this, but I do want to make a few related salient points. Continue reading NPR: For Every Woman Who Dies In Childbirth In The U.S., 70 More Come Close

Yet Another South American Alien Turns Out To Be Human

But a very interesting human. A human being six inches tall (if standing), with only 12 sets of ribs, about 7 years old at the time of death. Did I mention six inches tall? New research on the so called “Atacama humanoid” (not an alien, just a human) shows a wide range of interesting genetic differences, according to a just published paper. Continue reading Yet Another South American Alien Turns Out To Be Human

The Early Bird Crushes The Egg

Model I birds, the kind that lived during the Age of the Other Dinosaurs, may not have brooded their eggs. Today, birds sit on their eggs in such a way that the adult bird’s down surrounds the ovoids, and warmth from the adult can keep the eggs at a constant temperature. Depending on the bird, you may find additional intersting adaptaitons. For example, Penguins use their own feet as a nest, placing the egg there. One adult broods the egg for a long period (days, in some species) and then swaps with the other adult, with the swapping being very ritualized in some cases. Like this egg swqap between parent Adelie penguins (Tip: this video does not show the actual swap): Continue reading The Early Bird Crushes The Egg

Strange Survivors: Book Note

Strange Survivors: How Organisms Attack and Defend in the Game of Life by Oné R. Pagán is an excellent book with the evolutionary arms race, competition, and nature red in tooth and claw (and many other parts) as its theme. Well written and humorous, and scientifically accurate.

Mike Haubrich and I interviewed the author, and the Ikonokast Podcast of that interview IS HERE.

From the Publisher: Continue reading Strange Survivors: Book Note

Sexual Selection Up To Date: A Taste for the Beautiful

A Taste for the Beautiful: The Evolution of Attraction is a popular science book written by an actual expert on the field, addressing the ways in which the world of animals is shaped by sexual selection.

One of Darwin’s major contributions to the panoply of theoretical and observational work we call “evolution” was to recognize, describe, and model sexual selection. Continue reading Sexual Selection Up To Date: A Taste for the Beautiful

Darwin Quotes, Assembled

From Janet Browne, the author of Charles Darwin: A Biography, Vol. 1 – Voyaging and other works about Charles Dawin, The Quotable Darwin.

Quotes by Charles Darwin are not just the stuff of memes. Even the fake quotes. They can be the center of long arguments, or at least, they can significantly augment the arguments. For example, did you know that while Darwin never used the term “missing link” he did talk about missing links quite a bit, missing links are central to his thinking about evolution, and all those writers of today who claim that we must never speak of missing links are misguided? Continue reading Darwin Quotes, Assembled

Gene Therapy Is Starting To Be A Real Thing

Today, the an FDA advisory committee recommended that the FDA approve full clinical trials for a type of gene therapy that addresses a rare genetic condition causing deterioration of the retina. This is found in 8.6×105 of people world wide, so not many. the therapy involves injecting a virus bearing the preferred copy of the gene, the non-broken allele, into the eyeball, where the new gene somehow reduces, stops, and seemingly reverses, the deterioration.

The therapy was previously looked at in a preliminary study with a small sample of people. Here is the abstract from that study: Continue reading Gene Therapy Is Starting To Be A Real Thing

How long is a human generation?

How long is a generation, you ask?

Short Answer: 25 years, but a generation ago it was 20 years.

Long answer: It depends on what you mean by generation.

In US-biased Western culture there is a Biological Generation, the Dynamic Generation, the somewhat different Familial Generation, what is sometimes called a Cultural Generation but that should really be called a Societal Generation, and then there is the Designated Generation and finally, the Historical-Long Generation. You will find some of these terms identified on genealogical web sites, Teh Wiki and elsewhere, and some of them are introduced here. (References provided below.)

More broadly speaking, humans have identifiable meaningful generation-related terminology and cultural concepts in many but not all societies, and when it does occur, it is more common to find the concept in age-graded societies or societies in which marriage arrangements are fairly strictly enforced (or at least strongly hoped for) by the ascending generation.

A Biological Generation


…is simply the unscaled transition from one parent to one offspring. In humans, the Biological generation does not have a standard length but there are limits. So you are in one generation, your mother the previous, your child the next one after you, etc. regardless of when any of you were born. As long as your Uncle Willard does not marry your Sister Betty Jean, this is not complicated; This is what people often mean when they use the term “generation” but not what they mean when they ask the question “how long is a generation.”

A Dynamic Generation


…is a concept used by anthropologists but not usually with this term. This is similar to the biological generation but applied more broadly across a group of people. You (Ego) relate to everyone else of your age as being in your generation (your siblings, your parents siblings children, etc.). The first ascending generation (your parents and those in their generation), the second ascending generation (grandparents and their generation) etc. go one way in generational time. Going the other way, your children and their generation are the first descending generation. Your grandchildren and their cohort members are the second descending generation. Etc.

Those methods of reckoning generations have to do with the relationship between people. Another reason to reckon generations is either to do demographic (or economic) analysis or to test and analyze genealogies. For this you want to know how long a dynamic generation (or a biological one) usually is. For instance, a genealogist wants to know this: From the point of view of some long-dead relative, is the time span between the birth date of a grandparent and the birth date of a great grand child … thus, the span of time of four complete generations … reasonable? If such a span is 200 years, that means that an average of 50 years time passed from birth of a person to that person giving birth to the person in line. Implausible. If the total span is 40 years, that means ten year olds were having babies (on average). Also implausible. Either way, some part of the hypothetical genealogy is messed up and it’s back to the church records, vital statistics, and Mormon database for you. This is a Familial Generation.

In the “old days” (whenever that was) people often used the value 20 to represent Familial Generations. So, a person born on the first day of a century may well have had a great great great grandparent born around the beginning of the previous century. Today, with lager age at first birth for women being the rule, we tend to see 25 years as the recommended estimate for Familial Generations.

A Cultural or Societal Generation


…is a cohort (a bunch of people born during a specified range of time) with a name that has some sort of meaning to those who use it. The following are widely recognized, given here with the midpoint of the generally accepted range of birth dates:

  • Lost 1914
  • Greatest 1923
  • Silent 1935
  • Baby Boom (Boomers) 1955
  • Generation X 1968
  • Generation Y 1975
  • Generation Z or I 1992

(See comments below for people fighting about these names and dates. I accept Teh Wiki as the final word on this, so I take this list as perfectly accurate and complete.)

Several things are noticed in this list. The first three relate to major historical events (World Wars, the Great Depression) while the later ones are vague, stupid, and obviously little more than lame attempts by people who wish they were part of a generation to name themselves. This leads to the X and Y generations to be floating in broader time ranges (see Teh Wiki) and very arguable. The Z generation is clearly an afterthought. I assume everyone was so focused on the Millennium that they forget to be in a generation for a decade or so, and then had to catch up.

Some of the more primitively sexy and exotic tribal cultures of the world of the world have a strict age grading system. This is where individuals are in a specific age-defined stratum, and there are several strata. Often there are different age-grades for males and females, and often there are more age-grades for males than females. Individuals of a particular age grade always X and never Y (fill in cultural prescriptions for X and cultural proscriptions for Y). The Pokot of East Africa are one example. These age grades can be termed Designated Generations and include not only groups like the Pokot but also Americans who have very strongly age-graded designations.


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Among the Pokot males of a certain age wear a certain hairdo. Males of a certain generation get married. All the important things you can do or not do are defined by one’s age grade. As young men age they want to move to the next age grade, and often take serious risks to do so. In one Pokot group, the boys of one age grade would typically wear the hairdos of the Ascending Generation. Males in the Ascending Generation would then beat the crap out of them. When the beatings became too common and severe (sometimes deadly) the Ascending Generation of the Ascending Generation (the “Elders”) would declare that it is time for everyone to move up one generation, and a ceremony would be held.

In that particular group the ceremony applied to many different villages, and representatives from each village had to bring to the major chief’s village one head of cattle. The cattle were all slaughtered and the fresh meat laid out on racks to be guarded from lions and hyenas overnight by the chief, alone. If any of the meat was taken by predators, the chief was fired and a new chief appointed, everyone was sent home and were required to return with a fresh head of cattle, and the ceremony was re-started with the new chief. But I digress.

The Historical-Long Generation is my own invention. This is the period of time that is just short enough for a person to have a conversation with another person about shared memories where those memories are separated in time by the maximum amount possible for our species. Let me explain further:

Just today, the last surviving US veteran of World War I died. When I was a kid, I went to (or marched in) parades in which there were lots of veterans. Most vets in the parade were of World War II. Korea was not ever represented. The Viet Nam Vets were busy in Viet Nam being Viet Nam soldiers, so they were not in the parades. But World War I was represented by the grandpas and there were a lot of them.

And, leading all of the veterans in the parade was this one guy who looked quite dead, eyes closed, not apparently breathing, wearing a 19th century Slouch Hat and covered with a blanket and slumped in wheel chair pushed by members of the VFW Ladies’ Auxiliary, and he was the only remaining veteran in town of the Spanish-American War. I know he was not in fact dead because he was in the parade several years in a row. That war was in 1898, and the parades I remember must have been from the mid 1960s. I assume he was a drummer boy, perhaps 10 or 11 at the time of the war. The last surviving vets from Civil War were similar: Boys who served in the military as aides or drummers. The point is, one could argue that a historical-long generation is about a century, because that old guy and I share involvement in an event … marching in those parades … that link two memories, the parade and the war, which were about 100 years apart.

I have an even better memory. The Emancipation Proclamation was signed on Januray 1st, 1863. When that happened, a toddler who’s last name was Alexander and who was born as a slave in the Carolina’s became free. Later, his family moved to Albany, New York. In around 1968 or 1969, my father asked me to accompany our congressman, Representative Samuel A. Stratton (famous for introducing the bill to give us Monday Holidays, I am told) to an old tenement building in “Teh Ghetto” and bring him up to the third floor to meet Mr. Alexander, the now old former infant slave. I did so, and we all chatted for a while. I was about ten, and Mr. Alexander was closer to 110. He had memories of the assassination of Abraham Lincoln that were similar to my memories of the assassination of John F. Kennedy: Vague, mostly about the aftermath and not the event so much, but seemingly real. We shared memories that were a century apart in time, and in this case, interestingly parallel.

So, the Historical-Long generation is a century. If you meet me and shake my hand, you are shaking a hand that has shaken the hand of a man who was an American slave. Meaningless, yet profound.

Fox, Robin.Kinship and Marriage: An Anthropological Perspective (Cambridge Studies in Social and Cultural Anthropology)

Lutz, Catherine. Reading National Geographic

Teh Wiki. Generation.

Teh Wiki List of generations.