J.D. Moyer

sci-fi writer, beat maker, self-experimenter

Michio Kaku Should Stick to Physics (Evolution, Birth Control, and Mate Selection)

Future humans -- more attractive, more intelligent, more nurturing?

I’m generally a fan of the physicist Michio Kaku. I enjoy his speculations about the future of humanity, his realistic optimism, and his willingness to speculate about ideas from the realm of science-fiction. But recently, I watched a short video in which Dr. Kaku explained some of his ideas about evolution, and I found myself strongly disagreeing with a number of his points.

Here’s the post and the video:

Dr. Kaku says that:

1) Because of air travel, there are no more “islands” that divide humanity into disparate non-interbreeding groups (which would accelerate evolution).

2) Gross evolutionary pressures, those which would dramatically change human form and function, are pretty much gone.

We make our own islands; we rush to segregate along many lines.

Why Kaku is Probably Wrong — We Make Our Own Islands

First of all, let’s talk about “islands.”  Sure, we have air travel, and we have plenty of interracial couples and interracial children — so much so that it is unremarkable.  Roughly half the kids in my own neighborhood (in Oakland, California) carry genes that evolved on more than two continents.  So yes, we’re mixing up racially, and that trend is likely to continue.

The question is, do we make our own “islands” via cultural groupings?  How many children have parents that are from different social classes?  Different education levels?  Different political parties?

I don’t have the data, so I can’t answer the question definitively.  However, I suspect that human beings continue to erect cultural barriers that divide the “single gene pool” into multiple, only slightly overlapping gene pools.  Do social class or political party have any basis in genetics?  The question is irrelevant; if a cultural factor is keeping two groups apart (in terms of breeding) then those groups are as separate as Australia and Europe before air and sea travel.  The groups will evolve separately, and differently.

Why Kaku is Definitely Wrong — Gross Evolutionary Pressure

Dr. Kaku says that gross evolutionary pressures are pretty much gone.  We no longer live in the forest, we are no longer threatened by wild animals, and we no longer have to forage for food.

Kaku concedes that evolution is still occurring, but posits that evolutionary forces that change us radically, that are powerful enough to drastically alter our bodies and/or brains, no longer exist.

If that’s true, then why are we changing so rapidly?  In the last 40,000 years (roughly the beginning of human cultural evolution) we have seen an acceleration of human genetic change.  Human culture may remove certain environmental pressures, but it adds news ones.  The last few ten thousand years has radically changed the human genome, as related to skeletal form, dental structure, disease resistance, and digestive enzymes.  These changes are largely in response to switching from a hunter-gatherer (paleolithic) lifestyle to a agricultural (neolithic) lifestyle.

You might argue that acquiring the ability to digest dairy products into adulthood, or to more efficiently extract nutrients from grain products, does not constitute a gross evolutionary development.  Fair enough.  But there is another gigantic shift in human evolutionary forces that is changing us radically and quickly.

Female Sexual Selection

Widespread female contraception has been available to the majority of women for just a few decades.  The evolutionary consequence of this reality is that most women can now separate the choice of who they want to have sex with from who they want to have children with.

This changes everything.

Enhancing the evolutionary influence of mate preference.

For a man to successfully procreate, he now has to do much more than seduce a woman into bed.  She must also choose to have a child with him.  For most women, this choice will include a consideration of what kind of dad he will be.  In addition to his pure animal sexiness, she might consider factors like his reliability, intelligence, genetic predisposition to various diseases, his ability to be nurturing, his social status, etc.  While female sexual choice has always played a big role in human evolution, it’s now the primary driver.

Male sexual selection also plays a role, but it’s easier for a woman to find some willing sperm than it is for a man to find a willing womb.  In the U.S., roughly 80% of women end up having at least one child.  I can’t find a good statistic for the percentage of men with biological children, but in the past I’ve read it’s as low as 50%.  Still, male sexual selection is important too.  Men may value physical attractiveness in a mate more so than women, but many of the choice criteria (reliability, ability to be nurturing) overlap.

Birth control radically affects human evolution, because human mate preference now outweighs every other factor in terms of who “gets to” reproduce (I use the quotes because, of course, many people choose to not have kids).  The new evolutionary reality is sexual selection on steroids.  While sex partner selection has always been an evolutionary pressure, mate partner selection is a very new thing.

So What is the New “Fit”?

In our evolutionary past, “fitness” meant surviving until reproductive age, and for men, attracting a fertile sexual partner or taking one by force (finding a willing sexual partner has never been much of a problem for women, throughout our evolutionary past).

Today both those pressures are pretty much gone.  Most people, regardless of their genetic makeup, can survive until reproductive age.  Most people, at some point in their lives, can also find at least willing sex partner, regardless of their genetic makeup.  The huge hurdle, for both men and women who wish to procreate, is finding a mate that is actually willing and able to have a child with them.  “Fitness,” from an evolutionary perspective, is defined pretty much solely by this single criterion.

What does this mean for the evolutionary direction of the human race?

I think it means we’ll keep getting more attractive, smarter, more nurturing, and more reliable.  These are all factors that are important in both male and female mate choice.

Poor vision and color-blindness may increase, as this is easily corrected in the first case, and probably has little impact on sexual attractiveness in either case.

Strength and speed will probably stay about the same, or decrease slightly.  Neither factor is important for survival anymore, but a nice body is still an important sexual selection factor for men and women.  Form and function go together, at least to some extent, in this case.

Height may increase slightly, to the extent that tall men and woman are perceived to be more attractive.

Attractiveness is partially cultural, but some factors, like facial symmetry, are universal and have a strong genetic component.  There is some evidence that sexual selection is already making women more attractive.

Aggression may reduce, because even though aggression can be sexy, most women would probably prefer a non-breeding sexual affair with a highly aggressive male as opposed to a long-term co-parenting relationship (or a totally absentee father).  Also, rape (a form of violence, and thus linked to aggression) leads to fewer children than ever before, both due to oral contraception and voluntary abortion.  Aggression isn’t only genetic — it’s also influenced by nurture.  But there is evidence that genes related to dopaminergic neural pathways influence pathological aggression (high testosterone, on the other hand, is a red herring in this case; high levels of this male hormone are more related to friendliness, happiness, and sociability than they are to aggression).

Economic success is important to both women and men in terms of mate choice.  Factors like intelligence, the ability to communicate well, and personal initiative are all important to economic success.  Are any of these factors genetic?  They probably all have at least a genetic component (as well as a cultural/”nurture” component).

Reliability and the ability to be nurturing are qualities that both men and women consider in a potential co-parent.  Few parents want to be stuck raising children on their own (though many do so very effectively, and some do so by choice).  So to the extent that either of these qualities have any genetic basis, they are strongly selected for by modern mate choice.

Of course I’m speculating when I consider the future of human evolution.  What is not speculation is the fact that mate preference is the gorilla of modern evolutionary pressures on human beings.

Macro-Cultural Trends and Evolution

Differential birth rate also plays a role in modern human biological evolution, but it’s difficult to say which direction variable birth rates are pushing us, genetically.  If a country has a higher birth rate than death rate, but that country also has a very wide, diverse gene pool (Brazil, for example), then population growth in that country won’t push human beings, as a species, in any particular genetic direction.  Countries with a narrow, less diverse gene pool (like Iceland) are generally so small that even a relative population explosion is unlikely to have much global effect.

Do macro-cultural trends push the human genome in certain directions?  We know that some cultural traits (like active religious practice) are linked to increased birth rate.  We also know that some civic policies (like mandatory maternity and paternity leave, public health care, and state-support childcare) are linked to higher birthrate.  Developing countries that have a higher rural population, and less access to birth control, have much higher birth rates (but also much higher child mortality rates).  While all these cultural factors are no doubt influencing human evolution in some ways, I don’t see any clear directionality.

Go forth and multiply.

There is some evidence that “religiosity” has a genetic basis.  The economist Robert Rowthorn has developed a speculative model that shows “religiosity genes” becoming widespread due to higher birthrates in religious cultures (like the Amish, for example).  And the evolutionary biologist Daniel Dennett has argued that a genetic inclination towards religious practice has been adaptive in our evolutionary past.

If there is a “religiosity gene” (or set of genes), and it’s spreading, what does that mean for the development of the collective human character?

Politically progressive people fret that a genetic disposition towards religion would also be linked to social (or even political) conservatism, obedience, or even fundamentalism.

Actual research into possible links between genetic makeup and “religiosity” finds much narrower, and weaker, correlations.  This study found a significant correlation between the short AP-2β genotype and the personality traits “Self-Transcendence” and “Spiritual Acceptance” (from the Cloniger TCI test), but only in males.  Another study showed a correlation between a shortage of 5HT-1A serotonin receptors, feelings of social anxiety, and higher self ratings of religiosity and spirituality.  I suspect there are many genes associated with “religiosity,” with a wide range of character influencing potentialities.

It’s certainly too early to start worrying about the religious right, fundamentalist Muslims, or anybody else “over-breeding” and nullifying the Enlightenment.  While religious people have more kids, actual research has so far failed to define a religious genotype or singular religious personality type.

Human Biological Evolution Is Accelerating

Has human evolution slowed down?  Are the gross pressures on human evolution gone?  No way.  The gross pressures on human survival until reproductive age are mostly gone, at least for the moment (that’s why there are so many of us), but that sexual selection pressures have only increased with the advent of birth control.

Cultural and biological evolution influence each other.  With various cultural innovations (agriculture, birth control), some evolutionary pressures have been removed, but new ones have been added.  The overall trend is an acceleration of genetic change in human beings.

Advances in information technology may further accelerate our biological evolution, as we explore and begin to manipulate our own genome.  We’ll likely start by editing out or repairing genetic sequences that result in crippling diseases like Duchenne muscular dystrophy.  Eventually we may choose to proactively select genetic sequences that currently provide benefits to some, but not others (like the ability to digest lactose into adulthood, or a resistance to depression).  Into the realm of science fiction, we might choose to borrow genetic material from other species and give ourselves night vision, extreme visual acuity, supersonic hearing, color-changing skin, magnetic directional sense, or even photosynthesis.

The bottom line is this: humans are changing rapidly both biologically and culturally, and the rate of change is accelerating in both cases.


A Multi-Modal Approach To Solving Extremely Difficult Problems, Part III (Massively Iterative Failure)


How It Might Go Down (A Global Population Scenario)


  1. I’ve often wondered about this.

    As of now, modern medicine has enabled those who are genetically inferior to be able to breed and pass their genes on to the next generations. People that may have never survived are being saved by doctors, and reproducing. Our genome is still evolving, and getting worse, in my opinion.

    I’m not saying that I don’t think it should be done, because of course everyone has the right to live and be happy no matter what genes they happened to acquire but it isn’t helping the human genome.

  2. Kris,
    I somewhat disagree with your first point. I think the greater weight of mate selection in human evolution is probably pushing us in good directions.

    In terms of most physical characteristics, there is still pressure that favors genes that confer height, attractiveness, good musculature, etc. — many people prefer these characteristics in mates (of course diet and other environmental factors also play a big role in all of these characteristics).

    In terms of mental characteristics, to the extent that they are influenced by genes, I don’t see many negatives to the greater weight of mate selection. Perhaps we’ll become less impulsive, as a species, because impulsive sex is less likely to lead to a child. 😉

    I agree entirely with your second point. Historically, we’ve seen the horrors of eugenics, and no reasonable person wants to go down that road. If we want to deliberately improve our genome we should use genetic engineering.

  3. In terms of modern human evolutionary pressure, lifetime reproductive success is linked to extroversion, openness to new experiences, and lower anxiety (at least according to the research referenced in the article below). I wonder if the “low anxiety” trait or set of traits is more beneficial now because modern life is less dangerous but more stressful (due to information overload, more relationships to track and manage, etc.).


  4. Randall

    Shockingly sophomoric piece.

    I think you have an enlarged ego to write this for the whole planet to see.

    I will stick with Dr. Kaku, thank you.

    • Hi Randall. I’m not putting myself on the same level as Dr. Kaku (who I have great deal of respect for). I just think he’s wrong about this one particular thing (that human evolution has mostly stopped). I think many evolutionary biologists would agree with me, and disagree with Dr. Kaku. Care to rebut any of the content of the post? I’m open to debate!

  5. John

    Hi J.D.,

    Tiny issue– Dennett is a philosopher, not an evolutionary biologist. He has, however, written extensively on the philosophy of evolutionary biology and on religion.

  6. Rickjames

    J.D. I don’t think you have made a persuasive rebuttal of Kaku’s points. I think the main weakness in your rebuttal is that you seem to confuse gross evolutionary pressure/direction with directionless evolutionary change. While you do acknowledge that certain traits are more highly valued than others such as height or attractiveness, you don’t engage with his point that the lack of these characteristics do not prevent one from reproducing as it had thousands of years ago. Gross evolutionary pressure requires traits without with it would be much more difficult for an individual to pass on his genes during his lifetime. In the past, the “short/unattractive” genes would be weeded from a population over generations as those individuals carrying them would not be able to reproduce as successfully. Today however, only an insignificant number of genes hinder reproduction. The short, ungifted, unathletic and unintelligent among us can reproduce as easily, and often do so more frequently, than those with characteristics that previously led to evolutionary advantage as all of our basic needs are met.

    Keeping this in mind then, birth rates are not the issue. The birth could be .0000001 per woman, or 1000000 per women, but if there is no clear evolutionary pressure leading to the consistent selection of certain characteristics, there will be no gross evolutionary pressure.

    Don’t forget, the point he was making was whether the humans of the future would have evolved in a specific direction, towards a species with large heads and eyes.

    • Hi Rick — thanks for your thoughtful comment.

      My point is that evolutionary pressure has changed. Being athletic and having good eyesight are no longer as important in terms of human sexual reproduction, but other specific characteristics like being conscientious, nurturing, and intelligent DO greatly increase modern chances of reproducing sexually, and the lack of those characteristics can greatly hurt chances (especially for men, because a higher percentage of women have at least one child).

      The big change is birth control. The person you choose to have sex with may not be the person you choose to have a child with. I still believe that co-parent selection (as opposed to merely sexual selection) is an under-acknowledged factor in human evolutionary biology.

      That said, the population explosion of the last few centuries, in terms of creating so much more diversity in the human gene pool, is probably an even greater force of evolutionary change (but not, as you emphasize, specific pressure in any particular direction).

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