Why I am an evolutionist, part 3

The persistence of traits illustrated

I told you a nice little tale in my previous evolution post but, in doing so, I skipped over a major difficulty. In this post, let’s return to Jenkin’s criticism of Darwin.

Jenkin gave the example of a white man marooned on an island populated by black people. He chose a good illustration, because skin colour appears to be blended and diluted in just the way Jenkin supposed. We’ve all seen the evidence of this:  there is a range of skin colours, from blackest black to palest white.

Here’s the explanation. We now know that skin colour is not determined by any one gene. To be “pure white”, you have to receive a complete set of “white” genes from your parents. When a baby inherits some of the genes for each colour, her skin will be part way between white and black.

But the actual genes are not blended: each gene remains either “white” or “black”.1

Here’s living proof! Meet Kylie Hodgson, Remi Horder, and their twin girls, Kian and Remee (the blonde).

million-to-one twins

The parents are both of mixed race. Both grandmothers are white; both grandfathers are black. Against long odds, Remee inherited a complete set of “white” genes from her parents while Kian inherited “black” genes. The Daily Mail explains:

Skin colour is believed to be determined by up to seven different genes working together.

If a woman is of mixed race, her eggs will usually contain a mixture of genes coding for both black and white skin.

Similarly, a man of mixed race will have a variety of different genes in his sperm. When these eggs and sperm come together, they will create a baby of mixed race.

The article continues, estimating that the odds are a million to one against having a family like the one in the photograph:  where mixed race parents produce twins, one white and the other black. I’m a little suspicious of the tidy 100:1 odds they ascribe to each step, but let’s not quibble — I’m sure a million to one is close enough!

The point is, here’s a marvelous illustration of the persistence of traits.

Let’s return to Jenkin’s illustration one more time. Let’s assume that the hypothetical white man fathered enough children, both male and female, to establish his genes in the gene pool. Potentially, many generations later, one of those black women would give birth to a child as white as Remee.

Wouldn’t that come as a shock!

[This series trailed off after part three, but The Mouse’s Tale is a later follow-up]

~~~~~~~~~~~~~

1Of course, genes are neither white nor black — I’m speaking in shorthand here. Some genes code for white skin; other genes, for black.

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4 Comments (+add yours?)

  1. juggling mother
    Dec 03, 2006 @ 12:42:09

    There are a number of histprical cases documented where a white woman gave birth to a black child while married to a white husband. In most of the ones I’ve heard about she was usually then ostracised (if lucky!), although as a child I also knew a black/white twin – they were quite the celebrities in the local twins club:-), so I guess its not as unusual as the article says.

    Just think about hair colour – no-one thinks it strange that I have a blond daughter, even though I am dark haired, Aggie is Ginger, and all the rest of both families we know of are dark. Skin colour is the same genetically – if not socially.

    I watched a fascinating dosumentary about a herd of goats that had been stuck on the beach 130 years ago (I missed the start of it – I think there was a land slide or something & they couldn’t get back to the grassland). Obviously in the first few years, most died, as htere was no grass for them to eat, and that’s what they eat! But the ones that survived on the seaweed bred, and many of their offsp[ring survived on seaweed, and bred etc so now, if you feed them grass, they can not digest it – they need to eat seaweed to live. In 130 years they have evolved into a new species – since it is a constant of the goat species that they eat & digest grasses! I don’t understand how so many people can still dispute the existance of natural selection/evolution!

    Reply

  2. Stephen
    Dec 03, 2006 @ 17:24:33

    • JM:
    Regarding the math —
    You’re right, the odds of black parents giving birth to a white child are not a million to one. The article would estimate those odds at ten thousand to one. (100:1 multiplied by 100:1.)

    But there’s another unlikely scenario to factor into this story: the white girl is one half of a set of dizogotic twins.

    Regarding your goat illustration —
    That’s a perfect example of natural selection at work. I may refer back to it later in this series of posts. Thanks for sharing it.

    Reply

  3. Jamie
    Dec 03, 2006 @ 21:40:20

    JM: You say you don’t understand how so many people can still dispute the existance of natural selection/evolution. NOBODY that I know of denies either, and even hardcore creationists would acknowledge the legitimacy of the goat example you listed. The debate is over whether random variation and natural selection can produce increasing complexity, but not over whether or not they occur.

    Reply

  4. Flip
    Dec 08, 2006 @ 08:34:43

    I’m atheist and I certainly don’t believe in a god of some sort. I say this because below could be taken for the argumentation of creationists.
    I say that there is in fact no major random mutation (mostly with adverse effect anyhow) but I would call it adaptational mutation. Scientists have proven that there is a feedback mechanism of info going with the DNA of sperm and egg cells. Apparently a new species comes not from one beneficial mutation and then only a part of the offspring from this individual will give birth to a new species via natural selection?? Work out the maths it is too unlikely. No, if a certain threshold is crossed DNA will rewrite itself for the survival of the species. This happens when the crossover is done in the meiosis. And it starts not only at one individual but it starts with 1% of the group and over few generations 80% of the group will have had the beneficial adaptation. Look at the goats, they would have died waiting for this beneficial mutation to happen in the first place and then even if so it would have taken generations to build a group of individuals that would be able to procreate. There was no time for it. Adaptational mutations just pops up like mushrooms in a field. All individuals experiencing the same treat will eventually adapt. Some earlier then others. For the moment this is only proven in several cases for so called degenerative mutations and copy mutations. It remains a question how mutation for e.g. new organs are being formed. Where does the info comes from? In some countries humanity is experiencing adaptational degenerative evolution. Humans are loosing teeth and the mouth is becoming smaller because we don’t need to tear our food anymore. The food is becoming softer all the time… This is already enough to trigger a change in our blueprint.

    Reply

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