The “moment” of fertilization?


What moment? Fertilization is a complex process, with a series of steps.

  • First, the sperm cell binds to the pellucid zone surrounding the egg. This is specific; sperm and egg have to recognize each other and bind appropriately. You don’t want the sperm to bind to every epithelial cell of the reproductive tract, after all, and you don’t want the egg cell to be receptive to every passing white blood cell.

  • This binding triggers the acrosome reaction. The tip of the sperm cell ruptures releasing enzymes that break down the glycoproteins surrounding the egg and exposing the sperm cell membrane and the egg cell membrane locally.

  • Those two membranes then fuse, and the sperm cell nucleus is drawn into the cortex of the egg. This is called docking and invagination.

  • Docking triggers a wave of electrical activity in the egg cell membrane; from the point of entry, a ring of depolarization sweeps rapidly across the egg, causing vesicles to fuse and dump their contents into the space surrounding the egg, creating a barrier to additional sperm trying to enter. This can be visualized using chromophores that change color in response to membrane voltage, or that react to the binding of calcium, the important ion that crosses the membrane at this step.

  • The germinal vesicles, or nuclei, of sperm and egg then move via cytoskeletal transport towards each other and fuse to create a single diploid nucleus.

This is all routine and relatively well understood stuff. I’ve seen it in fish and frogs and sea urchins, it’s relatively easy to visualize. “Easy” meaning that it can be done with readily available reagents and gear: I’ve done it myself with calcium-sensitive dyes (not cheap), a fluorescence microscope (not at all cheap), a filter wheel for multi-wavelength visualization (another additional cost), an intensified digital camera (we’re still talking thousands of bucks), and special software (which in my case was cheap, because I wrote it myself). But still, lots of labs have the equipment necessary for it, so it’s not that unusual.

It may also be useful. As it turns out, healthy eggs have a strong depolarization response to sperm entry, which some researchers are suggesting could be helpful in assessing zygote health in in vitro fertilization. They’re visualizing the reaction with fluorescent molecules that respond to the release of zinc from the egg, and seeing that there’s variability in the strength of the response, and that it may be correlated with embryo viability.

Unfortunately, the media doesn’t get it. Bright flash of light marks incredible moment life begins when sperm meets egg, announces the Telegraph. Wrong in multiple ways. No, there is no bright flash of light. There is a chemical reaction at fertilization that can be visualized with chemical reagents and some fancy optical equipment in vitro — ova do not radiate photons and none of that stuff was present in the fallopian tubes of most women at the moment of fertilization.

Also, that is not the “moment life begins”. The sperm is alive. The egg is alive. What’s being seen is part of the process of forming a block to polyspermy, and it occurs before the actual fusion of two haploid nuclei.

But if the Telegraph is bad, wait until Ray Comfort gets hold of this observation. And his followers start gushing over it.


There’s so much nonsense there. Wow! Jesus said He was the Light of the world…this proves it! No, it doesn’t. No wonder we love fireworks so much. They happened when we began our lives!!! There were no fireworks at fertilization, unless you happened to be bathed in a specific fluorescent compound and had extremely sensitive eyes as a zygote. this proves life is at conception so its a baby no more early abortions. Life is the release of tiny amounts of zinc? And my favorite:

Unfortunately, the anti-God evolutionists will try to explain this away as simply a “natural” chemical reaction as the sperm and egg make contact. Scales will form over their eyes like Saul’s.

But it is! You can’t simultaneously declare that science ‘proves’ life begins at conception and dismiss the phenomena that science is describing!

Also, no one seems to be catching on to the core intent of the research. It’s looking at ways to evaluate embryos produced by in vitro fertilization and decide which ones are worthy of implantation, and which should be discarded. It’s also making it obvious that a large proportion of fertilized eggs are not particularly viable, and that fertilization is not a magic process bestowing insta-humanity. If that’s God’s finger touching the eggs, God is killing a lot of embryos.


  1. Jado says

    “You can’t simultaneously declare that science ‘proves’ life begins at conception and dismiss the phenomena that science is describing!”

    Can so!! You forgot who you were talking to. These people don’t need no “logic” or “sense” to know that GAAWWWDD is GRRRRRREAT!!!

    They can prove whatever they want to however they want. They are trying to convince politicians, not scientists.

  2. themadtapper says

    Ah yes, how predictable indeed that the godless heathens would assume a natural explanation for flashes of light produced by dyes and light that were both introduced by the observer instead of recognizing the miraculous wonder of this God-given light that wouldn’t actually be there if not for the one running the experiment. This is right up there with the “cross-shaped molecules that are the building block of all life” and “atoms are structured exactly like solar systems” garbage. A toxic combination of ignorance and confirmation bias to reinforce erroneous preconceptions (pun may or may not have been intended).

  3. says

    “God-given light… the one running the experiment”
    Well I’m now a PZ worshipper!!
    Bow down to HIM and all HIS not-particularly-cheap equipment you heathen swine!

  4. says

    Unfortunately, I had to leave behind some of my toys when I moved to Minnesota, so I no longer have the apparatus for ratiometric imaging.

    If someone wanted to send me $20,000, though, I could get it back up and running. Oh, and throw in another $10,000 for a supply of fluorescent probes.

  5. says

    And toss in another few thousand for a micropipette puller. I don’t need one for this observation, but I miss my old one so much.

  6. says

    I wish you luck with this, PZ. I’ve spent decades trying to get people to say “embryo” instead of “fetus” when describing first-trimester abortions, most of which take place by eight weeks gestation. I’ve also spent time showing them lentils and split peas to estimate the size of their “babies” rather than gigantic Tiny Tears dolls representing an embryo at four weeks. If they can’t (or refuse to) understand major facts about pregnancy, HTF do you expect them to understand more difficult concepts?

  7. says

    Fact A: God kills a lot of eggs.
    Fact B: I kill a lot of eggs making an omelet.
    Logically: I am God.

    I’m waiting for the money you collected in my name, Ray Comfort. Pay up.

  8. ealloc says

    The thing that annoyed me the most is the quote by one of senior authors, Teresa Woodruff, that “All of biology starts at the time of fertilization”. Ugh.

    The complete misunderstanding by the press that the “flash of light” actually only occurs because of the fluorescent dye the researchers added is pretty bad, but I am more bothered by how the articles repeatedly frame this as defining the “moment of conception”. No no, no, there is no “moment of conception”.

    In my opinion one of the most powerful ways to debate pro-lifers is to educate them on the process of fertilization, so they come to realize there is no single “moment”, and that becoming a human being is a gradual process. I was quite pleased after I debated this way on some apologetics forum, when after a few months of silence one of the most hardcore pro-life proponents came back to admit this argument has changed his mind.

    Articles like these will only make things harder, because the pro-lifer will just point to articles like these and say, “see, scientists say you’re wrong” and stop listening, even though the article is bullshit.

  9. says

    Those are people who will plough the fields, sow grains, work their asses off for the better part of a year and then thank god for the resulting food.

    I think this is slightly unfair jab ad farmers.

    I kind of understand that thanking to god, despite never being religious myself. I do not work the fields, but I have quite a large garden and I do work my “ass off” in it on occasion. And i know therefore first hand that no matter how hard you work and how good you work, there are things (weather in particular, and some diseases) that can render all your work useless at a stroke and you are powerless to do anything against it. If you do not work, you have a guaratnee of failure, but no matter how hard you work, you never have a guarantee of success.

    So on a gut level I understand the primitive urge to try and somehow appease the uncaring universe to be slighly fair and I understand the craving for a sucker in form of prayer/thanking to the deity for not totaly fucking up your hard work on occasion.

    Of course you are partialy right in the sense that many, if not most of religious leaders in western cultures (USA in this case) are just wilfully ignorant, not blisfully ignorant and they could and should know better. Ray Comfort and all of his ilk are essentially con artists milking their punters for cash.

    Creationists are certainly creative in their misrepresentations of science.

  10. slithey tove (twas brillig (stevem)) says

    re 12:
    understood. agreed.
    It is well understood that nothing we do has a 100% guarantee of success. There is always an error possibility. Recognition of such is one of the distinguishing factors between science and religion. Religion asserts that prayer will move the chances toward 100% success regardless of their starting value. Also assert retroactively that any success was due to holy intervention, disregarding all the work that went into accomplishing it. I know many doctors who’s efforts were so blithely dismissed as superfluous. (my recovery, from a TBI, being one of them).
    I understood the “thank god for food. by the farmers who worked for it” as an allusion to this longer explanation. ugh, sorry. just being verbose today.

  11. slithey tove (twas brillig (stevem)) says

    err correction. “thank god” was not the colloquial expression, but the formal: “Thank [verb] God[nominative]”

  12. Holms says

    I’m curious, how much time do the various stages of fertilisation take? And how long does the zygote have to implant before dying of, I guess, starvation?

  13. moarscienceplz says

    Light is the only thing that is its own origin

    So when I turn on a flashlight, it only works because someone has stored a bunch of photons inside it?

  14. Lofty says

    There is of course a difference between ordinary “life” that the egg and sperm cells share and the “LIFE!!!1!!!GODDIDIT!!!1” that happens at fertilisation.

  15. evodevo says

    @ Holms: A week or thereabouts – if the corpus luteum doesn’t produce enough progesterone, the conceptus is flushed out without implantation, and a new cycle starts. Probably 50-60% end up this way.

  16. chrislawson says

    “All of biology starts at the time of fertilisation.” Apparently making gametes is a non-biological process.

  17. emergence says

    This is one of my pet peeves about fundamentalist morons. They don’t really do any scientific research of their own that often, if at all. Most of the time, they steal the work of non-fundamentalist scientists, twist around what it says, and then declare that the research supports their narrow, simplistic view of the world. This case is particularly awful, considering that the fluorescence is artificial and not something hing their God makes embryos do.

    These are people who look at a report about fluorescent compounds being used to determine embryo viability, and start jabbering about “THE POWER OF THE LIGHT!”. Religious fundamentalism acts like a time capsule for superstitious twaddle that would have otherwise been abandoned millennia ago.

  18. emergence says

    Sorry, I didn’t mean to write that fragment of “thing” after “something”.

  19. chris61 says

    I think the most amusing thing about Comfort et al’s response is that none of those eggs have ever seen a sperm. According to the authors of the paper, restrictions governing working with human material and all, the eggs were chemically activated not fertilized.

  20. chigau (違う) says

    To rephrase
    I never understood why that
    That’s what she said thing is supposed to be funny.
    still don’t

  21. quidam says

    I never understood why that That’s what she said thing is supposed to be funny.

    It is a jab at the stereotypical male being blithely unaware that while his sexual performance may have resulted in his satisfaction, it failed to achieve the same result in his female partner.

  22. wzrd1 says

    @12, yeah, I worked my ass off and only one out of a dozen corn plants per kernel germinated. I’m thinking of not using that seed brand again, as I had lousy results in other veggies as well.

  23. wzrd1 says

    @PZ, that seems to be more than a little zinc there, relatively speaking. It seems to be a veritable shower of zinc reacting to that reagent.
    Cool imagery though! One ponders doing something similar with a high energy process, such as a calcium channel depolarization. If that’s a flash, the other’d be an explosion to the dweebs.

  24. Nerd of Redhead, Dances OM Trolls says

    So… still begins at conception though

    No, life continues at conception.