Feature Article - February 2016
by Do-While Jones

Looking For Sex

Valentine’s Day inspired us to look for sex articles in the professional literature.

Evolutionists have many sexual problems. For example, how did male and female variants evolve by chance at the same time in the same place? How did the instinct to mate come about by chance? Why are there so many different forms of sexual reproduction? What did bees and flowering plants do before the other one evolved?

Those are all interesting questions; but they are admittedly subjective and speculative. Now that more genetic research has been done, sex presents several objective problems for evolutionists.

Two recent articles in the professional scientific literature highlighted an evolutionary problem that has been discovered when studying sex chromosomes.

The major methods of sex determination are:

  1. Genetic sex determination (GSD)
    1. male heterogamety
    2. female heterogamety
    3. polyfactorial
  2. Environmental sex determination (ESD)
  3. Cytoplasmic sex determination
  4. Arrhenotoky (haplodiploidy)

We wrote extensively about them in a previous newsletter. 1 The important thing to know is that in male heterogamety, males have an X chromosome and a Y chromosome. Females have two X chromosomes. Having two different kinds of sex chromosome makes an individual male. In female heterogamety, females have a Z chromosome and a W chromosome. Males have two Z chromosomes. Having two different sex chromosomes makes an individual female.

Pecking Away at Evolution

Mammals have male heterogamety. Birds have female heterogamety. How could that happen if they both evolved from a common ancestor? But, aside from that, wouldn’t one expect all birds to have similar sex chromosomes?

Here we use the newly available genomes of 17 species spanning the entire avian phylogeny to decipher the genomic architecture and evolutionary history of bird sex chromosomes.

We surprisingly find that more than half of the studied species have a W chromosome that is not completely degenerated. Besides ostrich and emu, some Neognathae species like tropicbird and killdeer also have long PARs. The nonrecombining regions between Z/W of many species exhibit a complex pattern of “evolutionary strata,” resulting from the suppression of recombination in a stepwise and independent manner among some lineages.

Conclusion Our study uncovered an unexpected complexity of avian sex chromosomes. 2

The body of that report gets a little technical as they try to explain what is unexplainable in an evolutionary framework.

In many species with separate sexes, sex is determined by a pair of heteromorphic sex chromosomes that differ in their size, morphology, and gene content. Mammals have male heterogametic sex chromosomes (XX in female, XY in male), whereas birds have female heterogametic sex chromosomes (ZW in female and ZZ in male). Both sex systems have originated independently from different ancestral autosomes after the two lineages diverged more than 300 million years ago (Ma), yet they share many common features with respect to their genomic composition and evolutionary history. 8

They claim mammals and birds independently evolved sex determination systems after they supposedly diverged more than 300 million years ago. How did mammals and birds have sex before they evolved these sex determination systems?

The nonrecombining region of the Y/W usually has lost almost all functional genes present on the ancestral chromosome except for a few loci, often with sex-specific functions, and Y/W chromosomes are often largely composed of repetitive and epigenetically silenced (heterochromatic) DNA. Recombination suppression is thought to follow the origination of a sex-determining locus and may initially encompass only a small chromosomal segment surrounding that locus, but then progressively spreads along Y or W chromosomes, possibly owing to the accumulation of sexually antagonistic alleles at PARs that benefit one sex but harm the other. 3

In other words, they have no clue; but they are sure genes somehow got lost, recombined, relocated, and who knows what else. But, as we said before, it gets worse!

New Research

An article published last November brings some even more startling information to light. That article is about the adult sex ratio (ASR), which is the ratio of males to females in a population. They were looking for a connection between the ASR and sex-determination system. ASR has no bearing on evolution—but the sex-determination system certainly does. Some off-handed comments about the sex-determination system in this article should be very troubling to evolutionists.

One factor that could affect the ASR is the genetic sex-determination system. … While mammals and birds are fixed for XY and ZW sex determination, respectively, reptiles and amphibians provide particularly attractive opportunities for this study, since transitions between sex-determination systems have occurred many times within these clades. 4

The miraculous transition occurred many times! The article included this picture to illustrate the point.

Inner band shows the type of sex determination (red: XY, blue: ZW), and the outer band shows the ASR bias for each species included in the study (red: <= 0.5, blue: > 0.5 proportion of males). Sample sizes: 39 species for amphibians, 67 species for reptiles, 187 species for birds and 51 species for mammals (see Supplementary Data). 5

Please direct your attention to the inner band at the 3 o’clock position of the diagram.

The forklike structure is supposed to represent connections to common ancestors. Notice that some tines of the fork end in red, and the adjacent tine ends in blue. This means two “very closely related” amphibians have different sex-determination systems. How could that be if they share a close common ancestor?

Quick links to
Science Against Evolution
Home Page
Back issues of
(our newsletter)
Web Site
of the Month
Topical Index


1 Dsclosure, February 2003, “Birds and Bees”
2 Qi Zhou1, et al., Science, 12 Dec 2014, “Complex evolutionary trajectories of sex chromosomes across bird taxa”, http://science.sciencemag.org/content/346/6215/1246338.full
3 ibid.
4 Ivett Pipoly, et al., Nature, 05 November 2015, “The genetic sex-determination system predicts adult sex ratios in tetrapods”, http://www.nature.com/nature/journal/v527/n7576/full/nature15380.html
5 ibid.