Developments in Heredity, Evolution & Ecology

Instructor: Meredith Mikell
Advancements in the fields of evolution, heredity, and ecology have been significant in the past couple of centuries. Here we will investigate the major developments in these fields, with emphasis on the more recent.

Life Explained

The study of living things has been a dynamic and varied field of science, particularly in the last couple of centuries with the development of technology. Microscopes allow us to view organisms far too small for our unaltered vision, genes can be moved, removed, and altered to produce different outcomes in organisms, and genetic analysis of all species allows us to better weave the mosaic of ancestry that connects us all. Let's take a closer look at some of the most recent advancements in three areas of biological study during the past century: heredity, evolution, and ecology.

Heredity

Why do we look like our parents? Why is there so much variability of characteristics in living things? Why do some characteristics skip a generation?

These questions were largely unanswered until the 1800s, when Gregor Mendel performed now-famous experiments breeding pea pods of specifically defined characteristics and uncovered what we now know to be the most basic concepts of inheritance, the means by which living things inherit traits from their parents and pass those traits to their offspring. He defined the determinants of inheritance as genes, where each gene could have multiple variations called alleles. For example, the gene for eye color has several alleles: brown, blue, green, hazel, and other variants of those colors.

Gregor Mendel experimented with pea plants and discovered how traits are passed along from parents to offspring.
Mendel

Into the 20th century, the study of heredity honed in on genetic disorders and the transmission of disease. Some of this groundwork was set beginning in the 1930s, when researcher Barbara McClintock commenced work that she continued for over forty years identifying genes that can jump, or alter their own position on a DNA strand, and thus the expression of the gene. Such gene behavior was discovered to be responsible for many different genetic disorders and types of cancers.

Well into the 1940s and early 1950s, many other scientists refined Mendel's concepts regarding the dominance of some alleles over others, the patterns of inheritance, gene transfer by bacterial or viral cells, and the discovery of DNA as the gene-containing molecule of all cells. Even the shape of DNA was established in 1953 as a double helix by scientists James Watson and Francis Crick, marking a big turning point in genetic studies. Watson and Crick used data from Rosalind Franklin provided by Maurice Wilkins to solve the structure of DNA.

The DNA double helix, the gene-containing molecule of all living things.
DNA

These early discoveries established a critical foundation for the Human Genome Project, which, at the end of the 20th century, became one of the largest and most comprehensive biological cataloguing protocols in history, mapping and documenting the genome, or entire gene composition of human DNA.

The logo for the Human Genome Project.
HGP

Evolution

When we think of the concepts of evolution, genetic change over time, it is common to first think of the extraordinary discoveries of Charles Darwin. Although Darwin most certainly established what is arguably the most profound theory in the history of biology, the theory of natural selection, the work certainly did not end there. In the early 20th century, in conjunction with the genetic technologies and advancements we discussed previously, biologists witnessed greater complexity in how evolution occurs, and could even witness it happening before their eyes in bacteria.

A critical aspect of understanding evolution was the discovery of transitional fossils, fossils of species that bridge the gap between known species, the excavation of which peaked during the 20th century. Each fossil served as a puzzle piece in our understanding of evolution, often revealing new lineages entirely. Both DNA technology and fossil evidence began to indicate rapid and erratic changes in the traits of a given population under certain conditions, suggesting that evolution does not exhibit phyletic gradualism, a slow and steady process, as Darwin had thought; it can go through drastic spurts and lulls. In the 1970s, biologists Stephen Jay Gould and Niles Eldredge established the concept of punctuated equilibrium, that a steady rate of evolutionary change is frequently punctuated by rapid bursts.

The concept of punctuated equilibrium (bottom) shows how evolution occurs in bursts, rather than gradually, as is the case with phyletic gradualism (top).
punctuated equilibrium

These bursts lead to periods of high speciation, the arising of new species, as seen strongly in excavation sites such as the Burgess Shale in the Canadian Rockies. First discovered in 1909, this site has a high abundance of novel fossils from the Cambrian Era in an ancient speciation event called the Cambrian Explosion. Over 60,000 different fossils of marine organisms were uncovered during the 20th century!

Fossils like this ammonite contribute to our greater understanding of evolution.
fossils

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